Vox Pathfinder 15 Doesn't seem quite right.

[Commodore 64]

So, I picked up a Pathfinder 15 from Craig's List today. It's an older one, with no reverb. Off the bat:

1. Tremolo doesn't work.
2. Does not seem very loud. With the volume dimed, Gain at about 9-Oclock (1/4 turn), the volume is very low. Like barely audible. I was sitting next to it on a bed playing, with the volume dimed and the gain at 12-Oclock, and it wasn't even close to being too loud.
3. The speaker farts out horrificly. It really sounds like ***. Even at these low volumes, the E and A string open cause it to fart out. Sounds nasty.

The amp can't be this bad can it? There has to be something wrong, right? I have loads of capacitors and resistors and a soldering iron. Someone help me get started troubleshooting.

 

[sumitomo]

Well after soldering and testing don't work,break out the 5 lbs. precision adjusted and go to town!!! Sumi

 

[ZMAN]

I have the 15R and it is plenty loud. Mine is new and was impressed with how good it sounded. There must be something wrong and I am sorry I can't help with the electronics. If it doesn't work I take it to the shop. I can fix just about anything mechanical but electricity scares me!

 

[Eric]

My main guess, which is no better than yours, is that either something is loose or maybe they put in a new speaker that's ridiculously high resistance, like a 16-ohm or something (I think that would suck power out). That's the limit of my electronics expertise.

Do you have a multimeter? That would be your best tool in troubleshooting.

 

[Commodore 64]

http://aga.rru.com/TechTips/disp.cgi?file=RobertBraught/voxc30ldr.tt

by Robert M. Braught

As some of you techs know by now, the tremolo 'assembly' (opto-coupler p/n LT9914) has a reputation for failure... causing distortion in clean channel operation, poor/no tremolo... one on the frizz can make the amp sound like the output IC's blown...

Word from Korg USA last week, no 'recall' in the near future, no substitute part recommended, etc. From my field experience it appears the LDR portion fails, possibly linked to voltage/current (? customers have reported after 'blasting' signal through their amp, it 'quit'.) List price on the 'original' Vox(Korg USA) part $24

I've successfully tested a 'regular' Vactrol, ala Fender p/n 16282, OEM # VTL5C3/2 as a suitable replacement. Use both LDR elements in series (leave the center wire unconnected / clipped.) The circuit will require 'recalibration', twiddle ref VR11 and VR12 (on the main board) 'til tremolo sounds right ('normal' full depth) and signal pass is good with tremolo 'off'. No harm will come from the adjustments being dimed or turned back full CCW. This sub is less than half the part cost of the orig Vox part, and my experience with the Vactrol units (as in Fenders, etc) is that they are a very high reliability part, with long life expectancy. FWIW this will not change your tone.

Probably can't use something designed for a 30w in my 15w, though huh? But there does seem to be hope. Just gotta find the right part.

 

[Spudman]

Sounds like a connection of some kind. Either a lose wire or bad solder connection. Have you tried new tubes? :rollover

If you are getting any signal I would take that as a good sign. Probably your issue can easily be fixed.

 

[M29]

Can you try an extension speaker?

I would think it is a bad connection somewhere too. If it has a power fuse try a new one.
Try wiggling wires while it is on and see if you get any reaction like static or volume change. Wiggle the cord at the input jack, speaker wire.

Just a few things off the top of my head. :thwap

 

[Commodore 64]

I really don't think it's a connector or speaker problem It sounds a lot like the optocoupler problem on Cambridge series (this old pathfinder is probably same time period). There's a .rar file on this site that has a ton of info. : http://www.cruses.se/cam/index.htm.

Here's a little taste:

Vox Cambridge 30 Modifications from Harmony Central

The following comments were lifted from a Harmony Central review for the
Vox Cambridge 30 Twin Reverb.


FOR ALL C30 OWNERS!!!!! READ THIS!!!!!!! THIS IS VITAL !!!

The villain of all bad reviews of this amp has a name and location!! It is a crap part that was used on the amp!

It's the opto-coupler model LT9914 which is responsible for the tremolo and its located on the circuit board next to the volume pot, all users MUST change this part for a VTC5L3 optocoupler!! even those who didn't yet have the problem.

All you hear about crappy sound, low volume, volume variation while playing (after getting warm).....

Found a replacement part: http://www.alliedelec.com/search/productdetail.aspx?SKU=9800710

 

[Eric]

So...it's that optocoupler, but the guy was also talking about a couple of pots and an opamp? That was a little rough to follow. Probably didn't help you that he got the model of the replacement optocoupler wrong too.

Anyway, that's good that you have a probable culprit.

 

[Commodore 64]

So...it's that optocoupler, but the guy was also talking about a couple of pots and an opamp? That was a little rough to follow. Probably didn't help you that he got the model of the replacement optocoupler wrong too.

Anyway, that's good that you have a probable culprit.

I ended up getting in email contact with a guy. He rebuilds Cambridge amps. That chip stuff related to Cambridge amps, it doesn't apply to my Pathfinder, so I removed it, heh.

But yeah the actual part is a VTL5C3 . :dude

 

[Kazz]

Dude......did you buy this without testing it? I would think after your last Craigslist blooper that you would have insisted on testing it out before shelling out the cash.

 

[Commodore 64]

Dude......did you buy this without testing it? I would think after your last Craigslist blooper that you would have insisted on testing it out before shelling out the cash.

I bought it as-is for a good price. It's 50 dollars, not 500. I have no issue with the seller or the purchase. I just want to know how to fix it. And it looks like it's likely to be $4.50 part.

 

[Commodore 64]

Just got a schematic from a person, with whom I've dealt with on CL. I wish he'd make an account here, he knows a ton. In any case, he added reverb to a Epiphone Valve Jr., and I was thinking of maybe trying something similar with this Vox (as long as I have it apart), using a Belton module. Just gotta figure out where to get 5v from the Pathfinder.

 

[Duffy]

Vox

The Vox Pathfinder 15R is an awesome amp, very loud 15 ss watts, great tone and variability with a great reverb and tremolo, hallmarks of this classic amp, reminicent of the AC15 and AC30 style, but inexpensive and ss.

Your amp has serious problems, problems that you probably are not capable of diagnosing and fixing, certainly by touch and go methods.

I would take it to a qualified tech and have it checked to see if it is worth fixing. Many things could be wrong. More than one thing could be wrong. The tremolo should work for one and it should be loud. There are two standout problems right off the bat.

A new Pathfinder 15R costs 139 dollars and has a warranty, and should last over twenty years of trouble free play, with no problem.

Maybe someone tried to jack this one up to use in a heavy metal band and overamped the thing to the point of ridiculousness. It could just be blown out, blown out transformer or such and could be expensive to get looked at and fixed.

I hope you can get it checked out by someone without incurring too much cost and then make a decision if you want to work on it.

I have a Vox DA5 also, that is an awesome "Chromie" with modelling and effects and works off "C" cell batteries or wall current. It is great for taking camping and has a switch to switch down to a half watt, two watts or five watts. It is loud a a half watt and will play for six hours on a half watt. Great for camping trips.

 

[DeanEVO_Dude]

I don't know if I missed it or what, have you another speaker to try? It does sound like you might have a blown one.
As for the power rating of the speaker, it should not matter too much. If you have a 15 watt amp and put a 25 watt speaker in there, there should not be much volume loss at all. What you get with the hight wattage speaker is less or no speaker break-up. What will give you a volume change are the other two speaker specs; Sensitivity and Impedance. Lower impedance could/will cause damage to the amp and louder (precieved) volume, and higher could/will do the same. Lower sensitivity will have a lower volume and a higher sensitivity with be louder. I have a 30 watt amp that has a 75 watt speaker in it, it is not any louder than the one it came with originally, but it does not break-up at cranked volumes like the OEM did.

So, bottom line? I would try a different speaker before the 10lb adjustor. Hope this helps a bit. Cheers!

 

[Commodore 64]

My Allied order came today. Replaced the optocoupler, and the Vox Pathfinder rides again. All better now. I can't say for sure yet, but I think I might like the Vox tone better than my SF Champ (*gasp*).

Very simple, unsolder 4 leads remove bad part, put in new part and solder back on 4 leads.

Should anyone else stumble across this thread whilst troubleshooting or googling "Cambridgitis", shoot me a message, I ordered 3 extra optocouplers, and it won't cost much for me to drop one in a regular old envelope (they are very small).

 

[DeanEVO_Dude]

Good job! Great to hear that you got your new (to you) amph workin' again! Gotta love them easy fixes, huh!

Cheers!

 

[kerc]

Pathfinders are great little amps. I played mine constantly since 1998 until the tremolo went this year, and then it started sounding like crap.

I still have it there, wishing it'll come back from the ashes like the phoenix.

Sigh.

 

[Commodore 64]

Pathfinders are great little amps. I played mine constantly since 1998 until the tremolo went this year, and then it started sounding like crap.

I still have it there, wishing it'll come back from the ashes like the phoenix.

Sigh.

ONe of the symptoms of optocoupler failure is the trem....

 

[ZMAN]

Just got a schematic from a person, with whom I've dealt with on CL. I wish he'd make an account here, he knows a ton. In any case, he added reverb to a Epiphone Valve Jr., and I was thinking of maybe trying something similar with this Vox (as long as I have it apart), using a Belton module. Just gotta figure out where to get 5v from the Pathfinder.

Help me out on this one, I have no knowledge of electronics. That schematic shows how to hook up this Belton module. What does the belton module consist of? I see a 12ax7 which I know is a tube. I was wondering what the difference in price would be to use a reverb pedal instead, or do you just like to tinker? The reason I am asking is that I have seen guys do a ton of mods to a Blues Junior, and make it unsellable because they have too much in it.
Glad to hear you diagnosed the problem right off. The trem seems to be a common area of failure. Is the 15R basically the same design with a reverb added?

 

[Commodore 64]

That Belton is a digital reverb module. I don't know how much it costs off hand.

So I think the tremolo in the Pathfinder isnt' working as it should. The optocouple fixed all of the volume issues, but tremolo is very very weak. I was not able to get it to do much. You can hear a trem effect, just not much. So I'm looking into other things at them moment, and thought I'd add the schematic to this post, since they aren't super easy to find.

 

[Duffy]

Pathfinder

I really like the Pathfinder 15R and a brand new one costs 119 thru MF, no affln.

Mine has been a workhorse and never been a problem, with the reverb and tremolo circuits always working strong.

I would want to get it right.

I bought a Cambridge two twelve a couple years ago used and when I got it home it sounded really bad, with no volume, no tremolo, etc. I read all the fixes on the internet, octocoupler, etc., etc., and decided within hours to bring it back for a refund. That turned out to be really difficult to get. I wound up having to put the money I paid for it toword another purchase. The purchase I then made was a very solid brand new amp of very high quality.

I have a considerable amount of electronic experience, but not that much with amps in particular and I had a gut feeling that trying to fix that Cambridge was going to be a project that was going to cause me a lot of stress and result in very little reward. Plus my confidence that I could actually fix the amp the way it needed to be fixed was very low. It would have been a wild goose chase and getting it fixed by a tech would have cost way more than it was worth.

I hope you can fix that Pathfinder without stressing out too bad or wasting a lot of time and money. They are so inexpensive to begin with that you can get a factory clean one for a very small amount and have a great little amp.

I gotta say I really love my little DA5 Vox that runs off C cell batteries or wall current. Great for trips and camping and so forth and has some of the "Chromie" modelling and effects. Really a cool 139 dollar amp. I got mine for less, new.

 

[MoustacheMod]

My Allied order came today. Replaced the optocoupler, and the Vox Pathfinder rides again. All better now. I can't say for sure yet, but I think I might like the Vox tone better than my SF Champ (*gasp*).

Very simple, unsolder 4 leads remove bad part, put in new part and solder back on 4 leads.

Should anyone else stumble across this thread whilst troubleshooting or googling "Cambridgitis", shoot me a message, I ordered 3 extra optocouplers, and it won't cost much for me to drop one in a regular old envelope (they are very small).

Do you still have any extra optocouplers?
I have a Cambridge 30 Twin that has THE problem.

Cheers

 

[Commodore 64]

Do you still have any extra optocouplers?
I have a Cambridge 30 Twin that has THE problem.

Cheers

Yep. Send me a PM with your address and I'll throw one in an envelope.

 

[MoustacheMod]

swapped out the bad opto-coupler in the cambridge and its sounding great!
Thanks Commodore 64!

 

[Commodore 64]

No problem. I also sent out optocouplers to withnail and someone else, so I'm all out of them now, but I'm glad I could help out.

In any case, the link to the part from Allied should still be good, if anyone else finds this thread via troubleshooting (google).

 

[sub006]

I have the 15R and it is plenty loud. Mine is new and was impressed with how good it sounded. There must be something wrong and I am sorry I can't help with the electronics. If it doesn't work I take it to the shop. I can fix just about anything mechanical but electricity scares me!

I've heard the 15R speaker actually "breaks in". It loosens up after about 20 hours of use and sounds even better!

 

[jim p]

On reverb and added phase shift

I was just looking through this thread and would figure the quick test for a bad opto would be to parallel pins 3 and 4 with a resistor to bypass it. If you have good clean sound then either the opto or the drive on its LED would be your problem. I found a schematic for the Pathfinder on the web and posted a link here http://www.thefret.net/showthread.php/17811-Something-blew-on-my-Pathfinder-15R...-help! It is not a very good one hard to read but still gives you something to go by.
That drawing for adding reverb is a bit vague and I see some things that could be a problem. The input impedance of the Belton module is only 10k by there data sheet and I find it to be closer to 5k an impedance that low is a problem in a tube amp. You can hook it up after the first coupling cap in a VJ with a 220k resistor in series for a fixed input level that will still cause you to loose gain in the amp but not too much. The drawing shows a LM7805 for 5 volts with no added decoupling. The DC filament supply in a VJ is really pulsating DC because the filter caps are too small by a factor of 10 to 20. Also the LM 7805 needs 2 to 2.5 volts greater then 5 volts on its input so the 5 volts out of it will probably have a high ripple content. If you use an LDO 5 volt regulator that will solve part of the problem. Also a Shotkey diode anode to the plus heater supply with a filter cap of 2200uf connected to the cathode will give you a clean raw supply for the regulator. There should also be a filter cap on the output of the regulator another 2200uf there should work fine.

On the tremolo side just as a way to add phase shift as well as volume level change you could add a cap to ground after the variable resistor in the optocoupler. I can’t tell the resistance range of the opto from the schematic but figure 1k to 100k as the range would mean a cap of 1nf to 22nf added between the opto and C18 on the schematic would give you a phase shift as well as a volume change. This is more like the trem on a Magnatone amp if I am correct from what I remember. Another way to go would be to connect the added cap to ground through a pot to vary the degree of phase shift my guess a 100k audio pot would be a good choice.

For adding reverb using a spring tank would probable come to the same amount of parts and cost as the Belton digital module plus you will not need a 5 volt supply.