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Finding the phono input capacitance of a Pioneer SX-50

T

thared33

Active Member
I have to preface this with saying that I'm pretty darn ignorant compared to you guys when it comes to electronics stuff, so bear with me :)

I'm trying to find the capacitance of the phono input section of my receiver which is a Pioneer SX-50. I believe I have to look at the schematics in the service manual to find it: https://www.hifiengine.com/manual_library/pioneer/sx-50.shtml - scroll down a bit to the big page with the two drawings.

From what I see on the phono input section, locations C201 and C208 are the left and right phono inputs respectively, and I see a number saying '100p' next to both of them. I believe this means that the capacitance is 100 for both. If you go to the right a bit, which is in between those two drawings, you'll see some notes about capacitors and resistors that may be helpful.

The reason I'm trying to figure this out is that I've got a Technics SL-Q2 TT with an AT120eb cartridge which goes into the Pioneer SX-50. I noticed it was pretty darn bright, and that led me to this thread which explains the whole situation: https://audiokarma.org/forums/index.php?threads/at120eb-very-bright.767291/ - but in brief, the AT120eb cartridge wants somewhere between 100-200 capacitance, so if I'm not hitting that mark with my setup, I want to load this cartridge correctly which could in turn tame that annoying high end. I've got a couple multimeters, a soldering iron and some other tools if I'll need them.
 
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thared33 said:
From what I see on the phono input section, locations C201 and C208 are the left and right phono inputs respectively, and I see a number saying '100p' next to both of them. I believe this means that the capacitance is 100 for both
Click to expand...
Yep, 100pF (pico farads)

I'm guessing that the opamp is NJM2043DD which is a good choice, maybe there is some scope for tying others???
 
When you take the 100pF of the input plus the 30 - 50pF of typical interconnect cables, you are about 1/2 way between 100pF - 200pF as required by the cartridge. The AT cartridges are fairly forgiving of input impedance. As I recall, the AT120 is fairly bright sounding anyway. You could always change the input caps with higher values. It will modify the HF rolloff slightly, but will not otherwise damage anything.
 
I've measured as high as 400pF just at the TT side, just the TT wiring, specially when somebody replaced the wiring with some generic cable. A good cable can have 90 or 100pF. I've recently measured the original wiring of a Technics SL1210, it was 96pF total.

I'd say you need to measure your TT wiring too. Headshell removed, measuring capacitance at the RCA connector.

Or, disconecting that 100pF capacitor at the amplifier, that will lower 100pF from the total load.
 
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When you have a capacitor per channel, you should calculate it as 100pF and not combine the two L/R channels and say the input is 200pF, right?

I'm kinda new to this stuff, but I have a good Fluke multimeter, so if I can measure capacitance with that, I'll go take a measure and get back.
 
thared33 said:
When you have a capacitor per channel, you should calculate it as 100pF and not combine the two L/R channels and say the input is 200pF, right?

I'm kinda new to this stuff, but I have a good Fluke multimeter, so if I can measure capacitance with that, I'll go take a measure and get back.
Click to expand...

each channel separately

If your meter has "uF" scale, it can measure capacitors. If in doubt post a pict.
 
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