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Old 30th June 2020, 05:10 AM   #2701
autox is offline autox  United States
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Thanks for pointing out these things about transformers. Now I know what my next round of reading will be on.

This is starting to look a lot like Susan Parker's Zeus SE pre: Zeus SE MOSFET Preamp Line Driver
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Old 1st July 2020, 05:06 PM   #2702
autox is offline autox  United States
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Upon further listening, the tone is off. It's missing a warm, full, lower mid-range. There's plenty of detail, and it sounds great for lighter, acoustic content. But anything rock - Dire Straits, Santana, Jethro Tull, Rolling Stones - it sounds somehow anemic, flat, no body or oomph.

I tinkered with the wiring on the Edcor without any luck. Using the full primary, which raises the DCR to 60, made a clear difference for the worse, which I believe is a function of the ACP+ being tuned for 30R. Taking the gain from 16x down to 8x didn't improve things.

A white noise test with my phone's RTA app didn't show anything wrong with the FR. Next chance I get, I'll try wiring the Edcor as an autoformer, as well as bringing the ratio down further.
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Old Yesterday, 03:31 AM   #2703
Cinco is offline Cinco  United States
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Hi autox, I suggest that you take a look at Papa's Official M2 Schematic

The tranformer as shown in his schematic is wired as auto-transformer for 15dB of gain (all you need is the transformer and R5 and C1 for freq comp). Your ACP+ would easily drive it with MoFo as load.

ACP+ gain of 9dB + autoformer gain of 15dB = 24dB gain total.
With 1V source that's over 15V. About 28Wrms into 8ohms.

It's not the DCR that determines the transformers impedence, it's the turns ratio, output Z of amp driving it and input Z of the load...

I learned lots from ZM about this stuff and in particular autoformer ins and outs.
A good place to start studies is Pumpkin Preamp thread.

Cinco
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Old Yesterday, 04:28 PM   #2704
Cinco is offline Cinco  United States
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With the XSM10K:150 transformer, here's what I would try for auto-transformer wiring.
Since you chose a step-down transformer, notice the input goes in the output and the output goes in the input. Not ideal but may still work ok.

Luckily your ACP has less than 1 ohm output impedance.

By taking output from pin 2, you'd have a 2:8.2 + 2 (about 1:5) ratio, about 14 dB gain.

Compare from the HP out then the line out and see which one you prefer.

Cinco
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