Zirclotron: Question for the big guy

[Joe Berry]

I think I damaged a mosfet though as only on side biases up correctly. The other side pegs the current meter when I bring up the voltage.

Possibly, but there may also be some interaction between the two sides. When you try again, start with both bias adjustments set to minimum and bring both up (more or less) together gradually. This worked best for me in a similar setup. I did blow a line fuse before figuring this out, but the MOSFETs survived.

 

[Michael Rothacher]

It's Working!

The power follower version is working. The bias wasn't as tricky to adjust as I thought it would be. A quick square wave looked pretty good and the bias is holding steady albeit with my regulated bench supply. I'm using .47 Ohm source resistors and I could probably get away with something smaller. Here's a schematic of the current config. I'll get some more data, distortion, etc. and report back. 25 Volts is as high as my bench supply goes, but I'd like to try something more like 40V.

MuHahahahahaha.

Thanks everyone!

Mike

 

[Michael Rothacher]

Here it is...

P.S. Moderator: What do you use to resize these images? It was very kind of you to extract and display them.

Thank you.

Mike

 

[Nelson Pass]

I wish somebody would tell me how to get a decent
graphic to display automatically......

 

[jleaman]

Well if were all allowed to wish i wish i had a PASS-LABS pre-amp retail that was balanced Given to me. ANd i wish i could listen to my aleph 2's that i have.

 

[Michael Rothacher]

Here is the Distortion Vs. Frequency for the Zirclotron @ 1.2 A Bias. The resistors to ground lower the noise by 20dB. I'll try to do a Distortion Vs. Power graph tomorrow.

Thanks again

Mike

 

[Michael Rothacher]

You know, I think the cross-coupled loop feedback would work here. I'll give it a go and see

 

[Joe Berry]

Thanks for sharing your results, Mike. Don't forget to listen to it. 🙂

I think the cross-coupled loop feedback would work here.

A possible drawback with this is that it will reduce the gain of the output stage below unity, so you will need more voltage swing from your drive source for the same output swing. You could also try increasing the CURRENT output from your drive source. This should reduce distortion due to the MOSFET circlotron's nonlinear input capacitance, which seems to be the dominant factor here.

 

[Michael Rothacher]

Thanks, Joe.

I tried 4.75K feedback resistors last night. It reduced the distortion through the midrange, i.e. it moved the upward bend in the distortion curve out to about 2KHz at the expense of negative gain.

Yes, I'm definitely curious to see how it will sound! I'll start working on a listenable version of this thing. Which means I'll also need to build a Balanced Zen Linestage.

Mr. Pass:

Do you think the "Zen" power supply regulators will work okay in this floating power supply situation?

Thanks

Mike

P.S. I forgot to mention in my previous post - the distortion curve is for 1W

 

[Michael Rothacher]

And here's the THD+N Vs. Power...

 

[dshortt9]

Thanks for all the info. Can you hook a speaker on to see how it sounds? What is the output impedance of the signal generator used to drive the amp?

 

[Michael Rothacher]

I currently have only one channel built and it's wired point-to-point, hanging from the heatsink. Not pretty! I'll get a listenable version together and report back.

Thanks

Mike