Noise problem

I just finished Yocto2 and have a problem with noise. I can't adjust it at 130mV RMS. I changed trimmer for 100k and had to add 47k resistor to get around 160mV. It must be the hfe of SC828. The same problem is with Yocto1 (viewtopic.php?f=16&t=1328) but in Yocto2 noise sections is modded (suggested on page 15 of the TR808 service manual). Is anyone have similar problem?

i have problem with noise section no power on U24 like in yocto manual and i cant adjust it to 130 mV only 20- 30

I finished my board and all of the instruments sound alright except for the snare and clap. It sounds like the noise decay is too long and too distorted. I checked with my multimeter but it's around 130mv. However, it's not a proper meter.

It seems I fixed it. I replaced the trimmer with a 200k. Again, I don't have a proper meter, but things sound as they should.

I just finished the noise section but I have no power at the U24 like Bedroommusic mentioned. Did you end up fixing it? I have plus/minus 15v and ground at the supply bars next to the hihat section but not at the supply bars in the bassdrum section. Is that right? Also no continuity between +15V and U24 pin 8 or -15v and U24 pin 4. I followed the instructions and did the noise section straight after the sequencer parts required for the test mode. I'm assuming the 8 pin doesn't need to be connected and IC119 isn't required for the noise test.

Brownie_0403 wrote:I just finished the noise section but I have no power at the U24 like Bedroommusic mentioned. Did you end up fixing it? I have plus/minus 15v and ground at the supply bars next to the hihat section but not at the supply bars in the bassdrum section. Is that right? Also no continuity between +15V and U24 pin 8 or -15v and U24 pin 4. I followed the instructions and did the noise section straight after the sequencer parts required for the test mode. I'm assuming the 8 pin doesn't need to be connected and IC119 isn't required for the noise test.

Hi did you make the Psu IO board and Psu Busses ( the big board) if not you will not have power on the big board because you didnt finish the power section

on the individual voice parts is the PSU BUSSES PARTS

Yes I figured that out after I posted and just completed the PSU bus and I tested and tuned the noise section successfully. Thanks for your feedback!

Did anyone get to a root cause on this issue? I can't adjust below 320mV. Should I just order a larger trimmer?

Replacing U24 with a TL072 and changing TM4 for a 100k got it to 130mV RMS. I could only get it to 160mV with the 4558 and the 100k trimmer.

I had the same problem, a 100k trimmer for TM4 got me to 130mV RMS. Now just a potentially faulty IC3 causing intermittent clap failure is my only remaining problem.