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Old 5th April 2012, 05:40 PM   #1
TB is offline TB  United States
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Default Fred Nachbaur SET amp: input capacitor

Hello,
I would like to build SET amp from this site:
A Low-Cost Single-Ended Triode Amplifier
I have a question about input capacitor. The author used 0.1 uF plastic cap. I have calculated the corner frequency ( I am a newbie in electronics, but I think I got this one correct ) to be 16 Hz. I think it is enough, but for the better bass response is it enough? I do not have any problems with using bigger cap it is just I would like to use polycarbonate cap which I already have. The cap is 0.1 uF/50 Volts. I heard before that polycarbonate capacitors sound close to PIO ones. So, for this circuit, can I use 0.1 uF without ill effect or it is better to go with 1.0 uF or larger?
Thanks
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Old 5th April 2012, 05:46 PM   #2
Zen Mod is offline Zen Mod  Serbia
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my friend Fred was clever an practical guy

that cap was deliberately small

you can even go without it .
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Old 5th April 2012, 05:53 PM   #3
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Hello Zen Mod,
Thanks for the reply. I am not afraid to use caps in signal path. I would feel safer to use it for protection. I want to use these amps with single-drive speakers. So bass response is sort off important. But, if you think 0.1 uF cap is enough.... I will go with it.
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Old 5th April 2012, 06:00 PM   #4
Zen Mod is offline Zen Mod  Serbia
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that's small amp

FN chose to limit bass extension , exactly with that cap , to prevent small OPT of making garbage

better with limited bass extension than distorted one
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Old 5th April 2012, 06:03 PM   #5
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Thanks for explanation
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Old 19th May 2013, 01:50 AM   #6
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Default The best resistor type in PSU

Hello,
I have another question about this amplifier. It is about type of 100 Ohms/1W R1 resistor in PSU. What type of resistor would be the best sonically in this position: carbon composition, carbon film, metal oxide, .....or metal fim, wire resistor?
This is URL to the amp schematic:
The MiniBlok SET Amp: How It Works

Thx

Last edited by TB; 19th May 2013 at 02:04 AM. Reason: title change
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Old 19th May 2013, 07:54 AM   #7
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There is a video clip on you tube about this amp

13EM7 SET amplifier part 1 - YouTube


I made one too on a PCB. Here is a picture of PCB. I will post picture of amp too.
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File Type: jpg 13em7_amp.jpg (260.1 KB, 232 views)
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Old 19th May 2013, 02:07 PM   #8
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Picture of my amp of FN design. I have used polycarobate cap in input and carbon film resistors. In the output I changed the cap to Russian PIO ( not shown on PCB).
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File Type: jpg 13em7_amp1.jpg (332.2 KB, 199 views)
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Old 19th May 2013, 02:39 PM   #9
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Carbon comp resistors in the signal path will create noise and distortion, and are expensive and hard to find for a reason, they are obsolete technology. I would recommend using something more modern, metal film being the best all around choice, with corbon film or metal oxide a distant 2nd choice for small wattage resistors in the signal path. As far as using some kind of exotic boutique (expensive garbage) caps, stick with the quality offerings from reputable suppliers and you won't regret it. As far as I can tell the primary function of expensive/boutique parts is extracting as much money as possible from uninformed individuals.
My 2$ worth.

Mike
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Old 19th May 2013, 07:07 PM   #10
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IMHO carbon composition resistors still have a use as grid stoppers (blockers). Farnell still stock some carbon composition resistors.

ps I have a lot of low value (<5k) NOS carbon comp. resistors. It would be a shame to throw them away just because it is thought they are so much worse than other resistor types.
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