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Author Topic: Proamplifiers VSQ 65 combo having a weird problem  (Read 4688 times)

Meshuggah333

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Proamplifiers VSQ 65 combo having a weird problem
« on: June 21, 2016, 04:39:41 AM »
History :
This amp is a gift from a friend, it took dust in a corner as he wasn't using it anymore. I don't really know what happened to it in the 26 years it's been out of the factory :D
I just know the preamp was retubed 2 years ago (some GT 7025 in V1,V4 and GT 12AX7 in V2, V3. Done by idiots and thieves but that another story)
It's from the Proamplifiers brand from Suffolk, England. The brand did a lot of amps in the 70's, 80's up to the mid 90's then did crash due to them being dependent of the US market (through the KMD brand) and basically loosing their only contract.

Problem :
If I cut all volume down, on any channels, I still hear a faint signal from the input.
Let me explain: it's as if even with the preamp completely cut off, I had a slight bit of input signal leaking through to the power amp.
This is even more obvious when I put a pedal that boost the input signal a lot, it sounds like a wet/dry signal (with distortion/fuzz pedals it's just horrible)

Do any of you have an idea of what ​​the problem might be?

The amp inputs 1/4" connectors are switching the preamp in and out of the signal path (they are switching connectors, I imagine it was done to prevent noises when nothing is connected to the amp), that might be coming from that but I'm not sure...

I'm certainly going to send it to a tech for a check up but I'm trying to solve most problems before that.


This is not mine but I have the exact same.

My first post and I already need help  ::)
« Last Edit: June 21, 2016, 04:42:17 AM by Meshuggah333 »

phatt

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Re: Proamplifiers VSQ 65 combo having a weird problem
« Reply #1 on: June 21, 2016, 06:58:13 AM »
Hi Meshuggah333 and welcome :tu:

A pot may not be grounding fully and signal will bleed through or a relay might be working quite right.
Sounds like it's a very low level signal bleed through and I'd not worry about it unless it becomes louder.
I have an amplifier which has the same glitch but in 20 years it's never caused any problem.
Phil.


Meshuggah333

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Re: Proamplifiers VSQ 65 combo having a weird problem
« Reply #2 on: June 21, 2016, 07:40:37 AM »
Hi, thx.
Playing the amp by itself, the bleeding isn't a problem. But I love stomp boxes, and some of them have a very hot output and sounds nasty direct to a poweramp (most fuzz sounds terrible that way) and make the bleeding very audible and hard to manage.
So that could be a dry solder joint on one of the pot? I'm planing on extracting the amp from the combo in a few days, pots are in bad need of love with contact fluid, I'll check for bad solder joints.

phatt

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Re: Proamplifiers VSQ 65 combo having a weird problem
« Reply #3 on: June 21, 2016, 09:10:30 AM »
Just a long shot,, turn the Reverb knob full off and see if it makes any diff?

I'm a bit confused about the pedals?  Are you using the FX loops for the pedals?
That could be part of the issue,,, try using pedals Before preamp an see if that helps.
Phil.

Meshuggah333

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Re: Proamplifiers VSQ 65 combo having a weird problem
« Reply #4 on: June 21, 2016, 10:04:41 AM »
I've tried with all the knobs on zero, it's the same.
Fuzz boxes tend to generate a lot of hi end which is fine when it's mostly filtered out by the preamp tone stack, but here the piercing treble bleed through to the power amp. That sounds pretty bad.
Same boxes sound fine on other amps.
« Last Edit: June 21, 2016, 10:19:13 AM by Meshuggah333 »

Enzo

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Re: Proamplifiers VSQ 65 combo having a weird problem
« Reply #5 on: June 21, 2016, 07:55:37 PM »
It sounds to me like crosstalk.  Later points in the circuit are picking up the signal from the parts before the controls.

The question left in my mind is this:  You hear this with all the controls at zero, but we never PLAY with all controls at zero.  With all controls set like you were using the amp, what is the problem that way?

Meshuggah333

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Re: Proamplifiers VSQ 65 combo having a weird problem
« Reply #6 on: June 22, 2016, 05:39:12 AM »
As said, stomp boxes with a lot of hi end are unusable, as the piercing hi end leak through to the power amp.
Try to use a fuzz into the effect return of your amp, and you'll know what I mean.

J M Fahey

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Re: Proamplifiers VSQ 65 combo having a weird problem
« Reply #7 on: June 22, 2016, 09:38:37 PM »
Not necessarily a pot/solder problem, and I guess you´ll find nothing that way, it looks like plain old crosstalk which is through the air signal jumping from one point to a later one, that´s why volume controls don´t *seem*  to have full effect; truth is signal is bypassing them through other unseen "air" paths.

Being capacitive coupling, even 2 parallel wires 2 inches away will *still*  be coupled to each other by a *tiny*  cap, think 1 pF or thereabouts, then high frequencies are coupled more than any others, so it´s common to hear faint, tiny, buzzy sounds in the background ... what you seem to be hearing.

Meshuggah333

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Re: Proamplifiers VSQ 65 combo having a weird problem
« Reply #8 on: June 23, 2016, 03:55:33 AM »
After studying the amp a little closer my guess is it's a problem with the switching input jack, it switches the preamp out when you don't plug a cable in.
Unplugged state : input is wired direct to the power amp (it seems), certainly to prevent noise from the preamp when nothing is plugged in.
Plugged state : input is wired to the preamp, but it seems the path to the power amp is still ON, and it should be OFF. So that create a parallel signal. The signal leaking through is perfectly clear tho, like it's the full signal from the pickups into the power amp.
If it's as I guessed, it's an easy fix. But there might be something else going on, I won't know until I open it up.
The input part of the amp seems fishy anyway, as it doesn't properly load the pickups and brings a lot of noise on the Hi input and a lot less on the Lo input.

phatt

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Re: Proamplifiers VSQ 65 combo having a weird problem
« Reply #9 on: June 23, 2016, 09:01:05 AM »
More likely the input socket will be (should be) switched to Common when cable is removed which kills the input.
I doubt it would go to power amp input,, if it does it may even be part of your problem. Someone may have messed up in a previous repair.  8|

Found this page,,
http://www.chambonino.com/work/miscguitar/misc20.html
might be of some help in describing the issues.

Phil.
« Last Edit: June 23, 2016, 09:03:54 AM by phatt »

J M Fahey

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Re: Proamplifiers VSQ 65 combo having a weird problem
« Reply #10 on: June 23, 2016, 04:07:22 PM »
A common trick, used by Marshall among others, is to use an extra unused jack contact to *ground*  preamp out or power amp in, that must be the track you see .
It is not used to send any signal but to ground hiss when no guitar is plugged in.
So it´s more of a solition than a problem.

Again: won´t obsess with what happens while the guitar is unplugged.

 

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