Filter adjustments

[Omega]

Hi everyone,

I am new here and have a question on adjusting filters to the 1V/Oct characteristics.

MiniMoog Filter:...
- Set the filter to auto-oscillation (EMPHASIS turned fully clockwise)
==> o.k. understood

- Connect a keyboard (CV/GATE) to the V/Oct input
==> So far so good

- Play a tune and check the goodness of the tracking
==> How and what should I do here concrete ? Should I check for example, when I double the Voltage (from 0V to 1V) that the auto-oscillation will also double the frequency ?

- Slightly adjust T1 to achieve a good chromatic tracking.
==> Same question as above

Steiner Filter:


Trimming is very easy. Adjust the 2k trimmer in order to obtain a V/octave tracking.
==> No self oscillation ? How should I obtain 1 V/Oct tracking?

Thank you in advance answering my silly questions


Bernhard

[Omega]

Hi everone,

since I didn't get any response on my previous problem description, I will start again describing my problem with an ARP Filter, hoping to get a reply this time.

I just went through the trimming procedure for the 1V/Octage adjustments. I do not have any problem to ajust 0 V at the node given in Yves' trimming procdure when applying 0V to the V/Octave input.
Also no problems I have when adjusting via T2 to 18,7 mV when applying 1V to the V/Octave Input.
But I do have a problem in understanding and trimming the next step.
Why should I now, returning to 0V at the V/Octave Input adjust via T1 -187 mV? Even if I try the 47K Trimmer whouldn't give me the possibility to adjust the voltage much more below -90 mV..

What do I do wrong? Did someone had also in the past these problems?
Where should I start searching.

I am looking forward for any suggestions!

Thanks you a lot in advance


Cheers

Bernhard

[yusynth]

Which version did you build ? 2SA798 one, BC557 one ?
The values on my site are given for the first version. How do you power the module ?

[Omega]

Hello Yves,

nice to hear from you! I build the 2SA798 version and I powered the module with +/-15V from the Formant power supply.

The problem I have is the understanding of what I am doing... First I use T1 to adjust 0V when applying 0V at the V/Oct input. This is clear. Now I put 1 V to the V/Oct input. Then I use T2 to adjust to 18,7 mV. Also o.k. and understood. Now I lower the voltage again to 0 V at the V/Oct input. And as I expected I measure nearly 0V (as measured in the first step). Why should I now adjust the voltage to -187mV. I think that then applying 1 V I will not measure the 18,7 mV. Where do I have the misunderstanding.

Thanks a lot in advance for answering my questions.


Bernhard

[yusynth]

[kkissinger]

I know that this may seem a little un-technical -- however, when I calibrate my v/8ve modules I simply connect my keyboard voltage out to the input of the module being calibrated. I simply play an octave interval on the keyboard and adjust the volt per octave trimmer until to the interval is at or near one octave.

Then, I go through the calibration process knowing that I'm already pretty close.

At the end of the day, I always finish the calibration by ear -- moving from one octave to a four octave spread (I tune to fixed reference oscillator).

I have built two Yusynth filters, namely the Diode Ladder and the MiniMoog filter. The Diode Ladder tracks over a wide range -- around eight octaves. The MiniMoog filter tracks over about four octaves (I tried and tried, and that's about all I could get).

The Steiner Filter is the next VCF on my do-list.

[Omega]

Hi,

thanks a lot for all those explanations. I did some measurements and want kindly ask you to look at the results and tell me, if I can sleep better now and if everything looks fine

The basics for the measurements were always the same: First apply 0 V to the V/Oct input and adust T1 to 0,000 V. Second step apply 1 V to the input and adjust T2 to 0,0187 V. Then I increased the voltage step by step by 1 V and I measured the Voltage at the given node.

0 V ==> -187,0 mV ==> starting point
1 V ==> -166,1 mV ==> Delta: 20,9 mV
2 V ==> -145,9 mV ==> Delta: 20,2 mV
3 V ==> -125,6 mV ==> Delta: 20,3 mV
4 V ==> -105,4 mV ==> Delta: 20,2 mV
5 V ==> - 85,4 mV ==> Delta: 20,0 mV
6 V ==> - 65,5 mV ==> Delta: 19,9 mV
7 V ==> - 46,0 mV ==> Delta: 19,5 mV
8 V ==> - 26,8 mV ==> Delta: 19,2 mV
9 V ==> - 8,0 mV ==> Delta: 18,8 mV

So from my point of view it doesn't look bad regarding the linearity. So it's quite linear up to 7 Volt but I never reached these 18,7 mV I adjust at the second step in the overall procedure.

In a second step I apply 1 V and adjust the voltage with T2 to 168,3 mV which are exactly the 18,7 mV less then 187 mV from the beginning which I thought the delta should be. But again for the rest of the measurements it seems to be always about 20 mV difference.

0 V ==> -187,0 mV ==> starting point
1 V ==> -168,3 mV ==> Delta: 18,7 mV
2 V ==> -147,7 mV ==> Delta: 20,6 mV
3 V ==> -127,2 mV ==> Delta: 20,5 mV
4 V ==> -106,7 mV ==> Delta: 20,5 mV
5 V ==> - 86,4 mV ==> Delta: 20,3 mV
6 V ==> - 66,3 mV ==> Delta: 20,1 mV
7 V ==> - 46,6 mV ==> Delta: 19,7 mV
8 V ==> - 27,2 mV ==> Delta: 19,4 mV
9 V ==> - 8,1 mV ==> Delta: 19,2 mV

So, I only get the 18,7 mV at the first measurement. Then again I get about 20 to 20,5 mV for each step until 7 V

So what's your opinion ?

Thanks again for your patience

Cheers


Bernhard

[yusynth]

Thes figures look OK to me but don't be obsessed by matching exactly the values I gave on my page, they are given there to provide a rough indication of the trimming because in the end what is to be done is that one sets the filter into auto-oscillation mode (Full resonance setting with no input signal) and then by ear one checks that the filter is tracking well and if necessary readjust the V/oct trimmer.

Enjoy you filter,

Yves

[Omega]

Hello Yves,

thanks a lot for your quick response! So I will sleep better tonight .

But ... I'm afraid, I have the next stupid question.

What do you mean by : "...and then by ear one checks that the filter is tracking well and if necessary readjust the V/oct trimmer."

What should I hear and what not ? Playing the keyboard what should I expect ?

What can be heard, even when it's wrong ? How can I distinguish between "Bad" and "Good".


Sorry again for these questions. But understanding and learning is important for me.


Cheers



Bernhard

[yusynth]

[Omega]

Yves,

I just plugged in my keyboard and Midi/CV converter and I can measure the CV's perfectly. I plugged the CV into the V/Oct input of the filter and raise the Resonance poti. I see a nice sinewave at a given frequency. When I now play the lowest note and then the highest note on the keyboard, I see a very small change in frequency on the Oscilloscope.

Is that the point where I should readjust the V/oct to achieve the smallest change when playing the keyboard ?

Is that the process of "tracking" ?

Cheers

Bernhard

[Omega]

Hi,

I have to apologize, my last post was not correct. Don't know exactly what I was doing wrong, but after a while I saw the nice sinewave changing its frequency when playing the notes. The first surprise was, that I can see the sine wave but plugging into an amp I cannot hear anythng. Strange... Until I played a bit with the Frequency Pot. The whistles were in a range, that I simple cannot here (far behind 15 kHz). Turning the Pot i get now the sinewave auditable.
But now the next and hopefully last question. Which of the trimmer is the one for the 1 V/Oct? T2 ?
I tried it with T2 and it's a bit hard. So not more than 3 Octaves I get in sync with 1 V/Oct. Should I do anything to get it better or should I live with that results ?

Cheers

Bernhard

[yusynth]

T2 (2.2K) is the V/OCT trimmer just as it is written on the schematic, and the component layout silkscreen and T1 (47K) is the trimmer for setting the lowest frequency end (the cut-off frequency limit when the FREQUENCY pot is set to min).