Nakamichi Cluster****
I've acquired this SR-4A that I like.
Photo of SR-4A
It's 30+ years old now, and though it sounds very good and is in almost perfect shape, I have a suspicion it will sound fantastic with a recap - I think it is lacking that extra 20% in performance. I have never recapped a receiver, but I have done soldering, and have successfully done jobs on even smaller things like MacBooks, etc. I'm not sure if I'm being overambitious in thinking that a receiver that is this densely packed should even be recapped - it almost seems specifically constructed so as to prevent access to the things you need access to. The number of plugs & wires for which you'd have to remember where/how to reattach them is quite high. And I don't know where to start if the answer is 'yes, it should be recapped.' Among the questions I have are:
-Which capacitors exactly should I be replacing? There seem to be about 50+ of them in the unit, and I have no idea which to focus on. I have access to a schematic and all, but don't know if I should just replace the ones off certain boards, and if so *all* of them or just some.
-Is it reasonable to think I can access all of these capacitors? The receiver has a 'double deck' construction, along with a web of wires that I guess would all need to be disattached to get the main board out, etc. While some use color-coded PCB connectors, others don't.
-Am I insane for even thinking about doing this? Is this a pursuit a reasonable person would undertake, or am I gripped by madness? I am beginning to think the answers are 'yes,' 'no,' and 'yes.'
I'm hoping some kind soul can give me a little guidance with regard to these questions. I am just sort of marveling at this piece of work, looking at it. Is this generation of receiver essentially unsalvageable once it reaches a certain age, since it's so hard to recap? If so, that's too bad.
I've acquired this SR-4A that I like.
Photo of SR-4A
It's 30+ years old now, and though it sounds very good and is in almost perfect shape, I have a suspicion it will sound fantastic with a recap - I think it is lacking that extra 20% in performance. I have never recapped a receiver, but I have done soldering, and have successfully done jobs on even smaller things like MacBooks, etc. I'm not sure if I'm being overambitious in thinking that a receiver that is this densely packed should even be recapped - it almost seems specifically constructed so as to prevent access to the things you need access to. The number of plugs & wires for which you'd have to remember where/how to reattach them is quite high. And I don't know where to start if the answer is 'yes, it should be recapped.' Among the questions I have are:
-Which capacitors exactly should I be replacing? There seem to be about 50+ of them in the unit, and I have no idea which to focus on. I have access to a schematic and all, but don't know if I should just replace the ones off certain boards, and if so *all* of them or just some.
-Is it reasonable to think I can access all of these capacitors? The receiver has a 'double deck' construction, along with a web of wires that I guess would all need to be disattached to get the main board out, etc. While some use color-coded PCB connectors, others don't.
-Am I insane for even thinking about doing this? Is this a pursuit a reasonable person would undertake, or am I gripped by madness? I am beginning to think the answers are 'yes,' 'no,' and 'yes.'
I'm hoping some kind soul can give me a little guidance with regard to these questions. I am just sort of marveling at this piece of work, looking at it. Is this generation of receiver essentially unsalvageable once it reaches a certain age, since it's so hard to recap? If so, that's too bad.
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I don't see the point in changing capacitors of a circuit that works well, but in any case, don't touch capacitors that are parts of tuned circuits unless you have the equipment, documentation and skill to re-adjust the tuned circuits. The least reliable capacitors are the electrolytic ones, and those are never part of a tuned circuit.
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I'd replace the two large psu caps on the left and leave it at that unless you can see any obvious signs of impending failure.
Thank you guys very much.
@sq225917
Is that likely to affect/improve sound, or is it mainly to protect from catastrophic failure?
Does anyone have any genius ideas as to how to unsolder even those caps? Accessing even them seems to be quite a challenge, since there's a whole network of wires holding that board/unit in place - about half of which are soldered. The board itself is attached by four screws, but I would either have to angle the board in a way to get to the bottom of the large caps or somehow unsolder ten or twenty wires in order to lift the board out:
@sq225917
Is that likely to affect/improve sound, or is it mainly to protect from catastrophic failure?
Does anyone have any genius ideas as to how to unsolder even those caps? Accessing even them seems to be quite a challenge, since there's a whole network of wires holding that board/unit in place - about half of which are soldered. The board itself is attached by four screws, but I would either have to angle the board in a way to get to the bottom of the large caps or somehow unsolder ten or twenty wires in order to lift the board out:
An externally hosted image should be here but it was not working when we last tested it.
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Assuming DC coupled amplifier outputs, the power supply capacitors have to conduct much larger ripple currents than any of the other capacitors. This leads to self-heating and reduced reliability. If the original power supply capacitors are nonetheless still in good condition, replacing them will achieve nothing. If they are partly dried out, replacing them is likely to improve sound quality to some extent: less hum, less intermodulation between signal and mains hum, higher maximum output power so less risk of clipping when the amplifier plays very loud. I can't predict whether those effects will be audible; they might be when the old capacitors are way out of spec.
Thank you @MarcelvdG - just finished with big day with the niece & nephew, going to give this a fresh look tomorrow.
The one (per channel) electrolytic capacitor that I'd replace, as it's often the first to go bad, is in the feedback path with virtually zero volts across it. It's at the "long tail pair" that's near the input. This is two transistors with their emitters connected (or perhaps two resistors between the emitters). The base of the one on the left (presuming standard left-to-right signal flow in the schematic) is the power amplifier input through one or more resistors and capacitors, and a resistor to ground. The base of the other one connects to two resistors - one, maybe 10k, comes from the power amp output, and the other resistor (about 1/10th the value of the first) goes to an electrolytic capacitor whose other end connects to ground. This capacitor is somewhere around 50uF to 1000uF. It goes bad because there's no voltage (or very little, certainly less than one volt) across it. There's one for each channel, and they're the same value. A sign of this capacitor going bad is a reduction in bass response, but even if there's no sign of this it can't hurt to replace it.
See if you can find the long tail pair with that capacitor on the schematic and scan or take a pic of that portion to show us.
I agree with replacing the main power supply filter capacitors as well, and for the stated reasons. What is on the other side of that PC board? Often there's a plate that can be unscrewed to access the solder side of the boards.
See if you can find the long tail pair with that capacitor on the schematic and scan or take a pic of that portion to show us.
I agree with replacing the main power supply filter capacitors as well, and for the stated reasons. What is on the other side of that PC board? Often there's a plate that can be unscrewed to access the solder side of the boards.
@benb Thank you so much for sharing your advice and insight.
You know, it crossed my mind that this might be the case, but for whatever reason I didn't simply lift the unit and look underneath to see if there was an access plate. It looks like at least for the PC board, there is. So that's great. Makes this whole situation much more comprehensible. This is the type of insight I was hoping to get here - thank you much.
You know, it crossed my mind that this might be the case, but for whatever reason I didn't simply lift the unit and look underneath to see if there was an access plate. It looks like at least for the PC board, there is. So that's great. Makes this whole situation much more comprehensible. This is the type of insight I was hoping to get here - thank you much.
I would not replace any capacitor if the receiver is working fine and the capacitors look O.K.
(no bulging and no leaks).
What I think is much more useful, is to check and if needed, carefully resolder some solder pads on the printed circuit boards.
Especially those where hot components are mounted and those which are subject to mechanical forces and vibration.
My two cents, Frans.
(no bulging and no leaks).
What I think is much more useful, is to check and if needed, carefully resolder some solder pads on the printed circuit boards.
Especially those where hot components are mounted and those which are subject to mechanical forces and vibration.
My two cents, Frans.
No receiver should be recapped, however densely or loosely packed it is.sealrock said:
You can change faulty caps, and those which are likely to become faulty. This means some (but not necessarily all) electrolytics, and any caps with paper dielectric (only seen in very old equipment or very expensive 'high-end' equipment). As others have said, keep well away from caps in the RF and IF stages - don't even move them!
Only resolder faulty joints i.e. remove solder and remake the joint. Do not 'reflow' a joint; that merely hides a bad joint and can even turn a good joint bad.
Basically, ignore most of what you see on the internet about 'refurbishing' or 'upgrading' old stuff. The more you do, the more chance there is of breaking something.
As others have said, definitely don't go near the tuning side of the circuit.
I would personally check out the voltage behaviour of the power supply when under load and decide whether the main supply caps need changing out. They are probably the hardest worked in the amp and are responsible for setting up your smooth voltage for the rest of the device. If they are no good, you can get audible hum and distortion. Unless I am overhauling the amp, replacing the caps is associated with fault finding noise or performance issues.
Ultimately, you need to weigh up the cost and risks of replacing the main rectifier caps versus what the amp means to you, what your end goal is and what the benefit of doing so might be. If you want to run the amp for another decade or more, then changing out the electrolytics might be prudent, but you also might end up bricking the device.
I would personally check out the voltage behaviour of the power supply when under load and decide whether the main supply caps need changing out. They are probably the hardest worked in the amp and are responsible for setting up your smooth voltage for the rest of the device. If they are no good, you can get audible hum and distortion. Unless I am overhauling the amp, replacing the caps is associated with fault finding noise or performance issues.
Ultimately, you need to weigh up the cost and risks of replacing the main rectifier caps versus what the amp means to you, what your end goal is and what the benefit of doing so might be. If you want to run the amp for another decade or more, then changing out the electrolytics might be prudent, but you also might end up bricking the device.
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