MFOS Quad Timbre Bank Euro build

[rithma]

My summer project is complete!!!



After seeing almost NO videos or documentation out there other than Ray Wilson's original youtube post, I decided to build one of these. It is currently in a radioshack box, but I laid out the panel to fit in my eurorack. 5000hp.
I call it the PolyMFOS Resonator, after Ray wrote something like "This thing sounds like a polymoog resonator, and I'm pleased as punch about that!"
By far the most difficult build I have ever experienced, especially challenging panel wiring.

There's a couple things you must know if you build one, such as the silk screen has a couple backwards voltage regulators. Call me before you punch the wall.

/Etienne Rithers

[synthcube]

great build! can we please reference the youtube video on the website? Ray would have loved to see this!

[johnstilton]

I'm looking for some feedback from someone else who has a functional MFOS Quad Timbre Bank concerning the CV inputs:

One of the things that doesn’t seem correct about mine is that the on the CV inputs of the all channels, both the amplitude and cutoff CVs , do not result in a “zeroed” control if the input voltage to that CV if patched to 0V.

For example, a cutoff CV patched to 0V common will wield a 1830HZ sine wave at full resonance (although the HP/BP channel is a lower frequency).

An amplitude CV patched to 0V common will yield a bipolar output of 1.7Vrms

The manual controls seem entirely functionally normal though, full CCW rotation yields zero HZ F and 0V output respectively.

Making some measurements, it doesn’t seem like any amplitude or frequency reaches “zero” unless the input is less than -4VDC.

If it was only one or some channels I would conclude I have errors but because all of them behave very similarly, I cannot discount that maybe this is how they were designed. Maybe it was designed to turn off only near the bottom of a bipolar waveform?

For example if I patch the AR envelope on my MFOS ultimate is bipolar and rests as a negative voltage, for example, it will turn the channels of the QTB completely off. LFOs will turn the channels completely off at the bottom of their travel. In this manner, both of these work well with the QTB but true unipolar voltage sources are fairly useless for modulating my QTB the way it is right now.

So if anyone else can let me know how theirs behaves, I would appreciate it, thanks!

[johnstilton]

Bumping this thread to the top of the sub forum.

To recap: I build one of these and it was successful but I found the CV functionality of both the VCFs and the VCAs not to my taste as they require a voltage of -4V to be completely “off” or to put another way, at the bottom of a bi-polar signal.

Does anyone have any suggestions to modify the CV parts of the circuits so that 0V is the lowest amplitude and cutoffs?