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Old 24th July 2003, 09:12 PM   #21
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Quote:
Originally posted by keyne
the transformer needs to cope with 800mA DC - no go with a mains trannie. unless you have another winding and put a compensating current through this. (but then of course you have more active devices), yes like in schematic no. 3 on bonavolta's page. i think that looks like a very interesting amp...

transformer coupled transistor amps are rare..
my new preamp has an output transformer..
so why not a nice efficient SE amp with tx coupling for my horns..

regards
keyne
How about putting a cap in series with the output transformer primary, and in parallel run a low-resistance choke from supply to the drain? That would let you use a standard power toroid and a choke, no extra devices?

Jan Didden
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Old 24th July 2003, 09:21 PM   #22
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Hey Jan,

what you describe is "parafeed" in the valve world.
the coupling C can be made smaller than without a step-down transformer.

i think this is interesting for my horn setup which only has to do 60Hz + . So i don't need to massively oversize the transformer to cope with low bass. This might lead to better HF characteristics of the transformer.

regards,
keyne
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Old 24th July 2003, 11:51 PM   #23
lohk is offline lohk  Europe
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Have you looked at this?

http://www.tubecad.com/page11.html

http://www.tubecad.com/page12.html

I do not know if any of these amps have alredy been build and listened to - but well worth a try if somebody can calculate (and make...) suitable chokes.

Pathos is using the "inpol" circuit for a long time, the output section is a follower. The schematic was posted here before.

Klaus
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Old 25th July 2003, 08:26 AM   #24
Fuling is offline Fuling  Sweden
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tom-vdl: That schematic you posted is pretty much the same as I have in mind. What would happen if we put a zener diode across that 47uF cap to stabilize the bias voltage? I know that it is an active device, but it wouldnīt be directly in the signal path.

And by the way I donīt see any feedback, you must havea log of gain in that circuit?

lohk: Choke loaded source followers are excellent output stages in my opinion but the have one major drawback: they need a separate gainstage.
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Old 25th July 2003, 11:42 AM   #25
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Quote:
Originally posted by keyne
Hey Jan,

what you describe is "parafeed" in the valve world.
the coupling C can be made smaller than without a step-down transformer.

i think this is interesting for my horn setup which only has to do 60Hz + . So i don't need to massively oversize the transformer to cope with low bass. This might lead to better HF characteristics of the transformer.

regards,
keyne

So I invented parafeed?? Again?? What the heck!

Jan Didden
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Old 25th July 2003, 06:40 PM   #26
lohk is offline lohk  Europe
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Fuling, did you look at the TubeCad pages yet ?

Klaus
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Old 25th July 2003, 06:51 PM   #27
Fuling is offline Fuling  Sweden
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Looked, yes
Read them thouroghly, no. Shall do it.
Buffers with voltage gain?
Sound weird, but why not if it works?
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Old 25th July 2003, 06:52 PM   #28
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Quote:
Originally posted by Fuling
And by the way I donīt see any feedback, you must havea log of gain in that circuit?
What about the 0.33 ohm source resistor?

se
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Old 25th July 2003, 06:54 PM   #29
Fuling is offline Fuling  Sweden
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Ah, have a look at the last topology on
http://www.tubecad.com/page18.html

That looks like something!
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Old 25th July 2003, 07:25 PM   #30
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Quote:
Originally posted by Fuling
Ah, have a look at the last topology on
http://www.tubecad.com/page18.html

That looks like something!
Yeah, a mess.

se
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