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Yamaha Natural Sound Stereo Amplifier A-7

C

ChaseK

New Member
Hey guys first post/thread here, need some help.

Recently purchased this Yamaha Natural Sound Stereo Amplifier A-7, which as far as I can tell is a Japanese Domestic Market model of the A-960 which means it runs on 100V. I live in a 230V country, so I used a step down transformer rated at 110V and had, according to manufacturer, 3000W max. I did in fact check that it was working before buying and had a short audition and everything. Bought the same step down transformer the guy was using as well. Excited!!

photo_2021-09-26_23-12-18.jpgphoto_2021-09-26_23-12-29.jpg

Plugged it all in, turntable and all, and it worked! For about 30 minutes. The amp was heating up REALLY REALLY hot, and after about an half hour of play intermittent buzzing noise would come out of my speakers and an hour in after that the volume would just DIP to a really, really low volume. So I switched to an Aux line for CD, and the volume returned and played as if nothing happened. Switched back to phono, nothing.

Powered it down and checked the step down transformer, and turns out that 119-120v was coming out of the 110 outlet (according to its digital meter). Switched off the step down transformer, then switched on the step down transformer and BOOM, house shorted.

The step down transformer is busted and keeps shorting the house every time I try to switch it on.

So yes, the transformer is definitely the most glaring issue here and I will need a new one.
Questions are though, it is really difficult/pricey to get a 230/240V to 100V step down where I live, so would continuing to buy a 110V step down be good enough? Or is buying a 100V transformer the only option here? Did the 119-120V output of the step down cause this? Or is it that that the Amplifier is also to blame, considering how hot it got? The amp was reportedly recently serviced, according to the seller.

Would really appreciate any help that I could get, and if I made a really dumb mistake I'd really like to be told it so I know what not to do ;-; I'm quite lost here as using JDM stuff is new to me

Thanks
 
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ChaseK said:
so would continuing to buy a 110V step down be good enough?
Click to expand...
I wouldn't.. Power supply filtering caps are going to be pushed even closer to the tailored max voltage using 110-120.. Power supply voltage regulators will run hotter due to 10-20% increased in DC rail voltage.
 
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I don't see anyone offering a 230V-100V step down transformer except Alibaba, and I don't really trust anything on there. Nor do I see any suitable step-down inverters. I guess the other options are going to be to re-engineer the power section, or try a chain of step-down transformers, 230V-120V --> 120V-100V.

I hope that japanese market A7 has survived.
 
I just used a 110V transformer for a short while to confirm that the amp was still working, and thankfully it was! I'm going to pursue the options that you all have been very kind to send here, and will update when I get a nice 100v transformer.

By the way, does anyone have any information regarding this amp? Finding information on the web has turned up little results, other than a very basic spec sheet. The amp seems to have different specs from the A960 and A960II, what with its higher 120w speaker outs.
 
A-960/960II are X-power supply models like the A760/760II as well as the separate power amplifiers M-50,M-70 and B-6
 
Looks pretty much like what it is , the integrated amp that was relabeled as A-960 everywhere outside of Japan.

https://audio--heritage-jp.translat...l=ja&_x_tr_tl=en&_x_tr_hl=en-GB&_x_tr_pto=nui

https://www.hifiengine.com/manual_library/yamaha/a-960.shtml

a-7.JPG

a-7(1).JPG


Model Stereo Integrated Amplifier
Effective output (20Hz-20kHz, 0.007%) 120W + 120W (8Ω)
Power bandwidth (60W, 0.002%) 10Hz-50kHz (8Ω)
Damping factor 55 (8Ω, 1kHz)
Input sensitivity / impedance Phono MM: 2.5mV / 100kΩ, 47kΩ, 33kΩ, 100Ω
Phono MC: 160μV / 100Ω
Tuner, Aux, Tape: 150mV / 47kΩ
Maximum allowable input MM: 250mV
MC: 15mV
Output level / impedance 150mV / 600Ω
Headphone output / impedance 0.89V / 8Ω (0.01%)
Frequency characteristic Tuner, Aux, Tape: 20Hz-20kHz + 0 -2dB
RIAA deviation MM: ± 0.2dB
MC: ± 0.3dB
Total harmonic distortion (20Hz-20kHz) Phono MM → Rec out (10V): 0.003%
Phono MC → Rec out (7V): 0.006%
Tuner → SP out (60W): 0.005%
Intermodulation distortion Tuner, Aux, Tape (120W, 8Ω): 0.002%
Main Direct on (1W, 8Ω): 0.01%
Signal-to-noise ratio (IHF-A network, input short) Phono MM (2.5 mV standard): 87 dB
Phono MC (250 μV standard): 71 dB
Tuner, Aux, Tape: 103 dB
Input conversion noise (IHF-A network) Phono MM: -139dBV
Phono MC: -143dBV
Channel separation (1kHz, Vol-30dB, 5.1kHz) Phono MM: 70dB
Phono MC: 70dB
Aux, Tape: 70dB
Tone control characteristics Turnover frequency Bass: 　　　　　　　　 125Hz, 500Hz Treble: 2.5kHz
　　　　　　　　　　　　　　　, 8kHz
Maximum variable width Bass: ± 10dB (20Hz,
500Hz ) Treble: ± 9.5dB (20kHz, 2.5kHz)
Filter characteristics Subsonic filter: 15Hz, 12dB / oct
High filter: 10kHz, 12dB / oct
Continuous loudness control maximum correction amount 20dB (1kHz, depending on the hearing correction curve)
Through late 200V / μsec
Attached mechanism Disc switch
Main direct switch
Phono selector
Rec out Selector
mode switch
Listening level monitor
Speaker terminal (A, B, A + B)
AC outlet Interlocking: 2 systems (100W)
Non-interlocking: 1 system (100W)
Power supply AC100V, 50Hz / 60Hz
Rated power consumption 215W
External dimensions Width 435 x Height 133 x Depth 365 mm
weight 10.3kg
 
Mine A-960 sounds very nice. Make sure you do the service bulletins .

and the push button switches can become flaky. either take them apart to clean them or replace them with new ones.

Athanasios
 
geez

https://uk.yamaha.com/en/support/safety_information/amplifiers.html

Safety Information Yamaha amplifiers (1980-1982)
Yamaha Amplifiers (Years of construction 1980-1982) for European models, using 220-240VAC line voltages (This information does not apply to 120VAC models)

Models A-760, A-760II, A-960, A-960II, A-1060, M-50, M-70 and B-6

Yamaha products have a reputation for maximum reliability and durability.
Analysis of servicing data and our quality assurance system have revealed a potential safety risk which necessitates switch-off of all relevant models currently in operation. The models affected are A-760, A-760II, A-960, A-960II, A-1060, M-50, M-70 and B-6.
These amplifiers are now between 25 and 27 years old.

a-760-2_c3251bf77ed20d2ae90517f7e1352fac.jpg
a-960-2_11d7c6ab95d8d396722e5811368ba296.jpg
m-50-2_f7a68cc3554e5574b5b96265add20b6c.jpg


m-70-2_8bd6aa0e0f851624a130518c10c44809.jpg
b-6-2_8e7ad8021bbc14798abb092e6d72c727.jpg
a-1060-2_25fcb092b021b2c4d2bf95fdc2c764a4.jpg


Model name is printed on the Front panel.


The models listed above contain a component in the power supply assembly, which can in very rare cases suffer damage. This can be followed by significant emission of smoke and can in some cases even cause fire within the amplifier.
As a risk precaution, you should disconnect the amplifier from the power supply by removing the plug..

Please contact us

09.00 – 17.00 Tel. +49 4101-303 168

Email: EU.ServiceAdmin@contact.europe.yamaha.com

before reconnecting the amplifier and using it again.
 
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Just emailed Yamaha Canada, and they only keep service bulletins on hand for about ten years, before throwing them out, essentially. Is there some other archive of service bulletins about, other than searching the forum here?
 
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