Effects of metal enclosures on circuits

I look at that circuit at keep asking myself.... why would you?

It looks like one of those 'I do it this way because I can' type products.

TdP did the same with his power amp using banks of little ECC83s running in parallel. I asked him once why he'd chosen that method, and in typical TdP style he snapped back 'because I can and others can't!'

 

That's certainly an advance, but arguably not new design IMO. Its still a capacitor smoothed psu when all said and done.

 

Just about everything that is out there is based on application notes. Now that doesn't make them the same and they definitely don't sound the same. So circuit design is obviously only part of the picture. There are people who don't base their designs on application notes, I know that as the Tresham was not based on the Hitachi fet application note nor is the nva based on any bi-polar application note.

Though of course there are bound to be parallel lines.

 

If you had a profound distrust of output transformers you might!

Personally I don't have an issue with using them for impedance conversion. DB obviously does. If anything I think his solution is more 'characterful' but I can understand why people like the amplifiers.

 

Very high output impedance IIRC - certainly on the low feedback settings.
Any speaker system not possessing a flat impedance characteristic (so thats 99.9% of them...) is going to sound characterful.

I've heard a Berning driving Proac SC1s and it sounded fine, but that was with the speaker converted to sealed box and a big Velodyne active sub on the bottom. Might be a different story runing the Proac full range.

 

I don't think they are high o/p impedance in the way a feedback free SET amp might be. I heard some of his newer mono amps recently driving some very large speakers in a big room with no strain or evident FR anomalies being audible.

I'm not sure how much of an issue the load tolerance would ever be. Of course adjusting the feedback on a ZH270 changed the way it coupled to various loads but there was usually a setting that gave a decent result.

Anyhow, nobody with any sense uses punishingly low impedance & inefficient speakers these days do they?

 

Not in my case certainly.

At least not both combined

 

If it's the speakers I'm thinking of, they've been replaced by Tannoy DMT12 and they sounded fine to my ears.

 

It is

IIRC he has the feedback on the highest setting (or did have) which will help.

 

Martin Grindrod's design for the PA's in the AVI adm9 series is pretty good.

It's a generation beyond the Lab Series, and is in about it's fifth revision now. It's used in their Subs too.

It's not digital switching amp as is very common in active speakers btw.

JC

 

Digital switching amps aren't new either.

In fact we often think of digital audio as 'new' but it goes back many decades.
I was reading a BBC Research deocument yesterday on the requirements for a workable PCM audio system. The paper was dated 1965.

 

'Digital' amps aren't really digital ..........

 

You wont have a digital amplifier until you have a digital speaker, which strike me as pretty unlikely. So with current speakers at some point you have to have voltage and current gain and there is no point in doing that digitally as you just make the conversion back to analogue more difficult and complicated, and I really can't think of how a digital circuit can give you current and voltage gain, it just switches. It could control *another* circuit to give you that gain but that is all.

Anyway all an amplifier is is a regulated power supply where the signal being regulated happens to be music.

EDIT I remember in the dim depths of my mind someone trying to create a gas driven horn loudspeaker where the gas valve was regulated mechanically by music via a low gain source. And there was also one that used either a flame or a plasma to do it if I remember rightly.

 

You should have a listen to a Lyngdorf TDA amp if you can Richard, not perfect, but an interesting idea if your using a digital source (which i know your not dead keen on )

http://www.lyngdorf.com/content/view/14/33/

Acapella still make a Plasma tweeter, and i think Keith from Purite has just started to sell a speaker that has a plasma tweeter too.

http://www.acapella.de/en/

 

Hill Plasmatronics.

Needed a ready supply of helium but the dancing flames are very pretty in the dark!

 

This is more fun

http://www.auxetophone.com/Welcome.html

 

It is still not a digital amp, it is a switching analogue amp.

 

Wasn't there some problem about it giving off ozone as a by-product.

 

It only became dangerous when mixed with methane

Didnt say it wasn't, just asked if you ever heard one.

 

Hmmm, ... I don't like the term 'regulated' in this context .... 'modulated' is better ....

.... 'regulated' implies constrained to a constant level, .... which is the opposite of what is required.

... I think I know what you mean though, .. the output voltage at the pa terminals across a load, has to be an analogue of the music which of course is very variable in nature.

I agree digital amps are a nonsense concept when all loudspeakers are firmly and necessarily in the analogue domain, and likely to remain so, because we don't have 'digital ears'

JC