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Speaker matching transformer.
Speaker matching transformer.
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Old 29th September 2008, 03:20 AM   #1
GK is offline GK  Australia
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Default Speaker matching transformer.


I need an unusual audio power transformer - with a 2 ohm secondary and an 8 ohm primary (with a 4 ohm tap) rated at 200W. Needs good audio bandwidth too.

Does such a thing exist? if not I'm guessing that such a transformer should be a straight forward job for any of the custom winders our there?

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Old 29th September 2008, 04:44 AM   #2
jlsem is offline jlsem  United States
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This is close to what you're looking for, but it's only rated at 100W:


And another (auotransformer, though):


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Old 29th September 2008, 04:58 AM   #3
Geek is offline Geek
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Having EDCOR build you one will probably be far cheaper and perform just as good as those fancy shmancy things.

Contact Brian Weston.

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Old 29th September 2008, 01:55 PM   #4
pjanda1 is offline pjanda1  United States
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Have you seen Paul Speltz' autoformers? If I'm hearing you correctly, they may be what you are looking for. I don't know the max power rating, as they tend to be used by tube/SET guys. I bet the "naked" pair would suit you best, as that's a good chunk of $$ for a box.


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Old 12th October 2008, 12:45 PM   #5
GK is offline GK  Australia
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HmmÖ. I didnít think of an autotransformer, but that would work fine also. However I canít budge on the 2-ohm and 200W spec. I guess Iíll have to get one custom wound.

On the topic of transformers, does anyone have any experience with toroidal PA transformers such as this one:


The 3db spec is 20kHz but being a toroid I suspect this is conservative. Iíd like to experiment with one of these in a 6AS7 circlotron, with the DC bias on the primary nulled out with a servo.

However this leads to more questionsÖ.
I see plenty of 6AS7 OTL designs out there with fixed bias and multiple triode sections connected in parallel, but this RCA application note makes it plain that this is not a good idea:


I guess this is due to parameter inconsistency / aging / current sharing issues???
New production 6AS7ís are cheap(ish), but if I have to buy a bucket full in order to match them initially and as they age to make a working amplifier then thatís not much of an advantage.

How consistent are new production 6AS7ís, despite the fact that the manufacturers actually market these things for OTL designs? Alternatively Iím toying with the idea of microcontroller adjusted fixed bias for each triode.

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Old 12th October 2008, 11:51 PM   #6
DaveMcLain is offline DaveMcLain  United States
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Peavey makes the Automatch auto tranformer that is a 400 watt rated model. I have one that I use from time to time for matching guitar amp and speaker combinations. It's very simple to use too.
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