Simple OSC for a Bassdrum-Synth

metal_head_82 · Posted: Thu Aug 19, 2010 6:16 am Post subject: Simple OSC for a Bassdrum-Synth

Hey there,

I'm currently trying to build a little bassdrum-synth.
My problem is that I didn't find a VCO which gives me a square and a triangle out.

So my Idea was to build my own circuit. It consists of a simple OPamp-based circuit and a n-channel FET (BF245A).

I have attached a schematic of the basic OSC-circuit so that you know what I mean. I planned to add that BF245 in Series with R (the same way Ray Wilson did in his WSG mods, see here: http://www.musicfromouterspace.com/analogsynth/YOUR_FIRST_SYNTH/WSG_Reborn/WEIRDSOUNDGENERATORREBORN.php?page=WSG )

The Problem is, that the pitch-change is pretty small and the FET seems to change my wavesforms. Now I ask myself what I'm doing wrong... Perhaps you guys could point me in the right direction.

Thy in advance.

osc_basic.gif

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Juno60 · Joined: Feb 09, 2006 Posts: 27 Location: Germany

Hey metal_head,

if you need a simple VCO with Square and Tri Output you should have a look at Ray Wilsons WP20. You can find here:
http://www.musicfromouterspace.com/analogsynth/WP20/WP20_PG1.html
It offers a linear controlled core build around a LM3900 OpAmp. You can get the 3900 cheap at "Reichelt". The waveform-switch can be substituted by two outputs for tri and square waveforms or a simple mixer.

Grüße aus dem Ruhrpott,
Juno

metal_head_82 · Posted: Tue Aug 24, 2010 2:30 am Post subject:

Looks very promising!

I came up with something else while doing some research.
But it became another project Wink

My current vco design offers 1V/Oct CV inputs, adjustable PW AND a square sub-octave. As it offers only saw and pulse it's better to pit it into some sort of modular device... still thinking about that.

But I'll try the WP-20 VCO as soon as I'm back home. I wonder if I could substitude the LM3900 with another OPA. I got a bunch of TL07x lying around here.

Thx for the answer.

Greetings from Bavaria.

sonicwarrior · Joined: Dec 22, 2005 Posts: 266 Location: Cologne, Germany

metal_head_82 · Posted: Wed Oct 20, 2010 4:52 am Post subject:

I'll have to look for the drawings... Until now I didn't have the time to clean them up. These are just hand-drawings AND I didn't have the time to build it.
So as soon as I find the Papers I will post them as UNTESTED here. I'll try to post them today.

PickNick · Joined: Oct 16, 2009 Posts: 82 Location: BP

hi!
you can use NE566 sound chip for square and triangle.
check Thomas Henry's Electronic Drum Cookbook.

metal_head_82 · Posted: Wed Oct 20, 2010 5:22 am Post subject:

So I ran some basic simulations a while ago and they looked very promising.
But again I post these hand drawn schematics as untested.

The VCO has an adjustable PW for the SQR Out.
It's the trim-pot at the upper right opamp. This acts as a comparator to convert the SAW into a SQR...

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This is the basic VCO.
As I finished the drawing I was pretty sure that I have seen something similar before...

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This is the basicexpo-converter. Again the basic simulations were very promising

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richardc64