Yamaha C-4 pre

[wajobu]

While I'd like to say that I have NS-1000s or "m"s...I don't...

Oh boy! That should be some good listening wajobu! What speakers in the system?

...but I have ADS L520s, L710s and my testing speakers are some fixed-up and re-foamed Advent Prodigys. I'm out there with my eyes open for some NS-1000s, but I fear that the college bills will come due before I find affordable NS-1000s, etc. Until then...the ADS L-520s in my little living room are still pretty great. Also, the Prodigys sound like I have never heard them before when they are hooked up to the Yamaha B-2 amp...so I can only imagine what a pair of NS-1000ms sound like!

You know, I also have been testing (on another system in the house) some very inexpensive Infinity Primus 160s with a matching 8" subwoofer (with a Yamaha CR-2020)...before anyone guffaws with blistering criticism...for the price, they get the job done quite respectably...they have great clarity and depth...and they can handle the power.


oh, and P. Shivers...once I settle on a "final" pre-amp, if you are still looking for a matching pre-amp to go with your M-4...I'll keep you in mind...the one I just picked-up/cleaned-up has everything...literature, box, cable (though I am using another at the moment), etc....the C-4 in the photo above, that is. :yes:

 

[P. Shivers]

oh, and P. Shivers...once I settle on a "final" pre-amp, if you are still looking for a matching pre-amp to go with your M-4...I'll keep you in mind...the one I just picked-up/cleaned-up has everything...literature, box, cable (though I am using another at the moment), etc....the C-4 in the photo above, that is. :yes:

Yes, please do keep me in mind if you decide to sell your C-4. :yes:

 

[Susurus]

Just got these...M-4, C-4, T-7. :thmbsp:

Well the upside-down PCB has an interesting feature. I opened it up, and it looked brand new. Dust goes downwards, and there just wasn't any!

This is a 50-watt 'power control amp', higher than most 'preamps' --meaning higher heat?
The 2 little windows above the heat sinks might be enough. But modding is fun. Transformer wasn't getting hot, a good sign for the long term.

The M-4, on the other hand, was caked with dust.

Susurus

 

[avionic]

I was just looking at the manual online for the C-4, and it wasn't clear to me if it allowed you to run two amps at the same time. I see that it has two sets of pre-outs, but the manual says to select a or b, not and/or. The M-4 that I picked up cheap was dropped off at my tech's shop yesterday, so I should know in a few days what the humming problem is that scared off the other eBay buyers. In the meantime, I'm trying to decide what Yamaha Pre-Amp to mate the M-4 with. I'm leaning towards the C-4, for the matching looks, but am open to finding a newer model as well. What's the consensus on the best bang for the buck Yamaha Pre? I'm in the under $150 shipped budget category.

I run a C-4 driving two DIY MOSFET Power amps with no problems.The MOSFETS each driver a pair of NS-1000's similtaniously.The C-4 will run pretty warm .I also have a C-4 service manual if anyone needs one.

Dave

 

[merrylander]

IIRC the C-2 has no ventilation, may well be what contributes to its RCA jack problems.

 

[Chris Brown]

Aren't pre-amps generally placed on top of the AMP? I know back before my uncle gave me his M-2, he had what I believe was a C-2 (don't remember the model but it was a thin unit, not thick like the C-4) and he had it on top of the M-2. My M-2 gets extremely hot even with plenty of airflow around the heatsinks. I can't imagine the combo of heat it would create to have a hot preamp on top.

I’m used to seeing extremely high temperatures in the computer; it’s not uncommon to see CPU or Videocard temperatures as high as 80c or more, but those components don’t need to last 20+ years.

 

[Susurus]

I run a C-4 driving two DIY MOSFET Power amps with no problems.The MOSFETS each driver a pair of NS-1000's similtaniously.The C-4 will run pretty warm .I also have a C-4 service manual if anyone needs one.

Dave

Greetings! In another thread, I said this last night:

Mucho kudos to avionic for this post on adjusting the M-4.

And now you come through with a service manual ... :thmbsp::thmbsp: Is that electronic form or paper?

As far as I can tell my 'new' C-4 is working great; somebody who has got one on the blink needs a paper Service Manual more than me. Course I would scan it in for anybody who could use it.

But my T-7 tuner won't get any stations.

There appears to be a piggyback'ed little spliced-in filter or resistor on the main board...somebody wanted to turn it into a DXer?

will post a pic of this.

Susurus

 

[Susurus]

Aren't pre-amps generally placed on top of the AMP? ...

I thought one of the advantages of separates is that you can distance (separate!) them. The farther apart, the less electronic interference (cleaner sound) besides reducing heat buildup.

Unless you're in zero gravity heat rises. If you simply must stack things on top of each other :screwy::headscrat, put the hottest thing on top. And don't enclose it inside a shelf with no ventilation unless you like burning down the house when you play Talking Heads' Burning Down the House.

My little pool thermometer says the C-4 gets up to 104 F. It's not a cool cucumber like my Concept. My 'new' M-4 (less wpc-100 or 120, not sure) probably runs cooler than an M-2 or B-2.

Susurus

 

[morksbeanbag]

It is normal, my C-2x and CX-1000 does the same there is no ventilation so the heat can't get out.

The C-2x casing is made out of black anodised aluminium making it effectively one large heatsink for the inner heat to radiate from.

 

[avionic]

Greetings! In another thread, I said this last night:


And now you come through with a service manual ... :thmbsp::thmbsp: Is that electronic form or paper?

As far as I can tell my 'new' C-4 is working great; somebody who has got one on the blink needs a paper Service Manual more than me. Course I would scan it in for anybody who could use it.

But my T-7 tuner won't get any stations.

There appears to be a piggyback'ed little spliced-in filter or resistor on the main board...somebody wanted to turn it into a DXer?

will post a pic of this.

Susurus

Thanks for the Kudos.

Is that electronic form or paper?

Got both...Just PM me with a e-mail address...

 

[P. Shivers]

Here's the C-4 schematic. I have the C-4 that Wajobu mentions in this thread. It is currently at the repair shop, because it started blowing a fuse. The schematic I had wasn't too easy to read, so I found this pdf online, that is huge. I took it to Kinko's, and they actually had to decrease it in size, to print it out poster size! I'm still waiting to hear what is wrong with it. I'm using my Yamaha A-1 as a pre-amp for my M-4, in place of the C-4. Last week we decided to move some furniture around, so I had to swap my stereo gear too. In the process of pulling/plugging in patch cables, I think I did something to the phono input on the A-1. It now blows out snow from the left channel, with or without any cables hooked into it. I guess I'll trade amps with the tech when the C-4 is ready. All is not well with my Yamaha's at the moment.:sigh:

 

[Bauhausler]

Bumping this thread because I just got a C-4 and they seem to be somewhat scarce. My regular preamp is a C-2x that I've had for a few years. I like it very much in spite of terrible legibility of markings.
I picked up the C-4 off of That Auction Site expecting to need to do some repair to get it perfect, based on the description. I didn't expect it to be wrapped improperly and to be damaged in shipping. The bass control is punched in and destroyed. Other circuits appear to work although I haven't done a comprehensive test of all functions. The bass pot is a unique one. It's stereo, 10K with a center null tap. Absolutely a proprietary part that can't be duplicated. If Yamaha hasn't got one on hand this preamp will never have a bass control unless I build one with a rotary switch.
I'm so bummed.

 

[gonzothegreat]

In case somebody runs into a C4 with a noisy volume pot, here is how to fix it.

Use a small twist drill (found in hobby shops for model building) to *carefully* drill a small hole in the soft plastic of the sealed pot sections. Don't drill too deep and try to get the plastic shaving to come out as one piece by drilling with the unit on its side. Spray Deoxit into each hole, spin the volume pot a few dozen times stop-to-stop then hold a piece of paper towel up to the holes to help drain out the excess.

 

[Bauhausler]

That's brave! On my C-2x I removed the whole 6-gang pot from the board, disassembled it and cleaned/lubed each section individually.
There's a thread on that somewhere...

 

[riverrat]

I have a C4 as well- picked up for $70 at a pawn shop. Its in nice shape but had some scratchy controls which were mostly fixed with de-oxit.

One channel is louder than the other though. Does this mean I need to do a better job cleaning the balance control? Or might something else be going on?

 

[Bauhausler]

Could be anything. Might be the pot. I never use Deoxit on a pot. It's for metal on metal contacts like switches. I use Caig MCL or Fader Lube, which is for resistive controls. Makes a difference.
If it's not a pot it's probably a $0.07 transistor, one of dozens in there. Takes a LOOONG time to debug those things.

 

[Bauhausler]

Isolating a fault in a preamp starts with trying different inputs/outputs to narrow down the location of the problem.
It's 1:00 am and I need to sleep...

 

[brutal]

Bumping this thread because I just got a C-4 and they seem to be somewhat scarce. My regular preamp is a C-2x that I've had for a few years. I like it very much in spite of terrible legibility of markings.
I picked up the C-4 off of That Auction Site expecting to need to do some repair to get it perfect, based on the description. I didn't expect it to be wrapped improperly and to be damaged in shipping. The bass control is punched in and destroyed. Other circuits appear to work although I haven't done a comprehensive test of all functions. The bass pot is a unique one. It's stereo, 10K with a center null tap. Absolutely a proprietary part that can't be duplicated. If Yamaha hasn't got one on hand this preamp will never have a bass control unless I build one with a rotary switch.
I'm so bummed.

If all you need is the bass pot and there's no PCB damage, I have a parts C-4 here I could cannibalize that pot for you. let me know.

 

[Bauhausler]

I have the C-4 back together and running. I moved the pot from the Treble to the Bass position because I would rather have a Bass control than Treble. I faked up the Treble circuit with 4 X 5K resistors. The rest of the preamp works fine and it's in excellent cosmetic condition. The three front panel indicators were out and I didn't have any 14V 80ma bulbs of that size on hand. I replaced them with 6V bulbs and 120 Ohm resistors. The lights are dimmer but work OK. The next time I order from Mouser I'll find the right bulb and change them properly.

Brutal, there's a PM coming your way about the replacement pot.

This sounds really nice on the line inputs. I haven't tried out the Phono yet except on the bench. The C-2x has been my main preamp for some time. It has all of the control functions that I need and sounds quite neutral. Downsides: this C-2X unit has several intermittent connectors that need fixing. Better front panel legibility would be nice. My C-2X is missing the volume knob and has a truncated power switch that was once broken. Some day I'll find a similar switch and replace it.

I like the tone turnover controls on the C-4. The separate balance control is nice as well. The ability to switch off the pre-outs is a bonus for me as I usually have 2 or more power amps and sets of speakers set up. I think I'm going to enjoy using this.

 

[Bauhausler]

If all you need is the bass pot and there's no PCB damage, I have a parts C-4 here I could cannibalize that pot for you. let me know.

Brutal: The pot came today & I wasted no time installing it. The operation took 2.5 hours because I decided to rehab the main voltage regs while I was in there. The heat sinks were un-glued (no screws originally) so I screwed them down and changed the pass transistors for good measure to ensure longevity.

Pix are attached. It takes a ton of screws and panel nuts to get one of these apart. A sign of quality in my book. Nothing is particularly difficult or challenging, just a lot of fasteners.

The pre sounds outstanding. I'm wondering if it's possible that it sounds better than the C-2x. That seems unlikely but I have both here and the C-4 is every bit as good to my ears. Somewhat more versatile phono as well.

Thanks again, Brutal. Watch the mail...