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In Reply to: Grid choke and optimum coupling cap value posted by Deco-Doctor on July 2, 2006 at 02:07:04:
Martin, you have to weigh a few things. Normal thinking would say go with a big cap and push the resonant frequency down to 5 hertz or less so it won't get excited. But can you insure it won't be excited? With a CD I'd say yes but with a turntable I am not so sure. Now caps are a necessary evil but I didn't care to make mine any larger than I had too and also wished to stay with a film and foil if possible. While resistance can be used I couldn't help but feel it would "undo" much of what the grid choke brought to the table.So what is a guy to do? I measured, saw what I had, and made a compromise. I ended up with a peak (estimated to some degree) around 7 hertz. I felt this allowed me to notice when things were acting up from something like a warped record or poor tuning on a turntable's suspension. It also let me stay with a film and foil cap. But my grid chokes were 1,000 Henry with a DCR of 3K5 IIRC. So in the end I think it is a balancing act with what sounds good to you and what you feel comfortable with.
In your case I'd try a 1 mike cap and look at your response and see when gain starts climbing on the lower end. I doubt you need to go bigger than 2 mike but it is a personal choice. If you play vinyl remove the speaker grills and watch for woofer pumping.
Russ
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Follow Ups
- I just went through all of this - Russ57 06:06:28 07/02/06 (14)
- Re: I just went through all of this - Deco-Doctor 06:38:01 07/02/06 (13)
- For a cheap cap to try out - Russ57 08:02:28 07/02/06 (8)
- Re: For a cheap cap to try out - Deco-Doctor 09:27:13 07/02/06 (3)
- Why not? - Russ57 10:20:23 07/02/06 (2)
- Re: Why not? - Paul Barker 12:19:15 07/02/06 (1)
- A comment about grid current - Russ57 16:37:32 07/03/06 (0)
- Re: For a cheap cap to try out - Deco-Doctor 08:38:46 07/02/06 (3)
- Re: For a cheap cap to try out - mqracing 08:42:23 07/02/06 (2)
- Re: For a cheap cap to try out - Deco-Doctor 10:02:14 07/02/06 (1)
- Re: For a cheap cap to try out - mqracing 10:05:16 07/02/06 (0)
- Re: I just went through all of this - Paul Barker 08:00:07 07/02/06 (3)
- Re: I just went through all of this - mqracing 08:25:52 07/02/06 (1)
- Re: I just went through all of this - Paul Barker 08:46:16 07/02/06 (0)
- Re: I just went through all of this - Paul Barker 08:01:55 07/02/06 (0)
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