Do you know what this capacitor is doing there?

destroyer X · 23rd May 2009, 09:06 AM

this is a top performer Pioneer pré amplifier...i was looking and happy to see it looks alike the Dx amplifier...but i could not understand what this capacitor is doing there.

Do you know?

Please, explain.

regards,

Carlos

destroyer X · 23rd May 2009, 10:58 AM

well...i cannot be surprised... i also do not know.

strange that one!

regards,

Carlos

Jan Dupont · 23rd May 2009, 11:07 AM

As there 22V across the 15K resistor, it seems like being some decoupling?

SY · 23rd May 2009, 11:17 AM

It's there to hold the two DC rails (37 and 15V) at the same AC voltage. Probably a stability deal.

destroyer X · 23rd May 2009, 12:18 PM

some kind of effects with and without this capacitor.

in my imagination, AC is what we do not want to have there...well..maybe i could not get the point.

thank you,

regards,

Carlos

SY · 23rd May 2009, 02:45 PM

You're right, we don't want AC there, but for the sake of PSR, whatever IS there should be equal on both sides of the dropping resistor.

analog_sa · 23rd May 2009, 03:56 PM

Quote:

Originally posted by SY
You're right, we don't want AC there, but for the sake of PSR, whatever IS there should be equal on both sides of the dropping resistor.

I would have assumed the opposite - that one wouldn't want any ac components due to the output stage current draw to affect the input. In fact i have tried supplying the input differential from its own regulator and always liked the result. The capacitor is a bit too small for most audio frequencies anyway. Same as Carlos i am baffled.

Jan Dupont · 23rd May 2009, 04:01 PM

Still baffled tooooooo

Taking the size of the cap into concideration, one must assume that it has something to do with high frequencies.....
Maybe a kind of high frq. short circuit ?

SY · 23rd May 2009, 04:06 PM

PSR.

PH104 · 23rd May 2009, 04:08 PM

I go along with analog_sa and Jan. This is only a guess, building on Jan's comment. Maybe putting it across that R is a cost-saving trick. It still serves as bypass at hi-freq (well, above 2 kHz or so) as it sees an AC ground on the low voltage side but Pioneer can use a lower voltage cap. I know it sounds crazy but maybe there were a few accountants on the design team.

I've seen equally goofy tricks in scientific instrumentation when the accountants made the engineers design to a price-point.

23rd May 2009, 10:58 AM	#2
destroyer X diyAudio Member Join Date: Feb 2004 Location: Recife - Brasil Northeast	No one knows? well...i cannot be surprised... i also do not know. strange that one! regards, Carlos __________________ Try to build an amplifier folks ... it is pure adrenaline!

23rd May 2009, 11:07 AM	#3
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	As there 22V across the 15K resistor, it seems like being some decoupling? __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

23rd May 2009, 11:17 AM	#4
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	It's there to hold the two DC rails (37 and 15V) at the same AC voltage. Probably a stability deal. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

23rd May 2009, 12:18 PM	#5
destroyer X diyAudio Member Join Date: Feb 2004 Location: Recife - Brasil Northeast	Thank you Jan and SY... i will simulate to see if there are some kind of effects with and without this capacitor. in my imagination, AC is what we do not want to have there...well..maybe i could not get the point. thank you, regards, Carlos __________________ Try to build an amplifier folks ... it is pure adrenaline!

23rd May 2009, 02:45 PM	#6
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	You're right, we don't want AC there, but for the sake of PSR, whatever IS there should be equal on both sides of the dropping resistor. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache


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23rd May 2009, 04:01 PM	#8
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	Still baffled tooooooo Taking the size of the cap into concideration, one must assume that it has something to do with high frequencies..... Maybe a kind of high frq. short circuit ? __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

23rd May 2009, 04:06 PM	#9
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	PSR. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

23rd May 2009, 04:08 PM	#10
PH104 diyAudio Member Join Date: Nov 2001 Location: New Mexico	I go along with analog_sa and Jan. This is only a guess, building on Jan's comment. Maybe putting it across that R is a cost-saving trick. It still serves as bypass at hi-freq (well, above 2 kHz or so) as it sees an AC ground on the low voltage side but Pioneer can use a lower voltage cap. I know it sounds crazy but maybe there were a few accountants on the design team. I've seen equally goofy tricks in scientific instrumentation when the accountants made the engineers design to a price-point. __________________ "When I read about the evils of drinking, I gave up reading." -- Henny Youngman

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