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Author Topic: How do I setup the trimpots?  (Read 20990 times)

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FoneBone

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Re: How do I setup the trimpots?
« Reply #15 on: Time Format »

Thanks MArschallJMP and RobbHell! :bow:
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rnolan

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Re: How do I setup the trimpots?
« Reply #16 on: Time Format »

Marshall/Robb....W-O-R-D Dudes! Marshall I understand about the T4 Chorus Trimpot. Mine didn't sound right so I adjusted it & got it to sound 100% Killer. :metal: :thumb-up: ;)
Hey Steve, you like to fiddle LOL, good to hear you got it optimal (killer) and you didn't have a scope.  Have you run your stuff in stereo yet ???? :metal:
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FoneBone

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Re: How do I setup the trimpots?
« Reply #17 on: Time Format »

Now I bought an old russian scope to setup my trimpots. And I use this instructions. Here are some pictures:

1. Setting up T2 (OD1)



I've used an iPhone app as signal generator and set it for 600mVp-p (-13.5dB) sine wave at 2kHz.
The orange results/settings are the expected ones, the pink results/settings are what I got.

2. Setting up T1 (OD2)



3. Should I change V2???


4. Setting up T3



5. Setting up T4 (part1): I wasn't unable to find R223, maybe MarshallJMP could help ;)

6. Setting up T4 (part2)



Maybe some one can tell me what's the problem with T1 & T2, T3 & T4 seem to be okay?!

And a little addition: I'm a noop in electronics, but I like to learn :D
« Last Edit: Time Format by FoneBone »
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My gear:
Ibanez Jem 77FP - 1988
Ibanez Jem 2k DNA (Custom) - 2008
Takamine EF508KC - 2010
PRS Tremonti SE - 2011
PRS Swamp Ash Special - 1999

ADA MP-1 (Mod3.666, Noise Mod v2, Battery Mod, Rear Input Jack Mod)
ADA GCS-2
Roktron Intellifex On-Line
BBE Sonic Maximizer 422A
M-Audio Fast Track C400
Rocktron Velocity 100
Hughes & Kettner Tubeman plus
Digidesign Digi 002 Rack

More at: http://www.jem2kdna.de

Ludachris0606

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Re: How do I setup the trimpots?
« Reply #18 on: Time Format »

New happy ADA user here...
So last night I tried adjusting the trim pots for OD1 and OD2 with no major effect on amount of gain, then came across this thread...
Questions
-How much is this supposed to change the gain amount
-By messing with these did I potentially mess anything up where I need to readjust/fine tune with an oscillator and all that as shown above?!
« Last Edit: Time Format by Ludachris0606 »
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MarshallJMP

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Re: How do I setup the trimpots?
« Reply #19 on: Time Format »

These are just the factory settings,these are not intended to give more gain,just the correct gain.But you can safely play around with these.
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Cpt Adama

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Re: How do I setup the trimpots?
« Reply #20 on: Time Format »

Usually I don't necro a thread, but FoneBone did such a great job of documenting this procedure with pictures, that I felt this would be the best place to continue.
I have a version 2 MP-1 and I have done a complete recap of the unit. knowing that value tolerances of the old caps to the new could change alignment, I wanted to verify the settings.

Step one was to set the MP-1 to Clean Tube mode and OD1 at 10.0. Then inject a 600mVp-p sine wave at 2kHz. Measure U4 at pin 1 and set T2 (trimpot) to achieve 15Vp-p.

Well my initial setting was 9.4Vp-p but was unable to set 15Vp-p due to limits of the T2 trimpot being min 5.2Vp-p to max 10.4Vp-p.

Any insights anyone?  :dunno: I was wondering if those alignment instructions are for version 1 only but I don't think much has changed in version 2.
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MarshallJMP

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Re: How do I setup the trimpots?
« Reply #21 on: Time Format »

The instructions should work for the V1 and V2 MP-1's.

When you cranck the trimpot, does the signal distort?
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Cpt Adama

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Re: How do I setup the trimpots?
« Reply #22 on: Time Format »

The sine wave is not clipping even at the max I could achieve of 10.4Vp-p. I have played the preamp and the distortion presets seem to have decent amount of distortion when playing. I’m not truly familiar with this preamp so I couldn’t say what is a normal amount of gain. That’s why I wanted to align it per a service manual.

I wrote ADA for the actual service manual for this, but they just ignored me and didn’t answer. I wonder how accurate these hand written notes are? Maybe they were under pressure to copy it fast as it wasn’t supposed to be released and maybe some values or settings are off.

At this point the preamp is over 30 years old, I can’t see why they wouldn’t release the actual service manual.
« Last Edit: Time Format by Cpt Adama »
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MarshallJMP

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Re: How do I setup the trimpots?
« Reply #23 on: Time Format »

I never had any problems getting to 15Vpp unless there was a problem. If it's not clipping you can rule out the diode/zener circuit.
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Cpt Adama

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Re: How do I setup the trimpots?
« Reply #24 on: Time Format »

I rechecked some of the upper trace caps connections and reflowed some others and now have about 13Vp-p. Still not the 15Vp-p that it calls for but I was able to get a hold of another MP-1 v2 and it had the exact same output at U4 pin 1 of 12.8-13Vp-p. I'm going to call this case closed as I am getting 23Vp-p on output F with the sine wave clipping. I imagine there are going to be some tolerances from unit to unit and the fact two separate units had identical measurements lower than spec kind of confirms my suspicion that it's OK to be a little low.
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MarshallJMP

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Re: How do I setup the trimpots?
« Reply #25 on: Time Format »

That's strange, I serviced dozens of MP-1's and never had this problem. Are you 100% sure that your input signal is 600mVpp? Verified with the scope?
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Cpt Adama

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Re: How do I setup the trimpots?
« Reply #26 on: Time Format »

Well I'm never 100% sure as I'm not a trained EE, I did take 1.5 year of EE classes back in the day, but I went into aviation. Now that I'm about to retire I combining hobbies of Electronics and guitars. I've built many electronic kits, successfully recapped older vintage rack gear Furman PQ3, and Lexicon PCM41 and a Marshall 2204 that I reconverted back to EL34's from the American 6L6's.

Having said all that I'm still learning, and the MP-1 is the most complicated piece I've taken on yet. Here of some pictures of my setup. I have a dual signal generator set up both channels outputting the same signal. My oscilloscope is a dual channel and the MP-1 signal is the yellow trace and the blue trace is the signal generator straight in. The yellow trace is on 5V divisions and the blue on 100mV divisions.





« Last Edit: Time Format by Cpt Adama »
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MarshallJMP

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Re: How do I setup the trimpots?
« Reply #27 on: Time Format »

Are your probes set to 1X or 10X en is the setting in the scope the same?
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Cpt Adama

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Re: How do I setup the trimpots?
« Reply #28 on: Time Format »

Be back in a couple of days to verify, but I'm 99% sure both scope and probes are 1X.
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MarshallJMP

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Re: How do I setup the trimpots?
« Reply #29 on: Time Format »

Did you measure the input signal at the input jack?
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