Synthacon VCF Question

[DJBitFlip]

I am going to attempt to use this filter design for a line level 2Vp-p application instead of a typical analog synth application. Will this filter behave the same way with a lower level input signal?

[widdly]

"Behave" is not something the Synthacon filter does

I'd say it would work fine although the resonance might not be quite right.

You can always add an opamp gain stage in front of the filter. There is a good example here.. http://www.cgs.synth.net/modules/cgs60_sba.html

The CGS version has a opamp gain stage on the output. You should be able to adjust the gain here so your output levels are at line level.

[DJBitFlip]

If it doesn't behave I suppose that's okay too Excellent...I wasn't sure about line level though. My project that I am working on is going to have a sampler controlled by a DSP and 4 individual state variable analog filters based off the synthacon. I may vary depart from the chip selection a bit, but I'll have to figure out all the kinks along the way. I'm more than ready to do this as it will be my project I finish school with. I can keep you guys updated if you're interested as well. I appreciate your help!

-Mark

EDIT: Also I saw in the parts list for the synthacon a notation that I've never seen before for resistors. I'd assume that a resistor called 2k2 is a 2.2kOhm resistor and a 2M2 would be a 2.2MOhm resistor right? Also an 89R would be 89 Ohms? Sorry for the really ridiculous question, but just want to clear up the semantics.

[RF]

I think you got it right on the resistors.
Good luck on the project.

bruce

[DJBitFlip]

Thanks Bruce, I appreciate it! I'm going to order parts relatively soon to start testing. I was thinking of maybe using one of the Burr Brown Op-Amps to see how it sounded instead of the TL071 from TI.

[DJBitFlip]

How would I go about keeping this filter in stereo since it will be used in a DJ application?

[RF]

You'll need two of them....

[DJBitFlip]

That's what I figured, but was hoping for a different answer. Is there any ICs that convert -> mono back to stereo though?

[DJBitFlip]

Would I then use a double ganged pot in order to filter both channels simultaneously?

[Pehr]

[DJBitFlip]

I'm going for a filter sound to be used for all types of electronic music from house -> breaks -> drum and bass. This filter may not work best for me then I assume...could you make any recommendations on a filter that works in stereo or where I could find some info?

[Pehr]

Don't misunderstand me I love the synthacon filter. I've got three and use them often. The resonance is insane!

Here are some audio of different versions:
http://yusynth.net/Modular/EN/STEINERVCF/index.html
http://m.bareille.free.fr/modular1/vcf_synthacon/vcf_synthacon.htm
http://www.youtube.com/watch?v=GXF2XJN4jzM

What I like the most abt the filter is the very high HP COF

I'm just qurius if you have a special reason for choosing the synthacon vcf

[DJBitFlip]

After looking around a bit the Synthacon was one of the few that I heard audio samples of that I liked. Do you think you could record a whole track and mess with the filter with changing parameters and post it? That would honestly be the most helpful to me. I am doing this project along with a DSP based sampler for my senior design in school. The idea is that it will be a versatile unit that has 4 independent filters, 1 for each channel, and independently outputs on 4 line level outputs if that makes any sense. Basically I have found that people are interested in independent filters per channel.

I am very intrigued by the analog side of things and wish to complete my first synthacon for testing here soon. I am also entering an analog design contest with Texas Instruments so a big goal is to incoporate the analog side of things as well as DSP.

Thanks again Pehr!
-Mark

[bubblechamber]

you might want to set the FREQ and RES pots up so you can use a single ganged pot or 2 pots with a flip of a switch. there may be times in which you want to sweep the filters in opposition or have one side resonating while the other is not to screw with the kids on drugs...
david

[DJBitFlip]

I get what you're saying, but I think I want them to sweep uniformly on each channel. That would create a unique filter effect, but the problem is the board realestate. I'm trying to make this unit no wider than 12 inches, and probably about 7 inches tall in the back and maybe 5 inches in the front.

[DJBitFlip]

Pehr: Is there any way that you could record a track through the synthacon and upload it please?

[Pehr]

[DJBitFlip]

Awesome, I'd really appreciate it!

Thanks again,
-Mark

[Pehr]

I'm not sure if this one got recorded properly... it is really compressed since the audio in was a low level signal from my computer (random radio station). So the resonance realle take over quickly.

It is much better with synth level signals so you might want to boost the input a little

Ken has some adapters on cgs.synth.net for that.

[DJBitFlip]

What voltage level do synth signals run at? This very important for my application and I do not currently have any analog synth equipment. I have a feeling that I will be amplifying the line level signal into 'synth level' before it hits the filter, and then reduce the gain after filtering for final output.

[Pehr]

+/- 5V

http://cgs.synth.net/modules/cgs46_sba.html
http://cgs.synth.net/modules/cgs60_sba.html

[DJBitFlip]

How did you record that? I take it that for my application I will have to increase the gain of the line level signal -> 5Vp-p and then reduce the gain after filtering for output in order to get a clean sound. Do you think this is valid?

[Pehr]

Yes, that's correct.
With your 2V p-p you just have to amplify the signal by 5, to get 10V p-p, and then divide by 5 after the filter.

[DJBitFlip]

Right, that's what I figured...alright, awesome man! I appreciate the help once again...

-Mark