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Stax diy transformer step up math/application help

post #1 of 7
12/19/09 at 2:10pm
Thread Starter 
I plan on trying out stax sooner or later and I have been researching a bit on the transformers.

My first question is about the impedance across the transformer. I read that the primary sees a load of Zs * (Np / Ns)^2. When the headphones are hooked up across the transformer will it actually raise the load or will my amp still only be driving the 8-16 ohms of the transformer coils itself? can anyone with an srd box please measure the resistance across the power amp inputs with and without headphones attached to see if there is a difference?

Edit: Took out second question. I think I only need to really know the first.

I am looking at getting a couple Lundahl LL1623pp and wiring all primaries and secondaries in series(alt E). It would be 16 ohms on the amp side and 1600 on the stax side and would step up voltage by 13.4x.
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post #2 of 7
12/19/09 at 2:38pm
The transformer will work at a fixed ratio so the impedance presented by the drivers will be transformed over to the amp. As a guide, the Quad ESL57 is 8ohm nominal (as in the transformer was matched to that particular impedance of the drivers) but will drop to 2.8ohm in some spots and rise to 30ohm in other.
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post #3 of 7
12/19/09 at 3:10pm
Thread Starter 
Thanks Spritzer. I guess I will have to use the sowter 1:100 transfo's then because it will take that high of a ratio to drop the 170kohm of the 007's down to 17 ohms for the firstwatt @10khz ofc.

Edit: And F me they are $325 per. Prolly better off just doing an exstata or something.
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post #4 of 7
12/19/09 at 5:31pm
No need to use such a high ratio since you can compensate to some extent with resistors. The Stax transformers are 1:25 but you can go lower then that.
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post #5 of 7
12/19/09 at 5:59pm
Thread Starter 
Do you mean just putting a resistor in parallel with each stax speaker(using the 13.4x LL1623) so the F1 would always read the load as 16 ohms or something? I got about 2873 ohm for the resistor if I am understanding this right.
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post #6 of 7
12/19/09 at 6:05pm
Yup, that's what Stax did with the old SRD-5 boxes which date back to the age of low powered valve amps. They put a 4R/3W unit inline with the + input and a 30R/3W in parallel with the primary winding.
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post #7 of 7
12/19/09 at 6:20pm
Thread Starter 
Cool thanks again. I have a lot more numbers to crunch now then lol. At least I have beer so this won't be as bad.
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