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blackyellow



Joined: Feb 12, 2013
Posts: 19
Location: Los Angeles

PostPosted: Sun Feb 17, 2013 1:35 am    Post subject: envelope Reply with quote  Mark this post and the followings unread

Triangle
Last edited by blackyellow on Sun Mar 03, 2013 8:52 pm; edited 2 times in total
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blackyellow



Joined: Feb 12, 2013
Posts: 19
Location: Los Angeles

PostPosted: Sun Feb 17, 2013 1:57 am    Post subject: Reply with quote  Mark this post and the followings unread

seems changing VRE from 47 k to 100 k has increased clipping/distortion.... is that possible.

How can i fix the volume loss properly???
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-minus-



Joined: Oct 26, 2008
Posts: 761

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PostPosted: Sun Feb 17, 2013 3:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Not sure if this helps but I messed around with the WP-20 some time ago. I added a transistor amplifier on the output and boosted the signal. This is what I did with parts I had on hand. I made 4 of these on a single board. The BC548 is just what I had in stock. You could use another NPN I imagine.


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richardc64



Joined: Jun 01, 2006
Posts: 618
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PostPosted: Sun Feb 17, 2013 6:54 am    Post subject: Reply with quote  Mark this post and the followings unread

blackyellow wrote:
I have a lm324 op amp
Going into a 2n3904 VCA

And i tried:

-adding RF/R1 to negative input of LM324 (1M/100k)
-Changing REmitter-ground on the 3n2904 VCA from 47k to 100k....

Put the LM324 after the VCA.

In the original WP20 schematic, the transistor is followed by an opamp with a gain of 10. This is necessary because the output of the transistor is low, because the input is attenuated by a voltage divider of 39k and 4.7k. (8:1) And that's necessary I THINK because of the saturation voltages of the transistor junctions, (c-e, b-e) which are quite low. The same is true for the other 1-transistor VCA.

Having said that, I got output levels adequate for my pc's line input without amplification with a 3Vpp signal attenuated to 0.3V going into the transistor.

Question for -minus-: What waveforms at what amplitudes are going into your VCA(s)? That 1k/4.7K voltage divider doesn't provide much attenuation. Signals too large should be getting clipped. That would not be audible, however, if the waveforms are squares, pulses, or noise.

???

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blackyellow



Joined: Feb 12, 2013
Posts: 19
Location: Los Angeles

PostPosted: Sun Feb 17, 2013 8:45 am    Post subject: Reply with quote  Mark this post and the followings unread

THE WAVEFORMS ARE SAWTOOTH... he had discussed how it worked "nicely" with sawtooth. nicely being adequate and noisy Smile

this was the thread

http://electro-music.com/forum/topic-33190.html&postorder=asc
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-minus-



Joined: Oct 26, 2008
Posts: 761

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PostPosted: Sun Feb 17, 2013 10:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Reply to RichardC64:

To be honest, it was a long time ago I did this and I just used whatever junk I had on hand and fiddled around on a breadboard. I would have probably been feeding triangle waveforms into the CV and the input.

The part I wanted to draw attention to was the single transistor amp on the end. This was snipped from an old Dick Smith electronics book. I still have this board around somewhere. If you are really itching to hear whether it clips or not, I'll dig it out and do a recording.

I'm sure this was discussed elsewhere ages ago? Confused

OK, I found it. It's here:

http://electro-music.com/forum/topic-33190.html&postorder=asc&highlight=wp20&start=25

Anyway, these VCAs are crude. They might be alright for shitty noisemakers or drums, but you are better off using a proper VCA. I ended up building several Yusynth ones which do the job nicely.
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