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Output Transformer Madness (Read 1454 times)
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Output Transformer Madness
10/29/16 at 21:23:11
Hoping experienced voo-doo practitioners or physics majors may help me find a definitive answer? The question is, what is the preferred OPT for a kit build when solving for 8 ohm speakers?

Early gen kits used 9.8K input @ 6 ohm out. Thought of as universal for 4-8 ohm speaker owners.

Current recommended spec is 8K @ 6. Not much of a change and closest Edcor match available. This spec is known to be a variable in papers where Steve mentions the dark science of OPT/Speaker interaction. Something like 8 ohm speaks are really closer to 6. Thus the fixed secondary value at 6 ohm. So far, so good.

But looking at the new Zen's, they rock UFO's. These babies have a 6.6K primary and switchable 4 and 8 secondary's. Steve talks about reflected impedance. (Okay now it starts getting interesting) He mentions using 8 ohms speakers on the 4 ohm taps and 4 ohmers on the 8's. The result or reflective balance is the optimal load. Yikes, and I thought this was easy!

I'm curious why the Zens have higher rated primary's from the normally recommended 5K input for EL84 circuits? Many other designs are 5K in with a fixed 8 ohm output. Would Zens' 8K be best for 4/8 speakers where 5K is better balanced for 8 ohm speakers? I'd like to order the OPT's now and am leaning toward the 5K/6 ohm vs. 8K/6 ohm flavor.

The challenge to try some version of the new UFO's is interesting. Silk makes a close version with 6K in and dual 4/8 out. But wait, the new Zen is a different puppy here. Basically, tube rectified Zens may have completely different voltages and circuit behavior where a lower OPT primary value is optimum? Our SS rectified kits may hate 'em?

Zens have gone from less taps (originally stated as preferred over multi-taps) to switched output taps left up to the listener to chose. We are encouraged to enter the reflected impedance world reversing our speaker taps to opposite lugs. They have dropped the primary down from 9.8K to 6.6K and why 3K was ditched makes me wonder.

There may be a preferred single input/output spec knowing the 8 ohm speaker load? With Edcors line, where do you see this? (1) 5K in / 6 ohm out, (2) 5K in / 8 ohm out, (3) 8K in / 6 ohm out, or (4) 8K in / 8 ohm out?

I'm thinking number 1 is the pick? This is based on reading way too much and making things up in my head. Zen has dropped 3K so I dropped it too. The 6 ohm out seems safe supporting Steve's theory 8 ohm speaks are closer to 6.  

I know the real answer is buy a bunch and try 'em. My 8 ohm Tekton, M-Lores are efficient at 94db and have a simple cross-over. Seeing others having luck with 8 ohm speaks has me motivated to nail the OPT spec (the first time) and give 'em a go. One nutty option would be to go with an 8K primary (over but closer to 6.6 than 5K) with a 4 ohm secondary. This would be close to the UFO reflected value. Crazy talk?

What do you guys think? Remember the title has "madness" in it.
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