e-licktronic Forum

Hi Dyers,

My build is 70% completed but I have a few problems that I don't seem to be able to correct by myself.

Everything works as it supposed to, except that the bass drum is very quiet in comparaison to the rest of the instruments (master out and individual out). I've checked all the components value and they all seem right. I've tried swapping the UC with another one with no success. I've also noticed 3 things:
- When I turn the master volume pot I hear a slight crack and if I hold it on the exact position where it cracks I can hear the bass drum louder and distorted.
- I can measure +15v everywhere I'm supposed to but since yesterday I can't measure the -15v spots. I get strange values and at some point it seemed to stabilize around -17.9 or -20.1. I could measure it correctly before. Maybe something fried or I did a short with the multimeter. EDIT : The value seems to be -21.5v. (I've ordered a new regulator just in case)
- At some point when I tried to wiggle the J1 connector a bit, the kick seemed to be louder. So I reflowned the joints but it didn't do the trick.

Otherwise every other instruments seem to sound as they should and the OS and sequencer work as supposed.

Is it possible that a transistor is faulty? Is it a common thing?

I'm a beginner but willing to learn so any help would be greatly appreciated .
Thanks in advance.

More infos : Apparently it maybe has to do with the bass drum accent, as it has no effect. All other 11 individual accents work, the main one does too (except on the BD of course). Any ideas ?

So far I've tried swapping IC1 and the BD A733 transistor without success. I have to check again for continuity.

First step is to get your -15V stable. The way that the accent works on the 808 if i'm not mistaken, is the drum sounds are triggered with a 5v pulse and accent is somewhere between 5V and 14V. Check to make sure you're getting a proper 5V pulse into the BD circuit. (Q32) according to the TR-808 service manual

The Yocto2 individual accent circuit is different than the 808 but the drum voice circuits should behave the same

C46 and R178 are responsible for delivering -15V to the BD circuit double check your values for those components

Thanks for your replies!
So now that I've changed the regulator I'm back with +15v and -15.3v everywhere I should.

I get +5 at Q39 (trig) and something between +8 and +4 at Q40 (accent). But still no audible effect for the accent and still low volume in comparaison to the other instruments. I've tried using another separate out to see if the problem came from there but nope.

Good to hear that you got the +/- 15V going correctly! I don't have much more help to offer since I'm learning all this as I go myself but I'll keep an eye on this thread for sure

Thanks anyway!
I have to check with a friend who knows better than me and has an oscilloscope.

When you find the bug let me know!! I've got low output on my TR-606 BD and I'm interested to see if the issues are related

Today I noticed that the last 4 steps buttons (accent, ext, trig 1, trig 2) trigger the bass drum when played in tap mode. No pattern is written if I check afterward for those "instrument" lines. But it does write steps in the bass drum instrument pattern slot.

If I program an accent pattern via step programming the snare recognizes it though.

Any ideas?