NVA dual mono power amp. What model! ?

[samjmann]

This strange looking power amp has 2 transformers per channel. Two mains leads. No power switches.

But, no speaker protection at all. And there aren't any fuses apart from the 5A plug fuses. Is this safe?

NVA was always quirky, but isn't this taking things a little too far? It is operating, but both midpoints are at -78mV. I can only assume to be correct.

If anyone has used or had any experience with one of these, I'd be most interested.

Google AI does come up with it not liking high capacitance speaker cables and then self destruction.

SJM.

[Beobloke]

That’s one of their Statement models I think. A limited run of the best Richard Dunn could come up with, which doesn’t say much for the rest.

The shoddy build quality and complete absence of basic protection circuitry is normal.

NVA has restarted since his death so may be able to help if you need information.

https://nvahifi.co.uk

[samjmann]

The rough construction is part of the "design" apparently.
Richard Dunn hated screws and believed that they and metal casing causes eddy currents.

I frankly would not dare connect an expensive set of speakers to this amp. Richard Dunn said his designs were not "unconditionally stable" hence the use of their own low capacity speaker cable.

I've noticed that the screen of the phono input is directly bonded to the speaker ground. I didn't think that this was good practice, but could well be wrong. SJM.
.

[knobtwiddler]

It could be barking up the wrong tree, but are you sure that one of the 'transformers' isn't a choke, or a transformer wired as one? (custom chokes are pricey - a cheap way of faking one is to buy an off-the-shelf TF and wire it as such).

You'd think that if someone went to the lengths of avoiding metal fasteners due to the screw / eddy current theory, they'd also be weary of hot melt glue... It looks like a school electronics project, but at least eddy currents will be kept at bay!

I've noticed that the screen of the phono input is directly bonded to the speaker ground. I didn't think that this was good practice, but could well be wrong

You're not wrong. It really is bad practice!

edit:

Is this safe?

Do you feel lucky?

[Cobaltblue]

If this thread goes off topic discussing earthing, household wiring, power distribution then the thread will be closed without notice.

If you feel there are safety issues take them up with the manufacturer.

Cheers

Mike T

[samjmann]

OK, all I was commenting on was, how this product differed from how everything else is constructed today. If this thread breaches the forum's rules, then please delete the entire thread.

It was not my intention, to get myself, any other forum member, or indeed the forum itself, into a war of words with any other third party.

Regards, SJM.

[knobtwiddler]

We don't need a long discussion on whether it meets stringent safety regs.

A start would be to ascertain what you need to do with the amp? My instinct would be to pillage it for parts, but I don't know the amp well enough to know if it has any redeeming features (grounding the I/P at the O/P is a cardinal sin, which makes me doubt whether its designer knew what they were doing). It doesn't have protection, so unless you plan on adding some (Velleman protection modules are about £15 and do the job), you might want to think about selling it on. Maybe it has some good parts and with modification, could turn out to be a good amp? Decent toroidals and shields (mu-metal?) cost a few quid. If it has some decent O/P devices it could make a good amp. Does it have decent heatsinks?

[Radio Wrangler]

Originally Posted by knobtwiddler

you might want to think about selling it on.

Which makes it someone else's problem and gives them the same quandary. They could be soon back here with similar questions....https://www.vintage-radio.net/images/smilies/eek.gif

Sold as a collection of parts to someone who knows what they're doing would be fair.

Sadly, in the boutique hifi market there is no shortage of 'designers' who don't have a clue. Sometimes their market sees this as an advantage. The insistence on using only very low capacitance speaker cables is a serious warning flag.

David

[knobtwiddler]

Originally Posted by Radio Wrangler

The insistence on using only very low capacitance speaker cables is a serious warning flag.

David

Indeed. In fairness to the designer of this particular item, there have been famous OEMs with multi-million turnovers who've insisted that their amp needs low C cable...(and their catalogue contains such cable, with prominent branding on its sleeve). My mind boggles at the concept (the firm I am thinking of has great marketing!).

Personally, I would be looking to build / buy / rent test gear that throws the amp into the most uncomfortable position possible, before I marketed an amp. One designer I was talking to a while back informed me that he has a reel of particularly high C cable that he keeps specifically to torture new designs with.

[not directed at David, as he knows this better than I do]: I would say that as a rule, if you *suspect* a design could oscillate, it probably will. If you think the stability margin is cutting it fine, but it works ok on the bench today, tomorrow could be a different story... There is a law: that which is stable on your bench, will pick up Radio Moscow once in the client's system. Don't ignore that little kink in your square wave!

edit - Crikey! They are still at it, i.e. leaving out protection... https://nvahifi.co.uk/products/nva-m160-monoblock-power-amplifiers

If it doesn't have protection, it's not a complete amp.

[samjmann]

There's some cosmetic work on the amp to do. But making any electronic changes to this opens up an enormous rabbit hole for me. I've don't have a service manual, or even a basic circuit diagram. I was only looking at this as a first appraisal. This would be best looked at by NVA, albeit in their new guise.

The unusual construction may be seen by some as an indicator of distortion free sound. But whoever ends up with it should be made aware of no fusing/no speaker protection/ low C speaker cable requirements etc.

Not my cup-of-tea at all, but we're all different.

Thanks for the info from all who have responded.

SJM.

[knobtwiddler]

If you're not taking this amp on as a job (you made the right decision IMO), then maybe this thread could be integrated into the Audiophoolery one? That seems more appropriate.

I just noticed the '2 mains leads' in the 1st post. That's a curious one. I wonder what the logic was there? What if you use extra long leads, plugging it into sockets on either side of a room?

(forgive me if it's a bit of work to move it - I am not an IT expert)

[Beobloke]

Originally Posted by knobtwiddler

If you're not taking this amp on as a job (you made the right decision IMO), then maybe this thread could be integrated into the Audiophoolery one? That seems more appropriate.

I just noticed the '2 mains leads' in the 1st post. That's a curious one. I wonder what the logic was there? What if you use extra long leads, plugging it into sockets on either side of a room?

(forgive me if it's a bit of work to move it - I am not an IT expert)

My Yamaha PC-5002M power amplifier (dual mono, 750W per channel, 61kg!) has two mains leads.

As far as I’m concerned, any amp that purports to be dual mono should have two mains leads!

[knobtwiddler]

From an engineering standpoint, there is no justification for having 2 mains leads unless it's a massive PA amp and a single one can't handle the current. It's a ludicrous concept for a home amp IMO.

[Radio Wrangler]

It's a marketing ploy.

Anything to make a product appear more esoteric and stir their fan club up!

The audiophoolery thread grew out of the silly prices asked for audiophool-targetted esoteric stuff. At least this equipment ticks the craziness box, but not the price box.

The threads could be merged, but the forum software will interleave them, sticking each post by date and time, so this process often creates confusion. But the audiophoolery thread has been quiet for a while, so it might not be too bad this time. My logic for leaving it separate is that this thread starts from a perfectly normal question from the OP, who didn't realise the repercussions of just what he had. I'm not sure that moving it would be fair to him.

The mention, up-thread of uncomfortable test conditions got a smile out of me. The electronic products I designed for the last 14 years got tested at Antarctic and Death Valley temperatures, crash tested and explosive decompression... humidity, salt spray and altitudes to 80,000 feet! Yep, uncomfortable.

he propensities of amplifiers to want to oscillate is a standing not-really-a-joke. And yes, I know well the name of the firm whose super-expensive amplifiers did pyrotechnics without low-C speaker cables.

David

[knobtwiddler]

Anything to make a product appear more esoteric

Unless you need to drive a stack at Glastonbury, I cannot see an upside to twin cables entering the same enclosure. It strikes me as a scenario that introduces pointless pitfalls (especially if the stability margin isn’t up to snuff).

Uncomfortable test conditions today = fewer warranty claims tomorrow

[Craig Sawyers]

Originally Posted by Beobloke

My Yamaha PC-5002M power amplifier (dual mono, 750W per channel, 61kg!) has two mains leads.

As far as I’m concerned, any amp that purports to be dual mono should have two mains leads!

61kg is a real monster power amp. 1500W in bridge mode into 8 ohms is bonkers! I've just dowloaded the service manual, and Yamaha threw everything at this beast.

Craig

[Radio Wrangler]

If something is getting to the power level needing two mains cables, or >60kg, then it's time to ask the question 'Shouldn't it be two boxes?'

Twin power cables on something of normal duty is poseur territory, and the poseur is going to plug them into either a dual outlet wall socket or (shock horror!) one of those four way socket strips anyway.

Seeing something with two mains cables, I want to know what is there preventing live pins if one plug is pulled while the other is powered? It sounds stupid, but stupidity has no bounds and it has been done.

David

[TonyDuell]

Originally Posted by Radio Wrangler

Seeing something with two mains cables, I want to know what is there preventing live pins if one plug is pulled while the other is powered? It sounds stupid, but stupidity has no bounds and it has been done.

David

Possibly separate mains transformers, one for each channel? A separate mains cable for each transformer, no connections between the 2 channels (apart from signal ground?)

[Craig Sawyers]

If they were mono amplifiers, each would need a mains cable. So putting two mono amplifiers in the same chassis...

This really ought to be in the audiophoolery thread, but the d'Agostino Relentless 1600 monoblock has binding posts to connect the power https://dandagostino.com/products/relentless-epic-1600-monoblock-amplifier

6,400W into 2 ohms.

Quarter of a ton each, for half a ton per stereo pair.

Craig

[Beobloke]

Originally Posted by knobtwiddler

From an engineering standpoint, there is no justification for having 2 mains leads unless it's a massive PA amp and a single one can't handle the current. It's a ludicrous concept for a home amp IMO.

If you google the Yamaha PC-5002M, you’ll find it is indeed a “massive PA amp.

That said, it shares its internals with a very, very rare Yamaha domestic power amplifier and I assume that has two mains leads as well!