ADA Depot - A Forum To Support Users of ADA Amplification Gear
Let's Get Technical => All PREAMP Tech Tips & Support => Topic started by: Mxzx on January 09, 2015, 12:35:11 PM
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Just bought a modded Mp1, looks like the guy has done the MDRT transformer upgrade, and the Noise Mod V2 kit.
Guy says he tried to do the rear input mod, worked for a sec then died. Took out rear input mod and still nothing. That is the way I bought it.
We're would I begin to try to fix this? When unit is powered on, there is normal display and output hiss heard through headphones. Changes when programs change. I have moved the switch on top and cleaned it, no change.
Unit is opened up now on bench, and I can provide any pics or readings needed.
Thanks!
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What did you take out of the rear jack mod,what did you use in place of the mod?
Pics might be a good idea :thumb-up:
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I didn't do anything yet except open it up and check for obvious issues.
Let me know of specific pics or measurements that might help.
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Okay i understand now,he did the rearjack and he also reversed it back to original?Sorry tought that you reversed it,sorry my bad.
PLug in a guitar cable and measure with an ohm meter on the other end between tip and sleeve,you should have around 1 M ohm of resistance.
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Thanks,
Open circuit on front input regardless of switch position.
Rear input starts at about 4m and keeps climbing as long as leads are held on cable. That is with switch in rear position.
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It appears to be this input mod he tried without success.
http://www.marshalljmpmodshop.net/ADA-MP1-input-jack-harness-mp1-level2.pdf
He said the unit never passed signal after he modded it, then put it back to stock.
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Just an aside (I have moved the switch on top and cleaned it, no change.) The switch on top switches the MP1 "outputs" from inst level to line level (to plug into guitar amp (inst lv) or poweramp (line lv)), it has no affect on the input.
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Could be a bad trace on the pcb,maybe he destroyed during the removal of the old input jack.These jacks are hard to get out and sometimes you can bust a trace.
So check the input jack first,insert guitar cable again,measure between sleeve and point 4,should be near zero ohms.Now check the tip and point 3,again zero ohms.
Leave the cable in but now measure between point 3 and 4,should be 1M ohm.If not check connection between point 2 and 3 and between point 1 and 4.
Let me know.
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Ok, i will do. i did pull the input check, I can post a pic of that.
I'll go measure that now and get back to you.
You need me to measure anything in jack or with it off board?
Thanks
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With the input jack removed, I get 1M between 3 and 4, 2 and 3 is closed circuit, and 1 and 4 closed circuit.
With a cable plugged into the plug off the board, I get 7.4k on the corresponding 1 and 4 pins.
Should I put the plug back in?
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Here is a few pics of input removed
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I came across this while investigating the input mod, doesn't seem right to me.
Under the heat shrink, the ground shielding wire was tied to the white wire.
All the lugs on the jacks have continuity because of this?
Could this have caused something to go bad down the circuit in MP1?
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Yes that's normall because if nothing is plugged in ,the input is grounded,else you would get alot of static and feedback in the high gain modes.When you plug something in in either the front or the rear jack you will see it's open.Maybe you should try to put in the rear jack mod and we'll go from there.Don't forget to put in the bridge wire!!!
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Oh okay, I was looking at the instructions for the input mod, and it shows the shielding being soldered to one of the pins on the board. This cable on has two wires to be soldered to board.
Which pins would I solder these too?
http://www.marshalljmpmodshop.net/ADA-MP1-input-jack-harness-mp1-level2.pdf
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I think I would rather just put the normal jacks in, I don't ever plan on needing the rear jack.
Should I procede with that, or is there anything that needs testing with it out?
Thanks
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My guess is that that jack is busted,so i would suggest putting the jack mod in there.See pic for connections.
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Ok will do and report back.
Thanks
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Did the swap, still nothing on the input.
When I plug in headphones, and turn level all the while up, I can tap on components and hear it in headphones. It appears I have tons of output, just no input.
What should I do next?
Thanks
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Do this again and let me know,both front and rear input.
Plug in a guitar cable and measure with an ohm meter on the other end between tip and sleeve,you should have around 1 M ohm of resistance.
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Yes, I have 1M on the guitar cable, both inputs.
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Anyone have any more guidance on where I might go from here?
Thanks
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Ok measure again between point 1 , 4 and 2 , 3 again should be 0 ohms regardless if something is plugged in or not.
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Yes, just checked and that is what I read on those terminals.
Thanks
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Ok,do you have or know someone with a scoope?
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No I don't have access to one.
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Mmmm it will be very difficult without one.Now sometimes this could be a U4 (opamp OPA2604AP) problem.You could try to check if all the connections are in order.Compare them to the schematic.Most importent are the voltages + and -15V (pin 4 and 8),pin 3 should be grounded so measure between pin 3,4 and pin 3,8 there you should have +15V and -15V,pin 2 should be connected to R83 and pin 1 to C31.
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Ok thanks. Il do some digging and see what I can find.
I got a bag of old parts with it, and it looks like quite a few of the opamps were changed.
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Can you point out on the board where U4 is and the res/cap?
Thanks
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Mxzx,
I'm attaching two jpgs to this. The first one shows where U4 is -- from the perspective of taking off the top and looking down, with the front panel facing you. U4 has a red rectangle around it. :)
The second jpg is the schematic showing U4, with a red polygon around it. :crazy:
Good luck, I hope you get it working; they do sound nice.
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Mxzx,
U4 seems to be a non-inverting voltage follower. There appears to be no resistors or caps in U4's circuit and exists only to buffer the input jack and is a NE5532 (I think, the schematics are hard to read at times). Marshall will have more to offer, as he knows this stuff much better than myself.
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BTW, I should mention that the board stuffing diagram and schematic were gotten off this site, which makes this site a fantastic place. :thumb-up:
All i did was to outline U4 in red. Thanks to all that help keep these great preamps alive! :thumb-up: :thumb-up:
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Awesome, thanks for the help all!!
I'll get on it and see what I find.
Thanks!!
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Mxzx,
Hah, hah. ;) I'm such an idiot!
If you look at the schematic, there's a lot of front end before U4 that I missed, due to the fuzziness of many copies. I missed the double line of the input jack which sends the signal to the 1Meg ohm input impedance, then to a FET, then to a bipolar transistor -- then to U4.
Sorry, but at least you know where U4 is now. :thumb-up:
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No problem, thanks again for the help!
I'll dig into it tomorrow afternoon and report back.
Thanks!!
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Checked U4 and all the voltages check.
This opamp was replaced by the previous owner as it now has a mounting socket. I don't have that opamp but I do have a TI one, it has 24AJTRW then under it has NE5532P, will that work to replace it with?
I did notice some things under the board. The 2 middle pins on the left side of U4, where it mounts in the first pic, have continuity, is that correct. Looks like a drop of solder in between to me?
Also C31, next to the opamp socket, appears to have a resistor soldered to it in second pic, is that right?
Thanks
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First the U4 opamp is actually a dual opamp,so 2 opamps in one housing.The one with the red rectangular is not the one you need,that is used to feed the level led "input".You need the other one,which is a bit more to right (with pins 1,2 and3).
The NE5532 will work,just make sure you insert it the right way!!
Yes these are pins 6 and 7,they are supposed to have continuity (in the schematic you see pin 6 and 7 connected to each other).
The resistor is correct,this is R73 (100k).
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Ok, which way is the right way for opamp?
So is U4 the socket there or not? I'm confused. The voltages you said to check on the pins are correct, so I though that was U4?
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I'm at work but email me and i'll send you a pic how to insert it.
The socket is U4, that is correct, but i was refering to the schematics gtmm provided.
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Changed opamp and still no improvement.
On a side note, when the headphones are plugged in and turned all the way up, I can hear a faint guitar signal, its not much but it is there.
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Not to bring up a dead thread, but I now have an oscilloscope if anyone has any more ideas on this problem.
Thanks!
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Hey Mxzx, hopefully someone can help, I'm sure MJMP or others will again chime in, unfortunately under the hood isn't my area, but the thead is at least "alive" again :thumb-up: . and sorry we fell off the perch as it were...
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Thanks, it was my fault as I didn't have an oscilloscope. MJMP has been helping me along!
Thanks!
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No worries, MJMP will no doubt (as always, go MJMP :thumb-up: ) help you out. Hope you get it sorted soon !!
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I have both an oscilloscope and a signal generator now.
Thanks
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Ok insert a signal into the mp-1 of 2kHz 700mVpp and start measuring from the input,then see if you have a signal on U4 pin1.
Then see if you have a signal on the input and output of the tubeboard.
Let me know.
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Sorry haven't been around in a while!
I will get on that one of these days and report back.
Thanks for the help!
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ok keep us updated.
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Just sent you an email, i want to replace the front input jack with what was supposed to be there. It was converted to front & rear input, but I don't need that.
I did notice when I plugged the unit in to an amp, everything inside seems microphonic. When you tap on anything in there, you can hear it through the amp. Don't know if this gives any clues or not.
Thanks
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Mmm seems to be quite good,can you take a pic of the input jack and the pcb around it?
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Sure, here ya go!
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Ok i see now,it's connected the wrong way.The blue wire has to be connected to the second hole.So desolder it and solder it to the hole next to it.The jump wire is ok.It doesn't work because it's not connected to the input.
Maybe also clean up that bridgewire,get the white wire out and put in a small bridge wire like on the pic,this will lower the noise a bit.
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I'll get on it tonight!
Thanks!!
Hope the fix will be that easy!
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Ok keep us updated
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Ok, I'm a little confused.
My blue wire appears to be going the same place as your red wire, 2nd terminal to left of 2 resistors. Is that wrong?
What is the proper connection of the rear input to front? Blue tip to blue tip, white to white, ground to ground?
Is this right now?
Thanks
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Hey Mxzx, from looking at the pics (hey MJMP correct me if I'm wrong), your blue wire needs to be the same as MJMP's red wire (i.e. tip (+ve) of input jack) and your white wire, the same as MJMP's black wire (i.e. shield (-ve) earth), so plug a guitar lead in and check continuity. As +ve goes to the terminal that MJMP's red wire is in, and -ve is combined with the shielding into the terminal that MJMP's black wire is in (so sleeve on guitar lead, your white wire).
Then there's the bridging wire.. ok from MJMP's pic it should only be between 2 (horizontal) terminals, but in your pic it also bridges with the +ve input (blue??, red). So check the other side of the PCB to see maybe why? Now, if a trace has burnt out on the other side of the PCB between those 2 terminals, then ok leave it as is, otherwise why is it bridged there ???? (and may be your problem ??)
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Like R says you need to remove the bridge wire going from the blue wire to the hole next to it.The rest looks good.
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Ok thanks, I'll remove that jumper.
I'm still not sure on the connection between the two input jacks. When I wire them in parallel, blue/blue, white/white, I get continuity between the blue and white at board with no input jack plugged in at either end, is that right?
I bought this amp with this mod started, no idea who's mod it is. I looked at the mod on this website, and it looks like there is other stuff that needs to be done. Are there any other things that I need to be looking for here? I can take pics of anything you might need to see.
Thanks,
Michael
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With nothing connected you should get continuity between the blue and white.This is because when nothing is plugged in the input is grounded,else the input would float and it becomes an antenna which would pickup a lot of noise.
Can you take pics of the rest?
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Thanks!
Yes I will get some pics up in an hour or so.
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Here ya go.
Thanks!
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Couple more.
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Rear jack looks good,can you take a pic of the connections on the front jack?
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Here ya go!
Thanks!!
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Problem is i can't see which blue wire goes to the rear and which one to the front?
Saw you removed the bridgewire,does it work now?
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Both blue wires are soldered on the tip terminal.
Still no input after removing jumper. I did notice that tube closest to front is much more microphonic when tapping on it compared to other one.
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Are both blue wires soldered to the same terminal?
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Yes
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Ok that won't work,so the blue wire comming from the rear jack has to be soldered on the middle lug,the blue (short) wire comming from the pcb has to be soldered to left lug,white wires are fine like they are now.
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I'll swap it out and see what happens, thanks again!!
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Okay, swapped the wires and still no input on either jack.
When the level is cranked up, you can hear a faint signal through the amp, tons of hiss but it is in there. Doesn't sound like it is being processed, i have it on preset 1 and the faint signal sounds clean, no distortion.
I do have an oscilloscope and signal generator now if we need to go that route.
Thanks for all your time on this!
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Ok well hooup the signal generator and start with the scoope at the input and follow the schematic.Let me know if i can help.
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Ok, got the scope and signal generator hooked up. All tested out.
Where do I start probing? I'm a novice here so baby steps!
Thanks,
Michael
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Good starting point is U4 pin1.See if you have a signal there.
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Thanks, I'll let you know Friday afternoon.
I'm not at home, but is this easy to find on board?
Also should I have the MP-1 powered up while checking?
Thanks!
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It's easy to find,if not send me an email.
Yes powered on,else it won't work ;D be carefull with the high voltage.
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Yes I have input signal on 3 of the 8 terminals on U4.
Thanks
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Well the MP1 is finally fixed, many thanks to MarshallJMP!!!
Turns out it was a socket that was put in for U4 by previous owner. Used a little too much solder and bridged 2 terminals under socket.
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Well actually you found it,so all the credits go to you !!