Did I just scroe? NRG Class A monoblocks

Ah, I get it -- 50hz hum at full power into both speakers. :(

Sounds like something wasn't grounded.

I'm determined to find the cause today. Last night I noticed the earth cable from the plug had come off the chassis, could that have been the reason? Simce it wasn't plugged in I assume not
 
I'm determined to find the cause today. Last night I noticed the earth cable from the plug had come off the chassis, could that have been the reason? Simce it wasn't plugged in I assume not
I would fix the earth lead, but the whole unit not being plugged in could be (possibly big) part of the problem; it turns the chassis of the unit into one big antenna that picks up RFI and A/C hum.
 
I would fix the earth lead, but the whole unit not being plugged in could be (possibly big) part of the problem; it turns the chassis of the unit into one big antenna that picks up RFI and A/C hum.

Unfortunately nothing seems to cure the issue, there is a constant loud hum on the outputs from the pre. I've taken the whole thing apart, reseated all connectors and cards, corrected the earth issue and it's still humming like crazy. Tape out sounds fine, any ideas what to check next?
 
Unfortunately nothing seems to cure the issue, there is a constant loud hum on the outputs from the pre. I've taken the whole thing apart, reseated all connectors and cards, corrected the earth issue and it's still humming like crazy. Tape out sounds fine, any ideas what to check next?
I'd suspect a defective filter capacitor, or broken solder joint to a filter capacitor, on a power supply rail that supplies the pre-out circuitry but not the tape-out. Also check the solder connections on the pre-out jacks and associated wiring.
 
I'd suspect a defective filter capacitor, or broken solder joint to a filter capacitor, on a power supply rail that supplies the pre-out circuitry but not the tape-out. Also check the solder connections on the pre-out jacks and associated wiring.

Since the hum occurs even with the unit powered off would I be right in assuming it's more likely to be a broken solder joint than a dodgy filter cap (which I think were all replaced)

Currently listening to it via the tape out's in to the yamaha power amp and to say it sounds incredible would be a enormous understatement (even with a pair of kef t27's in place of the focal t120s)
 
Since the hum occurs even with the unit powered off would I be right in assuming it's more likely to be a broken solder joint than a dodgy filter cap
Yes, I agree -- it's more likely a wiring fault of some sort, though it could be multiple problems at once. Might be worth running the JVC pre out into the aux in of any integrated amp so you can investigate the source of the hum by listening for it without risking any speakers (or hearing loss!)
 
Yes, I agree -- it's more likely a wiring fault of some sort, though it could be multiple problems at once. Might be worth running the JVC pre out into the aux in of any integrated amp so you can investigate the source of the hum by listening for it without risking any speakers (or hearing loss!)

Right well I seem to have solved it. Out of curiosity I started playing with the huge number of rca connectors on the back, stuff for the quadraphonic matrix outputs ect that i've totally ignored from day one. By connecting a jumper between the matrix in & rear channel out the hum has entirely disappeared! I'm going to have a look around for some rca jumper caps and see if they do the same thing.
 
And for anyone curious this thing has the best eq i've ever heard, i'm usually strict about not touching tone controls. My tech said it's based entirely around inductors and is quite special. Definitely sounds much more natural than any graphic eq i've heard.
 
Here is a preamp like yours for sale in your neck of the woods. E2,200
http://hifivintage.eu/en/solid-stat...preamplificateur-hifi-vintage-reparation.html

Well worth that IMO, if it said Pioneer or Marantz on the front I know for a fact this would be a holy grail piece for collectors worldwide, unfortunately since nobody cares about JVC it will likely never sell, or if it does it will be for much less because 4 figures for anything made by JVC is absurd right?

To say it wipes the floor with my Yamaha C50 and Marantz 3300 would be a massive understatement.
 
Damn, that looks like an interesting preamp for sure. The schematic on top is interesting. One hell of a find really. Especially if you're running an equipment rack :)
 
Shes all back together, gets pretty damn warm and i'm a little worried about my electricity bill when the NRG's are done, considering some small fans to assist with airflow. Also took a picture of the volume pot, its entirely sealed and branded as ALPS JVC on the case along with something else I can't read, a magnificent piece of equipment. Now I've got both meters working I need to find some led bulbs as the originals are melting the plastic holder.
 

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Shes all back together, gets pretty damn warm and i'm a little worried about my electricity bill when the NRG's are done, considering some small fans to assist with airflow. Also took a picture of the volume pot, its entirely sealed and branded as ALPS JVC on the case along with something else I can't read, a magnificent piece of equipment. Now I've got both meters working I need to find some led bulbs as the originals are melting the plastic holder.
THAT, is well worth rescuing!
 
Well the left channel just died so I guess I won't be needing that! I'm at the point now where I regret taking on this entire project, the NRG's and this stupid JVC. If everything turns up on Ebay soon you know why.
If it's got tyres or wires, it's trouble.

(There's also a rather sexist version of that which I'm sure everyone knows.)
 
Well the left channel just died so I guess I won't be needing that! I'm at the point now where I regret taking on this entire project, the NRG's and this stupid JVC. If everything turns up on Ebay soon you know why.
This old shyt is really frustrating, especially those items so badly off that they were binned. Getting them back to snuff from EOL will be really complicated to say the least. Finding a vintage gear tech is even more difficult. One must be thick skinned.
 
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