ADA Depot - A Forum To Support Users of ADA Amplification Gear

Let's Get Technical => Troubleshooting Problems => Topic started by: Auntie Ada on July 27, 2015, 10:41:40 AM

Title: Low Volume & Unpleasant Distortion in one output channel.
Post by: Auntie Ada on July 27, 2015, 10:41:40 AM: What a coincidence.....I just joined this fab forum and my MP-1 starts to go wrong. On one side of the stereo output the volume has all but disappeared and when I play hard there's this spitty, farty distortion on that side only (even on SS setting). Is this indicating that one of the valves is going ? There's no microphonic squealing at all.....yet.

Help, dudes !
Title: Re: Low Volume & Unpleasant Distortion in one output channel.
Post by: MarshallJMP on July 27, 2015, 02:40:48 PM: Is this a V1 or V2 mp-1 (top switch or not)?

Plug in a stereo headphone in the headphone out jack and see if both channels works or not and let me know.
Title: Re: Low Volume & Unpleasant Distortion in one output channel.
Post by: Dante on July 27, 2015, 09:11:59 PM: Quote from: Auntie Ada on July 27, 2015, 10:41:40 AM
What a coincidence.....I just joined this fab forum and my MP-1 starts to go wrong.

I promise, it was only coincidence. I do not have a big enough brain to devise a device that makes your MP-1 go wonky as soon as you join. Don't you worry man, somebody in here will get you straight, they always do ;) and you're family now.
Title: Re: Low Volume & Unpleasant Distortion in one output channel.
Post by: Auntie Ada on July 28, 2015, 02:47:52 AM: Thanks guys, I feel right at home.
I think it's a v1 but I'm at work at the moment so I'll check when I get home and come back to you.
Watch this space...
Title: Re: Low Volume & Unpleasant Distortion in one output channel.
Post by: Auntie Ada on July 28, 2015, 10:07:59 AM: There's no top switch that I can see. I tried the headphones test (good call, Batman) and it sounds a-OK in the 'phones.
Does that give anyone a clue ?

:dunno:
Title: Re: Low Volume & Unpleasant Distortion in one output channel.
Post by: MarshallJMP on July 28, 2015, 11:46:43 AM: Ok,could be opamp U10 and/or C49 if it's out A or C48 if it's out B,and another thing (but i doubt it) the front volume pot.
Title: Re: Low Volume & Unpleasant Distortion in one output channel.
Post by: Auntie Ada on July 28, 2015, 11:32:34 PM: Ok, thanks JMP, I think I need to look up my friendly neighbourhood MP-1 guy (I'm not even sure he's still in business) and see if he can sort me out.....if my piggy-bank has enough money in it ! Your help is was much appreciated.
Title: Re: Low Volume & Unpleasant Distortion in one output channel.
Post by: rnolan on July 29, 2015, 07:51:19 AM: Quote from: MarshallJMP on July 28, 2015, 11:46:43 AM
Ok,could be opamp U10 and/or C49 if it's out A or C48 if it's out B,and another thing (but i doubt it) the front volume pot.
@MJMP Would the HP out still work if the front vol pot is playing up ?
@Auntie ADA, if (as you say) HP out is fine, you can use that as your stereo out to keep you playing (it has some top end reduction (like a cab sim) so you may need to adjust eq a bit (add tops) but it will keep you playing for now. Use an insert lead (stereo jack to 2 x mono jacks) but careful with HP out, it has LOTs of gain (keep it less than 12 o'clock). I it were me, I'd get the tech to change out both caps and the opp amp (C48, C49 and U10). And I suspect MJMP (as usual) is on the money).

So no top switch = V2 (so you know what schematics to grab for your tech) although MJMP has already posted the one you need ? or check the vault.
Title: Re: Low Volume & Unpleasant Distortion in one output channel.
Post by: Auntie Ada on July 29, 2015, 08:09:56 AM: All good advice. Many thanks for all your input.
Title: Re: Low Volume & Unpleasant Distortion in one output channel.
Post by: MarshallJMP on July 29, 2015, 02:26:50 PM: [/quote]@MJMP Would the HP out still work if the front vol pot is playing up ?
[/quote]

Yes because the HP signal is tapped before the front vol pot.

Another thing to try which is very easy to do is pull the red connector (near the front vol pot) and put it back in,just to make sure it's not a bad contact in the connector which i doubt but you never know.