Synth-DIY Yahoo! Groups Archives

VCA EG mode issue with replacement KLM-367A

2015-03-02 by etmachina@hotmail.com

I've recently put together & installed one of the replacement KLM-367A PCB's, and I'm thrilled that it is nearly 100% working. I have two Polysixes and it performs identically in each, so I assume the issue is probably somewhere on the replacement PCB.

The issue is that the EG mode of the VCA isn't working correctly. Gate mode works properly, but when switched to EG there is a constant drone of the oscillators (immediately, before even playing a note). Notes can be played over the droning oscillators and the envelope settings seem to function correctly (ADSR sounds fine), except for the constant droning of the oscillators. "Hold" in the key assigner section seems to be working properly. Everything else seems to be working properly.

I know there is a VCA attenuator topic active lately, pointing to issues around IC34 or IC35. I checked for continuity between a few points of IC34 and KLM366, but so far I still haven't been able to figure out my issue.

So close! Can anybody give me some more specific guidance or tips? I have a DVM but only soundcard scope software. Any help would be very, very appreciated!

Re: VCA EG mode issue with replacement KLM-367A

2015-03-03 by etmachina@hotmail.com

I'm sorry my Yahoo id is ridiculous, I don't know how to change it. I would really appreciate some help, vague tips, anything. I've asked for help in the past here and have never gotten any response at all.

Re: [PolySix] VCA EG mode issue with replacement KLM-367A

2015-03-03 by Johannes Hausensteiner

1. Please verify once more that the EG is working:
- set the VCA mode to gate (not EG!)
- set a patch that you hear the EG on the VCF

2. Check with DVM KLM-367/IC34/pin3:
- VCA in gate mode .. ca +5V
- VCA in EG mode .. ca 0V

3. Check with DVM KLM366/R22:
- VCA in gate mode .. ca 0V
- VCA in EG mode .. ca +5V
R22 is connected to +5V on one side; I mean the other side ..

4. Do the voice LEDs light properly?

5. Please explain more about the "droning" of the oscillators.
- Is it audible all the time (when in VCA EG mode)?
- Is it coming from all osicalltors or only from one?
You can check this with the keys you play
- else noticable about it (constant frequency, growling, influenced
by other settings, ...)
- ...

Johannes

On 2015-03-02, 11:04 etmachina@hotmail.com [PolySix] wrote:
>
>
> I've recently put together & installed one of the replacement KLM-367A
> PCB's, and I'm thrilled that it is nearly 100% working. I have two
> Polysixes and it performs identically in each, so I assume the issue is
> probably somewhere on the replacement PCB.
>
>
> The issue is that the EG mode of the VCA isn't working correctly. Gate
> mode works properly, but when switched to EG there is a constant drone
> of the oscillators (immediately, before even playing a note). Notes can
> be played over the droning oscillators and the envelope settings seem to
> function correctly (ADSR sounds fine), except for the constant droning
> of the oscillators. "Hold" in the key assigner section seems to be
> working properly. Everything else seems to be working properly.
>
>
> I know there is a VCA attenuator topic active lately, pointing to issues
> around IC34 or IC35. I checked for continuity between a few points of
> IC34 and KLM366, but so far I still haven't been able to figure out my
> issue.
>
>
> So close! Can anybody give me some more specific guidance or tips? I
> have a DVM but only soundcard scope software. Any help would be very,
> very appreciated!
>
>
> JT
>
>
>
>