[SOLVED] Finished Build 1.02 -- Few Issues and Notes

Discuss Nava construction and related issues
  • Anyone??

    Been working on the snare voice and I have yet to identify the issue --

    Snare does not respond to SNAPPY and TONE, just TUNE and LEVEL. It sounds like another TOM voice, as there is just low end, no high end frequencies; sounds like there is no noise getting to the circuit.

    Probed all points in the SNARE section -- VCO-1 and VCO-2 both have periodic functions on the scope, but they look asymmetrical and not like perfect triangles, as Vincent told me that they should look like. They have more pointed bottoms, and smoothed/buffed/rounded tops.

    Envelopes 1-5 are all there. Noise is there. Trig/Accent is there.

    Vincent told me to swap out a fresh IC36 4069UBE. I swapped out IC36 with a working 4069UBE from the MID TOM section. No difference to the SNARE sound. The IC36 is not the issue, as I put the one from the SNARE section into the MID TOM section, and the MID TOM sounded fine.

    My next hypothesis is either a bad pair of Q48/Q47 transistors, or some bad SIPs M5218 like IC40 because SNAPPY is not working — the low pass part of the routing is not working
    or maybe IC39, as TONE via high pass filtering is not working either.
    Any ideas?

    UPDATE ON SNARE: I probed around and found a perfect triangle at R305. I lose the perfect triangle waveform in the signal path after R305.
    Looking at the TR-909 schematics, the signal goes into the anti-parallel oriented diode clipping stage. On my build, VCO2 probe point displays an asymmetrical waveform, as I described in previous emails -- semi-pointed bottom, but buffed and smoothed top.
    I ordered new M5218Ls and a pair of 2SD1469. Will try and swap some ICs for the SNARE section.

    Ordered AN6912, BA6110 for a possible HCL fix.
  • HCL and SNARE solved

    Still would like confirmation on HH transients if anyone else has experienced similar phenomenon.
  • If you find out about the OH "echo" thing, let me know. Same thing happening on my closed hihats. It sounds like its being played back in reverse from the end of the sample, and the length of the reverse echo gets shorter when I increase the length of the CH decay