| DragonMaster |
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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| Conrad Hoffman |
| 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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| DragonMaster |
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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| Conrad Hoffman |
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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| jackinnj |
| the one on the left is of the garden variety pe film cap which Jameco used to sell decades ago. |
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| DragonMaster |
| 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.
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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 20µF.
| 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 1µF to 330µF so that's not a problem. The 3.3µF 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/...45/yammyca2010/ |
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| I_Forgot |
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.
I_F |
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| DragonMaster |
| 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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| I_Forgot |
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.
I_F |
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| DragonMaster |
| quote: | | 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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| I_Forgot |
| quote: | Originally posted by DragonMaster
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 ???).
...
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.) |
When a mechanical tweak like this fixes a problem it means there is probably a bad connection/solder joint causing the problem. I would resolder the SIP to make sure all the leads are connected well.
I_F |
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| DragonMaster |
| quote: | | When a mechanical tweak like this fixes a problem it means there is probably a bad connection/solder joint causing the problem. I would resolder the SIP to make sure all the leads are connected well. |
That's the first thing I thought, considering that the original soldering joints in that amp are not so great, but there was no change. I have the impression that the chip simply picks up less interference in that position.
Once the amp warms up, there's no more problems now. What do you think, should I remake each and every solders of that board, then, if it doesn't work, change the power caps?
One thing I noticed, the 1000µF power cap used on the left channel becomes warmer than the other, and when I touch it, sometimes, a pulse is output. I reworked it's solders. |
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| Conrad Hoffman |
| A 1000uF cap should never run warm. You've got a bad cap or a bad rectifier. Wait, as Dogbert said in one of the strips, "it could be both". Remember, everything you've described is not how the unit worked when they shipped it. IMO, no mods should be considered on any piece of equipment (unless you're gutting it), until it's been brought back to factory spec. |
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| DragonMaster |
| quote: | | until it's been brought back to factory spec. |
So, is it OK or not to change every caps from this 1978 unit with new ones using the factory values like I wanted to do from the beginning?
The only difference I was planning is in cap types, replacing two small(330pF and 47pF) ceramics in the audio path with WIMA FKP2s.
I was planning to keep the ceramics in the power circuit.
Also, I'm wondering if I should put some $2.50 PPs or some $0.22 'lytics to replace the current 3.3µF Nichicons used as output DC filter caps.
I just checked for AC in the DC power lines, and my DMM doesn't show anything wrong : ~15mV AC, which is displayed even when I short both probes together.
Both caps get warm when the metal casing is around the preamp. The left channel one is always producing a bit of heat even without cover.
It's the cap used in the same channel that buzzes until the amp has warmed up. EDIT: Oh, wait, there's a warm transistor touching it.
Caps seem to be a common failure item in this amp. Those in the protection circuit fail a lot. |
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| Conrad Hoffman |
| You're the "project manager", so obviously anything's ok if you decide to do it :cool: My point is that it isn't normal for the amp to hum until it's warmed up, so it might be better to figure out what's really wrong and fix it, before making a bunch of other changes. Odds are that replacing caps won't introduce other problems, but I like to work in a step-wise fashion, so if I screw something up, it's quickly evident what it is. I also like to avoid stressing new parts because I failed to locate a circuit flaw before installing them. Finally, the only way I know the new parts are better, is to be able to compare them with the correctly functioning version of the old circuit. As for the electrolytics in the output, I'd replace them with polypropylene or polyester, depending on what will fit well. If you have to reroute the signal to some far-a-way place to get them to fit, the benefits might be cancelled out. In that case, I'd just replace them with slightly higher value and higher quality electrolytics- kinda depends on how good the rest of the circuit is to begin with. |
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| DragonMaster |
| quote: | | My point is that it isn't normal for the amp to hum until it's warmed up, so it might be better to figure out what's really wrong and fix it, |
That's why I think it's the phono caps, the line inputs and the power amps don't hum, just the phono preamp, which uses the same power rails as the other preamp circuits, and the hum is even localized on a single channel.
| quote: | | As for the electrolytics in the output, I'd replace them with polypropylene or polyester, depending on what will fit well. If you have to reroute the signal to some far-a-way place to get them to fit, the benefits might be cancelled out. |
I'll have to go and check the PPs size at Solen, I think the 3.3µFs are about as large as the 1000µF filter caps, and there seems to be enough space to fit them in there. My only problem is that they're axial caps.
| quote: | | Finally, the only way I know the new parts are better, is to be able to compare them with the correctly functioning version of the old circuit. |
So I should rebuild one channel at the time.
| quote: | | I also like to avoid stressing new parts because I failed to locate a circuit flaw before installing them. |
The power lines seem OK, 'lytics are probably just getting old as well as the solder joints. |
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| Conrad Hoffman |
Sounds like a good plan. Another Murphy's Law: You'll have the perfect replacement cap in your stock, but it will be an axial when you need a radial. When you need an axial, the ones you have will be exactly 3mm longer than the lead spacing on the PCB :devilr:
I've fixed an awful lot of very old equipment, some of it going back to the '40s. I also have more than a sane amount of stuff for testing capacitors, so I check 'em all. What I've found is that caps certainly go bad, but even with reduced capacity and increased dissipation factor, most circuits will work ok, if not to spec. If it isn't leaky and it isn't open, it's probably not the root cause of a problem. The high value low voltage parts (like 500uF 3V) are first to go. Then the ubiquitous 4.7-33uF 25v parts that were probably as cheap as could be purchased. I've had very few problems with PS filter caps, except in tube equipment. Your phono stage might hum because of a leaky, open, or shorted cap. Going away as it warms up is a clue- try to get a can of freeze mist; that should locate the problem pretty quick, particularly if it's something unsuspected like a semi or resistor. |
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| DragonMaster |
| quote: | | try to get a can of freeze mist; |
Good idea! That could help me locate my protection circuit problem too.
| quote: | | I also have more than a sane amount of stuff for testing capacitors, so I check 'em all. |
I don't have this option so I change them all with stuff people recommend ;-) (I'm going to restore my EICO HF-12s one day, I went almost just with Sprague Atoms, Orange Drops and Metal Oxide resistors to fit in them when I got the parts last year.
| quote: | | Then the ubiquitous 4.7-33uF 25v parts that were probably as cheap as could be purchased. |
Probably, the 1000µFs are 6.3V! (Connected between ground and one of the transistor pins) I wonder why they tried to go that cheap in an amp that was worth $800 in the 70s.
:bigeyes: Wait! What did I just see? Brown stuff under one of the 1000µFs(The one on the channel that works fine). It looks like electrolyte that dried up a while ago, or old glue supposed to be stopping the capacitor from moving that apparently turns conductive after a while. (There's nothing under the other one though)
I think that 10V Nichicon HE caps will be going in there! |
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