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Old 19th April 2007, 12:50 AM   #1
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Default What are these caps?

What kind of caps are these?(Picture attached)

The green ones are found in 50V 6800pF, 1200pF, and 2200pF

The silver can is 390pF.

Both are bypassing film caps in the Yamaha CA-2010's phono preamp, which I'm about to recap since the two channels sound different.
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Old 19th April 2007, 02:03 AM   #2
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The "silver can" looks like a polystyrene cap, that you definitely don't want to replace with anything else except maybe a polypropylene. The green ones could be anything, but are probably common polyester film caps. Beg, borrow, or steal a bridge, because the problem between channels is probably not low value caps- unless it is. Those styrene caps are easily damaged by heat and solvent, but I'd be on a coupling cap, or maybe a switch or connector problem.
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Old 19th April 2007, 07:22 PM   #3
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Oh, OK. I wonder why they bypass polypropylenes(or polystyrenes) with the same kind of caps.

Also, an other question, there are DC filter caps at the preamp's output.

The only "audio" caps I found to replace the current 'lytics are ELNA Cerafines for 22 cents and Solen caps. (Solen sells the Cerafines, and I wouldn't have to pay shipping costs for an other place than Mouser)

So far, I'm looking to replace every small value caps(some ceramics are included) not directly in the power circuit with WIMA FKP2 caps. Does it sound right?
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Old 20th April 2007, 12:31 AM   #4
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I've no idea what the schematic looks like, but one possible reason for paralleled caps in the phono section might be to get values that aren't available standard, so the RIAA curve comes out right.

Before replacing caps, my advice would be to try and trace out the circuit to see what you're starting with. That can be a PITA, but otherwise you just don't know what you're doing. Once you have a schematic, you can make good decisions and also start to think about improving the power supply bypassing at the circuit.

Opinions will vary, but personally I never use anything other than polystyrene in the RIAA network, and I wouldn't try to change the ones that are already there. Chances are you won't get the values right. Do you have a C-meter of some type? I don't believe there's as much difference in cap types as some do, but I'd also avoid electrolytic coupling caps. The problem is often finding high enough values in a film to replace them. That's usually why they used electrolytics to begin with. Note that polypropylene is quite large for a given value, much larger than other films. It has better properties, but might not fit and is quite expensive.
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Old 20th April 2007, 12:44 AM   #5
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the one on the left is of the garden variety pe film cap which Jameco used to sell decades ago.
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Old 20th April 2007, 01:11 AM   #6
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Quote:
I've no idea what the schematic looks like, but one possible reason for paralleled caps in the phono section might be to get values that aren't available standard, so the RIAA curve comes out right.

Before replacing caps, my advice would be to try and trace out the circuit to see what you're starting with. That can be a PITA, but otherwise you just don't know what you're doing. Once you have a schematic, you can make good decisions and also start to think about improving the power supply bypassing at the circuit.
I have a crappy service manual scan doing the job.

Quote:
I never use anything other than polystyrene in the RIAA network, and I wouldn't try to change the ones that are already there.
Well I have a schematic, voltages, capacitance and tolerance for about every caps, I just don't know what are every originals in there. About not using PPs, is it because they get problems over time?

Quote:
Do you have a C-meter of some type?
Well my DMM works up to 20F.

Quote:
It has better properties, but might not fit and is quite expensive.
The "might not fit" part is the one I'm worried about(But there's a lot of blank space around the lytics).

The Solen Fast PP caps are available from 1F to 330F so that's not a problem. The 3.3F costs about $2.50 CAD, 10 times the cerafine price, but not that expensive compared to a lot of "snake oil" caps.

Quote:
the one on the left is of the garden variety pe film cap which Jameco used to sell decades ago.
OK, so the green ones are polyethylenes then!

Here's the schematic. Password=yamahaphono
http://s109.photobucket.com/albums/n...5/yammyca2010/
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Old 20th April 2007, 03:33 AM   #7
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What makes you think the caps are responsible for the different sound in the channels?

If you look at all the possible causes of the problem, and consider what will change and what won't, I would say it is far more likely that your phono cartridge is the culprit. Over time the stylus' suspension stiffens, the needle wears, etc. I definitely wouldn't start monkeying around with the caps in the preamp until absolutely everything else has been checked. Cap values in a phonopreamp are critical for matching RIAA equalization curves. Polypropylene and polystyrene caps are very stable and have loooong life. They would be the last things to go bad. If you start swapping them you'll never get the thing to sound right again.

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Old 20th April 2007, 03:11 PM   #8
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Quote:
If you look at all the possible causes of the problem, and consider what will change and what won't, I would say it is far more likely that your phono cartridge is the culprit. Over time the stylus' suspension stiffens, the needle wears, etc.
The sound is different with or without anything connected to the preamp's inputs. The P-mount Grado Prestige Black cartridge is almost new, it hasn't even played for 50 hours I guess. Other preamps are OK.

This one produces hum and noise on one channel, and the other buzzes a little(Turntable connected or not). One channel sounds clearer than the other too. I found the other day that the reason why one of the channels of the phono2 input was almost inaudible is that it's shorted to ground somewhere.(I think it's the resistor between input and ground, I still haven't checked.)

You're telling me that I should maybe switch the electrolytics first?
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Old 20th April 2007, 11:11 PM   #9
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Hum and noise are more likely to be grounding/cable routing issues than bad caps in a phono preamp. Keep the preamp and cables away from the turntable and power amp. There's a lot of gain in the preamp and it will pick up stray magnetic fields (from turntable motor, power amp transformer) and amplify them along with the signal from the phono cartridge.

Caps can fail short in which case they would probably prevent the preamp from funtioning in one or both channels but plastic film dielectrics don't fail that way unless they are subjected to voltages much higher than the caps rated voltage. The other thing that can happen is the value of capacitance can drift away from its rated value due to chemical changes in the dielectric, but that is more typical of electrolytics and isn't typical of plastic film caps.

You might have a look at the solder joints- they can fail over time resulting in intermittent or open connections and can be very hard to locate. A phono preamp won't have many solder joints so they can all be resoldered in a matter of minutes.

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Old 21st April 2007, 03:09 AM   #10
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You might have a look at the solder joints- they can fail over time resulting in intermittent or open connections and can be very hard to locate. A phono preamp won't have many solder joints so they can all be resoldered in a matter of minutes.
The problem is mostly solved now!

Yes, there was a solder joint shorting Phono 2's right input to ground(I still don't see *how* though, maybe the solder joint touched scratched solder mask on the ground plane ???).

Phono 2 works better than Phono 1 as far as I recall(I should get a DeoxIT can one of these days...)

To solve the buzz on the left channel, I do the same as ever, letting the amp warm up a few minutes.

To solve most of the hum on the right channel, I just bent the SIP chip of the right channel a little more to the other side than it was now. (The relay, the 22nF ceramics and the chip pickup hum just by approaching with a finger.)

Resoldering everything? Maybe not a few minutes. This one is fairly complex(The schematic I sent doesn't include the MC preamp, RCA jacks and source selector, which are on the same PCB). I did the PSU board last month, mostly solving my power-on problems.
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