Experimental Design - Comments, Flames Welcome - Page 5

Michael Rothacher · 26th June 2002, 02:14 AM

Joe:

Here's a diagram of my exact test setup:

To be certain I wasn't being fooled by the scope, I connected a 22k resistor to ground (as pictured) and obsevred a 1 kHz square wave ground referenced. The result is identical to the floating output (between the drains of the fets) I must be missing something terribly simple. Also, I tried the circuit with and without the source resistors (just to be sure) to no avail. I'll check everything thoroughly (values, connections, etc.) and have another go.

Thanks again.

Mike

Joe Berry · 26th June 2002, 02:53 AM

Mike -- From your test setup and reported 100 Hz rolloff, my best guess is that R21 and R22 are actually 220K ohms instead of 220 ohms. In addition, given the "open loop" topology you're using, R1 and R2 at 10K ohms also may be rolling off the HF too soon in conjunction with the diff pair input capacitance. I'd consider replacing them with 1K values.

Circlotron · 26th June 2002, 04:42 AM

I'm referring to circuit23.zip so we don't get confused. I get the gut feeling to disconnect the lower ends of R4 and R5 and run them to earth. Make R9 and R10 zero ohms.

One way to set the bias is to offset M1 and M2 gates a little negative but it will be very touchy. Probably unusable.

GP.

Michael Rothacher · 26th June 2002, 03:49 PM

Circlotron, Joe: I was thinking of using a modified current mirror in the LTP to control the output current along the lines of what Joe had suggested. I'll draw it up and show you what I mean. Not sure if it would work, but maybe worth exploring. Thanks for your recommendations. I'll try them soon.

Thanks

Mike

Joe: your guess about the 220k resistors is pretty insightful and would emulate the effect, but I've checked them. In your experience, are there any known problems with these experimentor plug-boards? I think Grey said that he built his Aleph-X on one and is not having problems.

Joe Berry · 26th June 2002, 04:51 PM

Sorry Mike, I don't have much experience with plug-in boards. I use one occasionally, but generally prefer to go from simulation to PCB layout, as I think I expose more problems that way.

That said, as a service tech years ago I learned that common airborne pollutants can deposit a semi-insulating film on contact surfaces over time. So if your plug-in board or components have any age on them, I'd probably at least try cleaning and reseating the component leads. As you say, the problem does resemble a high impedance (film?) in series with the gates of the input pair.

Circlomanen · 8th October 2004, 05:46 PM

I have designed and built a two stage solidstate circlotron amp without any couplingcaps. It uses 2SK170GR in the input/feedbackstage and IRF 9530 in the outputstage.
Its only giving me about 14 watts a channel but with more heatsink and bigger transformers i could get 50-60 watts.
It souds way better than my zen version 4 i tried prior too this design.
Right now it has current feedback, but it is easely changed too supersymmetry feedback.

Michael Rothacher · 10th October 2004, 12:18 AM

Hello:

It has been a long time since this thread has seen activity. I haven't had time to experiment with this one. I'd love to see your schematic, if you're able to post it.

Mike

Circlomanen · 11th October 2004, 07:30 PM

I could not post the picture, but i have it on another swedish hififorum.
www.hififorum.nu/forum/topic.asp?TOPIC_=32287

Tom2 · 11th October 2004, 09:51 PM

Your link sends me to main page.
I looked through the web site and found it?
Is this it?
Hopefully the attached schematic works.

Tom2 · 12th October 2004, 05:26 AM

Small correction:
I said "hopefully the attached schematic works", what I meant to say is "hopefully attaching the schematic works".

I am thinking of designing and building a circlotron/susy soon.
I am thinking of using a balanced line zen type or reflected cascode front end, then drive a balanced circlotron output. Probably use local or global feedback. I'm shooting for 100 watts class A into 8 ohms. I'll try low power version first just to see if my ideas work.

I have a singled ended circlotron design idea using an aleph type current source. It is based on the Penultimate Zen circuit. I don't know if I'll build it.

I also have a design idea based upon the Bongiorno 4229706 patent. It uses CFB amps for the SuSy topology.

I'll post the schematics if your interested.

Tom

8th October 2004, 05:46 PM	#46
Circlomanen diyAudio Member Join Date: Sep 2004 Location: Göteborg	I have designed and built a two stage solidstate circlotron amp without any couplingcaps. It uses 2SK170GR in the input/feedbackstage and IRF 9530 in the outputstage. Its only giving me about 14 watts a channel but with more heatsink and bigger transformers i could get 50-60 watts. It souds way better than my zen version 4 i tried prior too this design. Right now it has current feedback, but it is easely changed too supersymmetry feedback. __________________ We live in a horizontal world, why use vertical topologies???

11th October 2004, 07:30 PM	#48
Circlomanen diyAudio Member Join Date: Sep 2004 Location: Göteborg	I could not post the picture, but i have it on another swedish hififorum. www.hififorum.nu/forum/topic.asp?TOPIC_=32287 __________________ We live in a horizontal world, why use vertical topologies???

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26th June 2002, 02:53 AM	#42
Joe Berry diyAudio Member Join Date: Mar 2001 Location: USA	Mike -- From your test setup and reported 100 Hz rolloff, my best guess is that R21 and R22 are actually 220K ohms instead of 220 ohms. In addition, given the "open loop" topology you're using, R1 and R2 at 10K ohms also may be rolling off the HF too soon in conjunction with the diff pair input capacitance. I'd consider replacing them with 1K values.

26th June 2002, 04:42 AM	#43
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	I'm referring to circuit23.zip so we don't get confused. I get the gut feeling to disconnect the lower ends of R4 and R5 and run them to earth. Make R9 and R10 zero ohms. One way to set the bias is to offset M1 and M2 gates a little negative but it will be very touchy. Probably unusable. GP.

26th June 2002, 03:49 PM	#44
Michael Rothacher www.audiohobby.com diyAudio Member Join Date: May 2001 Blog Entries: 3	Circlotron, Joe: I was thinking of using a modified current mirror in the LTP to control the output current along the lines of what Joe had suggested. I'll draw it up and show you what I mean. Not sure if it would work, but maybe worth exploring. Thanks for your recommendations. I'll try them soon. Thanks Mike Joe: your guess about the 220k resistors is pretty insightful and would emulate the effect, but I've checked them. In your experience, are there any known problems with these experimentor plug-boards? I think Grey said that he built his Aleph-X on one and is not having problems.

26th June 2002, 04:51 PM	#45
Joe Berry diyAudio Member Join Date: Mar 2001 Location: USA	Sorry Mike, I don't have much experience with plug-in boards. I use one occasionally, but generally prefer to go from simulation to PCB layout, as I think I expose more problems that way. That said, as a service tech years ago I learned that common airborne pollutants can deposit a semi-insulating film on contact surfaces over time. So if your plug-in board or components have any age on them, I'd probably at least try cleaning and reseating the component leads. As you say, the problem does resemble a high impedance (film?) in series with the gates of the input pair.

10th October 2004, 12:18 AM	#47
Michael Rothacher www.audiohobby.com diyAudio Member Join Date: May 2001 Blog Entries: 3	Hello: It has been a long time since this thread has seen activity. I haven't had time to experiment with this one. I'd love to see your schematic, if you're able to post it. Mike

12th October 2004, 05:26 AM	#50
Tom2 diyAudio Member Join Date: Jun 2004 Location: Central CA	Small correction: I said "hopefully the attached schematic works", what I meant to say is "hopefully attaching the schematic works". I am thinking of designing and building a circlotron/susy soon. I am thinking of using a balanced line zen type or reflected cascode front end, then drive a balanced circlotron output. Probably use local or global feedback. I'm shooting for 100 watts class A into 8 ohms. I'll try low power version first just to see if my ideas work. I have a singled ended circlotron design idea using an aleph type current source. It is based on the Penultimate Zen circuit. I don't know if I'll build it. I also have a design idea based upon the Bongiorno 4229706 patent. It uses CFB amps for the SuSy topology. I'll post the schematics if your interested. Tom