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C1, 4.7uF cap [message #30221]

Sat, 22 January 2005 18:49

colinhester
Messages: 1349
Registered: May 2009
Location: NE Arkansas

Illuminati (3rd Degree)

Is there a minimum voltage rating? Can someone please make a little friendly suggestion as to what might possibly sound best?

http://audioroundtable.com/GroupBuild/messages/179.html

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Re: C1, 4.7uF cap [message #30222 is a reply to message #30221]

Sat, 22 January 2005 19:46

PakProtector
Messages: 935
Registered: May 2009

Illuminati (2nd Degree)

No problem! I like the ASC motor run. 440VAC/7.5 uF at ~$8 each from Allied Electronics. Slight preference to the lower voltage versions, but at a slight size penalty. It is what I have been running since Rev. 2 and I have tried a bunch of things. The ASC keep going back in.
regards,
Douglas

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Re: C1, 4.7uF cap [message #30224 is a reply to message #30222]

Sat, 22 January 2005 19:58

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

I have good luck with Allied. Julia is very helpfull. That cap is the output coupling cap; is that correct? If so would it be possible you might walk us through the Ohm's law math required to find that value? I understand if it is too much but I am attempting to access the Radiotron theory and struggling due to lack of math skills. I also happen to have the NEETS program I ordered a while ago. Anything pertinent in there. I see you have used it twice now. Thanks Douglas. We are very hyped about the 807 amp project to pair with the pre.
I have traded my EAR el 859 in order to do PP and this is right up the alley.

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C1, 7.5 uF/440VAC [message #30229 is a reply to message #30224]

Sat, 22 January 2005 20:21

PakProtector
Messages: 935
Registered: May 2009

Illuminati (2nd Degree)

it is indeed the output coupling cap. Since the impedance of a cap is 1/j-omega-C, we want the cap as large as is sonicaly reasonable. Forget about j and root negative 1. It is the real part of this we will look at.

At 20 cps, omega is 2*Pi*20 radians per second and C is 7.5 * 10^-6.
this yeilds 1061.03295 Ohms. At 40 cps, it is half that, and at 80 cps, half of that. This is close enough to the 10:1 ratio of input impedance to output impedance which keeps us from rolling off too early, even with a 10kOhm SS amp. For a 100kOhm Valve amp and several tens of pF of cabling capacitance, we're still good.
regards,
Douglas

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