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Old 17th February 2012, 03:29 PM   #5471
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I am home and got transistors and diodes from Hesener, thanks.
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Old 17th February 2012, 03:37 PM   #5472
brianco is offline brianco  Ireland
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Location: Scottish Borders - Kelso; on the famous Tweed River!
Quote:
Originally Posted by Joachim Gerhard View Post
I am home and got transistors and diodes from Hesener, thanks.
So, you will be listening to this within an hour or so.

[I am still so no transformers in post yet. (Heavy red wine is OK, its the green vegetables, you know, the healthy stuff, makes my foot and knee swell up so painfully]
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Old 17th February 2012, 03:58 PM   #5473
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No, i still miss the Dale resistors. Anyway, i speed up.
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Old 18th February 2012, 01:09 AM   #5474
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It is a little quiet here so i decided you should have some fun and look at the first power amp i build in 40 years. Actually my power amp career came to an abrupt halt after i had build my first kit at the age of 13. I had saved the little money i had for several month to build a power amp. I soldered it together and fired it up. With a big bang the electrolytic´s went up in smoke. I had connected them the wrong way around. That frustrated me so much that i decided to take the road to speaker building and making low level stages, like preamps, filters and phono stages.
Since then i have repaired and updated several power amps and have studied numerous schematics, books and threads. So theoretical i know about most of what is going on in power amp design. I even had designed a SUSY amp based on power Opas. I have given that circuit to Brianco but again karma struck, preventing Brianco from finishing it. Still there was this spell on me that one friend of mine had formulated : "You are not allowed to design with more then plus-minus 24V and 1A."
I thought that after 40years in no power amp prison i break free and try something.
Actually what i wanted to build is not a complete power amp but a power buffer.
There are several good designs by Macura, Ciuffoli, Tubecad and others. Mostly they are single ended with N-Channels that work on a constant current source. I chose another circuit that i found one day on the web. I drew it by hand and put it away. Recently i discovered it again in a pile of papers and i must say that i like it. It uses only 3 transistors per channel, One N-Channel, one P-Channel and one BJT driver. I will draw the schematic over the weekend. It is a push-pull Class A amp. I run it on plus-minus 33V with 1,65A idle. That draws around 100W per channel so the amp gets rather hot. I think the Fets can stand that because they are robust but i may reduce the voltage somewhat and-or use bigger cooling finns. In 8 Ohm the amp produces around 20W in Class A. That is enough to drive my MPLs without leaving Class A much. So far i could not check
clipping because my generator produces only 20V. I will do that tomorrow when i have made the voltage amplification section. The buffer is fast with -3dB at 7MHz. It has a small overshot so i filtered the input at 1,5MHZ -3dB. I have not measured or simulated distortion but i will measure it ones in a while. If somebody want to do that, please put it in the simulator. It worked right away and does not produce any nasty on-off transient.
There is a small hum, because PSRR is not that great. It has potential for improvement, so when you have any idea, i am open for suggestions.
Here are some pictures.
Schematic comes later.
Attached Images
File Type: jpg MosFet Power Buffer 1.jpg (134.6 KB, 278 views)
File Type: jpg Mosfet Power Buffer 2.jpg (132.0 KB, 272 views)
File Type: jpg Mosfet Power Buffer 3.jpg (139.1 KB, 269 views)
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Old 18th February 2012, 01:33 AM   #5475
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Here is the schematic.
Attached Files
File Type: pdf Spider Web Power Buffer.TSC - TINA.pdf (7.4 KB, 136 views)
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Old 18th February 2012, 02:37 AM   #5476
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I plan also to make a voltage amplifier with tubes.
I like the octal Aikido.
Then this is a kind of Moskido.
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Old 18th February 2012, 06:34 AM   #5477
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Here is an alternative output stage. It could be redesigned for DC coupled.
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File Type: png Alternative Output Stage.png (69.6 KB, 262 views)
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Old 18th February 2012, 06:52 AM   #5478
MiiB is online now MiiB  Denmark
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For class A I would go down the Hiraga route...even i hot class A iI find the mosfets too tame and restricted compared to the warm expansive dynamic slam of the bipolar Hiraga class A
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Old 18th February 2012, 07:00 AM   #5479
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I made a version of the 8W Le Monstre.
It was on the Frickelfest. Actually i do a lot thinking about Power Amps and also Pre Amps.
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Old 18th February 2012, 07:02 AM   #5480
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Here is a picture of the new Le Monstre.
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