Cooking With a Yamaha C-4

D4vidG4rr3tt

Started off with midfi. Soon hit the harder stuff.
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Found a Yamaha C-4 preamp on my local CL about a year go -- $40. The only problem was that I was going out of town the next morning. Of course, it was gone when I got back.

When another C-4 came up last week, I emailed the seller immediately. It was more than the first one, and I had to take an M-4 power amp with only one working channel. He did have the original manuals for both units.

It needs new lamps. Going to clean the pots and see how it sounds compared to the C-6 avionics recapped for me last year.

(Despite the threadline, it won't be living in the kitchen. )

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It runs hot enough that you can cook where ever it is.

not really but that left side vent does get warm up front.

there is a pile of maintenance that these might like to receive to make them good for the long run. I enjoy the one I have and redid, with a special thanks to Avionic for all his guidance.
 
The pass transistors in the regulated +/- 30 volt PS. Is the heat generator.. Thats why they are mounted on heatsinks.;)
 
Thanks. I've been looking at the forums and saving links.

I dunno what it is, but I really like the way the Yamaha's look!

It runs hot enough that you can cook where ever it is.

not really but that left side vent does get warm up front.

there is a pile of maintenance that these might like to receive to make them good for the long run. I enjoy the one I have and redid, with a special thanks to Avionic for all his guidance.
 
No tragedy to be "forced" to buy the M-4 if the price was right and it can be fixed. That is one very nice power amp as you surely know!
 
Yes, it is a nice amp. Embarrassed to say I now have three of them!

No tragedy to be "forced" to buy the M-4 if the price was right and it can be fixed. That is one very nice power amp as you surely know!
 
The amp doesn't sound to serious if one channel is working and producing sound. Try cleaning the mode switch on the rear panel.
 
Okay, so I hooked up the M-4 this afternoon and both channels on both sets of speakers, A and B, work. But. . . the C-4 preamp isn't working at all. My tech skills are rudimentary -- I've replaced caps and a volume control, and recently replaced all the lamps in another M-4. But I'm willing to open it up and take a look around if it might be a simple fix.

The guy I bought it from said a tech he took it to said there might be a broken board in the C-4, but he wasn't clear on whether the tech actually took it apart or was just making a guess. I opened it and looked for something obvious -- like a board with a crack in it, but didn't see anything. The speaker lamps need replacing, but otherwise it's in pretty good shape.

A couple of questions: Can I bridge the M-4s to use one on each speaker? If so, how? Also, can you still get the green boots that slip over the lamps? The guy who put the red LEDs one of my other M-4s cut the boots apart and just kept the collars to keep the LEDs in the hole. A tech I take stuff to says color 'em with a green Sharpie.

Thanks!

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Does the C-4 light up at all ? From a cold start. Put your ear up close to the pre -amp top cover. Push the power switch button. A few seconds later you should be able to hear a very faint " tink" sound. Its the muting reed relays energizing . Do you hear this noise ?
 
Can I bridge the M-4s to use one on each speaker?
Yes. Easiest way is to get either a C-70,C-80 or C-85. Or other preamp with Normal and inverted pre-outs. The owners manual for either on of these pre-amp shows you how to wire them up.
 
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