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Old 17th November 2009, 01:56 AM   #1
AndrewF is offline AndrewF  Australia
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Default 6021 phono pre-amp

Hi
I have built a phono preamp using 6021W sub-minis (as yet untested). The schematic includes a capacitor to ground on the input (in parallel with a 47k resistor). The value of the capacitor is not given, just "value of C1 depends on cartridge."

Is this capacitor standard on phono preamps? If so,could someone tell me how the value of this capacitor is to be calculated?

The website containing this schematic seems to have gone, otherwise I would include a link. I can post the schematic if that is allowed.
Thankyou
Andrew
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Old 20th November 2009, 04:48 AM   #2
rman is offline rman  Canada
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Hi.

Try searching the analogue source forum on this site. Maybe try it without the capacitor. the capacitance of your interconnect plus the cin of the first stage could well be enough.

Cheers.
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Old 20th November 2009, 05:05 PM   #3
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by rman View Post
Hi.

Try searching the analogue source forum on this site. Maybe try it without the capacitor. the capacitance of your interconnect plus the cin of the first stage could well be enough.

Cheers.
I agree, start without the capacitor and add it if needed. Note that the information you seek will usually be part of the cartridge specification. For example if the capacitance recommended is 400pF and the equivalent miller capacitance at the input is 200pF then you need to figure out the capacitance provided by the cable and add that to the c miller - if that is less than the recommended capacitance you can add a small cap in parallel with the input resistor to make up the difference. In many cases you will not need to add any capacitance at all as you may have a bit too much.
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Old 20th November 2009, 05:07 PM   #4
kevinkr is offline kevinkr  United States
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I think a redrawn schematic should be ok to post, but I wouldn't post the original without permission from the owner. I'd be curious as to what topology would get sufficient gain out of one these triodes unless it has 3 stages. I've used this tube in conjunction with 5744 and barely eked out 38dB @ 1kHz. My designs all use just two stages excluding the occasional CF required for low output Z. (These days I use high transconductance tubes with low rps and no CF needed)
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