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

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Messages - Deregorn

Pages: [1] 2
1
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

2
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

3
@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. ;)

4
*bump*
What should I do now?

5
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.

6
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 ???.


7
Makes perfect sense, I will do that tomorrow and let you know. Thanks!

8
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... :(

9
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 :-[

10
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?

11
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.

12
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.

13
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.

14
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 ;)

15
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.

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