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Baby Huey-ish phono?

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martyh

martyh

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#1
I was goofing around this morning thinking about phono stages and wanted something to hang off the back end of a d3a triode with a passive riaa. I only use MC carts so there would be a transformer on the front end ( I really like transformers 😀) Anyway what do you think of this idea? I’m not thinking that a lot of feedback would be needed, just enough to keep things nice and linear.

Thanks,
Marty
 

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#2
Marty,

Trafos inside NFB loops are VERY tricky business. Unless that feedback winding has an extremely low impedance, the idea will not work. AAMOF, even if great care is exercised, the idea may never work. Given that such "iron" is custom made and grotesquely expensive, why run the risk of failure?

You stated that you need something to follow a passively equalized D3A 1st gain block. Consider "appropriating" the 2nd gain block from the tweaked RCA preamp (schematic uploaded). As you seem to like Octal types, replace the 12AX7 with a 6SL7.
 

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#3
Eli Duttman said:
Marty,

Trafos inside NFB loops are VERY tricky business. Unless that feedback winding has an extremely low impedance, the idea will not work. AAMOF, even if great care is exercised, the idea may never work. Given that such "iron" is custom made and grotesquely expensive, why run the risk of failure?

You stated that you need something to follow a passively equalized D3A 1st gain block. Consider "appropriating" the 2nd gain block from the tweaked RCA preamp (schematic uploaded). As you seem to like Octal types, replace the 12AX7 with a 6SL7.
Click to expand...

Thanks for the advice Eli,

The shunt feedback might be a bit much and the fet output version of the RCA does look simple to build.

For the record though, 15K:600 with feedback winding is an off the shelf item from a few reasonably priced manufacturers. They are built as replacement transformers for the Ampex 351 output which as far as I can see has a few more poles to deal with than a simple diff splitter/diff output would include so maybe…maybe workable enough for someone like me to figure out.
 
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