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-   -   Technics SU-V7 - some questions. (http://www.diyaudio.com/forums/solid-state/220964-technics-su-v7-some-questions.html)

ashleycox 4th October 2012 06:37 PM

Technics SU-V7 - some questions.
 
Hi all,
I recently purchased a Technics SU-v7 integrated. It's going great - fantastic amp, in near perfect condition (not a scratch on it, impressive after 33 years!). I've got a few questions:

Is there anything that due to the amps age I should be looking for to prevent possible issues in the future? I took it apart and cleaned the controls, the main capacitors (15000uf 38v look fine - should I be replacing these anyway due to the age of the machine? If so, what do I replace them with that won't affect the sound of the amp too much?

I've read that pure class A amps get pretty hot - is this true?

If the amp is switched to an input with no source connected, and turned to near full volume, it makes a faint hissing sound - is this normal? The yamaha I have (modern) is pretty much silent, so was wondering if it may have something to do with the caps.

is there anything else I should look out for, change, have serviced, etc to get this running like new? (it runs perfectly at the moment, just want to be sure!).

Thanks for any and all help!

Rundmaus 4th October 2012 06:42 PM

Hi there,

definitely all electrolytics are prone to failure after 33years. I would change them out, especially the big filter caps in the PSU. Replace them by physically fitting modern caps of roughly the same capacitance, if possible with a 105C temperature rating. Don't worry about the sound - if correctly chosen filter caps affect the sound, you either hear the audiophool grass growing or something's seriously wrong with the circuit!

Greetings,
Andreas

KatieandDad 4th October 2012 06:43 PM

All electrolytics will deteriorate with both age and heat.

With old amps you can generally get away with the next highest value and next highest voltage (if required), so your 15000uF 38V would be substituted with 15000uF 40V or even 22000uF 63V.

The hissing is not caused by caps. you would need to look at the op-amps for reducing circuit noise.

Rundmaus 4th October 2012 06:53 PM

One should be careful with higher capacitances on replacing caps - the rest of the PSU circuit must be up to the task of dealing with the inrush current and the charging current peaks...

Andreas

KatieandDad 4th October 2012 07:18 PM

Sometimes you don't have the choice as the older values are no longer available, don't go silly, just use the next higher available value.

Also remember the tolerance on most electrolytics is usually +100% -50% so the next higher value will usually work perfectly.

Ian Finch 4th October 2012 07:19 PM

Heat
 
SUV series Technics amplifiers are not really class A. These types, developed from Sandman's class S principle, were given a few names like "New class A, Class AA+, Class A++, with VC4 etc, when new ranges were released. They work on a variety of undisclosed schemes somewhat related to Quad's "current dumping" principle where the class A amplifier is tiny and and real power requirements are augmented by a large class B amplifier on demand. Most versions actually run very cool in typical domestic use AFAIK and yes, they do sound good compared to standard AB class amplifiers, even some real class A amplifiers.

Hissing as you describe can often be just a consequence of higher available gain, which was common in older amps in the days of widely varying input levels. Noise levels of equipment were typically higher too, as we have actually made some progress in audio over the last 30 or so years.

'Hope you enjoy it!

Ian Finch 5th October 2012 09:36 AM

Re: Main electrolytic caps.
This an 80W amplifier, rated for both 4 & 8 ohm loads which means that the transformer is small and the windings and thus rail voltages may be switched for either load impedance. It also means the main electrolytic capacitors will be rated higher than 38 or 40V - more like 50-60 volts because that's what's needed to supply an amplifier that size. Be careful with ratings because overvoltage can lead to really violent explosion of electros. Take care with reading labels and make sure you get the working voltage correct along with any overall size restrictions, pin spacing and value.

Caps can look pristine but that has zip to do with the inside of a 20+ year old wet cell.

tvi 5th October 2012 10:45 AM

You can get the Service Manual here
technics_su-v7

"15000uf 38v look fine" Schematic says 15000/50V and are filtering 37ish volt rails

This Japanese site might be of interest, the relay seems to be a common problem as its also mentioned here and here.

Most newer 15000u/63v caps like these should fit, but I'd double check the sizes.

rgds
James

wahab 5th October 2012 11:25 AM

Seems to be an iteration of Sansui s Diamond circuit , a single differential
driving a symetrical differential.

ashleycox 6th October 2012 06:47 PM

Wow, loads of information -thanks everyone! I'll look into all of your suggestions. Not quite as easy as I thought it would be... :-)


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