Cooking With a Yamaha C-4

Thanks Avionics and Blue Shadow.

After I posted, a guy I'd given a pair of DCM TF-500s to last week came over -- I'd forgotten to give him a part. He asked if he could buy me some beer or a bottle of wine to thank me for the speakers. I said, How about some advice instead? He protested that he didn't really know much about electronics. But when he came over, he took one look at the C-4 and advised doing what you guys said I should do -- remove those two boards.

Plus he brought over some home-made Chinese dumplings. I am now a believer in Audio Karma!

I'd already taken off the top and bottom covers and front panel. I'll pull those two boards tomorrow. . .
 
Dang Dumplings getting in the way of moving forward. Always good to spend some time with AKers. Since you have other gear playing, fixing this one while you have guests wouldn't have been the best move.
 
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Here's picture of the top and bottom of the board. Where do I go from here? There's stuff on the bottom of the two caps -- not sure if it's a leak or just glue to hold them down during factory assembly. Thanks again.

top.jpg bottom.jpg
 
See those two large black heatsnks behind the volume control ? Slightly wiggle each one while observing there soldered connections for circular cracks.
 
Really, that was all it needed? Heck I coulda told him that a couple pages ago or even fixed it if he had taken me up on the offer to listen to the ADS. Dave (avionic) has mentioned that these get hot enough, even with those big honking heat sinks to make the solder connections bad over the years. Heck if you had the unit at ehoove's we coulda looked it over there.

Now D4vid, when you drop by to hear the ADS, bring your C-4 so we can listen to your unit vs. a recapped unit to see if the 75 or more caps I replaced along with some VRs, diodes and transistors make any difference at all. I'll have a group of guys drop by for a listen, too. Least I could do if you have to come in from NoVA.

I'm just glad you have the unit working.
 
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Ever since this comment from you, we have heard nothing. Have you had a chance to compare it to the avionic C-6? Since the 4 is expected to be better does it live up to that expectation or does the 4 maybe need a refresh? Just curious as you have a couple of very close units that should sound close to each other with one being like new compared to one that is well aged.
 
I'm curious too, but I need to clean the pots and switches. I shot some Deoxit into them last week, but some are still noisy. Then I'll need to lug it out to my office, where the C-6 lives. I'll check back in once I do.

Ever since this comment from you, we have heard nothing. Have you had a chance to compare it to the avionic C-6? Since the 4 is expected to be better does it live up to that expectation or does the 4 maybe need a refresh? Just curious as you have a couple of very close units that should sound close to each other with one being like new compared to one that is well aged.
 
Pots and switches cleaned, I took the C-4 out to my office and listened to it with my T-1 tuner and some FLAC files on Raspberry Pi streamer I built a while back. Speakers are two pairs of Original Large Advents, stacked.

I gotta say it was hard to tell the difference. I'd listen with one and hear something I hadn't heard before, but when I switched preamps and listened to the other, I could hear the same things. I'm thinking maybe there's a very, very slight hum coming from the C-4, and that it runs hotter than the C-6.

Both are keepers.

Ever since this comment from you, we have heard nothing. Have you had a chance to compare it to the avionic C-6? Since the 4 is expected to be better does it live up to that expectation or does the 4 maybe need a refresh? Just curious as you have a couple of very close units that should sound close to each other with one being like new compared to one that is well aged.
 
That hotter C4 is those two heat sinks that have holes in the board above them to allow some heat to escape but not all of it does. Since we know to address those transistors on a decade major maintenance basis and there is a lot of metal on the cabinet taking that heat, it doesn't seem to have been a problem over the life of these preamps.

Thanks for letting me know that the time and effort to recap my C-4 has changed it to the level of an avionic redone C6. I was hoping for more. I didn't listen to my C4 before getting inside it and making it righter than it was when I got it. I would have had the switch issues that I eventually got under control with Dave's help.
 
Also the transformer would be the primary source for mechanical hum.
 
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