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Re: Insanity Box (for Aron)

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11/8/1999 2:24 PM

Re: Insanity Box (for Aron)

Here's what I think about c-mos devices, based only on my personal experience:

1) They sound good for a slight overdrive, IMHO much better than any diode clipping circuit. For heavy distortion I don't care much for them also.

2) They sound better when used just as "waveform shapers". Leave the gain for other devices, maybe an opamp like in Mark Hammer's design.

3) You need an extremely clean power supply, very good board layout and very good shielding.

I have not tried any discrete mosfet design, just the c-mos.

11/8/1999 7:27 PM

>They sound good for a slight overdrive

Yes. Very nice if you just want a little soft distortion.

>They sound better when used just as "waveform shapers".

Yep, I've had good luck boosting before the inverters BUT I've had those frequency response issues that I mentioned before. Loss of bass mainly. I think that freq. response issue could be used to create a speaker simulator if enough work was done on it.

I built a bunch of versions based on Frank Clarke's Hot Harmonics, but never really got it where I wanted it. All versions had some bass loss and I couldn't compensate for it. All of them had interesting harmonics generated that I liked.

That's why I decided to use it as only part of the distortion equation in the Insanity.

11/11/1999 12:38 PM

Re: bass loss

quote:
"I built a bunch of versions based on Frank Clarke's Hot Harmonics, but never really got it where I wanted it. All versions had some bass loss and I couldn't compensate for it. All of them had interesting harmonics generated that I liked."

Aron,

The open loop gain of an AE device is roughly ~30. While the input impedance of a CMOS inverter is huge, when you put the feedback resistor to bias it into linear operation, this resistor is "reflected" as a much lower resistor at the input of the inverter (this is called "Miller" effect - I think Randall Aiken has an explanation of this on his site).

If you use 31K as you used on the Insanity's 1st CMOS stage, this is reflected to the input as 31K/30 or ~1K. If you use the UB series, the open loop gain is much higher, at least 1000, so the 31K is reflected as ~31R or less. The input impedance of this stage will be 1K plus the 6.8K series resistor or 7.8K (or just 6.8K with the UB). With the 0.1u cap this gives a high pass at 200Hz (234Hz with the UB).

With Frank Clark's you have 250K (at maximum gain) that is reflected as 250R or less. There's no series resistor. 1M5//250 is ~250. With the 0.1u you get a corner freq of 6KHz... To be more accurate you need to consider the output impedace of the JFET stage (~4K) and this gives 374Hz. The lower the gain the higher this frequency will be (that's generally not desirable - you normally want the opposite to avoid IM with chords). The second stage does not have a series resistor also, so the corner freq will also be high because it is mainly dependant of the preceding c-mos inverter output impedance (which is low).

I think the design is prone to have bass loss, no blame on the c-mos chips. If you want to design for a good bass response, try the following:

1) When the inverter is capacitively coupled to the previous stage, use a big series input resistor;
2) When you up the input series resistor you need to up the feedback resistor or you'll have less gain;
3) When you direct couple inverters like you do on the insanity it's OK to have low series resistors or no series resistor at all;
4) Try the lower gain AE devices.

11/11/1999 5:45 PM
Ed Rembold	5) use larger caps w/10K res. GFR, Thanks for the Tech. it's always welcome. IMHO, the IB is not for the Blues, I say -Go with Gain, as Aron says "this thing's meant to scream" Ed Rembold

11/11/1999 7:08 PM
Aron	Thank you! I will keep these tips in mind when I design the next version! Aron

11/8/1999 7:45 PM
Ed Rembold	Re: Insanity Box (for Aron) Jack, I have tried countless attempts with mosfets including using them as clippers in the IB, No luck, way to much harshness and Hi-harmonics. Ed Rembold

11/8/1999 7:21 PM
Aron	Thank you GFR!!!! Maybe this explains almost everything about why my 4049AE chips could sound different than others. Makes sense to me.

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