Amp problem-need Tech. help ..

[Blaze]

Blackstar effects loop-need Tech. help

I have purchased a second hand Blackstar Ht 5 wich sounds realy nice..

I have this problem when switching from the Od channel to the clean ..
There s a delay ,means the effect comin from the OD channel and effects loop (delay, verb) play over and pretty loud
in the clean channel for few seconds when switchin(no pedal involved in the amp front here) .


I tried changin the + 4 db to -10 db switch (effects Loop)
but still.The modulation pedal reverb and delay are set in a normal way , not to loud..(There s no mix pot for the effects loop )

the delay and Verb are nt soundin the same in the clean and the od channel..

the effects, being placed after the pre amp, should not be affected , is nt

Seems to me that the effects loop does nt work right..Could it be..

Link to Owner manuel :http://www.blackstaramps.co.uk/pdf/handbooks/ht-5%20handbook.pdf

Just wondering if you amph tech guys could help me on this one ..

 

[tunghaichuan]

Blaze,

My best guess is that something is malfunctioning in the switching circuitry. Since I don't have a schematic, I don't know what they are using for switching. Could be some kind of relay.

From your description it sounds like the clean channel is not being grounded out when switching over to the drive channel. This would allow some bleed through when switching.

Have you tried contacting Black Star's tech support? I would email them and see if they can't help you out. What you're describing could be a known fault and they might be able to advise you the best way to fix it.

Here's a contact page:

http://www.blackstaramps.co.uk//resources/index.html

tung

 

[Blaze]

Blaze,

My best guess is that something is malfunctioning in the switching circuitry. Since I don't have a schematic, I don't know what they are using for switching. Could be some kind of relay.

From your description it sounds like the clean channel is not being grounded out when switching over to the drive channel. This would allow some bleed through when switching.

Have you tried contacting Black Star's tech support? I would email them and see if they can't help you out. What you're describing could be a known fault and they might be able to advise you the best way to fix it.

Here's a contact page:

http://www.blackstaramps.co.uk//resources/index.html

tung

Thanks to you Tung , i found this .

http://www.thegearpage.net/board/sho....php?p=6800818

I wrote to Blackstar ,we ll see

Good day !

 

[Blaze]

No reply from Blackstar...


Found this vid showing the problem



I found a schematic if some tech wants to have a look..

http://www.thegearpage.net/board/showthread.php?t=624537

 

[marnold]

Oh! Now I understand what you were talking about. That's very odd. Seems like there's definitely some weird problem with the effects loop.

 

[jim p]

Ic1?

Looking at the schematic IC1 looks to be the latch for gating which preamp chain you are going through. Problem I have is the schematic does not make sense can’t see how you get the latch to toggle by how it is drawn. Any chance for a PDF of the schematic? All the signals in the preamp chain are gated through p channel fets the J175s you see all over but I don’t think one of the fet is your problem.
As far as operation when pin 1 of IC1A is low (approx -15 volts) that is the effects/overdrive channel active at that time pin 7 of IC1 should be high (+approx 15 volts). For clean it is the opposite pin 1 at high pin 7 a low.
Hope this helps you some.

 

[Blaze]

Looking at the schematic IC1 looks to be the latch for gating which preamp chain you are going through. Problem I have is the schematic does not make sense can’t see how you get the latch to toggle by how it is drawn. Any chance for a PDF of the schematic? All the signals in the preamp chain are gated through p channel fets the J175s you see all over but I don’t think one of the fet is your problem.
As far as operation when pin 1 of IC1A is low (approx -15 volts) that is the effects/overdrive channel active at that time pin 7 of IC1 should be high (+approx 15 volts). For clean it is the opposite pin 1 at high pin 7 a low.
Hope this helps you some.

Thanks Jim,

I found this schematic on a forum , don t know if it is accurate..

Too bad Blackstar does not cooperate much ,no schematics ,no instructions..

 

[jim p]

The Schematic maybe inaccurate

I was just looking for the schematic myself and found the one you posted is drawn from pictures so good chance it may be wrong in the section showing the latch.

 

[Blaze]

Here s a pic

 

[Blaze]

Here s some pics

 

[marnold]

Just a ping to see if you heard anything from Blackstar yet.

 

[Blaze]

Just a ping to see if you heard anything from Blackstar yet.

No reply from them , i don t expect any..

My tech is lookin at the schematic and pictures i ve sent him ,i should have news pretty soon ..

 

[jim p]

No simple solution

I saw at the other site you posted the problem at that someone said it is because the signal from the reverb is still from the overdrive channel do to reverb delay and is then switched into the clean channel. As he stated you would probably need to locate the reverb effect after the two volume controls in the amp to even the signal level out. But even if you did that the reverb is anywhere from one second to three seconds of delayed signal so if the switching is sudden you will have a few seconds of the old sound from the reverb. If the levels between the two are close then the the overlap will probably be less abrupt but would still be there. You would need to mute the signal from the reverb equal to its delay when channel switching to prevent this from occurring. So a solution for this would not be easy you would need a wet and dry signal mix the reverb being the wet and a one shot that would create a 3 second mute on the wet signal when channel switching.

 

[marnold]

jim,

That would seem to make a lot of sense. I suppose it would be worse if you had a massively long delay/echo. Although you could probably make some interesting/weird sounds with it. My guess would be, then, that this would basically happen with any multiple-channel amph with an effects loop?

I hope the problem is that simple because I'm still leaning towards a Blackstar. I really liked the way that mini-stack sounded at GC.

I am somewhat surprised that you haven't heard back from Blackstar because when I emailed them about the mains voltage problem that was in the original run (none of which made it to North America AFAIK), they responded quite quickly.

 

[Blaze]

jim,

That would seem to make a lot of sense. I suppose it would be worse if you had a massively long delay/echo. Although you could probably make some interesting/weird sounds with it. My guess would be, then, that this would basically happen with any multiple-channel amph with an effects loop?

I hope the problem is that simple because I'm still leaning towards a Blackstar. I really liked the way that mini-stack sounded at GC.

I am somewhat surprised that you haven't heard back from Blackstar because when I emailed them about the mains voltage problem that was in the original run (none of which made it to North America AFAIK), they responded quite quickly.

Well if you watch the vid again ,the delay tail boost is pretty loud and annoying,seems that time-based effects(delay-reverb) are specifically affected in this case..

Is the effects loop path wrong or defective ?

I guess a wet - dry signal control would help but if reverb & delay are placed before the volume control in the path they act an uncontrolled way ..

I d like to know if it s my own amph or if they all do the same..

Dispite the problem this is a very cool sounding little amph..

I e mailed them again ,hope to get some reply..:crazyguy

 

[Blaze]

Well ,my tech fix it by sending the signal post to the volume level so now the effects, mainly time-based are sounding just like they are suppose to , no more tail boost between channels..

It seems that the amph is designed this way so before buyin a HT- 5 ,ask yourself if you want the effects loop to function this way cause you might have to modify on your own expense..

I do not know if Blackstar has changed the design, i have never received no response or cooperation from them.

 

[marnold]

Well ,my tech fix it by sending the signal post to the volume level so now the effects, mainly time-based are sounding just like they are suppose to , no more tail boost between channels.

I guess I'm unclear as to exactly what he did. Can you amph gurus translate this into, erm, moron so I can understand?

 

[jim p]

the levels are more in balance

Without a marked up schematic to be totally certain sounds like the effects mix is added in at the volume control section so the level will be more equal between clean and boost (distort). This will equalize the sound level from the reverb when switching but still being reverb, chorus or any time delay effect there should still be some old sound when switching. I would think it is less noticeable due to the levels being more in balance between the two. He posted the same question at the gear page and the one of the answers there pointed out the levels being a problem and a solution might be to keep both volume levels the same between the two channels. This short chunk of old sound should occur in any amp the only way to stop it would be to mute the effect for a few seconds when channel switching. Think of it as thunder and lightning you see the flash and know the boom will follow you could cover your ears and lessen the effect but that sound is still in the pipeline.

 

[marnold]

Without looking at a schematic it's probably hard to say for sure, but if that is in fact the way Blackstars are wired, how would that compare with the circuit for any other two-channel amph with an effects loop?

 

[Blaze]

Here s a schem. of the mod. my tech made..Follow the blue line..

 

[jim p]

It all goes back to the volume levels being different between the clean and overdrive channels. If the amp was set up with a gain and level control before a master volume with the loop in and out at the master volume you would be about where you are now. What I find interesting about the schematic is it looks like the clipping on the overdrive channel is done in an op amp stage IC3A with diodes in the feedback. Instead of clipping the 12AX7 that is in the preamp section, it would be nice to check the amp out with a scope to see if that is really the case.