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

Let's Get Technical => Troubleshooting Problems => Topic started by: guitardude57 on December 01, 2016, 08:36:45 AM

Title: Viper probs, info moved from Schematics section
Post by: guitardude57 on December 01, 2016, 08:36:45 AM
Howdy all,
Thanks for the quick response with the schematics for the ADA Viper!

After going over the amp yesterday, and finding most of it not working well...
took out the chassis, and discovered the cut pot for the speaker emulator was broken
by whomever messed with it last.  And the wrong value by what the schemo shows.

R166 is supposed to be a C50K (reverse taper audio) according to the drawing.
There was a A100K in there.  Since I don't see any ECO's (Engineering Change Order)
for a revision of the pot value, I am assuming the last guy couldn't find the correct value,
or it was placed by the factory.  In any case the phenolic card between the pot body and the terminals was broken, skewing the wiper contact.
The emulator IN/Out switch was stuck, hence no audio...

Now with the pot turned full open, and tweaked to make a contact internally, emulator works
and passes audio.  Switch to turn off now works.

Both channels function, after cleaning all the pots with Blue Shower.
There is a noticeable hum on Red and Green channels with and without audio inserted in input.
Plugging audio into power amp in (FX Return) Audio is clean, and dead quiet of any hum.
So somewhere around the mixer, is a bad filter cap.

My Techtronix O-scope shit the bed on my last move... so finding the hum will be a bear...

Any others out there find a similar hum issue in these...in the front end, or mixer circuit?

Much Thanx!

Trying to find a US supplier for the R166 cut pot.  C50k value.

Update:  CE Distribution has a snap on pot that will work for R166, just have to remove the snap bracket first.
Title: Re: Viper probs, info moved from Schematics section
Post by: MarshallJMP on December 02, 2016, 07:50:54 AM
What happends if you turn the gain pots down, do you still have hum?
Title: Re: Viper probs, info moved from Schematics section
Post by: guitardude57 on December 02, 2016, 11:32:50 AM
Hi,

Yes, with the gain pots on either channel turned all the way down,
the hum is there.  Since the lossy nature of the tone stacks, with the TMB turned down,
the hum is gone.

With the drive controls up, the hum is there as well as expected hiss with no input.
Masters turned down, it is dead quiet.  Either channel.  So problem is before the Master Volumes.

So either the mix circuit before the FX loop, (B4 Masters) or after the shared input where the signal separates to the 2 different channels is a bad cap...perhaps.
I would think if the problem was in the PS filters early on, the hum would be in the FX Return...where it is not.

My O-scope is fried, so hunting for hum and hash is problematic the easy way.

FX return input to amp with audio...clean and quiet.

Whatcha think?
Title: Re: Viper probs, info moved from Schematics section
Post by: MarshallJMP on December 02, 2016, 11:53:17 AM
I would start with the high voltage PS. There is a testpoint TP 5, it should be 220Vdc, can you measure it and let me know?
Title: Re: Viper probs, info moved from Schematics section
Post by: guitardude57 on December 02, 2016, 12:04:51 PM
212.5V
Title: Re: Viper probs, info moved from Schematics section
Post by: MarshallJMP on December 02, 2016, 01:30:59 PM
Ah that's a bit low, usually they go up in value and then you start getting hum.Or something is drawing more current. Maybe you should replace the high voltage caps. Could be one is leaking. There are 3 10µF/350V caps.
Title: Re: Viper probs, info moved from Schematics section
Post by: guitardude57 on December 02, 2016, 01:47:23 PM
Already ordered them... :)  In my cart anyway...

Funny, whoever was in here before, changed the 2 - 10 uF 450's between the mid and treble pots C28 ...and treble, and master, C33 ...and c19.  So I think someone tried to fix this hum, and replaced some caps...
Title: Re: Viper probs, info moved from Schematics section
Post by: MarshallJMP on December 02, 2016, 02:09:21 PM
Does the voltage go up if you pull the tubes out? Since this combo has a regulated high voltage I find it strange that it's too low. So it seems somethings is either drawing too much current or there is something wrong in the regulator.
Title: Re: Viper probs, info moved from Schematics section
Post by: guitardude57 on December 02, 2016, 02:19:40 PM
Weird...pulled tubes expecting the voltage to go up considerably higher...
Reads 183.7

WTF...lol
Title: Re: Viper probs, info moved from Schematics section
Post by: guitardude57 on December 02, 2016, 02:28:40 PM
C19 and C33 are two of the 220V filters...They were replaced with 10uf 450V...those are right off of the tube power entry for pin 1 and 6...

 C108 which is right on the power supply area, that is the 1 of 3 filters on the PS, is original.
Subbed in a big ole 16uF 450 axial, that barely made contact...got 220.4V  YAY!

Ordered some extra 10 and 22uF radials for the bin, and new 12ax7's...the ones in there are original...this thing has been pretty beat up.

Should have parts by Tuesday.

Thanks for your assistance, my friend!
Title: Re: Viper probs, info moved from Schematics section
Post by: MarshallJMP on December 03, 2016, 08:46:23 AM
No problem, glad you got it fixed !!!
Title: Re: Viper probs, info moved from Schematics section
Post by: guitardude57 on May 18, 2017, 01:15:03 PM
Customer loves the amp, as it functions well, even up to now.

Does anyone know if someone has a foot switch available for this beast?
Or maybe the circuit board I can retrofit into a new switch box?

I suppose I could make one from scratch... but prefer to at least find the foot switch board.

Thanx!
Title: Re: Viper probs, info moved from Schematics section
Post by: Kim on May 18, 2017, 05:20:16 PM
I have access to a footswitch for the Viper.  I'll check into it this weekend and provide some info for that.
Title: Re: Viper probs, info moved from Schematics section
Post by: guitardude57 on May 18, 2017, 05:44:24 PM
Thanks KIM!
Maybe get a close up shot of it, and any numbers on the circuit board.

Depending on what they have going on, may be able to etch a board...
Title: Re: Viper probs, info moved from Schematics section
Post by: MarshallJMP on May 19, 2017, 10:18:22 AM
I think I have a circuit board of the switch.
Title: Re: Viper probs, info moved from Schematics section
Post by: guitardude57 on May 19, 2017, 05:10:21 PM
 :banana-rock:
Title: Re: Viper probs, info moved from Schematics section
Post by: Kim on May 19, 2017, 07:49:45 PM
Meanwhile, here is the schematic.  More info over the weekend.....
Title: Re: Viper probs, info moved from Schematics section
Post by: guitardude57 on May 20, 2017, 11:18:44 AM
Thanks KIM!

I suppose I could etch one of these boards...if I could see a size relationship.

Any chance that you have one laying around,
that you could photograph?
Title: Re: Viper probs, info moved from Schematics section
Post by: Kim on May 20, 2017, 11:31:47 AM
Any chance that you have one laying around, that you could photograph?

Stan said he would bring it over sometime today.  I'll give it a good documentation when it arrives.  :thumb-up:
Title: Re: Viper probs, info moved from Schematics section
Post by: guitardude57 on May 20, 2017, 11:56:32 AM
Outstanding!

Thanks guys!
Title: Re: Viper probs, info moved from Schematics section
Post by: guitardude57 on May 26, 2017, 06:16:01 AM
Any luck on the board Kim?
Title: Re: Viper probs, info moved from Schematics section
Post by: Kim on May 26, 2017, 07:10:34 AM
Any luck on the board Kim?

Ah, sorry....the owner kept forgetting to bring it to Band rehearsal, or to otherwise drop it off at my place.   :(
I'll see him tonite and hopefully get it from him then.
Title: Re: Viper probs, info moved from Schematics section
Post by: Kim on May 27, 2017, 08:54:40 AM
And I have the pedal now in my possession.  Stay tuned....   :thumb-up:
Title: Re: Viper probs, info moved from Schematics section
Post by: Kim on May 27, 2017, 10:30:47 AM
Here we are.
Now, this may or may not be the original pedal for the Viper.  It appears to use a different housing, and has a mysterious label on it that suggests that it is some kind of prototype.   :dunno:  Strange, but this was the pedal that came with the Viper when I first got it; it works and does what it is supposed to.  Is it a factory ADA prototype?  Something that someone else came up with using leftover/spare parts?  I have no answers on any of that.  Here are the pics.
Title: Re: Viper probs, info moved from Schematics section
Post by: Kim on May 27, 2017, 10:47:21 AM
(http://i270.photobucket.com/albums/jj118/casey71us/0527171103_HDR_zpsmgiyl4df.jpg)
(http://i270.photobucket.com/albums/jj118/casey71us/0527171104_zpsrgg46m9e.jpg)
(http://i270.photobucket.com/albums/jj118/casey71us/0527171105_zpsb7jdeozv.jpg)
Title: Re: Viper probs, info moved from Schematics section
Post by: Kim on May 27, 2017, 10:49:52 AM
(http://i270.photobucket.com/albums/jj118/casey71us/0527171130a_zpsyp4dqt2q.jpg)
(http://i270.photobucket.com/albums/jj118/casey71us/0527171130b_zpszva4ywf4.jpg)
(http://i270.photobucket.com/albums/jj118/casey71us/0527171132_zps1ghrhlq5.jpg)
Title: Re: Viper probs, info moved from Schematics section
Post by: Kim on May 27, 2017, 10:52:35 AM
(http://i270.photobucket.com/albums/jj118/casey71us/0527171131b_zpsgvvq8idk.jpg)
(http://i270.photobucket.com/albums/jj118/casey71us/0527171131a_zps2xut7ktf.jpg)
Title: Re: Viper probs, info moved from Schematics section
Post by: guitardude57 on May 27, 2017, 09:28:42 PM
Looks like a proto box...(perhaps a reconfigured midi jobby) and a Rev 3 board. 
Most interesting.

I still see some ADA footswitches in pawn shops...once in a while.
Title: Re: Viper probs, info moved from Schematics section
Post by: MarshallJMP on May 28, 2017, 12:16:30 PM
Which footswitch do you mean, ADA made many different ones?
Title: Re: Viper probs, info moved from Schematics section
Post by: guitardude57 on May 29, 2017, 11:23:15 AM
I have seen a couple that had the 4 switch buttons in a row, before.  But don't recall for which models. 

I had back in the day, a rack mount 4 effects unit, (TFX4  Chorus, flange, doubler, and echo) that had a TRS connection that I changed to an XLR.  I once had set up for a gig, and it was on, unbeknownst to me... when I plugged in the footswitch.  That took out a dozen chips...lol  So changed the rack unit to XLR, to prevent the gross short out, again.
I don't know what happened to that unit, or the footswitch.
Title: Re: Viper probs, info moved from Schematics section
Post by: MarshallJMP on May 30, 2017, 08:11:15 AM
You can also make a footswitch without the leds then you only need 4 resistors, 4 buttons and a stereo jack. Downside is you don't know the status since you have no leds to show you.
Title: Re: Viper probs, info moved from Schematics section
Post by: guitardude57 on June 01, 2017, 01:35:30 PM
Nope...won't work.  This is a logic based foot switch...powered from the amp, though the TRS.
Put a set of switches not sending high and low info, will fry the amp decoder...
Title: Re: Viper probs, info moved from Schematics section
Post by: MarshallJMP on June 02, 2017, 03:28:21 AM
The logic and the opamps are only for driving the led's, the rest is actually analog. It doesn't send out some pulses but 4 different voltages. Nothing will get fried.