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

Please login or register.

Login with username, password and session length
Advanced search  


Lets get Technical > All Things Tube All about preamp and power amp Tubes.

Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Messages - Deregorn

Pages: [1] 2
I measured all the pins on U4

Pin 1: 0.35 V
Pin 2: 0 V (it actually changed between -0.00 and +0.00 so there might be some really tiny voltage)
Pin 3: 0 V
Pin 4: -15 V
Pin 5: +14.7 V
Pin 6: 0 V
Pin 7: 0 V
Pin 8: 0 V

Ah, okay. Well in that case it's around 0 Ohm, so it should be fine.

I hope you're not running out of ideas ;D

@Sparker: Checked U9 - Pins 2 and 3 show 0 V, Pin 1 shows around 1.6 V (constant)

@MJMP: I'm still a bit confused about that optocoupler. I attached 2 photos (top and bottom view), maybe you can help me to see things clearer... :-[
From the top I can only see 2 pins at the right side. I marked them yellow and green, because I have no idea which pin is which (are these 1 and 2?).
At the bottom view I also marked those same pins green and yellow. Are the other 3 pins you talked about the ones I circled in red (with the question mark next to them)? And what exactly do I measure? :???:

Sorry for my bad understanding of electronics. ;)

What should I do now?

Ok, I just did everything as suggested and this is what I measured:

Pin 3 - Ground: ~ 2 Ohm
Pin 1 - 2: 37.7 kOhm

turned on

Pin 4 - Ground: -15 V
Pin 8 - Ground: +14.7 V

By the way, if I just put the two contacts of my multimeter together it also shows around 2 Ohm, so I guess it's just inaccurate and actually is 0 Ohm.

No problem ;)
I just tried to measure everything as suggested. It seems that the traces to U9 are all fine (around 0 Ohm). However there are 2 pins on U4 that I cannot really follow, I can't see where they're going so I don't know where to measure. The other ones are fine too.

I think they're pins 5 and 8 (the first and last one on the left side when looking on it from above with the tube board to the left). I attached a picture to show you what I mean. It looks like the traces are going down and then disappear under whatever that big black thing is ???.

Makes perfect sense, I will do that tomorrow and let you know. Thanks!

Since no one answered here for 2 weeks: should I give up on this unit and just buy a new one? It really makes me sad that I cannot use it atm... :(

I have a digital multimeter. A cheap one. Guess it's not very accurate, but maybe it gets the job done. The problem is I have no idea where and how to measure. Would you mind giving me detailed instructions? I'm a newbie :-[

It's getting worse... I turned the OD1 gain down to 4.0, because as I said there was no clipping at that level. I played a bit and now it's clipping like crazy even at 4.0. So it looks like the longer I play the amp, the worse it gets. Any ideas?

Introduce Yourself / Re: Hey hey hey
« on: Time Format »
Thanks, I just really hope I can get my MP-1 back working like it should, at the moment it's not really fun playing it. It sounds like crap on mid to high gain settings. I opened a thread on the "Troubleshooting Problems" board. If anyone with some technical knowledge wants to help, please have a look at it.

Yeah I do, but most of the pins broke while desoldering it (had to apply some force).

Also checked the trimpots - the one between U4 and U9 is almost all the way down, the others are around half way up.

Ok, I just checked everything again. All the caps and op-amps are installed the right way.

By the way I forgot to mention that I changed the tubes aswell. The unit came with PL (Penta Laboratories) 12AX7A, I replaced both of them with Tung Sol 12AX7. However I did this before the noise mod and there were no issues, so I guess something went wrong when I replaced the caps and op-amps...

Anything else I can check? I could provide pics if that helps.

Edit: I just realized the OD1 Clip LED lights up all the time when I play. My OD1 gain is at 7.0 and I've seen that LED lighting up before, but only once in a while, not all the time...
Edit 2: Just turned OD1 gain down a bit. At 5.0 it's still lighting up like crazy. When going below 5.0 it's getting better and finally at around 4.0 it almost never flashes.

Introduce Yourself / Re: Hey hey hey
« on: Time Format »
Hehe, that's just a nickname I picked up a long time ago. It's a character from an old fantasy RPG. If you prefer real names you can call me Nico, that's my real name ;)

I replaced caps C1, C2, C8, C129, C130 and C131. I'm pretty sure they are installed correctly but I can check them again. The op-amps I replaced are U4 and U9 (installed IC sockets). I used NE5532P first, but they seemed to amplify too much, the gain went from slightly crunchy when OD1 was at 2.2 to really high gain when increasing to 2.4. So I replaced them with TL072IN. Again, I'm pretty sure they are installed correctly.

Pages: [1] 2