Nasty clicks (glitch) in VCLFO 2

[kupfer_m]

Hi,

I finished two VC-LFO2 boards. I'm able to do all the calibration and get all 4 waveforms nicely tuned however there is a nasty spike on each wave form every period which is very annoying when using the LFO with a VCF or VCA.
These clicks occur on both speed settings.

Waveforms look like the ones posted by LektroiD here in this topic

What I've already changed/tested with no result:
-replaced the 10µ tantalum cap with a new one
-tried a 2,2µF MKP on that location.
-replaced the cmos 555 i had with a 'real' 7555.
-removed the sync transistor
-bypassing the 7555 with a bigger capacitor (1µF)

To be honest... I don't know what to try next.
Any suggestion are welcome!!!

Thanks,
Jim

[yusynth]

Did you trim the balance of the sawtooth correctly and for both rate ranges ?
Did you match R19,R20,R21, (within 0.1%) ? Did you use a 51K or a 49.9K for R22 ?

[kupfer_m]

Hi Yves

I did not match those resistors to 0,1%. I used 1% metalfilm for these.
I used 51k for R22. Can you explain how these can affect the saw and rectangle outputs? The clicks occur on these outputs too.
The clicks happen at the same moment the rate LED dims.
I tried disconnecting the LED but again, the clicks remain...

I will do the saw trim again.

I tapped the output of U2b (pin7) and connected it to a VCA with the same result : saw with clicks.

I hope this gets solved as all the rest, sync, fm & pw is working fine!

[kupfer_m]

hi,

I did the saw adjustment again. This reduced the clicks but they are still present.

As an experiment I placed a 22nF across R11 (200k feedback resistor of U2a).
This eliminated the clicks on the saw and triangle waves however also reduced the output voltage on the higher LFO settings. (which of course makes sense)

Tonight I'm going to try a separate PSU for the LFO.

[yusynth]

[kupfer_m]

Today I did some more measuring.
I found out that the clicks are much larger with an HA17555 than with a TLC555 on the x1.0 range. Did not check the x0.1 range.
What type of 555 (manufacturer) do you use?

Jim

[yusynth]

I don't know, I'll check that

[LektroiD]

I wish I knew the answer, both VCLFO 1 & 2 are both giving clicks at each cycle.

I'm still stuck on my saw animator add-on board, once I get that sorted I'll get back on troubleshooting this, unless a solution is reached here first.

[kupfer_m]

So yesterday I tried a rather expensive MAXIM ICM 7555.
Result still the same

The search continues...

[LektroiD]

I'm still stumped on this myself (the glitch happens on both VCLFOs).

Have you matched the resistors to 0.1% yet? I've not managed to source any, but I guess they could be hand-matched.

[yusynth]