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Vintage threads from the first ten years

BAD STONE info

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5/27/1999 12:07 PM
Gus	BAD STONE info I have a bad stone in for a mod at arons site there is a schematic IC types not listed BAD STONE I looked at had IC a,b,c,d 4558's IC e CA4009(not made any more) CA4049 might work have not tried (being used in liner mode?). IC f LM324 .047uf mylar caps FWIW the Mutron phaser (not Biphase) is 6 stages using .047uf(cer) caps and 4.7k resistors with 4558s.

5/27/1999 1:29 PM

quote:
"IC e CA4009(not made any more) CA4049 might work have not tried (being used in liner mode?)."

Yeah, the 4009 is being used with the N-channel devices as linear variable resistors. It's a way to get matched FETs for use in a phaser without paying for matching, same as I did on a small scale with the Mos Doubler and the 4007. You can probably make the 4049 or 4069 work, subject to pinout. I think the 4049 is same pinout, but has some other differences to the 4009 it replaced.

5/27/1999 1:47 PM
Joe Fuzz	Thanks for the info, Gus. Can you verify that there's only 1 battery in the Bad Stone? I thought the 4558 series needed 2 batteries much as the NE5532s do. Are the 4558 a FET-based op-amp like the TL072?

5/27/1999 2:00 PM
Gus	One 9v battery 4558s are bipolar jellybean opamps, cheap and good enough, TIs and JRC seem to be better than others in effects PS Voltage, overload etc. (jellybean is from the art of electronics book) The way the effect is set up the IC "thinks" it has a +-4.5volt supply. Check out the writeup at R.G.'s site they are very good

5/27/1999 2:26 PM
Joe Fuzz	I see. So "jellybean" is a technical term? I gather from comments that you and R.G. have made that the CA4009 could possibly be replaced by 5 matched JFETs? In comparing the circuit to the MXR/DOD phasor, this makes sense. I'm curious: since the Bad Stone has 3 extra op-amp/FET stages, is it a 90 degree phasor whereas the MXR/DOD is only a 45 degree phasor?

5/27/1999 3:49 PM

quote:
"I gather from comments that you and R.G. have made that the CA4009 could possibly be replaced by 5 matched JFETs? In comparing the circuit to the MXR/DOD phasor, this makes sense."

Almost. The CMOS devices are enhancement mode, not depletion mode like JFETs. The DC bias is different. The CMOS devices have to have a voltage on the gate that varies on the positive side of the source. The JFETs have to have a voltage on their gates that varies on the negative side of the source.

To use JFETs, you'd have to prop the source contacts up by several volts so the gates could be held below the sources.

Phasers always have an even number of stages (one variable resistance element per stage), because it takes two phase stages to make one notch in the response. The MXR P45 and Dod??? have two stages, and are a one-notch phaser. The MXR P90 has four stages and is a two notch phaser. The Bad Stone has six stages (as I remember) and is a three notch phaser.

5/27/1999 5:08 PM

To use JFETs, you'd have to prop the source contacts up by several volts so the gates could be held below the sources.

Gotcha. Now the 4.7V Zener running to the JFET's sources on the MXR/DOD schematic makes sense.

The MXR P45 and Dod??? have two stages, and are a one-notch phaser. The MXR P90 has four stages and is a two notch phaser.

So theoretically I should be able to add another dual op-amp to the MXR/DOD design to turn it into a 2-notch phasor.

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