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Old 31st December 2007, 01:41 AM   #1
jn2630 is offline jn2630  United States
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Default Question about phono preamp schematic

Im a beginner here so bare with me. I need a phono preamp, so I found the attached scamtic. I have a few questions:

1. do all the capacitors need to be rated 250volts? If yes, where do I find the right ones? If no, what do I need.

2. The power supply schematic was not included, is there a generic 250vdc output schematic out there?

There also may just be something I'm missing, cause I'm a beginner. Any help would be greatly appreciated. Thank you.
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Old 31st December 2007, 01:53 AM   #2
chrisb is offline chrisb  Canada
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Default Re: Question about phono preamp schematic

Quote:
Originally posted by jn2630
Im a beginner here so bare with me. I need a phono preamp, so I found the attached scamtic. I have a few questions:

1. do all the capacitors need to be rated 250volts? If yes, where do I find the right ones? If no, what do I need.

2. The power supply schematic was not included, is there a generic 250vdc output schematic out there?

There also may just be something I'm missing, cause I'm a beginner. Any help would be greatly appreciated. Thank you.

For a complete beginner looking for a tubed phono preamp, I'd suggest the Bottlehead kit. It's an easy build, everything is included but the tools, glue and finishing materials, and unless you have a healthy stock of spare parts, the price is impossible to beat, even with the C4S upgrade.

http://www.bottlehead.com/et/adobesp.../seduction.htm

(Eileen not included)
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Old 31st December 2007, 02:25 AM   #3
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...agree with chrisb. The seduction is a well thought out circuit, especially in regards to grounding. If you want to roll your own, I'd recommend building a line stage or two first. After that, I'd recommend the phono stage designs of Allen Wright and Steve Bench.

A phono stage isn't the easiest 1st project (by a long shot), and you could end up spending months trouble shooting it without any guarantees as to the outcome.
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Old 31st December 2007, 03:19 AM   #4
KP11520 is offline KP11520  United States
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Hi Chris and pedroskova,

I was just stopping by because I am interested in a Modwright SWLP 9.0SE Tube Linestage. The Phono stage added to the Modwright really raises the price significantly over the regular Linestage without the integrated Phono stage.

This looks very interesting and would allow me to get the SWL 9.0SE (no P) instead (used) and maybe employ this instead and eventually move up to something better down the line.

Do you have one of these? If so, what do you think of it relative to other designs and choices for MM cartridges? What would be your next step up? Are you familiar with Modwright? Maybe the Phono stage is worth the extra bucks?

Thanks for this link and your opinions! Oh... and my regards to Eileen, that's marketing!

Regards//Keith
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Old 31st December 2007, 03:31 AM   #5
jn2630 is offline jn2630  United States
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I'm not really looking for a kit. I have the tubes, the housing, some connectors, and transformers. I all really need are the resistors and capacitors. I think I can get the resistors and capacitors from small bear electronics for way under the price of the kit. What I really need is some clarity on reading the schematic.
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Old 31st December 2007, 09:40 AM   #6
EC8010 is offline EC8010  United Kingdom
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I've moved this thread as it will get more answers here.
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Old 31st December 2007, 11:35 AM   #7
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Default Re: Question about phono preamp schematic

Quote:
Originally posted by jn2630
Im a beginner here so bare with me. I need a phono preamp, so I found the attached scamtic. I have a few questions:

1. do all the capacitors need to be rated 250volts? If yes, where do I find the right ones? If no, what do I need.

2. The power supply schematic was not included, is there a generic 250vdc output schematic out there?

There also may just be something I'm missing, cause I'm a beginner. Any help would be greatly appreciated. Thank you.

That's a Bob Danielak design. C1, C2 and C4 should (IMO) be 400 WVDC, to provide a healthy margin of safety. C3 can be low WVDC, as it's protected by C1. The value of C2 should increase, for mating to low I/P impedance equipment. A silvered mica part is OK for C3. Panasonic ECQ-P(U)s are fine for C1 and C4. A GE 40L3501 is good for C2. Jim McShane should be able to help with the caps. and (perhaps) other parts too.

You need a DC heater supply, along with a well regulated B+ PSU. FWIW, I previously worked out a pseudo choke I/P filter 250 V. B+ supply. Let me go to the "archives", after work, and I'll post again.
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Old 1st January 2008, 05:34 PM   #8
jn2630 is offline jn2630  United States
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Thanks man, thats great info. Now its just the power supply I have no clue about.
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Old 1st January 2008, 06:22 PM   #9
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Quote:
Originally posted by jn2630
Thanks man, thats great info. Now its just the power supply I have no clue about.

You can get a very satisfactory B+ supply by voltage doubling a Triad N-68X isolation trafo. Follow the doubler cap. stack with a LC section. Finally, a Maida style regulator gives you the 250 VDC, on the dot.

A "Rat Shack" 273-1512 25.2 VCT trafo will power the DC heater supply. FW rectify the trafo's secondary with a MBR20100CT common cathode twin Schottky diode. Filter with a 15000 muF./25 WVDC 'lytic. Follow the 'lytic with 3X 7812 3 terminal regulator ICs. Each 12SN7 gets a dedicated regulator and the 2 12SL7s share a regulator. Don't forget clip on heat sinks for the TO220 case regulators.
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Old 2nd January 2008, 07:53 AM   #10
jn2630 is offline jn2630  United States
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That also helps, but I wouldn't know where to begin without a schematic for the supply.
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