YAMAHA B-2 Amplifier and YAMAHA C-2 Measurements ( Vintage Gear )

[cay-uwe]

I am opening this thread since I have been asked to post some of the measurements I made of my reacently refurbished YAMAHA B-2 amplifier and its matching YAMAHA C-2 preamplifier.

@NTTY posted already a very good review of the YAMAHA C-2 preamplifier and I was happy to see that his measurements pretty well correlate with mine.

Both units had defects when I bought them and it turned out that it was mainly contact problems of switches due to corrosion.

The YAMAHA B-2 had additionally brocken potentiometers that needed to be replaced with equivalents that were hard to find ...

The YAMAHA C-2 had severe corrosion problems at all selector switches which can been seen well on this picture.

I run my measurements to check the equipment and it is supposed to be for verification purposes.

Theses are my findings after I have repaired the YAMAHA B-2 amplifier.

The spectral analysis of a 1kHz sinus signal is actually very good and what I like is the low level hum ( 50Hz / 100Hz Europe power ).

Also the frequency response looks very good and it matches the published specifications by YAMAHA on their brochures.

The red curve is full range, the blue curve with a high pass filter at 15Hz and the following measurement is from YAMAHA.

The YAMAHA C-2 preamplifier was partially working when I got it and therefore I was able to run some measurements before repair.

The spectral analysis of a 1kHz signal looked very bad below 1 kHz since it shows a lot of power noise. Initially I tought I will need to rework the power supply and probably some capacitors.
I started cleaning the selector switches first, because some of the sources were not selectable at all, or only partially and after that I got this spectral analysis.

As one can see, once the contacts have been cleaned, all of the power noise was gone and that saved me a lot of soldering work...

Finally I also checked the frequency response for both channels, red = right, blue = left. I was impressed about the very good matching of both channels.
It had a difference of <0.1dB in three different positions, 1/4, 1/2 and 3/4 volume level. For a > 50 year old volume potentiometer that is very impressive !!!

As a teenager this equipment has been a dream and for me 50 years later the dream got reality. Still from todays standards it is fantastic ...

 

[cay-uwe]

I am adding some more measurements that I made for my YAMAHA C-2 preamplifier, just for completness reasons.

An important finding are non-linear distortions also refered as intermodulation distortions. This type of distortion is more critical as harmonic distortions or linear distortions.

I like to use a measurement at 10kHz : 11kHz in 1 : 1 relation, since on one hand these frequencies represent the upper limit of acoustical instruments, and on the other site they show the behaviour of non-linear distortions. Non-linearity leads to several add-on frequencies and sidebands at the signal frequencies. The results for the YAMAHA C-2 preamplifier are very good.

The YAMAHA C-2 is famous for its phono preamplification, especially for the MC section, which according to YAMAHA brochures, uses an input stage especially developed for this preamplifier. I measured the RIAA frequency response and did not corrected it. As said, I run these measuremnts mainly for repair verification. Anyhow, my measurements showed a minor issue in the PHONO section of my preamplifier.

Overall the result is very good and accurate, but as one can see, there is a level difference between both channels, red = right, blue = left. That discrepancy is found across all PHONO entries and it is coming from the RIAA stage which seems to have a slight different amplification for each channel.

However, altough it did not measure it explicitely, the SNR of the MC stage seems really to be very good. Switching to the input, even with no connected eqipment to it, does not create any audible or disturbing noise from my high sensititvity loudspeakers ( 95dB SPL ).

For me, one of the greatest looking gear that ever has been designed and produced ...