so I finally got something boxed up
quick demo, just to give an idea what the class-A jFET version can sound like :
https://youtu.be/4pMuMS7g34I
the audio is kept raw for obvious reasons // panned hard R-L
recorded the with two amps to see what the experience would feel like
(worse case for noise, etc ...)
I'll just say it sounds way more pronounced in the recording
but still pretty cool in person ... not unlike a Univibe set on low, let's say
even with tightly matched jFET's the unit sounds a little wobbly (un-even)
which is not a bad thing in itself, adds chracter ...
the Source circuit trimmers are very sensitive here ...
even though they're 1k's set around half-way
indeed, they could be tweaked for more or less steady oscillations
I extracted signal, as before, using a Y-cable in the FX loop of a first Crate V50
then thru the CTPrev2 ... (with several volts p-p signals)
and to the front of a second Crate V50 (both modded/matched)
with matched mics (e609's) .. that's my noise test
as Dave has mentioned before
another way would be to go off the speaker
//with the advantage of LowZ for noise immunity
but possible noisy ground as well ...
which is cured with a chassis isolated jack anyway//
and then from the output of the CTP to a separate channel in recording console
in THAT scenario we would yield better noise performance
that's one big reason
AND, also to gain the ability of working with cranked out amplifiers
where the CTP chain doesn't interact dynamically within the circuit
like I'm using it here
(hey, there's gonna be lots of room for more experimenting later ... which i will leave to the rest of you to do))
since I'm not running at cranked levels here I'm eliminating the issue for now ...
and focusing on the bare bone aspects (time constraints, etc ...)
to be honest,
the only problem was a little bit of hum from the CTP's on-board 22vdc supply line
still, I had a pretty effective line filter on there ...
which means this class-A circuit is particularly sensitive to supply ripple
in the final opto-PWM version this will not be an issue
since I'll be using op-amps throughout the signal path
point taken,
---
ok, I'll say it again ... this version was difficult to build
not to mention it can take a minute or two of diddling the start switch to get the oscillators going
like rubbing sticks ... archaic to the max // kinda cool actual
and, I wasn't happy with the CMOS-opto "slowed-down" start/stop circuit performance, so I disabled it ...
so, it's hardly a stage friendly device at this point
even the (easier to build) BJT version would have these issues I suspect
so, there's no great advantage to going BJT other than having more ease at matching devices for the modulator
not sure if the modulation quality would change though ... I suspect it would be minor
still, I encourage other DIY'ers to check out that version of the circuit
---
on the brite side,
Tek is burning me a couple of "3-phase LFO" programmed pro-mini PIC boards
and as soon as I get those I will draw up a proto-board that will cradle them,
alongside all the necessary accouterments: ladder network, amplifier stages, etc
I may include the option of running the unit in mono
ie., with a dry/wet mix control ...
and output gain amp, so that the unit can be run at unity gain (as a plain ol' stomper)
we'll see if that 10~12db of insertion loss means eating too much noise later in the make-up stage ...
~jcm