e-licktronic Forum

Hi folks,

I have a problem with my SD. The VCO decay time is too long as you can hear in this audio example:

https://vocaroo.com/i/s0PIgOB4e5yx

I already checked all envelope caps and resistors, but couldn't find anything wrong here. Any ideas where else I should look? Vincent? Never experienced this with one of my Nava's up to now...

This is how it should sound:

https://vocaroo.com/i/s0KdGLUPVfyZ

Hi there,

Could you probe ENV1, ENV2, ENV3 and IC36 between pin7 and 14?
It seems that ENV1 does not pitch bend the VCOs correctly.

(HI KlangGenerator... making my thoughts public - instead of PM)

My guess is, your problem is in any of the two OSC AmpEnvs - ENV2 / ENV3. They both should have a Decay time of about 100ms - but one of yours is way to long! So after 100ms you should hear just the Noise portion.

I've attached some snapshots of the ENV's...
also scope ENV2/3 at C79/C70 - those are the 'real' Envelopes - also pay attention to the curve below 0,5V thats where the coresponding AMP-Transistors Q50/Q51 should close (BE forward Bias?)


ENV1-Pitch


ENV2


ENV2 - C79


ENV3


ENV3 - C70

btw. I would be very much interessed in following scoped curves - if you (or someone else) can get them:
- BD-NoiseDecay / at C12
- BD-PitchDecay / at IC12A Output
- SD-PitchAmount / at IC35A non-inv-Input
I'm currently preparing the enclosure design for my Expansion-Kit that shalls display original 909 values of the mods.

Ok, here are a few curves...

SD env1



SD env2



SD env3



SD env4

Finished a second v1.02 Nava a couple of days ago. Again all instruments fine except too long snare vco decay. Tried and checked out everything, no chance.

It seems that ENV3 is too long.
You can replace C83 value by 82nF or 68nF.
Try it and let me know

e-licktronic wrote:It seems that ENV3 is too long.
You can replace C83 value by 82nF or 68nF.
Try it and let me know

Thanks Vincent. I tried this, even with 56nf no change. And to be honest, I would prefer to find the reason for this bug without changing the original values. It's really strange that I am having the same problem with two Navas. All components definately have correct values, I checked a thousand times, replaced all transistors, ICs. Even checked all(!) traces with the help of the original schematics. I can't find the reason. I'm very interested to know if other builders experience the same with the new version...

My snare also has more of a tom sound with the snappy/noise turned down. KlangGenerator did you ever find a fix for this?

I knew that this must be a v1.02 bug. I have spent countless hours on my two Nava's so far, but up to now I am not able to find the reason for this. Still working on it. If I find something I'll let you know...