There's a Yamaha C-2x in the house!

ChateauAudio

ChateauAudio

New Member
Eureka! I just scored a stunning C-2x preamp!. It arrived in truly mint condition cosmetically, although it was a bit ill and clearly in need of some TLC (I was told it was INOP).

After the photo shoot and complete disassembly of that extraordinary chassis, I gave it a good cleaning in all the connections, switches and pots (save the ALPS). I checked all the RCA's for continuity to the PCB and re-soldered them anyway for good measure.

The audio emanating from the C-2x is savory, with most of the odd hum now gone (when one is not fiddling with interconnects) creating a sense of vacuum in certain passages. Only fly in the ointment is that the output on the R channel falls out for a second or two every few minutes. I think I'll have to go back in and clean the ALPS pot.

Talk about gain...now I know why people say this thing is HOT! Gives new purpose to the Audio Muting switch! The walls of my house are sure to shake once I get the C-2x paired up with its new partner: my Carver TFM-75 beast as soon as I can get it out of rehab. Thankfully the TFM-75 has front panel attenuators...
 
ChateauAudio said:
Eureka! I just scored a stunning C-2x preamp!. It arrived in truly mint condition cosmetically, although it was a bit ill and clearly in need of some TLC (I was told it was INOP).

After the photo shoot and complete disassembly of that extraordinary chassis, I gave it a good cleaning in all the connections, switches and pots (save the ALPS). I checked all the RCA's for continuity to the PCB and re-soldered them anyway for good measure.

The audio emanating from the C-2x is savory, with most of the odd hum now gone (when one is not fiddling with interconnects) creating a sense of vacuum in certain passages. Only fly in the ointment is that the output on the R channel falls out for a second or two every few minutes. I think I'll have to go back in and clean the ALPS pot.

Talk about gain...now I know why people say this thing is HOT! Gives new purpose to the Audio Muting switch! The walls of my house are sure to shake once I get the C-2x paired up with its new partner: my Carver TFM-75 beast as soon as I can get it out of rehab. Thankfully the TFM-75 has front panel attenuators...
Click to expand...

Welcome to AK. I used a C2x for about 5 years. The phono stage is wonderful.
 
stoutblock said:
My C-2x works great in my main system. IMHO the RCA terminals are the weak link. I upgraded mine http://www.audiokarma.org/forums/showthread.php?t=448946 with very good effect.
Click to expand...

Stoutblock, I agree. I had already checked out your Connex RCA mod and was impressed...nice work. I'll probably do the same!

First I need to determine the source of the distortion anytime the vol is more than 9 o'clock. It's not apparent through the headphones jack but certainly is at the pre-outs. Tried it with my refurbed JBL S650 Synthesis amp and then confirmed the same effect with a Rotel RB-1050 amp. Guessing it's the output stage. I had not check the bias yet; those TP's are a pain to reach behind the twisted wires...

Any other suggestions appreciated!
 
ChateauAudio said:
Stoutblock, I agree. I had already checked out your Connex RCA mod and was impressed...nice work. I'll probably do the same!

First I need to determine the source of the distortion anytime the vol is more than 9 o'clock. It's not apparent through the headphones jack but certainly is at the pre-outs. Tried it with my refurbed JBL S650 Synthesis amp and then confirmed the same effect with a Rotel RB-1050 amp. Guessing it's the output stage. I had not check the bias yet; those TP's are a pain to reach behind the twisted wires...

Any other suggestions appreciated!
Click to expand...

You need to check muting transistors, they could be leaky. Also check the health of the muting control circuit and switching circuit for line/headphones outputs.

Do not forget to verify power rail voltage - should be almost exact +/- 20V.

I am working on one right now, it's pain - very hard to find components were used there. Let me know if you need a copy of service manual.
 
Last edited:
Thanks for the tip...much appreciated. I definitely look into the muting circuit. I understand some IC's are Yamaha proprietary and it looks like those fancy Soshin caps might be hard to source. Are there hard to find semiconductors in this thing?

Thanks for the service manual but I was able to locate one. What issues does yours have and what have you found?

Cheers
 
try moving the RCA interconnects to see if it causes feedback or distortion. I have seen this on many Yamaha components from this era. The stamped terminals and how they connect to the board is often the root cause of problems.
 
Scytales said:
Hello,

There is no proprietary IC inside a C-2x. The IC are 9 terminals SIL NJM2041 and 2043.
Click to expand...

There are no Yamaha specific parts, but Toshiba transistors, like single die JFET pairs are very hard to find. Specialized muting transistors are not in production anymore either.
 
ChateauAudio said:
What issues does yours have and what have you found?

Cheers
Click to expand...

Main problem was power regulator failure. It seems to result in cascade of secondary failures - leaking transistor in muting control, several failed muting transistors and one op-amp. I fixed all those, but now MC preamp low frequency (under 200 Hz) noise level is 5 dB higher than in my reference - CX-1000. From specs it should rather be 5 dB lower. I will try to replace electrolytes in MC headamp. Unfortunately I wasn't able to find ultra low noise transistors used there or even their latest equivalents to try replacement.
 
Last edited:
for_p1 said:
You need to check muting transistors, they could be leaky. Also check the health of the muting control circuit and switching circuit for line/headphones outputs.

Do not forget to verify power rail voltage - should be almost exact +/- 20V.

I am working on one right now, it's pain - very hard to find components were used there. Let me know if you need a copy of service manual.
Click to expand...

I finally printed a large scale version of the schematic that I can actually read! I would appreciate your guidance on checking out the muting transistors. Are they in the secondary 0dB amp sections? Can you specifiy which TR nos. I should look at?
Thanks!
 
ChateauAudio said:
I finally printed a large scale version of the schematic that I can actually read! I would appreciate your guidance on checking out the muting transistors. Are they in the secondary 0dB amp sections? Can you specifiy which TR nos. I should look at?
Thanks!
Click to expand...

All 2SC2878 transistorts. They are used for muting and audio signal switching exclusively in this preamp.
 
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