Valve amps - do measurements tell it all?

[anthonyTD]

I was just thinking the same John,
Yes, Paul described his amp, and the impedances of the speakers, which i think was about an ohm, or even less...
perhaps he will link to the page when he gets chance.
A...

If you look back on AOS you can find that Paul designed his own amp for this

[DSJR]

Thoughts on the original question - don't valve amps have very low distortion at very low volumes, which only climbs when they're pushed harder and the transformers get near to their saturation-ceiling? The little T-Amp seems the same - phenominal clarity at low volumes but getting rather nasty if welly is involved into less sensitive speakers..

[John]

http://theartofsound.net/forum/showt...nes+line+array Paul starts to discuss the approach

[lurcher]

Thoughts on the original question - don't valve amps have very low distortion at very low volumes, which only climbs when they're pushed harder and the transformers get near to their saturation-ceiling? The little T-Amp seems the same - phenominal clarity at low volumes but getting rather nasty if welly is involved into less sensitive speakers..

Certainly true with SET's, thst the main point of them (IMHO) and why you need loads of headroom. Push Pull, maybe, depends on the op point and if they are A or B, or where between.

[jandl100]

This is presumably a dig at me.

Nah, I'm pretty sure they were putting me to rights, Mark.

There sure are a lot of Tannoy DC fanboyz around here!

[Paul Hynes]

Bob,

The drive units are 8 x Visaton B200 6 ohm units per line giving a nominal 0.75 ohm load. It is easy enough to design an amplifier with enough balls to drive this (I have had no complaints about my balls either) but most audio amplifiers are designed to drive higher impedance and therefore would struggle with this load.

There are actually some benefits driving such a low impedance load that allow me to get rid of a lot of distortion generating clutter in the signal path. The required voltage swing for a given power delivery is much lower than with an amplifier required to drive 8 ohms. In practice I need no voltage gain in either the power amplifier or the line preamplifier. That is two or more stages of electronics out of the way of the music, as I only need current gain. The power amp is effectively a high current DC coupled buffer amplifier with just one high power depletion mosfet in the signal path running in single ended class A on split rail supplies. This is only one active device in the signal path from the input of the line preamp to the output of the power amp, and very nicely musically transparent it is too.

The overall concept or the system design is to remove or reduce as many frequency dependant phase shifts in the audio spectrum as possible and to remove unnecessary distortion from electronics in the signal path and from room interaction. I do like the physics of the line array as it helps reduce room interaction and reinforce the bass response (eight 8” drive units per side can easily move enough air to reproduce a large drum in my lounge). As this is an open baffle design there is no cabinet honk to consider so there is another quite large distortion in conventional loudspeaker designs that is removed from the system. The rear wall reflection has to be considered and optimised by careful positioning but there is very little in the way of floor or ceiling reflection and little side wall reflection due to cancellation of front and rear wave fronts at the edge of the open baffle.

I had no requirements to follow accepted convention with this system design, so I allowed my mind to roam free, and this is the result.

[cloth-ears]

http://theartofsound.net/forum/showt...nes+line+array Paul starts to discuss the approach

Thanks for putting that thread up. Beautifully simple MOSFET design, I love it. I think I’ll have a go myself one day

[Reffc]

Nah, I'm pretty sure they were putting me to rights, Mark.

There sure are a lot of Tannoy DC fanboyz around here!

Not having a dig at anyone in particular Jerry...you know me! Just trying to point out that the design isn't like a 2-way with a large woofer trying to stretch to high and a small tweeter trying to stretch too low. The design uses the shape of the woofer as an extension to the horn tweeter so that mid frequencies are essentially handled by a "third" driver made from the tweeter horn firing into the larger woofer area. It's a clever design and as Ynwan points out, it's nothing new and others have used the same principle. It's just that as a DC design, it works wonderfully well as many recording and broadcast studios know.