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Old 28th March 2012, 04:33 AM   #1
pixpop is offline pixpop  United States
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Default Depletion mode B1

Since I had a bunch of DN2540s left over from another project (Laser diode drivers, if you must know), I've been looking for a good project for them.

So I decided to try a version of the B1 follower using them. It's very similar to Nelson's version.. I only changed component values to suit parts I had on hand. I wanted to build a single channel mock up first, and if it behaved reasonably, then make a proper 2 channel version. I'll probably try it out as a headphone amp.

Click the image to open in full size.

I tests out pretty well. The simulation shows rising response around 1 MHz, but in real life, it starts to fall off around 150 kHz. Also, the sim says it has some 50 mA bias, but as built, it has 100 mA. I see 2V across R1. So much for simulation.

The response is flat from 10 Hz (as low as my sig gen goes) up to about 150 kHz. I'm not going to listen to it until I have two channels built properly, but looks very promising. I'll be making some caps larger, and adding a pot at the input.
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Old 28th March 2012, 02:22 PM   #2
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If you're playing with the TO-220 version, they might make a great choice for a BOZ, you could lose the input cap and bias circuit from the original BOZ...

Roscoe
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Old 28th March 2012, 06:09 PM   #3
pixpop is offline pixpop  United States
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Quote:
Originally Posted by Roscoe Primrose View Post
If you're playing with the TO-220 version, they might make a great choice for a BOZ, you could lose the input cap and bias circuit from the original BOZ...

Roscoe
I would still need a source resistor, I think. With 0V on the gate, it clips very soon.
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Old 28th March 2012, 07:17 PM   #4
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Yeah, but you could get rid of R101, P102, R103, R108, C102 & C104....

Roscoe
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Old 30th March 2012, 06:35 PM   #5
pixpop is offline pixpop  United States
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I have a theoretical question about the output impedance: In a circuit such as the B1, or the version I posted above, what is the relationship between the output impedance, and the bias current? Or stated otherwise, in such a circuit, how do I compute the output impedance?
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