Article: Beast With a Thousand Jfets

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portreathbeach

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Joined 2010
Here is a schematic I drew that has 4 op-amps in parallel. Each has a gain of 17.6 and an output resistor of 560ohms to limit the current. R1 and R2 are used at the front end to drop the voltage as the OPA2134 has in input voltage limit of +/- 0.7v. With a pk-pk input of 4v and the volume pot turned fully up, there is only +/- 0.66v at the input to the buffer.

Will this work? And if so, could I simply parallel a load more of the devices?

OPAMP_Amp.png


If this could work, maybe it could be 'The Beast with 100 Op-Amps'

:)
 
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Loudthud

Loudthud

Member
Joined 2007
The parallel combination of 100 opamps with 560 ohms in series with the output would give an output impedance of 5.6 ohms. The opamps have short circuit protection, they don't need that big of a resistor. The input offset is low enough that something like 10 ohms would work fine.
 
Loudthud

Loudthud

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Joined 2007
At an output of 20mA each opamp the output voltage can swing to about 2V from the rail. With 18V rails you have 16V peak, 2 A peak (20mA per) , that's 16W rms with 8 ohm load. Distortion raises quite a bit if you want too much gain or too much output current, especially at higher frequencies. Keep the output buffers at a gain of 1 or slightly higher. There is probably a better part out there.

I didn't try to figure out which package is best, probably the dual in 8 pin DIP.

Data sheet: http://www.ti.com/lit/ds/symlink/opa134.pdf
 
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Antoinel

Member
Joined 2011
Maybe Large Scale Integrate [LSI] this Beast

Nelson Pass said:
Maybe you want to see what Douglas Self has done with this.

:cool:
Click to expand...
This Beast may lend itself to LSI on a Si and/or a SiC wafer. Afterall, each individual P and N channel FETs belonged to a field of hundreds or thousands simultaneously made on a wafer by TOSHIBA or other. There is a precedence with CMOS Hex Inverters. Ditto for OP Amps which are also made by the tens or hundreds on a single wafer. Just link'em up.
The meticulously hand-wired prototype Beast worked with impeccable performance. The ongoing interest by DIYers worldwide may drive demand for the handmade and LSI Beast versions. The LSI Beast may have a lower cost than hand made.

Best regards.
 
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