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How to: transformer-based impedance-matching box


Les_Garten
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I'm not technically proficient enough to be able to say for sure one way or the other but I can't see how parking a pair of transformers on the output of an otherwise non-transformer coupled amp can be a good thing.

Why? That's all a parafeed amp is. Or the Maple Tree stuff. Or the L'espressivo. It's just a matter of using the right transformer.

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It looks like it's already transformer coupled. The proper solution is to just fix the hum. It could be power supply noise, heater noise, grounding, or magnetic coupling.

It seems that it is a Family characteristic of this amp in that it hums a "little" with Low impedance cans.

Here's the inside of the amp for anyone interested. The JPG is big, beware.

http://www.turbonet.biz/misc/337seReview/AAA_1430.JPG

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It looks like it's already transformer coupled.

I take that back. It looks like power transformers on both sides, and tubes in the middle? Does it really take 2 power cords? Odd.

Anyhow, it looks like a solid state bridge rectifier sunk on the side and a CRCRC filter for B+. It also looks like AC heaters. Either of those could cause hum. To lower B+ ripple, you could add a choke -- it will not only reduce ripple, but it will also take some edginess off the sound. Heaters are a little harder as the 6080's draw a lot of current which means big diodes and a lot capacitance. It is also tricky to get 6.3VDC out of a 6.3VAC winding.

Honestly, I'm not sure I'd bother.

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I take that back. It looks like power transformers on both sides, and tubes in the middle? Does it really take 2 power cords? Odd.

Anyhow, it looks like a solid state bridge rectifier sunk on the side and a CRCRC filter for B+. It also looks like AC heaters. Either of those could cause hum. To lower B+ ripple, you could add a choke -- it will not only reduce ripple, but it will also take some edginess off the sound. Heaters are a little harder as the 6080's draw a lot of current which means big diodes and a lot capacitance. It is also tricky to get 6.3VDC out of a 6.3VAC winding.

Honestly, I'm not sure I'd bother.

Hey, yeah it has 2 Power cords, each feeding a Transformer. I was looking at those heater runs as well, but they would be kinda a pain to change.

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It's the one size fits all approach that has me doubting. I'm sure that it could be designed to work well, but with any amp?

Yeah, well, I doubt there is anything that will work with every amp. But, you can probably come close. Pretty much any off the shelf amp can drive a 300 ohm headphone. So, with a 300:32 step down and you can probably get decent results.

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NG,

Autoformers is a newb concept to me. I read up a little on a number of sites and graps the concept as espoused here:

Zero Autoformers, Impedance Multiplying Transformers [English]

The commercial implementations for speakers is mega expensive!

However, not sure how you have those Transfos, switch jacks etc in you box wired.

Do you have a drawing, like for Autoformer Dummies?

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