Yamaha C 4 preamp in comparison with ca 1000II preamp

I posted these observations in another thread, but perhaps it is worth repeating them here.

"A week or two ago I got my Yamaha C-4 pre back from a complete re-cap. This is a unit that is 35 years old, typically runs fairly warm and plays an average of 10 hours per day so the work was done as a precautionary measure. It had been problem-free and sounded good so I wasn't expecting much real change in performance. When I first hooked it back up in its usual system (C-4/Epicure M1/Vandersteen 2C) the bass was noticeably leaner than previously and the top end brighter. Over the intervening time the bass has returned to normal (perhaps even going a touch deeper), but the treble is still hotter than before. I'll give it another week or two and if it doesn't settle in I will turn back the tweeter control a bit.

In another aspect I really got a surprise, though. The sound stage with the combination has always been quite satusfying. The space the system is in is about 15' wide and 25' deep. I have the speakers about 9' apart on either side of a fireplace and generally sit about 8-10' away. The perceived stereo image has never extended much to the outside of the speakers. Imagine my surprise when listening to a favourite jazz quartet recording when the upright bass was suddenly positioned approximately 4' to the right of the right speaker whereas when listening to the same recording before it was always right at the speaker. The piano now seems extended from left of centre to perhaps 3' outside the left speaker. The image also seems noticeably taller and more coherent. Spatial detail is also clearly improved. Anyone have an explanation for this? I wasn't expecting anything of the sort, but it is impossible to ignore. Please note that none of the caps removed tested bad, not a one."
 
^^^my guess is better channel separation and less noise floor^^^
 
^^^my guess is better channel separation and less noise floor^^^
Could be. Certainly sounds plausible. No matter how you look at it, I'm pleased. Amazing that a pre with so much going on in it can sound so incredibly clean and musical. I had a nice Anthem Pre 1 tube pre on loan while the C-4 was in for the work and I think the C-4 is now better, pretty much in line with my CJ PV-12, actually. Slightly different, perhaps, but the quality is remarkably similar. Given how good the PV-12 is that is saying something I think.
 
Could be. Certainly sounds plausible. No matter how you look at it, I'm pleased. Amazing that a pre with so much going on in it can sound so incredibly clean and musical. I had a nice Anthem Pre 1 tube pre on loan while the C-4 was in for the work and I think the C-4 is now better, pretty much in line with my CJ PV-12, actually. Slightly different, perhaps, but the quality is remarkably similar. Given how good the PV-12 is that is saying something I think.

As impressive as my Avionic rebuilt C-4 is, my rebuilt C-2x takes things to the next level.
 
I finally got to it yesterday to test my C2a. I hooked it up via the pre-out to my C4. I used the tuner connection and so hoped to soften the blow that the C2a gave and let my M4 to protection mode. After 2 hours a soft pop came in and my right channel was dead for only a couple of seconds, than it came back again. It was for a small time stable than it fainted without a pop, to came back again. I used the mute switch and went up and down to see it would have any effect. I noticed (or I think) that the right channel was functioning again while with the switch was on -20db. While using the the mute switch the right channel popped when there was no sound. But when there was sound in the right channel it did not pop and functioned like it should. The only thing I can think of, or just to start with is clean the switch or completely bypass it. The switch is a bit scratchy anyway.
Any suggestions?
 
I finally got to it yesterday to test my C2a. I hooked it up via the pre-out to my C4.
Any suggestions?
:scratch2:
Don't try and run them together.
Does the C-2a by itself. Run OK with the M-4 ? How about the C-4 by itself, with the M-4 ?
 
:scratch2:
Don't try and run them together.
Does the C-2a by itself. Run OK with the M-4 ? How about the C-4 by itself, with the M-4 ?

Hi Avionic, thank you for your reply.
OK, maybe I was not very clear with the set up. First when I runned the c2a with the M4 alone after a while a very loud plop came out of the right channel and brought my M4 into protectionmode and then it came out of it and went on playing. As I do not want to damage my m4 the thought occured me that I can use the C4, which is running great, as the pre amp between the c2a and m4, using the pre out of my c2a to the tuner connection on my c4. And then use the pre out of my c4 to connect to the m4. The volumecontrol of my c2a half way and use the colume control of my c4 to compensate to the M4. This set up allowed me to examine the disfunction of my c2a a bit more. It is now not a loud plop but a very soft one. It was then that I discovered the right channel came and went again and that moving the mute switch did have some effect, I think.
So to get things clear, the c4 and m4 both are functioning fine. The c2a not.
 
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the thought occured me that I can use the C4, which is running great, as the pre amp between the c2a and m4,
:no: You could use the Tape Monitor (REC OUT) of the C-2 into the TAPE 1/2,AUX or TUNER of the C-4.I wouldn't use the pre out.
 
First when I runned the c2a with the M4 alone after a while a very loud plop came out of the right channel and brought my M4 into protection mode
On the C-2a-----
Check the solder connections on the P/S pass transistors TR255,256 and 262.
Also there are 8 or so VD1212 diodes ( D217,218,219,220,507,508,511 and 512) that can create hisses and pops.
 
On the C-2a-----
Check the solder connections on the P/S pass transistors TR255,256 and 262.
Also there are 8 or so VD1212 diodes ( D217,218,219,220,507,508,511 and 512) that can create hisses and pops.

:thmbsp:OK! Thanks for the suggestions. I will try the rec out as you suggested and check the diodes and transistors.
 
:thmbsp:OK! Thanks for the suggestions. I will try the rec out as you suggested and check the diodes and transistors.
Don't bother checking the diodes.Replace them!
Replace the VD diodes with a pair of 1N4148 diodes wired in series for each VD1212.
 
Don't bother checking the diodes.Replace them!
Replace the VD diodes with a pair of 1N4148 diodes wired in series for each VD1212.

Check, i've ordered new diodes. I've also replaced the 1913/913 transistors, but no effect. Right channel comes and goes when the amp is on temperature.
 
Well, replaced the diodes, eight of them, recapped, cleaned the switches....no effect. Still a plop on the right channel after a while.....but via the rec out no problems
 
Well, replaced the diodes, eight of them, recapped, cleaned the switches....no effect. Still a plop on the right channel after a while.....but via the rec out no problems

Most likely a leaky transistor in the EQ amplifiers front end.
 
I posted these observations in another thread, but perhaps it is worth repeating them here.

"A week or two ago I got my Yamaha C-4 pre back from a complete re-cap. This is a unit that is 35 years old, typically runs fairly warm and plays an average of 10 hours per day so the work was done as a precautionary measure. It had been problem-free and sounded good so I wasn't expecting much real change in performance. When I first hooked it back up in its usual system (C-4/Epicure M1/Vandersteen 2C) the bass was noticeably leaner than previously and the top end brighter. Over the intervening time the bass has returned to normal (perhaps even going a touch deeper), but the treble is still hotter than before. I'll give it another week or two and if it doesn't settle in I will turn back the tweeter control a bit.

In another aspect I really got a surprise, though. The sound stage with the combination has always been quite satusfying. The space the system is in is about 15' wide and 25' deep. I have the speakers about 9' apart on either side of a fireplace and generally sit about 8-10' away. The perceived stereo image has never extended much to the outside of the speakers. Imagine my surprise when listening to a favourite jazz quartet recording when the upright bass was suddenly positioned approximately 4' to the right of the right speaker whereas when listening to the same recording before it was always right at the speaker. The piano now seems extended from left of centre to perhaps 3' outside the left speaker. The image also seems noticeably taller and more coherent. Spatial detail is also clearly improved. Anyone have an explanation for this? I wasn't expecting anything of the sort, but it is impossible to ignore. Please note that none of the caps removed tested bad, not a one."

So I droppped the C2a project and recapped the C4 using elnas and nichicons, cleaned the switches. The recap improved the sound a lot.:thmbsp: Very nice soundstage!
 
Cap list laying around?

I will try to find my notes, otherwise I have the order list included the caps for the C2A.
About the C-4 now....It has incredibly improved after the recap. The soundstage is huge and the treble is sooo sweet, I can’t believe my ears :music:. The channel separation is also great, and improved after the recap. Musical pieces sound dead quiet when they supposed to be. I’ve tested with the cd’s “Morning Phase” and “Sea Change” from Beck and several AIR cd’s. The phono section is also very very good, I’ve listened to the Privateering Album from Mark Knopfler and The Last Ship from Sting. I guess that the phono section of the CA 1000II was already great as I did not find the improvement a lot, but your cd will sound analog!!!
Now that I am so enthusiastic I wonder what kind of improvements I can make to make the C4 even better. Fiddlefye suggested to replace certain diodes and solder the boards directly. Not that I will tear the C4 apart again…I have too much fun listening…..:D
 
Personally, I prefer the sound of a C-4 over the C-2 or a C-2a. Have yet to audition a C-2x.:thmbsp:
 
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