Buchla 258b Clone Project

Peake · Posted: Wed May 25, 2011 12:34 pm Post subject:

It may not be a crossfade between the sine and either square or saw (via the Waveshape control/CV). It's likely just an FET VCA that -adds- the saw/square to the sine. Duh...can't believe I'd missed that all these years.

decaying.sine, I was very interested in seeing how the vintage circuit sounds/behaves with certain iterations of components. Replacing the uA726 and 2N3802 matched trannies with matched BC550C/BC560C results in a drift-o-matic experience, as indicated in Bergfotron's experiments. Placing a TEMPCO seriously reduces the drift, but not completely. Less so than the Verbos mutant hybrid/J3RK version currently building/for sale at muffwiggler.com, using a THAT 340 in place of the 726, without a TEMPCO. Edit for clarity: The J3RK version using a 340 without a TEMPCO is more stable than the original using a TEMPCO and BC550C/560C. I'm considering an iteration of my circuit using a THAT to replace the 726 and 3802.

Anyone interested in this circuit would be wise to get a couple of the J3RK boards. I'm only listening on cheap earbuds but the sine sounds very similar once calibrated. Will soon attempt installing exponential FM which is my most important feature and see if they sound the same. Very important as the triangle-core expo FM sounds like no other oscillator I've used (two sines modulating each other can go out to pitched noise/chaos, and at a lesser index, does broken robot sounds for days).

I'd release the artwork if Don gave the thumbs-up, but not otherwise. This is the important thing. But like decaying.sine said with tongue in cheek, sourcing some of these components is "fun". And becoming increasingly impossible. I'm hoping that the Verbos variation is a "close-enough" variation, and yes, I'll be very picky about the results. It IS a relief to know that certain modern FETs can seemingly replace such unobtanium as the 2N4339. (J201 Idss range falls just below the maximum upper value indicated as preferable for the sine-shaper FET. Calibrates fine but sounds weird just outside the small sweet spot.)

decaying.sine · Joined: Aug 31, 2009 Posts: 92 Location: New Haven, CT, USA

I just got a quote from UTsource. UA726HC for 8 USD if you buy 10 of them.

I have really good luck with UTsource over the past 6 months. Fairly quick shipping and good quality parts.

Peake · Posted: Wed May 25, 2011 1:56 pm Post subject:

ericcoleridge · Joined: Jan 16, 2007 Posts: 889 Location: NYC