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Re: Phaser boards

6/10/1998 7:21 AM
R.G. Re: Phaser boards
The number of stages is primarily a function of how much you want to spend on stages and circuit board space, as the basic stage can be repeated ad infinitum - till the noise buildup gets you.  
I would like to see the various phaser schematics you mention, as part of the continuing quest to see the schematic of every effect that ever existed...  
On the all CMOS phaser, actually, I suspect that it could well be made to work. I have used CMOS in all the various guises you mention, just not all together. The problem, if it is one, is that even high feedback can't mask the inherent soft distortion of the amplifier's transfer function. It would always add some soft limiting. Maybe good, maybe bad.
6/10/1998 7:51 AM

I can post you the various schematics, if your e-mail is working (seems you have a lot of trouble with it). In case it's not, can someone suggest a ftp place to upload them?  
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6/10/1998 8:02 AM
Jack Orman

I have interest in the switched cap phaser because I have worked on a design of this type using some of the National Semi chips. Could you please e-mail it to me, and I'll send you a phaser design in return that has a really unique oscillator design.  
Another thought: wasn't there an RCA chip that had several FETs in one DIP? Or maybe National Semi; seems like the old NSC Analog Design books had a phaser design that used something like this. I'll dig them out and see.  
regards, Jack
6/11/1998 7:04 AM
Jack Orman

The monolithic FET chip was the AM9709CN by National Semiconductor. Can't find that one in any of my catalogs; could be long gone.  
6/12/1998 1:28 PM

I sent to you and RG the SC phasers I have. One uses 4016 CMOS switches and the other two uses a MF10CN (dual sc state variable filter) chip.  
In the Elektor where appeared the Bi-phase there was a FET matching circuit. It seemed to match IDss.  
6/13/1998 12:36 AM
I sent to you and RG the SC phasers I have. One uses  
4016 CMOS switches and the other two uses a MF10CN  
(dual sc state variable filter) chip.
Thanks! Received in good shape.  
regards, jack
6/10/1998 7:26 AM
I had a few minutes and messed with it a bit. I got all eight phase stages and the opamps for the oscillators and I/O amps on a 2x3 board, and got the phase stages laid out and wired. Looks like there is, in concept at least, enough room to wire the rest up.  
I answered my own question. Given the historical interest, it makes sense to wire the thing up using JFETs to make an 8-stage "Phase 180", same circuit as the P90, just twice the number of stages. The original JFETs in the P90 were 2N5492's, and I don't know of a good source for them right now.  
I still have to figure out how to get a matched set of eight. That might take as many as 50 to 100 devices to select out of if you can't get them all from the same wafer lot.  
We'll work on that one. Someone else want to find fets?
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