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Yamaha C-4


Yamaha C-4
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Specifications:
1. General
System: Transistor
Colour: 1=Silver, 2=Black: 2
Pre Amplifier
Inputs: 2 Phono (MM, MC), 1 Tuner, 1 Tape, 1 Aux
Quadro: no
Inp. Sensitivity High Level: 150 mV
Inp. Impedance High Level: 47 kΩ
Signal/Noise High Level: 106 db
Inp. Sensitivity Phono MM: 2.5 mV
Inp. Impedance Phono MM: 0.1 k Ω ( 33, 47, 68, 100 k Ω switchable) kΩ
Frequency Response Phono MM: RIAA
Signal/Noise Phono MM: 97 db
Inp. Sensitivity Phono MC: 0.1 mV
Inp. Impedance Phono MC: 0.05 kΩ
Frequency Response: 5 - 100,000 HZ
Harmonic Distortion: 0.0035 % at rated output
Equalizer
Tone Controls: Bass, Treble
Frequencies: Bass ± 10dB/ 20 Hz, Treble ± 10dB/ 20,000 Hz
Loudness: no
2. Physical
Dimensions in Inches: 17.13 x 5.73 x 14.74 (w) x (h) x (d)
Dimensions in mm: 435 x 145.5 x 374.5 (w) x (h) x (d)
Weight in lbs: 40.79 lbs
Weight in Kg: 18.5 Kg



Reviews

GV Wrighty - 04/15/2020  4 of 5 Stars!
I've not heard this yet. I bought a clean looking C4/M4 set on ebay and have been rebuilding it. I chose the C4/M4 after scouring through schematics on full discrete units with accurate, well designed RIAA sections as I was looking to upgrade my current preamp, which was one I made back in the 80s and has served me very well over the years.

The C4 stopped me in my tracks. It has the most unusual RIAA/Phone Eq circuit I've ever seen. A really nice MC stage of parallel transistors on input to keep noise down, then a really unusual feedback system in the RIAA stage that reamplifies the output with a reverse RIAA equalization and feeds it back into the input via an array of resistors. I had to get my hands on one.

I've not heard it yet, but I'm really looking forward to finishing. I've recapped throughout and hand picked the crucial caps and resistors, especially the RIAA time constant components. Initially I just matched their values, but on redoing the maths, the 75us time constant is bang on, but they compromised on the 3180us (and therefore the 318 time constant). The 3180us is easy to sort, but affects the 318us as they are interellated, so I'll come back to it later.

What is really interesting is the reverse RIAA amp that in addition to -ve feedback in the phono eq amp section, has a separate feedback loop to the input resistors. I'd be interested in anyone that happens to have looked at this as well. My thinking is that the reverse RIAA amp is there to create a virtual input resistance. Rather than have switchable input resistors of 100/33k/47k/68k&100k, (the actual resistances are around 10 times these values), they feedback the -ve output signal back to the input via the reverse RIAA amp so that the input 'sees' these input resistances (voltage divider across a resistance 10 times larger across a signal -10 times the value looks like the correct input resistance) but without the Johnston noise. So around a 3db decrease in noise.

I'm really looking forward to hearing this once all sorted.

James Hansen - 03/09/2019  4 of 5 Stars!
In the late 1970's I was working in a very busy audio store in New York City. Our main product line
was Yamaha. Although there were 3 other audio stores right nearby, peeople kept coming in
to buy Yamaha - which none of the other 3 places sold.

The biggest sellers were the receivers, particularly the CR620 and CR820.
Just about everybody swooned over the superb sounding, gorgeous T2 tuner,
but few were sold. Very pricey, and the general sense among the buyers was
that the T2 was better than most of the gear used in broadcast studios as the time.
Perhaps only WNCN, a great classical music station back in the day was using
equipment worth the purchase price of a T2. Though, as noted, the slim, minimalistic
and matte black styling - along with the obviously superb build quality - drew
many favorable comments and looks of leaving a loved one behind.

I listened to the C4 a lot, day to day, in the store and at home, and I thought that
sonically, it was a middling preamp. Not great with dynamic range, and a lack of
real clarity. Overall, though, it was definitely respectable and had the benefit of
looking good. It was a bit too large (vertically) in my view.

Probably the C4's biggest fault was with respect to the rather large square
buttons on the face which lit - green or white, depending on the function.
It was a soft type of internal lighting (the buttons were plastic) which many
found to be attractive and even useful.

The problem was - and yes, it was definitely a problem - was that these
lights were continually going out. Not all the time, not on every unit, but
much more often than they should have been. And because they were
specifically a Yamaha design, they could be serviced (at the time, anyway)
only by repair shops licensed by Yamaha. Which were few and far between,
in keeping with Yamaha's tightly controlled retail distribution (again - at the time).

Moreover, although not to make too big a deal about this, since these "lit up"
square switches were so large (relatively), and placed so prominently on the
face, when one went out it corrupted the entire look of the preamp. It looked
very obviously "broken". Had to go out for service, which took a while...

We saw way too many of these relative to the number we sold - and of course,
conversations with our fellow Yamaha dealers confirmed that we were not alone.
I simply cannot imagine how these lights could be fixed today except perhaps by
a gifted hobbyist or electrical engineer able somehow to source these 30 year old
parts or perform some type of custom workaround.

It's the main reason I wouldn't buy a C4 today if I saw one used (and I do see them;
I guess we all do). But also the look never really grabbed me, and neither did the
sound. Other than those lighted switches, though, it was very nicely made.

____________

Now the C2...(but that's a different story for another day...)

Pekka J. Poutiainen - 09/05/2013  5 of 5 Stars!
Yamaha C-4 are build like a dream pre amplifier. However, 30 years old needs a fresh high quality electrolytic capacitors. As I can remember theres a 100 ones and some are bipolars !!! Its a damn hard work to do that kind of service. Also, its a wise to use much more larger ones for power supply section. Please , dont put that to the power line before all the electrolytic capacitors are replaced to the fresh ones. Otherwise, those very rare phono section transistors would be dead !!! Be carefull ! Nowadays, I have a Yamaha C-45 , but like to own C-4 again.

Otto Kiær Engelschiøn - 11/21/2012  5 of 5 Stars!
I totally agree with previous review, but now something has happened, and I am struggeling
to find someone dedicated to fix my beloved C4 to run 2 x monoblocks and my turntable.
Mine is also now over 30 years old........

JD Daniels - 05/31/2011  5 of 5 Stars!
I've owned this preamp for over thirty years of almost daily play and had one minor problem that was an easy fix. This amp was made when Yamaha was building, IMO, some of the best amps and preamps on the market. If you are into vinyl there is no better preamp out their for the money. They are rock solid and you would spend thousands today to find a comparable preamp.

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