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Author Topic: strange & loud micro phonic feedback on my ADA mp-2  (Read 4938 times)

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joe perry

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Hi. I bought this Ada mp-2 in 1997. A couple of weeks ago it started to do a loud micro phonic feedback when I turn on the drive channels. More the gain more this noise. I changed both valves but it still does that feedback no matter the sound level I play. Do anyone knows something about this and how I can fix it? Any help would be appreciated. Thanks
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rnolan

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Hey joe perry, can you give a bit more detail (please) of the valves you changed ((from what to what), the patch settings that are causing issues (list them? e.g OD1: 7 OD2: 5 etc), also, how you plug/connect your MP2 in (effects, power amp, cabs etc) it will help (me/us think about it)), also what Mp2 voices are causing trouble (there are 10 to pick from), e.g. if you dial this one up (http://adadepot.com/index.php?topic=126.0) (first rhythm patch), how does it go ?? if you try this lead patch (2nd one) how does it go ???  BTW these 2 sounds are "live sounds" and handle being very loud, they both sound fine in the bedroom/lounge room, but much better live (where they were created).
Cheers Richard

PS, there are some noise mods for the MP2 that can help (depending....)

If you changed to new ("good" high gain, low noise, 12AX7 tubes), and there are still issues (particularly with factory settings e.g. 001 Marshall) and it still sounds "not good" (very mush also depending on power amp speaker cab etc) then maybe requires MJMP advice ?

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Studio Rig: MP2/MB1 > Eurorack UB2442FX-Pro > TC M-One XL > Behringer Truths (with Truth Sub) / QUAD ESL 63s
Live Rig: MP2/MB1 > Alesis Quadverb > Alesis Midiverb 4 > Yamaha AM802 > B200s/Carvin TS100/DCM200L > ADA Split Stacks/Mesa P112s

joe perry

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Thanks for answering. I leave here this link where you can hear and see exactly whats the problem. I saw this on youtube and its exactly the same problem I have on mine.  The tubes that  I put on the Ada are brand new and same reference as the originals.                                                                               https://www.youtube.com/results?search_query=ada%20mp-2%20feedback&sm=1
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rnolan

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No worries, I had a listen to the clip, very disturbing squeal.  I did a quick (similar i.e. no input signal, drive levels at default (50)) test on my spare MP2.  I don't get the squealing but voice 9 and 10 are quite noisy (the default OD 2 setting was 100 though).  I then checked my lead patch (posted) and it was also very noisy, I had to turn the noise gate threshold to 88 before it got quiet (again no squeal though).  One difference with my MP2 and the one in the clip is I have the last (v 1.41) EPROM revision installed, his was an earlier version (v1.33), although I don't think it matters for this problem.

I think some of the other depot members have had a similar issue, also not sure if the MP2 noise mod helps with this ?

Hey MJMP, any thoughts ?
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Studio Rig: MP2/MB1 > Eurorack UB2442FX-Pro > TC M-One XL > Behringer Truths (with Truth Sub) / QUAD ESL 63s
Live Rig: MP2/MB1 > Alesis Quadverb > Alesis Midiverb 4 > Yamaha AM802 > B200s/Carvin TS100/DCM200L > ADA Split Stacks/Mesa P112s

joe perry

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Hi Nolan. Thanks once again. The noise mod is really good (although i stil dont have it done in my mp-2) when everything else on the pre-amp is working as it should. In this case clearly it doesn't.  I don't know man, there's something definitely wrong with this unit... and I didn't change the settings I used before, it suddenly started doing this from one day to another. Also the valves I installed are brand new Groove tubes High Gain low noise 12AX7.  :dunno:
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rnolan

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I agree this is something else  :crazy: , hopefully MJMP or Sparker can help, they know the technical ins and outs of these preamps.  The squeal seems to be some sort of high frequency oscillation in the circuit, interesting how the pitch of it changes between voice 9 and 10 (BTW this article is worth a read (http://en.wikipedia.org/wiki/Motorboating_%28electronics%29) to get some background)

The GTs (they are probably GT tested JJs) should do well once you get that squeal sorted.
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Studio Rig: MP2/MB1 > Eurorack UB2442FX-Pro > TC M-One XL > Behringer Truths (with Truth Sub) / QUAD ESL 63s
Live Rig: MP2/MB1 > Alesis Quadverb > Alesis Midiverb 4 > Yamaha AM802 > B200s/Carvin TS100/DCM200L > ADA Split Stacks/Mesa P112s

joe perry

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Yeah Richard, im sure GTs will do their job pretty well. And once (if) i get this problem sorted out I will do the noise mod 'cause its really fundamental.
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Sparker

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So, a quick hit on this would be to replace R913 (240k) with a high voltage / metal film resistor. R913 is part of the HV regulator feedback chain and according to MJMP was a known noise prob with the MP-2, as the resistance sometimes went a bit "squiffy" with age. Try this first.
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ADA Gear: MP-1 Tube Board

rnolan

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Hey Sparker, thanks for chiming in man  :thumb-up:
JP, this makes good sense, HV regulator "feedback" chain (did you read the wiki thing ?, high frequency osculations/feedback stuff)...  BTW schematics etc are here (http://adadepot.com/index.php?topic=148.0).
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Studio Rig: MP2/MB1 > Eurorack UB2442FX-Pro > TC M-One XL > Behringer Truths (with Truth Sub) / QUAD ESL 63s
Live Rig: MP2/MB1 > Alesis Quadverb > Alesis Midiverb 4 > Yamaha AM802 > B200s/Carvin TS100/DCM200L > ADA Split Stacks/Mesa P112s

MarshallJMP

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Like sparker says,replace R913.You can also measure the high voltage,there is a testpoint to check the high voltage,this needs to be around 190Vdc,if it's higher (above 200) replace R913.Email me and i'll send you a pdf with the location of the testpoint and R913.(file is too big to attach here).
« Last Edit: Time Format by MarshallJMP »
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joe perry

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Thank you all guys. I really appreciate your help!  :thumb-up: I will check everything you said and will send  you an email MarshallJMP. Thanks once again, hope to have good news soon about this little guy mp-2. Cheers
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mikeskory

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Sorry to bring up and old topis.  I am experiancing the same noise as being talked about.  Does any one have a board diagram for the MP2?  I can see about where the R913 is and the mentioned caps via the schematic.  I want to know exact before I give an estimate.
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Samuraipanda

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Just a thought on this squeal issue. Check the input jack as well. I had similar squeal on my MP1 years ago and the jack was toast. Replaced it and Bob's your Uncle.

 :metal:
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rnolan

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Hey mikeskory, as Samuraipanda suggests, it's also a good time to change the input jack socket (it takes the most ware over the years), it's an easy swap out/in in the MP-2 but you need to use a switching jack socket with a slightly longer thread to normal (@MJMP what's the switchcraft part number ?). I got a few jacks from MJMP when I bought some other bits from him.

R913 is under one of the tubes so you have to take the tube out to see/get at it. See attached picture in the noise mod instructions which also shows the test point just above it (the pic shows the new R913 resistor (blue) not the original (beige).  Measure at the test point first (dc volts, +ve on test point, -ve on case) with unit on, tubes in etc but lid removed (careful !!).  If you get around 187Vdc (up to ~190Vdc) then this is probably not the problem and it's more likely to be the jack or tubes.  IIRC, above 190Vdc is where the problem starts as the resistor fades over time ?? All 4 of my MP-2s are a little less than 190Vdc (with or without the new R913 (2 have new R913, 2 don't and are still fine)).  If you search my MP-2 posts I listed the various test point values in my MP-2s.

If your tubes aren't reasonably new, I'd change them (and the jack) out first (I "highly" recommend a pair of New Sensor Mullard 12AX7 re-issues long plates, perfect match in the MP-2).

To change R913, don't do it from the top (like one youtube video does  :facepalm: ).  You need to take off the bottom cover (easy) and desolder/solder from underneath.  Be careful not to overheat the pads (I did and wrecked one of them  :facepalm: ). Let us know how you go (maybe start a new thread ??)
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Studio Rig: MP2/MB1 > Eurorack UB2442FX-Pro > TC M-One XL > Behringer Truths (with Truth Sub) / QUAD ESL 63s
Live Rig: MP2/MB1 > Alesis Quadverb > Alesis Midiverb 4 > Yamaha AM802 > B200s/Carvin TS100/DCM200L > ADA Split Stacks/Mesa P112s
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