Roland TR-808 – Noisy Snare, Clap and Toms

This Roland TR-808 had very noisy snare, clap and toms. The toms especially sounded very coarse. It was a bit like when you try to stop your car on a road with gravel.

The claps and the snares also sounded a bit tame or muffled. The common denominator between these instruments is the white noise section (the toms use pink noise which is generated from the white noise).

My initial thought was that there was an issue with the calibration of TM4 (noise). I tried calibrating this but it was very hard to get the adjustment right. The TP4 test point should be calibrated at 130mV AC but it was pretty much impossible. It would wander around that point +/- 10mvA.

When measuring the white noise in the 808 in the white noise it varied a lot in amplitude. I compared this to my Yocto and there it was very stable. When looking at the PCB of the 808 it was obvious that someone at some point had desoldered both IC24 and Q35 in the noise section. I also noticed that Q35 had been replaced by another transistor, 2sc289A, not the 2sc838.

IC24 had poor soldering and Q35 is not the correct type

As I didn’t think at the time that I had a suitable replacement for Q35 I tried to replace IC24 just to rule it out. It didn’t make a difference to the issue though. When looking through my stash I noticed that I had 2 pcs 2sc945. I tried using this as Q35 and the issue went away. Now the noise had a consistent amplitude.

Some samples before/after the switch of Q35:

Clap – Before
Clap – After
Low Tom – Before
Low Tom – After
Mid Tom – Before
Mid Tom – After
High Tom – Before
High Tom – After
Snare – Before
Snare – After

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