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Phono input cap to preamp

Currently reworking a Hafler DH-101. The question is regarding the input capacitor for the phono stage from the cartridge/turntable. If the phono cartridge only outputs an a.c. Signal, is a capacitor needed in that location? Is the capacitor there to prevent backfeed to the cartridge in case of failure? Currently there is an Elna 10uf 16v BP cap at c2. Seems as though one would not be needed but the interweb appears to be short of answers on this topic. Perhaps M.C. could drop a Truthbomb on this topic. 

128x128wturkey
lcoblentz3's avatar
lcoblentz3
2 posts
 

I think I would trust Mr. Hafler before MC.  Just my opinion.

lewm
13,108 posts
 

You got a plausible explanation for the capacitor from Atmasphere. I wouldn’t second guess him, but I do wonder why Hafler chose to use 10uF there and why he didn’t use a film cap, as well. Is this an MM stage or MC? If MC, what is the value of the load R? (“MC” defined here as moving coil, not the guy you asked for).

lewm
13,108 posts
 

I looked up the schematic. C2 is the top half of a capacitative voltage divider network. C1 is the other half. Together these act on AC frequencies delivered to the input transistors. R1 is your phono load resistance. I have never seen this topology before, and I don’t quite get it. But Hafler was one of the greats. Don’t mess with it except maybe to upgrade the capacitors. Do NOT change their values.

 

lewm
13,108 posts
 

Also, C1 and C2 protect the coils of an MC cartridge from any DC offset at the transistor gate. I’d love to have that confirmed or refuted by any pro in the audience. Thx.

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