Crate V5 mods... anyone?

[deafelectromark]

Mod and mod

It may be my lack of skills but I tried all of this and for some reason it didn't work right. I had really low volume and really bad distortion with the amp wide open.

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It sounds like a lot of work to me, and I am an electronics technician. One of the main problems with doing a mod is to do them one at a time so you can see where you had success, or worse- catastrophe. If you put the amps (modded and unmodded) side by side, you should hear a big difference in the sound of each. But the question remains--exactly what circuit mod made the most improvement (happiness divided by dollars).
There is nothing wrong with taking a cheap and amp making it better and learning how all the parts relate to each other and to learn electronics. The fact that you are a member of the FRET is indicative of your passion to tinker and improve.
There is so much information on the websites about this stuff, it is hard to just say, " I want it to play loud and clean". It can't and it wont. Clean sound needs efficient speakers and/or powerful amps to keep them from distorting. You can play clean and soft- you are staying withing the amps power levels. If you need 50 or more watts for clrean and loud ya gotta go big. Dirty and small and reasonable levels for today's living is easy. Look at how many amps there are out there that sound good and can be made much better; but then you are getting into higher price level where a more expensive amp is really what you wanted and you needed in the FIRST PLACE. That is why I limit expenditures on small amps. Sure I could add hundreds of dollars to get all the best parts and the best circuit, But it still will sound different than someone's amp and cost more that a 'better amp'.
I have a saying on 18watt- Tone is subjective!
Mark

 

[jim p]

LiteIIb tone control

Thanks for the info about C3 and R16 in post #111.




I have bypassed the op amp and have replaced C2 with a 0.022uf 715 Orange Drop which feeds into an 18 watt LiteIIb volume and tone control which then connects back to R7.

I just removed C8 on a friends V5 and wow did that clean it up, nice bright cleans at lower volumes that break up with higher volumes and harder attack, now it dimed is about the same gain as my amp on two or three. Since we both like more of a blues/classic rock sound, it's a lot better amp cleaned up.


Thanks again!

I found a schematic for the amplifier that has the tone control that you have used I think. This is 500k log pot for tone 500k log for volume 500 pF at top of tone stack 10nF at bottom is that correct? In the schematic for the amp it is in it is input to a long tail pair or differential amplifier whatever you prefer to call it which most likely has less gain (need to work out gain for it) then the second triode you are connected to. First did you use the same values for the pots and caps? If you used the 250k pots in the amp the cap values will need to double. Also to offset the greater gain in this amp may need to reduce signal across this tone stack and volume control. If the mod was in the amplifier that you removed C8 on and it improved that backs that assumption. So you could put a resistor in series with the volume control and tone stack to reduce the signal across it. Another thing you could try is to reduce the signal at the grid of the EL84 by increasing R31 probably will need to remove or reduce C3 if you do that

 

[jim p]

problems with mod

It may be my lack of skills but I tried all of this and for some reason it didn't work right. I had really low volume and really bad distortion with the amp wide open.

What tools do you have to work with do you have a DMM, scope, signal generator ect. If you just have a meter can give you locations for ohmeter tests to see if things are wired correctly.
One quick possable problem is the volume pot shorted to it's self or the PCB if you have no insulation or the insulation on the PCB is broken. I had that happen once to me after having the board in and out to make a change.

 

[deafelectromark]

Mods

What tools do you have to work with do you have a DMM, scope, signal generator ect. If you just have a meter can give you locations for ohmeter tests to see if things are wired correctly.
One quick possable problem is the volume pot shorted to it's self or the PCB if you have no insulation or the insulation on the PCB is broken. I had that happen once to me after having the board in and out to make a change.

The most irritating thing that I have to deal with when making changes are cold solder joints (looks good but nothing gets through) and solder bridges that I make when I solder close to adjacent traces and the sound goes to lala land. I agree with JP that using only a meter should find all but the worst problems (like oscillations, grumbly hums, wolf tones and all that stuff- you really need a 'scope to see inside the circuit and pinpoint where the problems start).
Another very frustrating issue is much like what JP said, shorted or open parts, or parts that don't have the value printed on them in color code. Remember that some parts have a silver band or gold or on the end making them 1/10 or 1/100 of the color code value. Putting in a 0.3 ohm resistor is far from 3 ohms and things will get nasty and 'look OK'.
Dirt and corrosion has me scratching my head in most of the problems that I work on. Tarnish, rust, salty bridges, intermittent pots, and controls (switches) are almost ALWAYS the first thing that I check now and save myself from hours of 'exploratory surgery' and part replacement. Don't forget that the people who sell the parts and the manufacturers make mistakes and it can make you go loony when you put in a 'correct value part' and it still doesn't work and you spend hours looking elsewhere. New parts are always OK? No they are not. Even switches have been faulty- the least complex of the parts you use. Caveat Emptor!
Mark

 

[rock_mumbles]

I found a schematic for the amplifier that has the tone control that you have used I think. This is 500k log pot for tone 500k log for volume 500 pF at top of tone stack 10nF at bottom is that correct?

Yes that is the volume/tone control I used. I got the amp working like I want it today, I put a 150K resistor between C2 and the volume pot and a 470K from the volume pot side of the 150K to ground (effectively have a 250K volume pot). Now the amp works fine! BTW, I have removed C3.

Now I can have the second split cathode resistor bypassed on the first triode and have an on-off-on switch hooked up on the second triode to have full bypass (most gain) no bypass (lowest gain) or partial bypass (medium gain).

Now I'm pretty much OK with the amp, it's a nice little portable combo amp. It's not quite as powerful or quite as good sounding as my modded Valve Junior but I paid more for the Valve Junior Hammond 125ESE output transformer and mod kit than I paid for the V5.

Thanks again

 

[jim p]

initial look on third V5 amp

Well I am working on my third V5 think I may do a full make over to a 6V6GT output tube and two 12AX7 for overdrive and cathode follower driven tone stack and reverb(op amp drive and recovery). Probably just make it a head instead of a combo amp. The 6V6 conversion saves you enough heater current to add the second 12AX7.
I looked at the turns ratio again and saw in another post that the impedance for a 8 ohm speaker to be a 4 to 5 k ohm plate load is wrong, that looks to be right. I measured it before and came up with 20:1 but talked myself out of it but that is what I am seeing now. For what it is worth the reflected impedance is the turns ratio squares times the load (20X20 = 400 X 8 ohms = 3200 ohms). Going by the Mullard data sheet you want 4.5 k to 5.25k at the plate approx 24:1 turns ratio. On the up side the triode mode is looking for a plate load of 3.5k so this transformer is good for the triode mode which is your lowest distortion mode if you are in to that sort of thing. But this is a single ended output and harmonic content is suppose to be what you are looking for if not you should go push pull or solid state. From what I see at the plate with a scope the distorted portion of the waveform is when the tube is off which is flyback time. When the tube turns off it is the magnetic field of the transformer collapsing that is going to drive the load think of it as a flywheel or water wheel the tube spins it up then stops and it keeps going for a while. But the speaker is a load on this so the less load the longer it spins so a 16 ohm speaker is less of a drag then an 8 ohm speaker. But a 16 ohm speaker is not a 16 ohm speaker and an 8 ohm is not 8 ohms either, that is there nominal or average impedance. So bottom line what are you looking for? A single ended output is suppose to give you second harmonic distortion for that fat sound if you undampen the output with a higher impedance you will reduce it and increase the third harmonic. Another thing to keep in mind a resistor is not a speaker to get a more realistic load you can do what I did and stuff the stock speaker in a box or Ted Weber makes a load that is a speaker with no cone.
Also looked at the cathode bias on this amp but I first moved the screen grid from its connection to J4 over to junction of R25, R26 and C16 where it should be. From testing on this tube the cathode resistor should be 270 ohms that resulted in a plate current of 38mA screen grid current of 4mA with approx 315 volts across the tube for 12 watts at the plate.
Has anyone thought of converting there amp over to being a RAT, if you remove the c and e from crate on the front of the amp you get a well centered RAT on the front. Or maybe you like that sleeper stock look.

 

[jim p]

Nmos fet for bypass switching

Instead of running the ground lead of the capacitor used for switchable cathode bypassing back and fourth through the chassis I think it may be better to use a nmos fet switch. This way there should be less chance of noise pick up and you keep the ground loop tight around the cathode resistor. I have attached a schematic that shows the basic set-up. I may also use this same circuit to parallel the output tube cathode bias resistor when switching between triode and pentode mode. In that case I will use a four or five pole double throw switch for isolation from the screen grid connection with a two pole switch I think a high voltage arc might occour within the switch. The BS270 fets in the schematic are available from Mouser electronics for 19 cents each.

 

[jim p]

Gain in 18 watt Lite II

Yes that is the volume/tone control I used. I got the amp working like I want it today, I put a 150K resistor between C2 and the volume pot and a 470K from the volume pot side of the 150K to ground (effectively have a 250K volume pot). Now the amp works fine! BTW, I have removed C3.

Now I can have the second split cathode resistor bypassed on the first triode and have an on-off-on switch hooked up on the second triode to have full bypass (most gain) no bypass (lowest gain) or partial bypass (medium gain).

Now I'm pretty much OK with the amp, it's a nice little portable combo amp. It's not quite as powerful or quite as good sounding as my modded Valve Junior but I paid more for the Valve Junior Hammond 125ESE output transformer and mod kit than I paid for the V5.

Thanks again

I calculated the gain of the differential pair used as a phase splitter and it should be approx 26. That is close to the same gain as the second triode without cathode bypassing in the V5 (gain 25). One thing about the Lite II that looks wrong is that the plate load resistors are equal values in the phase splitter. From what I have read and simulated the plate load resistor on the input tube (R6) should be approx 20% smaller then the other plate load resistor to have equal amplititude signals. Anyway the V5 overall gain should be the same as the Lite II with the input triode bypassed and the second triode unbypassed.

 

[larryx]

Crate V-5 Mod Help!

Hello folks,
Well I'm just another confused and frustrated Crate V-5 owner. I like alot of V-5 owners am looking for some (simple) mod instructions. Not the long winded ones written by technological geniuses. I'm talkin about something the average guitar player who can read tab and paint by numbers can do! I'm getting tired of reading about Jonnie Multimeter and his triumph over bypassing the op amp section and making his personal CrateV-5 an all tube circuit. While the rest of us dread the day we bought one! How about someone with this knowledge sharing some easy to understand mods. Information like what resister and capacitors do we change? R-? and C-?. And what values do we change them to? Alot of us guitar players are just looking for a solution to get a good sound out of our V-5's. Is anyone willing to put together some ((easy to understand directions)) for making these amps worth owning ? Most of the info out there is way to difficult to understand. I CAN HEAR THE AMEN BROTHER!, COMING FROM THE NON TECHY GUITAR PLAYER CROWD OUT THERE ON THE FRET!!!

Many Thanks to who ever steps up!!!

 

[SciHi]

...Well I'm just another confused and frustrated Crate V-5 owner...

I spent the last couple days playing around with a v5, I recently completed extensive mods to my crate v18 and figured the v5 would be a piece of cake. BUT the v5 is pretty screwed up. As bad as people said the v18 sounded, it was just a couple of resistors and capacitors away from great sounds. The v5 however, is a trainwreck, and not in a good way. There are no really simple fixes because, #1 it doesn't have a volume control and #2 it doesn't have a working tone stack. So those two things need fixed before you can worry about any small tweaks here or there.

What is currently called volume is a gain on the opamp. It is fine to have it there, just don't ever turn it up! The amp needs a volume control, preferrably between the two tube stages of the preamp. So you either pull the existing tone pot, fix the gain on the opamp as suggested by Jim P, or pull the pot and totally bypass the opamp totally, running the input to the first stage of the preamp tube. Your option, you get to choose. Jim P does give step by step instruction so you can keep the opamp working and move the volume control to the correct place. If you want to try and locate another pot on the amp somewhere, then you could add it for volume control and leave the gain on the opamp (this is more like the earlier models of this amp). So that is a third option to fix the "no true volume control."

To fix the tone stack, Jim P has step by step instructions and they are about the easiest. But many different one knob tone stacks, such as the tweed could be adopted. You could even add 2 (or 3) pot tone stacks by using dual pots, such as Verne A. posted on HC for the Palomino 8, a close cousin to this amp. Pick your favorite, or follow Jim P step by step instructions for the simplest. Once these two major problems are fixed, then you can start simple resistor and cap changes to voice the amp to your liking.

The amp I played with was modded by Rock_Mumbles. He jumpered the opamp, used a modified liteII tone stack, and added switchable cap bypass on v1b cathode. Real nice mod, very close to a well modded VJ. Maybe we can shame Professor Mumbles in posting his modified schematic drawing...

 

[rock_mumbles]

Hello folks,
Well I'm just another confused and frustrated Crate V-5 owner. I like alot of V-5 owners am looking for some (simple) mod instructions...

Like Scihibmxer posted, unfortunately the Crate V5 is not as easy to mod as some other amps I've modded in the last year, you won't gain much by just changing out a resistor or cap like other amps. We both thought - a nice little combo amp for a decent price, only 5 watts so it won't make quite as much noise in the house as the 18 watt amps, it's a 2 tube amp should be no problem to modify.
I probably spent about 10 hours working on my V5 last week (I was on spring break), so I am also "Confused And Frustrated"
My response to the V5 after the initial mods (bypassing the op amp and adding in the volume/tone control) "what the heck is up with you???" I spent way too much time for very little progress. I finally have the amp so it's OK as a test amp for guitars and pedals.

So...

What kind of guitar do you play??? (my modded V5 is OK with my Tele but doesn't sound very good at all with my brother's Dimarzio humbuckers, it would need to be throttled back for humbuckers)

What do you want your amp to do??? (you have to remember it's a simple 2 tube amp so do you want some cleans with breakup or completely overdriven - for complete overdriven sound listen to 777funks modded amps he sells on ebay, they are a one-trick pony)

In my opinion the speaker has to be replaced, what kind of speaker are you thinking about??? (the Weber Sig 10 or Sig 10S are good sounding reasonably priced speakers)

The things I have done that I could help you with is an easy way to:
(a) bypass the op amp and correct the input jack. (this involves removing the volume pot )
(b) remove the stock tone stack, and move the volume control and add a simple one knob tone control into the circuit where the stock tone stack was.
(c) deal with the amp's gain, if it has too much gain for you.

I wouldn't work on the amp unless you have some spare 16mm pots (and some new knobs handy) it's really easy to mess up the pots desoldering and soldering them. I help out at a friends music store so I have access to lots of parts and a good solder station, volt meters etc., so when I burned out the volume pot soldering the ground wire on, I just got another one out of the parts drawer.

You'll also need a couple of caps for the new tone stack three or four values of resistors and maybe a new 400V capacitor that goes in the circuit before the volume/tone stack.

Again, I can help you with the mods I have done, but anything else is just a guess. If you're interested, I'll put up a mod layout and parts list.

 

[jim p]

A basic mod

The most basic mod you can do that should have a significant change to the amp (with exception of replacing the speaker) is to use the tone pot for a volume pot and keep the volume pot for a gain control. I posted a list of components to remove and replace for this and how to jumper the tone pot to the control grid of the second triode for a volume control. I could draw up a small schematic to show what the changes are if someone wants. But a basic thing you may need to know is how to read a schematic and I will guess you might be able to read about just that subject on that thing they call the WEB. If you don’t know about something here open a new tab and Google it. Where do you find those tabs you have been using eh? So Google resistor, capacitor, and inductor heck you can find sections of college courses on electronics on this web thing.
Anyway doing the tone to volume control mod you do not have to remove the pots so no chance of damage to them. Other amps out there do not have a tone control so? The gain op amp set up in this amp is better then the Crate VC508 because that only had +/- 7 volt supplies which may not have been enough headroom to prevent clipping in the op amp before the tube.

 

[Tomko]

So you can decrease the voltages on the EL84 by increasing the cathode bias resistor? I'm still over 330 volts on the plate and screen grid but the amp works fine. I see the cathode bias resistor for the EL84 is R17, 330 ohm, 5 watt. What would you increase it to to get the voltages below 300v?
Also, you keep saying increase R16 to 10K but it is already 220K. Is this a typo, mistake or what? You're confusing me- easy to do.

 

[goonrick]

So you can decrease the voltages on the EL84 by increasing the cathode bias resistor? I'm still over 330 volts on the plate and screen grid but the amp works fine. I see the cathode bias resistor for the EL84 is R17, 330 ohm, 5 watt. What would you increase it to to get the voltages below 300v?
Also, you keep saying increase R16 to 10K but it is already 220K. Is this a typo, mistake or what? You're confusing me- easy to do.

If you look through this thread, you can see where Jim P recommended to make it a choke input power supply by ganging C14 and C15. I did this by removing C14 and replacing C15 with a larger cap. It did reduce the B+ by a number of volts and it got the screen running at around 296V on my amp.

I believe there were changes to the screen resistor and R25 as well, though I don't recall offhand what the changes were.

 

[Tomko]

Thanks for the info Goonrick but I really don't want to mess with the filter caps and I have no replacements for them (nor can you get them in this town) so I think I'll try a 4.7K grid screen resistor for the EL84 and see how what it does. Hope I don't mess something else up!

 

[jim p]

Screen grid voltage question

So you can decrease the voltages on the EL84 by increasing the cathode bias resistor? I'm still over 330 volts on the plate and screen grid but the amp works fine. I see the cathode bias resistor for the EL84 is R17, 330 ohm, 5 watt. What would you increase it to to get the voltages below 300v?
Also, you keep saying increase R16 to 10K but it is already 220K. Is this a typo, mistake or what? You're confusing me- easy to do.

If this is a question to me I lowered the cathode bias resistor to get to 12 watts at the plate of the EL84. The stock value is conservative probably for tube to tube variation (so plate current is low). Regarding the value of 10k I did mean R18 but what should be done is to remove the side of R18 connected to J4 and connect it to the junction of R26 R25 and C16+ this is where it should be (look at schematic). Bad thing is you will have to remove some of that clear RTV they gooped everywhere to get to this junction. Also would be best to change R25 to 7.5k (6ma across R25, this is from 4ma screen current and 2ma from 12AX7) should equal a 45 volt drop from the voltage at J4
To explain my changing the cathode bias resistor you can calculate the cathode current by the voltage across it (Vk/Rk = Ik) subtract 4ma for screen current(what it is in most cases) to get the plate current. Then the plate dissipation is the voltage across the tube (plate voltage minus cathode voltage) times the plate current.
On this amp with a 275 ohm resistor I had 11.4 volts at the cathode equal to 41.5mA – 4ma screen current for a plate current of 37.5mA with 326 volts at the plate minus 11.4 cathode voltage for 315 volts across the tube. So 315 volts times 37.5mA for 11.8 Watts.
Best way to try lower values is to parallel the resistor with a higher value if you know how to calculate resistors in parallel. A good method is reciprocal method example R1 in parallel with R2 there total resistance is 1/(1/R1 + 1/R2) = Rtotal What you are doing this way is changing them into the current that would be through them with one volt adding the total current then dividing the one volt by the current to get the resistance. Surf the web for more on calculating resistors in parallel for a better understanding.

 

[rock_mumbles]

Should I (could I) add another filter cap?

... Regarding the value of 10k I did mean R18 but what should be done is to remove the side of R18 connected to J4 and connect it to the junction of R26 R25 and C16+ this is where it should be (look at schematic). ...

Hi Jim,

Would it help to add a 22uf 450V filter cap (to ground) in the B+ supply where R18 was connected to J4?

I just happen to have several caps without amp "homes".

Thanks

 

[Tomko]

Question for Jim P

Yes the question about R16 going to 10K (or 5K) was meant for you. I think you were the only one who mentioned it. I realized later you meant R18 after re-reading the whole thread and checking the schematic. I picked up a 4.7K today to try. I tried to hookup at R25 but must have ruined the resistor removing the RTV as all I got was a bunch of noise. Put it back the way it was and still got a bunch of noise. So now I will be replacing R25. I do know how to calculate both resistors and capacitors in series and parallel. Had Basic Electronics 101 in route to BSME. I am not an expert when it comes to electronics and I don't have anything but a basic working knowledge of amps (4 books), a soldering iron and a multimeter. I have worked extensively on my BF Bandmaster and they sure are easier to work on than PCB amps and in particular the V5. It was bad in its original form. I went for the basic tube amp with a 18 watt vol/tone circuit in between the two triodes. Had it working fine until I tried to hookup at R25.:thwap: Thanks for your knowledge and especially the explanation of the cathode bias.

 

[jim p]

Sorry about your problems with the screen grid

Yes the question about R16 going to 10K (or 5K) was meant for you. I think you were the only one who mentioned it. I realized later you meant R18 after re-reading the whole thread and checking the schematic. I picked up a 4.7K today to try. I tried to hookup at R25 but must have ruined the resistor removing the RTV as all I got was a bunch of noise. Put it back the way it was and still got a bunch of noise. So now I will be replacing R25. I do know how to calculate both resistors and capacitors in series and parallel. Had Basic Electronics 101 in route to BSME. I am not an expert when it comes to electronics and I don't have anything but a basic working knowledge of amps (4 books), a soldering iron and a multimeter. I have worked extensively on my BF Bandmaster and they sure are easier to work on than PCB amps and in particular the V5. It was bad in its original form. I went for the basic tube amp with a 18 watt vol/tone circuit in between the two triodes. Had it working fine until I tried to hookup at R25.:thwap: Thanks for your knowledge and especially the explanation of the cathode bias.

Sorry for how things are working for you on the amp. One thing to watch out for is that RTV getting into the solder joint when you go to resolder this could give you a cold solder joint problem. First place I worked at used humaseal on there PCBs in the high voltage section (portable ultrasonic flaw scope) and it was a pain to rework things. You should look to make sure the PCB traces and plated feedthrough are OK. If the circuit is open you will have no supply to the plates on the triodes. So I would buzz things out with an ohmmeter. I put a triode/pentode switch in the amps I have so just needed to solder to the lead of the resistor in the board. If you move the screen grid to the plus side of C16 you should use the stock value of 470 ohms for R18 sorry if that was not clear in post. A higher value may work but will probably cause degenerative feedback with the changing voltage on the screen grid (which may be OK?). That is why I posted the fact that the screen grid should be at C25 plus. If you check the daddy of this amp the VC508 you will see on that one they got it right.

 

[jim p]

Use for high voltage caps

Hi Jim,

Would it help to add a 22uf 450V filter cap (to ground) in the B+ supply where R18 was connected to J4?

I just happen to have several caps without amp "homes".

Thanks

No you would just be paralleling C15 the 47uf cap in that same circuit if the amp is quiet no real need. One area that looks like it could use decoupling is the plate load resistor of the first triode R5. I posted before how you can get sound through the amp with the volume control at minimum and think this is due to no separate decoupling on the triodes. So one thing you could do is put a 10k resistor between plus C17 and R5 then decouple the junction of the new 10k and R5 with the 22uf cap you have. I can draw a small section of the schematic if it would help to explain. If you look at a Bravehart amp schematic you will see that they have both triodes decoupled. Without the decoupling and with a tone stack between the triodes the signal feedthrough is not 180 degrees out of phase and will not be canceled. If you were going to use it to decouple the screen grid instead of moving R18 to C16 plus I would put a 10k in series with the 470 ohm R18 and decouple at the junction of the two resistors.

 

[schenkadere]

I bought one of these after I sold my perfectly modified Epiphone Valve Junior with the help of 18watt members and 300+ pages of chit-chat. I get bored rather easy, and was going to go with the Valve Junior again (I sold it to see if I could get the combo and do similar things, but the price increase told me that there were greener pastures) as a platform, but decided to try out the Crate V5 since it was a combo not much bigger than the VJ. I like 10 inch speakers, I liked the looks of the amp, and thought that even if I have to replace everything and even make up a tagboard for it, it would still be cool. I also was hearing what others have been saying about the Crate and when I got it, surprise! I agreed that there was something amiss and decided that to just accept it and give it back would be like throwing in the towel. I knew that it could be better and I systematically worked on each section to see how my $100 initial investment could be improved on.
Speaker was pulled first. Weighing about a pound and with a tiny magnet, tiny voice coil, stiff suspension and a plastic (!?) cone, I could tell just by tapping on it that this was a tone sucker and big part of the bass weakness. I figured that it could be used in an amplifier to take to the beach or other dirty, wet place. The chassis looked awfully close to the speaker magnet, and I didn't think I could get anything in there that would be decent.I measured the depth of other speakers that I had and found that I was wrong. There WAS room for a better speaker. I popped in a 50 watt Eminence 10 inch and it cleared the chassis. Hooked it up and fired it up- better tone and bass, but the amp was still shrill and unmusical.
Looking inside the amp on the circuitboard I saw of all horrors, an op amp!. OK, I know, you can get good sound out of op amps, but looking at the circuit with the volume control in the feedback loop in the second stage, was didn't sit right with me. After the op amp, the tube circuit was fairly conventional other than a quasi- parametric tone circuit between two tube sections of the 12AX7. But looking at the output of the second triode section, I could see that 90% of the signal was dumped just before it got to the grid of the power tube. I guess that is why they needed the op amp in there- to make up for lost gain in the output tube's voltage divider at the grid. (Why?)
So what I did is to cut some traces and add some jumpers to make it an all tube amp. After the input resistors (1.5Kohm and 1 Meg) I cut that trace going to the input of the op amp and sent it straight to the first tube grid and cut away any other parts that were there that might have influence. I decided that the tone control was not a bad thing, just different- and I left it as is. Since I now had a 250Kohm volume pot out of the circuit, I put that between the tone circuits and the grid to the second triode in place of the attenuation scheme that was there and to maintain grid to ground loading and control. I cut the traces around the volume pot and ran jumpers to the appropriate places (the pot connects to the output of the tone circuit, the two lower resistors were cut out, and the other end of the pot was run to ground. The wiper fed the second triode's grid.
I checked for stability (good) output power-6.1 watts at clipping; up to 9 watts fully overdriven. and residual noise 7mV rms (from the power supply). The tone control can be more easily understood when you use a fuzz pedal or other distortion box into the input. It changes the midrange tone in weird ways, but it is better than just a treble cut, since your guitar already has that. Put your metal pedal in front of it and see how much range of tones you can get from it.
Clean on this amp is very good. You can have your amp set at 12 noon, and your guitar all the way up and it will be clean until you start hitting notes hard (or if you have hotter pickups, perhaps a bit sooner. Alternately, you can turn the amp all the way up and still get clean tones with the guitar just cracked open and swell into the realm of output tube distortion. It is very easy on the ears and very pedal friendly. Using external EQ helps you get the tone that you need/want from various axes.
I had ordered a new transformer for this amp (EDCOR 15 watt- the same one I used in my Valve Junior with great success- $20.64 plus $6.37 shipping), but I am happy enough with it the way it is (the output transformer in the Crate is much bigger than the Valve Juniors'- 10 watts instead of 5). I get deep tone from only a 10 inch speaker and I have to be careful not to use the neck pickup too much- it rattles the pictures and things on the wall in the living room. That transformer is going to have to wait for my 6550 single-ended project. One big output tube- should be cool and about 10 watts!
If you just want to add lots of gain easily and just get your feet wet in trying things, pull out resistor R27 (10K) and short out R 15 (100K) and that will get all the lost voltage (the sound) to the output tube and not lost in those 2 resistors. That way you still have the 2-stage op amp pre driver and it might be more of what you want (if more is better- like metal tone). I wanted pure tube and I got it with only an Exacto knife, 3 pieces of short wire, and some cutters and soldering rig, I didn't need to replace the output transformer, or add any parts in any location. Other than replacing the speaker, that was my only expense. I got the 50 watt Eminence for $12.00 each when I bought 4 from a music outlet store on line. I have used those speakers in amps from this 5 watt one to a stereo 15 watt rig and for a 40 watt combo as well. Tubes are all stock. Surely a better transformer and/or tubes will make a difference, but I got night and day difference with these simple mods. Sounds great for little $$$. If you want, and you can pull the board and replace it yourself, I can mod it for anyone for $40.00 plus shipping (which would be nominal in a Priority mail flat rate envelope ($5.00). There is hope for Crate V5 to become the 'next big thing in small amps.

Deafelectromark (alias manoteal):rockon:

Curious what Eminence speaker you used that actually cleared the chassis? It's a tight squeeze in there.

I really love the cleans on this amp.

 

[timothymegg]

Changed the speaker

I changed the speaker to an Eminence Red Coat Ramrod 75w speaker. Sounds great and it cleared the chasis. The height of the speaker is 4.3"

 

[schenkadere]

I changed the speaker to an Eminence Red Coat Ramrod 75w speaker. Sounds great and it cleared the chasis. The height of the speaker is 4.3"

Weird...maybe the magnet shape is different. Mine is 4" high and it touches. I can't imagine all the specs and tolerances are exactly the same on these cheesy Chinese amps. Guess you got lucky and I didn't.:thwap:

Just looked that one up...it's like 70 bucks...I only paid 80 for the amp...my mind can't justify that. LOL.

 

[deafelectromark]

Speaker fitting problems and solutions.

I used a 50 watt, 4 ohm Eminence that had a height of 3 1/2 inches, which is the same for most Fender Custom-made, 10" speakers. The original speaker is 3 3/4", so they both cleared easily. The actual opening depth before you hit the chassis is 4 1/4 inches. A friend wanted a Kustom, 50 watt, 8 ohm and 10 inch speaker and I decided to put it in my amp to see if it was clear. Well the speaker looks to be 4 1/4 measuring it out of the cab, and I popped it in and then bolted down the chassis screws and it felt like it WAS touching the chassis. But then I pushed down a little with my hands and found that the magnet was filling the gap due to it powerful magnet strength. I wedged in some credit cars to measure the gap and it came out to be 0.10 clearance (1/10th of an inch!) with 3 credit cards fitting in, and so I thought it was doable. So I pulled the amp out again and bolted the speaker to the proper torque, and put the amp back in again. But now the clearance was 0.20- twice as much. That was due to the speaker's cardboard mounting material being squished a bit by being bolted down.
There may be variations for this useful measurement, but I am convinced that any 10 inch speaker with a thickness of 4.05 to 4.15 will be able fit with at least 0.10 clearance between the amp chassis and speaker magnet. The Kustom sounds great and produces over 100dB with 5 watts input. Nice, no-shrilly tone and very good low extension, too.
I have two orders on the board mod I am doing to return it to a basically all-tube amp. I hope that their ears as as pleased as mine- I play this guy everyday and have no complaints. Wait and see their impressions after I send them back their modded boards.
Mark

I really love the cleans on this amp.[/QUOTE]

 

[schenkadere]

I used a 50 watt, 4 ohm Eminence that had a height of 3 1/2 inches, which is the same for most Fender Custom-made, 10" speakers. The original speaker is 3 3/4", so they both cleared easily. The actual opening depth before you hit the chassis is 4 1/4 inches. A friend wanted a Kustom, 50 watt, 8 ohm and 10 inch speaker and I decided to put it in my amp to see if it was clear. Well the speaker looks to be 4 1/4 measuring it out of the cab, and I popped it in and then bolted down the chassis screws and it felt like it WAS touching the chassis. But then I pushed down a little with my hands and found that the magnet was filling the gap due to it powerful magnet strength. I wedged in some credit cars to measure the gap and it came out to be 0.10 clearance (1/10th of an inch!) with 3 credit cards fitting in, and so I thought it was doable. So I pulled the amp out again and bolted the speaker to the proper torque, and put the amp back in again. But now the clearance was 0.20- twice as much. That was due to the speaker's cardboard mounting material being squished a bit by being bolted down.
There may be variations for this useful measurement, but I am convinced that any 10 inch speaker with a thickness of 4.05 to 4.15 will be able fit with at least 0.10 clearance between the amp chassis and speaker magnet. The Kustom sounds great and produces over 100dB with 5 watts input. Nice, no-shrilly tone and very good low extension, too.
I have two orders on the board mod I am doing to return it to a basically all-tube amp. I hope that their ears as as pleased as mine- I play this guy everyday and have no complaints. Wait and see their impressions after I send them back their modded boards.
Mark

I really love the cleans on this amp.

[/QUOTE]

I used your post. I removed the chassis and pressed down hard on the speaker while tightening the screws down hard. Then(fighting the magnet)I repositioned the chassis and pulled it away from the speaker while tightening those screws. I did it...I got clearance...may only be .10" but it is definitely no longer touching and that speaker is definitely 4". My cabinet wouldn't take anything larger unless I opened the chassis screw holes larger. I'm happy because I really like the Warehouse speaker. It was a pain in the *** for sure...it's hard to be that firm and be careful at the same time, but I did it. No damage I can see...or hear...sounds great. Thanks for the post!:dude:

 

[jim p]

Not a tube screamer

The first stage op amp is not a tube screamer it is an overdrive stage for the first triode. I have seen some postings for the V5 and its father the VC508 calling the first stage a tube screamer it is not. The VC508 has problems in that the op amp has only +/- 7 volt supplies while the V5 has +/- 15 volt supplies so you should not run into the rails (op amp clipping) with the V5. If you are worried about the supply limits R19 and R20 can be lowered in value to raise the rails to +/- 18 volts for more headroom. A tube screamer is an op amp with two diodes in the feedback to cause clipping which is a poor mans version of what a tube will do. Also the choice of op amp in a tube screamer is based on the op amp recovery time from clipping which should never occur in the V5. Changing the op amp in this amplifier to a JRC4558 would be a bad idea because its low input impedance will kill your highs from the guitar (plus the over all spec for the TL072 is better in noise and input impedance it is a fet op amp not a bipolar). The classic Ibanez tube screamer is a 250k load on your guitar while most of you tube types like the idea of 1 Meg to keep the highs. If you like the sound of a tube screamer fine but it is trying to simulate what an overdriven tube will do and you have a tube to overdrive so no reason to use it. If you want to overdrive a tube amp using an Ibanez tube screamer is not the way to do it, you want to up the signal level into the amplifier without clipping so the tube in the amp will clip.
Of course you need to get a volume control between the first and second triodes in the V5 to use the op amp as an overdrive if not it is just a volume control. So you will have a solid state preamp with tube output .

 

[jim p]

Easiest bang for your buck mod

The easiest mod to do that I can think of is to keep the volume pot as a gain pot and convert the tone pot into a volume control. You will have no tone control on the amplifier but there are other amps sold that do not have a tone control. In another post I talked about the op amp as an overdrive so that should give you an idea of how things will work. There are no cuts in this mod and the pots do not need to be removed from the PCB (see that some people have had problems removing the pots). The tone pot will short or pass the signal from the first triode to the second relative to its resistance setting. The attached photos are of the marked up schematic and the PCB with orange arrows on the parts to be removed C4 is hard to see it is hiding on the right hand side of the tone pot.
1) Components that must be removed for mod C5 C6 C4 and R27

2) R13 I think should be removed you do not need the extra gain in op amp stages.

3) C24 should be removed and replaced for better bass with 47nf or for more bass change to 100nf

4) C26 should be removed for a flat signal output from amplifier it can be changed to 22nf for a bright output which may be better for overdrive if you save C6 you can parallel C26 with it to get 20nf (see other brightness mod in this post I would not do both)

5) Jumper from feedthrough (PCB hole) of C5 not connected to ground (right next to tone pot) to feedthrough (PCB hole) of R27 not connected to ground (hole connected to R15 by trace).

Note: Damage to pots can occur when you remove the knobs so take it easy and walk the knobs off do not just pry on one side protect the front panel with thin piece of wood and use a flat blade screwdriver against the bottom of the knob.

Note: That the resistor and capacitor leads have been bent outwards or inwards so heat the solder joint on the back side of PCB up and use soldering iron tip to straighten before you try to remove them. If not you may damage the plated hole the resistor or capacitor is attached to causing a break in the circuit on the PCB.

Note: The clear RTV (room temperature vulcanizing is what it stands for) can be removed with needle nose pliers and careful scraping (wood or fingernail) if it is still on the board and gets into your solder joint you may get a cold solder joint due to it so keep an eye out for it.
Note: In pictures you can see that the screen grid resistor has been attached where it should be at R16 R25 and C16+ junction

Other possible tweaks
For brightness remove C28 replace with 4.7nf (If you got C4 out in one piece you can put it here)
For more gain short out R15 with R15 as stock you get 0.316 of the signal at the plate of the first triode. With R15 shorted you get 0.362 of signal 14% more. If you want go crazy and short out R30 or R29 for more yet but if you used C28 for brightness need to make it 10nf insted of 4.7nf

If you want I can use a schematic capture program to make a schematic that may be clearer then attached photo.
If you see any error in this post or any others that I have done let me know do not want to misinform anyone (the web is good for that).
Thanks and Happy Motoring

 

[jim p]

Bad PCB to chassis ground location

For those of you that are into possible noise problems due to ground loops the PCB to chassis ground is in a bad location. If you look at the bottom of the PCB you will see that the PCB attaches to the chassis close to the front end of the amplifier (near guitar input). I have cut the traces around the mounting hole then moved this ground to the power supply side of the PCB by attaching the plated hole to the ground plane with solder and solder braid. Just need to scrape off solder mask on bottom of PCB with razor blade, tin the area with solder and bridge plane to plated hole. See attached photos of before and after.

 

[jim p]

Weber beam blocker

It’s been posted that with the 10” speaker in a small box the output is boxey. Has any one used a Weber beam blocker to see what effect this would have on changing that?

 

[jim p]

beam blocker test and DIY beam blocker

Well rather then wait for an answer to my beam blocker question I tried a simple test of using a relish jar lid propped against the grill cloth to see how things sound. I like the result the highs are slightly muted and the sound a bit more off axis. It is an easy thing to try yourself to see what you think. (See attached photo)
So instead of buying a blocker have decided to do the arts and craft thing and make my own. Looking in the recycling bin decided to use the bottom of a Mountain Dew can with some prepunched pipe hanger I have. You have to be careful cutting up the soda can to not lacerate yourself, once it is installed in the amp children and small animals should be safe from its sharp edges. The inside bottom of the can is domed so it looks like the real thing. To keep the dome in place I filled the void in the back with some calk I already had open. I might paint the thing or just use a magic marker to make it black. And yes that speaker in the picture is the stock V5 speaker it also makes a neat refrigerator magnet.