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Old 11th May 2009, 01:46 AM   #1371
Sheldon is offline Sheldon  United States
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I honestly don't know what the limits are, only that for a given core size a toroidal transformer is more sensitive to current imbalance. At least that's the general assumption. The issue is mentioned here, but not quantified: http://www.plitron.com/PDF/Atcl_1.pdf

Sounds like you have pretty good balance. Thinking a bit more about it, the primary inductance for this application will be lower than for a typical tube PP output transformer. So maybe that puts us back in the same ball park. If there is any resistance imbalance, you can correct that with some added series resistance. Me, I'd give it a try.

Sheldon
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Old 21st September 2009, 11:26 PM   #1372
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Default Output transformers for sale...

I have a NOS in sealed original boxes pair of UTC LS-667 output transformers which should be ideal for these amps. I originally bought them to use in my pair of monoblocks, but finances require the sale. These are big, heavy transformers at 15lbs each, complete specs here: http://www.bunkerofdoom.com/xfm/UTC_1960_WEB/034.jpg
Pictrure here: http://www.aiko.com/images/ebay/LS-667s.jpg

$250 + shipping...
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Old 22nd September 2009, 05:34 AM   #1373
Stee is offline Stee  Italy
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Default 0dB amplifier - no gain

see the best amplifier
good for SRPP VAS
but also for Transformer VAS
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Old 27th September 2009, 08:06 PM   #1374
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Hi Roscoe,

Thanks for the post.

Quote:
Originally Posted by Roscoe Primrose View Post
I have a NOS in sealed original boxes pair of UTC LS-667 output transformers which should be ideal for these amps. I originally bought them to use in my pair of monoblocks, but finances require the sale.... $250 + shipping...
Regret that for the UK the shipping costs would be very high.

Hope you can find someone who would like to use them.

I am prototyping a pair of amorphous C core transformers (waiting on them, probably a few more weeks till they arrive), which will be interesting comparison to the M6 EI laminations. When I get them and have runs some tests I will post up the results.

Hi Stee,

Yes, putting an output transformer in there would give the whole PP output stage a nice solid reference point, then one can cut back on the negative feedback.

Have long intended to try out something like that, but not found the time yet.

Meanwhile I am putting together a new pair of monoblocks which will use the C core OP transformers, but with internal power supplies. The PSU transformers which I already have are also C core type, a bargain e*ay purchase. I have come to the conclusion that toroids for mains power are best avoided as they pass too wide a bandwith of noise and (here in London) we have very poor symmetry mains line power with appreciable DC offset which makes them hum.

Best wishes,
Susan.
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Old 30th September 2009, 09:43 AM   #1375
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Hi Susan,
congratulations on your work. The output transformer is a crucial part (a bottleneck).
Quote:
I am prototyping a pair of amorphous C core transformers
Something like this?
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Old 30th September 2009, 09:49 AM   #1376
AKSA is offline AKSA  Australia
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Gee Lumba,

The're purdy, real purdy!!

Hugh
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Old 30th September 2009, 10:07 AM   #1377
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Hi Hugh,
I instinctively gravitated towards double C-core.
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Old 30th September 2009, 03:15 PM   #1378
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Sold.

Quote:
Originally Posted by Roscoe Primrose View Post
I have a NOS in sealed original boxes pair of UTC LS-667 output transformers which should be ideal for these amps. I originally bought them to use in my pair of monoblocks, but finances require the sale. These are big, heavy transformers at 15lbs each, complete specs here: http://www.bunkerofdoom.com/xfm/UTC_1960_WEB/034.jpg
Pictrure here: http://www.aiko.com/images/ebay/LS-667s.jpg

$250 + shipping...
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Old 4th October 2009, 08:27 AM   #1379
Stee is offline Stee  Italy
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Default Hi Susan

don't worry about the time
we have 3 Year until 2012!
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Old 9th December 2009, 06:01 PM   #1380
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Quote:
Originally Posted by john curl View Post
This design is almost exactly the circuit with germanium transistors that I have in my almost 40 year old Telefunken Bajazzo portable radio. Just used it today. Sounds great! PS Dick Sequerra (hi end guru) was a consultant on that project. This portable radio runs rings around ANY portable component that I have ever heard, including Class D portable circuits.
Hallo John, do you know the model number of the mentioned Telefunken Bajazzo portable radio?
by the way... the weblink of Dick Sequerra is very interesting
http://www.sequerra.com/

Hallo Susan, do you know about commercial amplifier models, what use basicly the topology of the schematic about post #1?
Perhaps the Paravicini-M100A about
Paravicini M100A Twin Tower2 and
M100A
http://www.envogue-24.de/Bilder/ear/...ttmeter400.jpg
http://www.envogue-24.de/Bilder/ear/100A%20Oben400.jpg

Here my overview of all amplifier topologies with only one kind of power devices in the output stage (yours see about number 3) :
Only N-Channel MOSFETs (NMOS); better Audio from non complements by Audio Power?
perhaps of interest

Last edited by tiefbassuebertr; 9th December 2009 at 06:05 PM.
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