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#51 | |
diyAudio Member
Join Date: Oct 2019
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Quote:
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#52 |
diyAudio Member
Join Date: May 2018
Location: Cambridge UK
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Any 33pF will do, its not critical, it increases HF stability and has only the slightest effect on audio frequency performance.
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#53 |
diyAudio Member
Join Date: Oct 2019
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#54 |
diyAudio Member
Join Date: Jan 2010
Location: Jeffersonville, Indiana USA
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No. Hope they are ceramic, wound plastic has more inductance. Inductance resists high frequencies, you want inductance of RF short capacitor at a minimum. Impedance of inductance is directly proportional to frequency. Capacitance of X7R diaelectric varies with voltage, which is between +- 15 at this point, negligible IMHO. 1 uf ceramic caps in between RCA input & op amp input, you might be able to hear X7R versus tantalums, but the X7R will last longer. 1 uf caps are 30000 times bigger than a 33 pf cap.
I'm listening to 4.7 uf COG ceramic caps in the sT120 right now, sound fine to me. Speaker distortion is way above the 3rd digit of HD where John Curl made some money on all those books.
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Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300 Last edited by indianajo; 22nd November 2019 at 10:19 PM. |
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#55 |
diyAudio Member
Join Date: Apr 2017
Location: greater Kansas City
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39pF will be just fine. Inductance and dielectric won't matter as much since this is only a 'does THIS make any difference' test.
How do you get along with the people upstairs? If it's an office, they have printers/fax machines. Ask them to let you know when they're about to run a multi-page print job. (So you would at least have a stable, consistent symptom.) Or at least trade phone numbers -- maybe they wouldn't mind an occasional 'Hey, what do you have running Right Now?' call. My bet is still on line-conducted/transmitted, vintage CPU-sourced -- but I've been wrong before. ![]() Rick |
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#56 |
diyAudio Member
Join Date: May 2018
Location: Cambridge UK
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39pF doesn't need a highly wound construction, it doesn't take much area with a thin film dielectric.
1 cm square of ordinary paper is about 20pF if between metal foils, and plastic films have higher dielectric that that and are thinner. |
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#57 |
diyAudio Member
Join Date: Oct 2019
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Okay so I tried to locate the feedback resistors around the op-amps; the thing is, I don't have a schematics, and I can't recognize what is what :-( I'm not good enough
So I started with putting those caps on the RCA plugs; turns out those caps must be pretty bad because I immediately got some hum (or maybe I shorted one by spreading its legs too far apart, they seem to crumble easily - **** quality, I don't wanna use them), so I removed them. So I'm back where I used to be. I think I will buy a Schaffner Filter and go from there... |
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#58 | |
diyAudio Member
Join Date: May 2002
Location: Westende Resort, BE coast
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Quote:
If it disappears, what happens if you only connect ONE input cable, L or R? Does it then whistle? Jan
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Cable: a potential source of trouble interconnecting two other potential sources of trouble - Erik Margan Linear Audio articles - SilentSwitcher - Treg high voltage regulator - High-voltage delay unit |
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#59 | |
diyAudio Member
Join Date: Oct 2019
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Quote:
connecting the preamp straight to the high pass amplifier using the same cable yields a very slightly higher level of hiss, barely noticeable difference; that's the noise floor of the preamp coming trough probably then why does connecting the cables to the crossover input causes noise? I've noticed: there are two ground planes as far as I can tell: one for the PSU section of the PCB, that one is grounded to the aluminum enclosure; and one for the signal part of the PCB wich, as far as I can tell, isn't connected to the enclosure... should the signal ground plane also be connected to the enclosure?... |
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#60 |
diyAudio Member
Join Date: Oct 2019
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How about connecting the outer part of the RCA to the enclosure using a small ceramic cap?
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