I have a ~40 year old Nakamichi PA-5 and CA-7 combination which I adore. Lately the system intermitantly produces a very Loud Noise from Speakers (that sounds like AC Hum only full volume), which is not controlled by volume control. I'ts so loud I can't take time to see if it's channel specific but it doesn't appear to be. It happens when listening to music or TV Audio and also sometimes when nothing is playing (ie: no audio signal) Could this be the large capacitors failing? Any other ideas of what to do?
I have reseated all connections and had it go for up to month after doing this.
I have reseated all connections and had it go for up to month after doing this.
bench time
first visual inspection, then measuring everything suspicious***, then methodical check
simple as that, but hard to make exact tutorial
*** switches, soldering points (especially where current/heat is involved), thermally stressed resistors and diodes, caps ........
first visual inspection, then measuring everything suspicious***, then methodical check
simple as that, but hard to make exact tutorial
*** switches, soldering points (especially where current/heat is involved), thermally stressed resistors and diodes, caps ........
Good advice. I inspected, as you suggest, then I measured the ohms between the wires and the RCA connections because reseating these cables fixed it for over a month before it began making the intermittent noise again. Then I replaced the RCA cables between CA-7 and PA-5 after cleaning the contacts with alcohol. When connecting the L & R on the CA-7 I discovered the RCA ring had completely come off on one channel and was inside the cable end! I’m now using the 2 output and am confident this fixed it, finally. Thanks for the great approach. Pretty much describes what I did!
Good one. As it so happens I did replace the power cord on the PA-5 already. I also taped up the cracked insulation on the CA-7 power cord, for now and will need to replace that power cord at some point.
UPDATE:
The very loud hum is quite intermittent & just came back suddenly today, in both channels, after 8 weeks of daily usage, so I think that illuminates many of the cabling type issues, which I would think would only appear in 1 channel. Am I correct?
I have a 4K TV connected via a Optical to RCA converter to a 40 year old Nakamichi CA-7 (pre/control amp) to a PA-5 (power amp) to 2 (also old but upgraded tweeters) KEF C-80 loudspeakers.
I believe I have eliminated the converter because it happens when I’m playing the stereo from a DVD player connected via RCA connectors to the preamp. I have replaced the RCA cables going between the two units, and in fact, I found a faulty RCA connecter when doing so, but even though this has been corrected, it did it again; I think if it was in fact related to this faulty connecter it would (agin) only appear in one channel, but I let it go long enough today to verify it is definitely coming through both speakers, in other words through both channels. This leads me to the conclusion that it may be power supply related.
I’m sure you would concur that my problem is in the preamp or the power amp, and sounds like it may be in one of the the power supplies. But if it’s the transformer that is failing, intermittently, or a capacitor (there are some very large capacitors in the PA-5 power amp), why would they be intermittent?
Your thoughts are much appreciated! Any suggestions on how to go about troubleshooting this are also appreciated. Thanks to Northpaw above who helped me the last time with some great suggestions...and I will now replace the CA-7 power cord which I tapped up because it was cracked almost all the way along!
The very loud hum is quite intermittent & just came back suddenly today, in both channels, after 8 weeks of daily usage, so I think that illuminates many of the cabling type issues, which I would think would only appear in 1 channel. Am I correct?
I have a 4K TV connected via a Optical to RCA converter to a 40 year old Nakamichi CA-7 (pre/control amp) to a PA-5 (power amp) to 2 (also old but upgraded tweeters) KEF C-80 loudspeakers.
I believe I have eliminated the converter because it happens when I’m playing the stereo from a DVD player connected via RCA connectors to the preamp. I have replaced the RCA cables going between the two units, and in fact, I found a faulty RCA connecter when doing so, but even though this has been corrected, it did it again; I think if it was in fact related to this faulty connecter it would (agin) only appear in one channel, but I let it go long enough today to verify it is definitely coming through both speakers, in other words through both channels. This leads me to the conclusion that it may be power supply related.
I’m sure you would concur that my problem is in the preamp or the power amp, and sounds like it may be in one of the the power supplies. But if it’s the transformer that is failing, intermittently, or a capacitor (there are some very large capacitors in the PA-5 power amp), why would they be intermittent?
Your thoughts are much appreciated! Any suggestions on how to go about troubleshooting this are also appreciated. Thanks to Northpaw above who helped me the last time with some great suggestions...and I will now replace the CA-7 power cord which I tapped up because it was cracked almost all the way along!
It sounds to me like you have a grounding issue. It could be a fault in one of the power cords, or it could be in the outer shield/collar of the RCA connectors/cables, with a jack connector (particularly its solder connections to internal boards) being more likely than a cable if the cable has not been damaged. Since the hum is loud and independent of volume setting, it presumably is after the preamp circuitry. This means it could be in the Main Out RCA connectors of the preamp, or in the power amp.
You have already described a broken Main Out RCA jack connector on the CA-7, that you have bypassed by using the second Main Out connector. I'd look carefully at that first broken connector, to make sure there that the RCA pin socket and remaining shield parts have no possibility of making connection with each other or anything else nearby. And I would check the second Main Out and other RCAs for related damage, because the type of failure you described is often caused by the stresses from installing/removing cables with too-tight RCA connectors, and that may not be limited to the single jack you discovered. Also, I believe both for the PA and CA units, the Left and Right signal grounds are shared internally, so if you have a bad connection affecting the RCA shield on one channel, it seems you will get hum on both.
Beyond the outright breakage of the RCA jack you've already seen, too-tight connectors can also stress the solder joints where the connect to the internal boards. In my CA-5, the RCA jacks are mounted directly to small PCBs, so they are subject to this kind of stress. One simple thing you can do to check for this is to manipulate the RCA connections while music is playing, gently pushing sideways on the connectors at the rear panel jacks, one-by-one and from all directions, to see if any flexing of a RCA panel jack induces the intermittent behavior. If it does, you will have to inspect where the RCA jack leads connect to the internal boards, as you likely have a cracked solder joint somewhere there. You can also check out if your cracked power cord on the CA-7 is having issues by gently flexing/bending it while music is playing to see if you can induce the intermittent behavior.
More generally:
You have already described a broken Main Out RCA jack connector on the CA-7, that you have bypassed by using the second Main Out connector. I'd look carefully at that first broken connector, to make sure there that the RCA pin socket and remaining shield parts have no possibility of making connection with each other or anything else nearby. And I would check the second Main Out and other RCAs for related damage, because the type of failure you described is often caused by the stresses from installing/removing cables with too-tight RCA connectors, and that may not be limited to the single jack you discovered. Also, I believe both for the PA and CA units, the Left and Right signal grounds are shared internally, so if you have a bad connection affecting the RCA shield on one channel, it seems you will get hum on both.
Beyond the outright breakage of the RCA jack you've already seen, too-tight connectors can also stress the solder joints where the connect to the internal boards. In my CA-5, the RCA jacks are mounted directly to small PCBs, so they are subject to this kind of stress. One simple thing you can do to check for this is to manipulate the RCA connections while music is playing, gently pushing sideways on the connectors at the rear panel jacks, one-by-one and from all directions, to see if any flexing of a RCA panel jack induces the intermittent behavior. If it does, you will have to inspect where the RCA jack leads connect to the internal boards, as you likely have a cracked solder joint somewhere there. You can also check out if your cracked power cord on the CA-7 is having issues by gently flexing/bending it while music is playing to see if you can induce the intermittent behavior.
More generally:
- to better determine if the problem is the amp or preamp, connecting each to other equipment, if you have some, would be helpful.
- determine if it is 60Hz or 120Hz hum. There are free frequency/spectrum apps for smart phones/tablets that are simple to use: just start the app and hold your phone in front of the speakers. If it is 60Hz, it is power line hum that is being picked up; if it is 120Hz, it is post-rectification hum.