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Old 22nd February 2015, 11:58 PM   #1
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Default I Call it INFINITRON

The amplifier disclosed here is actually a Circlotron, implemented with bipolar transistors. I call it Infinitron because I found it easier to visualize Circlotron topology not as a circle, but more like a figure 8, or even better, the symbol for INFINITY (see Logo attachment). This same visualization follows to the schematic, and to a certain extent, the PC card.

If one sees a schematic resemblance to Jean Hiraga's 'le monstre', it is not a coincidence. My original plan was to bridge a pair o'monsters' to realize a balanced amp. This 'monster pair' idea eventually morphed into Infinitron.

Infinitron is running class A, with about 1 Amp Iq. Power out is a nominal 20W. Output BJTs are KSA1220Y/2SC5200. The input is a MAT02 with BC550 cascodes, but matched BC550s would work as well for the inputs.

I'm quite pleased with the performance and stability of this amp. I have been using it with a Cambridge Audio DacMagic+ for over a year now, with no issues at all.

Enjoy!..

Attachments are; Infinitron logo, schematic, 20kHz square wave trace, completed 2ch amp in a gutted pro-amp enclosure.
Attached Images
File Type: jpg logo3a (2).jpg (42.4 KB, 588 views)
File Type: jpg IFTNfinal (2).jpg (200.7 KB, 607 views)
File Type: jpg 20kHz sqr (2).jpg (99.4 KB, 596 views)
File Type: jpg assembly.jpg (183.5 KB, 575 views)
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Last edited by polyphaze; 23rd February 2015 at 03:11 AM.
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Old 23rd February 2015, 12:12 AM   #2
Bonsai is offline Bonsai  Taiwan
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Very nice! Thanks for sharing!
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Old 23rd February 2015, 03:09 AM   #3
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Very cool, refined design - like it a lot. Congratulations and thanks for sharing!
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Old 23rd February 2015, 01:51 PM   #4
banat is offline banat  Serbia
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Hi Polyphase !

Thanks for sharing that nice SS Circlotron A class amp design !

And few question :

- that circle with arrow inside represent some CCS unit ?
- it is possible to run that amp in SE mode ?, but not only in balanced mode , with let`s say IN (-) connected to ground .
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Old 23rd February 2015, 02:22 PM   #5
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My pleasure.

-Yes, that is indeed a current source. It should be adjustable between 2ma and 4ma,
as this is what sets Iq.

-Yes, it will run in SE mode. IN(-) should be grounded via an input capacitor.
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Old 23rd February 2015, 02:46 PM   #6
banat is offline banat  Serbia
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Polyphaze thanks for your answer !

All is clear now !

With that CCS in tail of input cascoded LTP SE mode is quit possible , ( but as always balanced drive mode is preferable option over SE mode for this type of basically fully balanced amp .) , and yes I like that global balanced negative current feedback design solution .
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Old 23rd February 2015, 05:14 PM   #7
thimios is offline thimios  Greece
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Interesting!Can you share the pcb?
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Old 24th February 2015, 04:26 AM   #8
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Sure. The current iteration, rev0, it not ready for prime time, as it has some 'cuts and jumps', no silkscreen etc. Rev1.0 will be ready soon though.
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Old 24th February 2015, 05:03 AM   #9
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super !

A 100W 4ohm version in AB is possible ?
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Old 24th February 2015, 05:34 AM   #10
freddi is offline freddi  United States
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beautiful amp - the concept sketch triggers mainly a slot car set in my feeble mind......
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