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musical noise 19th January 2013 05:39 PM

SPP power supply choke
I would like to insert a small choke in front of resistor R109 for additional filtering of the power supply at the input stage. I am thinking of the Hammond 158L rated at 15H and 75mA at 411 Ohm DCR. Would a substitution of the resistor to one whose value is 1.1K work? This would give a total value of 1.5K (411 + 1100=1511 Ohms) as initially intended.

If the answer is yes, I figure that the $50 dollars spent on the 2 chokes should (emphasis on "should") offer a decent improvement. What do you guys think?

rknize 20th January 2013 05:45 AM

That choke has too much DCR for the currents that the SPP needs. Even if you bypass it with a resistor like that, it will still see ~125mA. It will also diminish the choke's effect.

A common choice for a budget choke is the Triad C-14X (6H, 200mA, 150ohm) from Allied. It's only $16, has the same DCR as the resistor it replaces, and can handle the current required.

musical noise 20th January 2013 01:50 PM

Hi Russ,

Thanks for your reply, but you probably misunderstood what I am looking to do. Besides the main power supply choke which could be the Triad, I am trying to put another filtering stage in front of the input/driver stage. If you look at the schematic, cap C102 is the last filter cap that the the small signal tubes see and along with R102, they form a second filtering stage. I would like to insert the small choke in parallel with R102, and reduce that resistor's value to 1.1K so that the total resistance across this choke-resistor pair remains at 1.5KOhms. Do you think this would be worthwhile sonicwize given the relatively small outlay?

DUG 20th January 2013 04:11 PM

How much of the power supply ripple/noise is getting through that filter stage and how much do you need to decrease it?

That is where I would start...then you know what you need in terms of increased filtering at the appropriate frequency of ripple/noise.

ronaldw441 21st January 2013 05:09 AM

A choke is not necessary on a SPP. I have 3 SPP's and they're all very quite without chokes.

rknize 21st January 2013 05:40 AM

Hmm...sorry about that. I guess that my concern is the opposite. :) There is only about 8mA going through there. That is a very large choke for that job.

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