Author |
Message |
gabbagabi
Joined: Nov 29, 2008 Posts: 651 Location: Berlin by n8
Audio files: 23
|
Posted: Fri Oct 27, 2017 1:37 am Post subject:
|
|
|
i would be interested in the results too - if they are good, may i go and make a pcb for it
cheers |
|
Back to top
|
|
|
maltasynth65
Joined: Jul 20, 2016 Posts: 10 Location: MALTA
|
Posted: Fri Oct 27, 2017 4:04 pm Post subject:
latest mods |
|
|
I have done the mods suggested and I have to report that the filter is now worse then before!!! Half the frequency pot is dead, the resonance pot has reversed its function and resonance behaviour is erratic. Bearing in mind that others have reported favourably, I am accepting the fact that I may have made similar major mistakes on the two different perfboard layouts and will for now pause this project and move on until I would have the time to rethink things again... |
|
Back to top
|
|
|
gabbagabi
Joined: Nov 29, 2008 Posts: 651 Location: Berlin by n8
Audio files: 23
|
Posted: Tue Oct 31, 2017 10:26 am Post subject:
|
|
|
Even multisim is reluctant to show a "usable" result |
|
Back to top
|
|
|
maltasynth65
Joined: Jul 20, 2016 Posts: 10 Location: MALTA
|
Posted: Wed Nov 01, 2017 12:21 am Post subject:
Subject description: ACTUAL RESULTS |
|
|
thing is that the circuit actually works. However it needs to have those two resistors in circuit, cos like I stated earlier, without them, it goes nuts. I made them switchable, kinda "MODE A/B" and can get some mean madness out if it. As it happens, this is my very first filter build so I did not have anything to compare it to, but now that I have built YuSynth's Parker-Steiner, I can say that this DOES work. It would be nice if someone else who have actually built the SVVCF would kindly comment on the results achieved. |
|
Back to top
|
|
|
etheory
Joined: Feb 20, 2013 Posts: 13 Location: Sydney
|
Posted: Mon Nov 06, 2017 6:29 am Post subject:
|
|
|
I'm really sorry guys, I didn't realize how many issues the original schematic really had....
Here's the fixes + a simulation to show it really does work:
The main changes are removing the 10uF caps inside the feedback loop, which shouldn't be there, along with the biasing of the +5V which now isn't needed anywhere.
The other change is the 10K resistor in the top of the main feedback loop to 100K. And basically all resistors aside from the ones just before the gm cell transistors (the 10K and 220R dividers) should be 100K.
Now it'll work.
The main reason it was oscillating for you was the 10uF caps and the 10K feedback resistor.
The LTSpice sim works perfectly with these changes.
Description: |
|
Filesize: |
848.14 KB |
Viewed: |
634 Time(s) |
This image has been reduced to fit the page. Click on it to enlarge. |
|
Description: |
|
Filesize: |
699.37 KB |
Viewed: |
489 Time(s) |
This image has been reduced to fit the page. Click on it to enlarge. |
|
|
|
Back to top
|
|
|
maltasynth65
Joined: Jul 20, 2016 Posts: 10 Location: MALTA
|
Posted: Mon Nov 06, 2017 2:11 pm Post subject:
Subject description: revised circuit |
|
|
wow! thanks, mate.....no cause for apologies..it is all part of the loop....and I for one appreciate your efforts and your listening to us, that's how things get done!!! I'll take on board your new findings and see how it goes.....again, thanks. |
|
Back to top
|
|
|
etheory
Joined: Feb 20, 2013 Posts: 13 Location: Sydney
|
Posted: Mon Nov 06, 2017 6:27 pm Post subject:
Subject description: revised circuit |
|
|
maltasynth65 wrote: | wow! thanks, mate.....no cause for apologies..it is all part of the loop....and I for one appreciate your efforts and your listening to us, that's how things get done!!! I'll take on board your new findings and see how it goes.....again, thanks. |
You are more than welcome.
I don't stop until something is working properly, we'll get there! |
|
Back to top
|
|
|
gabbagabi
Joined: Nov 29, 2008 Posts: 651 Location: Berlin by n8
Audio files: 23
|
Posted: Wed Nov 08, 2017 10:41 am Post subject:
|
|
|
thanks.
now it somehow works in my simulation programm.
But i would still put a questionmark on R7. With 100k it will not work right. 10k is doing better.
so far, keep well |
|
Back to top
|
|
|
etheory
Joined: Feb 20, 2013 Posts: 13 Location: Sydney
|
Posted: Wed Nov 08, 2017 4:48 pm Post subject:
|
|
|
g.gabba wrote: | thanks.
now it somehow works in my simulation programm.
But i would still put a questionmark on R7. With 100k it will not work right. 10k is doing better.
so far, keep well |
In order to be a true state-variable filter, and fulfill the s-domain math equation, the feedback resistors need to all be the same value, whatever that is (aside from the bandpass filter feedback, which should have half that value, to keep the feedback values 1, 2, 1 for high pass, bandpass, lowpass, which is the true SVF configuration).
If you make them all 10K, they can be, with a difference in centre frequency, just don't mix 100K and 10K.
How does that affect your simulation? I'm guessing you've accidentally mixed some values. The 10K/220R divider before the gm cells should stay the same.
Make sure you are aware that the resonance control works "backwards", i.e. at lowest output, the resonance is the highest. That might effect the way you view your sim also. |
|
Back to top
|
|
|
|