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

Let's Get Technical => All PREAMP Tech Tips & Support => Topic started by: shredbaron on March 06, 2017, 05:37:29 PM

Title: HELP! Clean/Distortion channels reversed!
Post by: shredbaron on March 06, 2017, 05:37:29 PM
Hey folks, have an issue after doing some work to one of my units - not sure what happened, but now the "Clean" tube patches are heavily distorted, and the "Dist" tube patches aren't - it's as if the clean/dist channels got reversed.

Any idea how I managed to do this and how to correct it? I did the noise mod, installed an MDRT and battery mod - nothing too fancy. Compared it to my other MP-1 and looks like everything is soldered in the right place.

Ideas?

thanks!

*used to be a member on the Depot many years ago before it crashed...the MP-1 I'm talking about hadn't been turned on since 2010!
Title: Re: HELP! Clean/Distortion channels reversed!
Post by: rnolan on March 07, 2017, 05:03:04 AM
Hey shredbaron, good to have you back with us all  :thumb-up: , hopefully MJMP or others can help you with the issue. Of the cuff it sounds like something got reversed (signal go this way, or this way ? possibly in the voicing switching ?).
So question though:
Is SS voice still normal ? (ie issue is patches with clean tube voice selected in the patch are now routed to dist tubes voice and vis versa) ??
Title: Re: HELP! Clean/Distortion channels reversed!
Post by: MarshallJMP on March 07, 2017, 07:45:32 AM
Did you desoldered the tubeboard?
Title: Re: HELP! Clean/Distortion channels reversed!
Post by: shredbaron on March 08, 2017, 06:47:42 AM
Hi, thanks for the responses. Good to be back, when I was last on the site (before the crash) there had been a project for everyone to record some clips to be patched into one big song - just as that was underway, the site was lost - so disappointing, as it was an incredible treasure-trove of info. Glad to see some of the ol' regulars still here all these years later!

RNolan - yes - SS voice is fine, you described issue perfectly - patches with clean tube voice selected in the patch are now routed to dist tubes voice and vice versa.

MarshallJMP - yes, I had originally pulled the tubeboard, replaced all the filter caps etc. When I wasn't able to get any sound out of it (years ago) I packed it up, only finally got back to it the other day - seemed to me that one of the wires that ran from the tube-board to the mainboard wasn't soldered correctly, so I removed the old solder, redid it, and presto - had sound - but the reversal issue described above.
 
I haven't had it apart again to play around to try to fix it, I thought someone might have an idea of exactly what it could be before I start playing around and potentially cause myself more trouble :)

Title: Re: HELP! Clean/Distortion channels reversed!
Post by: MarshallJMP on March 08, 2017, 07:31:52 AM
There is a wire that goes to the tubeboard called the G wire (see the pad's on the boards called G).On that pad you should have -15V when set to clean and 0V when set to dist.
Title: Re: HELP! Clean/Distortion channels reversed!
Post by: shredbaron on March 08, 2017, 07:48:23 AM
Thanks, Marshall - I'll grab my multi-meter and take a look at in the next day or so (I'd do it tonight but have guests coming for dinner.)

I have a feeling I've reversed something, it seems like the most logical explanation. Appreciate your input (as always...kind of trippy to talk to someone who I bought stuff from 8+ years ago...did the MDRT, noise mods and bought some other parts from you back in 09/10)

I'll update once I've had a chance to take a crack at it - thanks again!
Title: Re: HELP! Clean/Distortion channels reversed!
Post by: MarshallJMP on March 08, 2017, 01:52:05 PM
You get a lifetime tech support on it  ;D so no worries :thumb-up:

Ok keep me updated.

Title: Re: HELP! Clean/Distortion channels reversed!
Post by: shredbaron on March 12, 2017, 10:44:42 AM
There is a wire that goes to the tubeboard called the G wire (see the pad's on the boards called G).On that pad you should have -15V when set to clean and 0V when set to dist.

Well, this is interesting, but I'm not sure what it means (or how to fix it?)

Distortion I'm reading 0.14

Clean I'm at -0.48

Voltmeter set to DC volts at 20V scale.

Thoughts?

Title: Re: HELP! Clean/Distortion channels reversed!
Post by: MarshallJMP on March 12, 2017, 11:40:13 AM
Measured to ground right?

Could be a bad fet or a busted cap.
Title: Re: HELP! Clean/Distortion channels reversed!
Post by: shredbaron on March 12, 2017, 01:36:42 PM
Measured to ground right?

Could be a bad fet or a busted cap.

I put the ground pin of my multimeter on the chassis of the MP-1...should I have put it on the green wire ground pad on the PCB?

I'll try again and see if there's a different reading just in case I had a bad ground.







Title: Re: HELP! Clean/Distortion channels reversed!
Post by: MarshallJMP on March 12, 2017, 03:20:14 PM
The chassis is fine.So could be C30 or Q5, or both.
Title: Re: HELP! Clean/Distortion channels reversed!
Post by: shredbaron on March 12, 2017, 05:06:43 PM
The chassis is fine.So could be C30 or Q5, or both.

Thanks! I just ruled out C30 (replaced it with another 33uF cap I had in my parts bin) and I'm getting the same reading.

Hate to ask, but what does Q5 look like and where is it located? Is it one of the transistors on the tube board?

I've just spent half an hour looking at the schematic trying to figure it out and I'm lost. (I'm not an electronics guy by trade, just someone brave/stupid enough to play with a soldering iron :) )

EDIT: FOUND IT! found a layout file on the web, clearly labelled.

Looks like I will be ordering some parts from Mouser. Going to replace *all* the electrolytics that I didn't replace in 2010, as well as upgrading the LF347N in the EQ section.

Thanks so much for taking the time to reply, it's very much appreciated. Hopefully replacing Q5 does the trick!

George
Title: Re: HELP! Clean/Distortion channels reversed!
Post by: rnolan on March 13, 2017, 03:41:19 AM
Hey George, excellent, if you found a better or more easy to read layout chart (that we don't already have in the schematics section), please post it  :wave: or link to it ?
Title: Re: HELP! Clean/Distortion channels reversed!
Post by: shredbaron on March 13, 2017, 07:02:56 AM
Hey George, excellent, if you found a better or more easy to read layout chart (that we don't already have in the schematics section), please post it  :wave: or link to it ?

Found a pile of schematics here - the one I found useful was labelled "ADA-MP1-009-027-component-layout-1989.jpg"

this site also has a zip-file with all of the contents in the directory -

http://www.kylheku.com/mp1-files/mp1-schematics/

EDIT: at the bottom of this page are some schematics that seem to be a bit less blurry than others I've seen on the web:

http://www.lydian.ca/ada-mp-1-rebuild/
Title: Re: HELP! Clean/Distortion channels reversed!
Post by: MarshallJMP on March 13, 2017, 01:46:49 PM
C30 is not a 33µF cap, it's only 100nF (small yellow cap)

Q5 is a 2SK364 N-channel FET (don't use anything else)
Title: Re: HELP! Clean/Distortion channels reversed!
Post by: rnolan on March 14, 2017, 03:21:01 AM
Hey George, thanks for the links  :thumb-up:
Title: Re: HELP! Clean/Distortion channels reversed!
Post by: shredbaron on March 14, 2017, 06:21:19 AM
C30 is not a 33µF cap, it's only 100nF (small yellow cap)

Q5 is a 2SK364 N-channel FET (don't use anything else)


MJMP, thanks! I haven't had a chance to get back to it, but was thinking to myself "How the heck am I going to figure out what type of FET it is without pulling it?" - you just saved my bacon. Now to start putting together a big Mouser parts order :)

Quick question - in my other MP-1 I replaced most of the op-amps with OPA2604s if I remember correctly.

In this one, on the main board,  U4 is an OPA 2604, U9 is a LF412. Both socketed, so I must have done them in 2010.

U11 and U15 are socketed TL072s.  From recent reading it seems TL072s are inferior - should I replace them with OPA2604 (I have a few lying around) or would NE5532 be better? Just leave the LF412?
Title: Re: HELP! Clean/Distortion channels reversed!
Post by: MarshallJMP on March 14, 2017, 06:35:42 AM
Those 2SK364 Fet's are obsolete now and there are a lot of counterfits on ebay so be careful what you buy.You can also use the 2SK363.
Title: Re: HELP! Clean/Distortion channels reversed!
Post by: shredbaron on March 24, 2017, 12:21:31 PM
The chassis is fine.So could be C30 or Q5, or both.

Hey MJMP, sorry to bug you - been solderin' up a storm last couple of days when I've had some spare time.

Stupid me...the one cap I forgot to order was C30. 100nF.  Also need to order a few oddball 50v caps (33uF and 4.7uF) - I mistakenly counted a bunch out as 0.47uF

Question: if I replace C30 with a cap that has a higher value than 100nF would it still work in this application? I know more capacitance is fine for filter caps, but not sure what the cap is doing here leading into the diode. I did manage to get my hands on a new 264 diode (and kept the old one, just in case).

desperate to fire this up, but don't want to take a chance that is IS the bad cap, and then I have to replace another diode :)

I have an extra 10uF (10,000 nF) non-polarized electrolytic - could it work in that application?