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Faulty Yamaha C2X

Soimmvt

Soimmvt

New Member
It has been a while since I was here. A lot happened the past 18 months......but the good news is I bought a Yamaha C2X Pre amp from a certain Danish second hand hifi store......I received it last june.

Now here's the catch:
1) turning the amp on and off
When I turn on the amp, a powersearch reaches my Yamaha b2 vfet poweramplifier causing a loud noise through my speakers. The same thing happens when I turn it off.

2) noise
There is still 50 hz humm. I have tried to solve this using a non-earthed plug. However the problem remains slightly.

3) using the subsonic switch
When I turn on the subsonic switch, a humm appears in the sound.

4) using the phonosection
I have two turntables which I use. When I connect them to the amp, both TT have a humm and some backgroundnoise. I use mm cartridges.

So I've send it back to the company and they promised to repair it. Two weeks ago I received the amp again after a period of more than six months of waiting.....Anyhow none of these problems were solved. Since I do not have the patience and trust to send it to Denmark and wait for another period, I am considering to let it repair it here in Holland, or maybe repair it myself if it is not too difficult......

Does anyone have had the same experience with a C2X or might have any suggestions of where to look?
Thanks for the suggestions.......

By the way my C4 still plays beautifully after the recap......definitely a keeper........
 
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If you want to get rid of the C2X problem, just give it to me :D

Loose soldering joint, bad cap could be giving you the trouble, but I would wait for a real expert to chime in with other suggestions.

I would definitely not send it back to that shop. There are at least a couple of AK'ers on your side of the pond that would run circles around most corner store service techs. See if any of them is willing to take it in.
 
OK, thanks for the reply. I will wait for more reactions. Anyhow I'm not in a hurry........or am I. The sound of the C2X is tremendous!!!!
 
Soimmvt said:
1) turning the amp on and off
When I turn on the amp, a powersearch reaches my Yamaha b2 vfet poweramplifier causing a loud noise through my speakers. The same thing happens when I turn it off.
Click to expand...
I never turn a pre-amp on or off while connected to a powered up power amplifier. Turn the pre-amp on first, then the B-2. Turn the B-2 off first, then the pre-amp.
 
Turntable hum could be cracked solder connections on the phono RCA input jacks ground connection. Verify your grounding thumbscrew on the pre-amp is a good chassis ground connection for your TT's.
 
Soimmvt said:
2) noise
There is still 50 hz humm. I have tried to solve this using a non-earthed plug. However the problem remains slightly.
Click to expand...
Solder connections as previously mentioned. Could also be a dried up e-cap .
 
avionic said:
I never turn a pre-amp on or off while connected to a powered up power amplifier. Turn the pre-amp on first, then the B-2. Turn the B-2 off first, then the pre-amp.
Click to expand...

Hi Avionic! Thank you for your replies!

My C4 has no problems with turning on or turning off. But it makes sense to follow up your advise. The rca inputjacks have been recplaced by new ones. Perhaps they have forgotten to plug the groundcable. I will check this. I will also check the solderconnections.
 
Soimmvt said:
Hi Avionic! Thank you for your replies!

My C4 has no problems with turning on or turning off. But it makes sense to follow up your advise. The rca inputjacks have been recplaced by new ones. Perhaps they have forgotten to plug the groundcable. I will check this. I will also check the solderconnections.
Click to expand...

I'll let you know!
 
Well, one year later. I purchased another one which works fantastic. My tech could not find the problem in the amp. What he did find, and I was present, were some transistors with broken legs, or not soldered very well. He also noticed some several other mistakes, so to speak....After spending more than 20 hours on this amp, we've have decided to give it up. It has been fully recapped, with new transistors...and it it works now without a hum. The only thing is that it keeps popping when turning on or off....So I can use it with the C2x turning on first and turning off last.

Soudwise........GREAT!!!!!!!!
 
My C-2x was completely redone by a guy out of Chicago and though it was not cheap it works flawlessly and sounds amazing. It is dead silent, no hum, no pops just clean sound. If you want his name you can pm me but I won't broadcast it here. I run it with a matching B-2x amp I got from hifido and that works equally as well. They truly are quite the pair.
 
808_state said:
My C-2x was completely redone by a guy out of Chicago and though it was not cheap it works flawlessly and sounds amazing. It is dead silent, no hum, no pops just clean sound. If you want his name you can pm me but I won't broadcast it here. I run it with a matching B-2x amp I got from hifido and that works equally as well. They truly are quite the pair.
Click to expand...

Thanks! .
In Chicago that's a long way from the Netherlands.. But I may consider it. There must be someone in Europe who can work his magic on my c2X? I use my other one with a b2, very very nice sound....= understatement :music:
 
It could very well be that the muting circuit at the output of the C-2X is not working.

Almost all pre-amps with a balanced power rail design like the B-2X are equipped with a muting circuit to cut off the output terminals during start-up, exactly for the reason as the issue that your are experiencing. Balanced power rail amp designs are notorious for charging their power supply capacitors in the positive section and negative section in a different speed, and hence the imbalance causes a surge.
To make things worse, it's a DC coupled design, so any DC imbalance is perfectly copied to the connected power amp.

In power amps, the start-up delay (in connecting the speaker terminals to the actual amplfier output) is handled by the speaker output relay: the delayed click after power up.
As a pre-amp is handling a small signal only, many pre-amp design use transistors instead of relays, and so does the B-2X.

These are for the left channel TR457 and for the right channel TR-458. These transistors should be "on" during start-up, and turn "off" soon after. Going up into the power supply section, TR428 seems to be the controller, which is forced open by zener diode D428. TR423 is there to switch off TR428 after some time.

So, somewhere in that entire circuit there is a bug. Zener D428 seems fine, since the muting circuit is not cutting off the output. So, I would then go see if TR423 is perhaps faulty, and then going further to what is connected to its base.... TR427.

TR427 is a timing circuit. It will initially be off, until C428 is charged, which in return depends on C429 being charged. So, this circuit drives the muting circuit delay
For example, if zener diode D427 is faulty, then TR427 is on immediately.... effectively switching off the muting transistors directly from power up

This should give some ideas where possible faulty parts might be regarding the muting circuit being off during start-up in lieu of being on.

my 5 cents :)

EDIT: swapped 'on' and 'off' here and there; I lost count... should now make sense :)
 
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