filter overdrive + diode clip distortion R62

by evostars on Thu Jun 07, 2012 4:54 pm

Hi,
I looked at the "muffler" distortion, and the filter overdrive.
I will combine them into one at R62.
So the filter overdrive can be clipped by diodes (how much clip is controlled by the pot) I do this, so the cut off of the VCF can take away any "harsh" clipping sounds. I will use germanium diodes GA103

Because there is 5.33V dc on R62 (I will replace it with a 220K pot) I will add a 1uF (or 10uF) C in front of R62 (after the VCO).
This will make it possible to clip the signal with diodes to ground, without messing with the 5.33V

But I wonder, should I reverse polarity of C17? the signal is still pretty hot, but on the otherside(VCF) is 5.33V DC again...
Can some one tell me how the polarity should go :?: (and why? I love to learn :D )
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Re: filter overdrive + diode clip distortion R62

by Altitude on Thu Jun 07, 2012 7:32 pm

I'm not sure a distortion circuit is what you want at that spot. The filter overdrive is just tweaking the input level of the VCO into the VCF its not like a VCA overdrive, the muffler distortion is usually added post VCA
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Re: filter overdrive + diode clip distortion R62

by evostars on Thu Jun 07, 2012 7:36 pm

Altitude wrote:I'm not sure a distortion circuit is what you want at that spot. The filter overdrive is just tweaking the input level of the VCO into the VCF, the muffler distortion is usually added post VCA

Yes i really want it. Lets call it the evo mod ;-)
I put in 1 uF caps, poly, so no polarity problems.
Still would like to know the polarity...
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Re: filter overdrive + diode clip distortion R62

by Altitude on Thu Jun 07, 2012 7:47 pm

you have it right, + to -, same as the external input mod. If you are replacing R62 with this mod, make sure you add a resistor in series otherwise you will load down the VCO when the pot is near short
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Re: filter overdrive + diode clip distortion R62

by evostars on Thu Jun 07, 2012 8:46 pm

Altitude wrote:you have it right, + to -, same as the external input mod. If you are replacing R62 with this mod, make sure you add a resistor in series otherwise you will load down the VCO when the pot is near short

Thanks :D
So just look at DC and forget about ac when looking at polarity off caps?

Resistror in series: that won't really change the impedance (mismatch), I think. isnt r70 2.2K more responsible for that?
I had a 1k in series, but choose to keep it out, for mor interesting sound options :P

I build loads of guitar fx pedals, thats why I make these choices. 8)
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Re: filter overdrive + diode clip distortion R62

by Altitude on Thu Jun 07, 2012 8:51 pm

it will definitely mess your VCO tuning without it. I use a 3.3K on the boxes I build
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Re: filter overdrive + diode clip distortion R62

by evostars on Thu Jun 07, 2012 8:59 pm

Altitude wrote:it will definitely mess your VCO tuning without it. I use a 3.3K on the boxes I build

tuning, hmm thats important! don't want mess with that. :shock:
Thanks. I'll put one in.
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Re: filter overdrive + diode clip distortion R62

by evostars on Thu Jun 07, 2012 9:00 pm

Does it mess with the tuning of both square wave and saw?
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Re: filter overdrive + diode clip distortion R62

by Altitude on Fri Jun 08, 2012 6:37 am

yes, but its only at the extreme settings. I say try your circuit and see what it does
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Re: filter overdrive + diode clip distortion R62

by evostars on Wed Jun 13, 2012 7:24 pm

When I was testing the VCF I noticed that the signal was unchanged when I switched the germanium diodes to earth.
Maybe I reversed the diodes... I'll check as soon I've got firmware on my cpu.
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Re: filter overdrive + diode clip distortion R62

by evostars on Mon Jun 18, 2012 6:17 pm

evostars wrote:When I was testing the VCF I noticed that the signal was unchanged when I switched the germanium diodes to earth.
Maybe I reversed the diodes... I'll check as soon I've got firmware on my cpu.

I checked the diodes and they were placed right, but when i looked at the signal again, i noticed it was to low to clip the diodes (max 0.5V I believe I measured).
So i removed the diodes (and extra cap) and placed it at the volume pot, like the muffler.
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Re: filter overdrive + diode clip distortion R62

by evostars on Sat Jun 23, 2012 6:40 pm

Allright. I've got my banned finally running.
I changed the diodes to the volume pot as with the muffler.
But i still dont hear clipping. So maybe my switch melted and doesnt switch any more. Gonna check that.

And i will remeasure the signal between the vco and vcf, i can believe i isnt strong enough to clip a diode. So, maybe I'll put the diodes back in there.
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