A Class Designs

Brain_Dead

Tube, Transistor, FET, what sounds the best to you, is it push-pull A SECA or like Nelson Pass Bootstrap single ended design.

I did like the OTL that Croft did in the early 1980,

So what have you tried and compared and prefer.

Brumjam

Not much experience with valves here but I did recently here a modified Art Audio Quintet driving my speakers.  This is a push pull EL34 design (whatever that means) and it sounded frankly stupendous.  When I come out the other side of my house extension I shall be investigating valve power amps further.  For all the detail offered by my Hypex amps they don't drive my speakers as well as the Art Audio did - any idea why this should be Colin?  My speakers aren't difficult to drive but the dynamics I heard listening to the 20-30w valve power amp trounced my current monoblocks.  Perhaps it's just system synergy or maybe I buggered up the build of my own amps.

I've bought a cheap class A EL34 amp to see if I can recreate some of the magic I heard with the Art Audio. The drive is still there but it's rounded off the bass and treble....oh and it gets bloody hot!

Brain_Dead

Are the Hypex Class D?

Alan

It is, and very interesting it is too. Especially with large linear power supplies (but that's for another day).

Looks like you have found something pretty special James - we'll be needing a system pics thread from you methinks!

I have had almost no experience of class A or valveyness, save hearing a few other's systems. I must say I prefer (thus far) a decent valve amp to a class A (like MF A1 etc), but then I have hardly heard much of anything.

My guesstimate is that it would be foolish to be slavishly loyal to a particular class of operation or circuit topology, as there are bound to be many poor performers in all classes/types and a few exceptional ones which transcend their mode of operation. My current fave system is a blend of class D, valve amps, active Xover & OBs, knocks the socks of most things I have heard TBH.

Brumjam

I should have mentioned that at the time I was using a Pure Sound L300 pre. But I've heard this with my Hypex monoblocks as well and it doesn't account for the performance difference. The Art Audio amp sounded very good with the L300. Ironic that the first time I heard the L300 really sing was the day I sold it!

Like Alan I've not heard enough different amp topologies to say for sure which one I prefer. The world of valves looks like a foreign language to me :-)

PAC

Heard two that stood out:  Horning Sati 12w SET (using 520B's) driving Horning Agathon Ultimates.  Possibly the best sounding hifi sound I've ever heard in terms of realism and musicality.  My current and relatively modest Croft set up (Class A with MOFSET output on the power amp and valve line stage) isn't too shabby either.  As good as most of the so called "high end" amps I've auditioned and better than many.

Brumjam

Interesting Paul. Which Croft models are you using?

PAC

I'm using the Croft Micro25 (the one up from the basic) and the Series 7R power amp with the regulated power supply.  A big, beefy and ballsy presentation with none of the disadvantages of traditional valve amps (high impedance outputs) thanks to MOFSETS.  Quite detailed and refined too and very low circuit noise.  Seems like a win-win.  The 3-D like valve presentation thanks to a superb valve pre and the gutsy grip of that hybrid power amp.  Drives difficult speaker loads with ease too despite the modest 50 watts or so rating.

Brain_Dead

In the Audio Design Book from Mullard I found a SECA with a huge inductor in the O/|P with Germanium Transistor, OC28 and capacitor coupled. A massive 10W RMS. It is amazing how many transistor manufactures get DATA wrong so far two have said a OC28 is a NPN, bloody fools it a PNP.

I think I will build it and try it out for fun, I have few proper transistors somewhere. 

Brain_Dead

I think it is ODD the Douglas Self ran down MOSFETs has non linear devices that could not be controlled and produce a good sound well Croft and Nelson have, shame FET's cant read Douglas.. 

chrisb

Anyone seen or used bedini amplifiers , supposedly very good but temperamental class a .

PAC

I think it is ODD the Douglas Self ran down MOSFETs has non linear devices that could not be controlled and produce a good sound well Croft and Nelson have, shame FET's cant read Douglas.. 

Absolutely.  Douglas Self should know better,  what a ridiculous statement to have made!  MOFSETS are amongst the most STABLE of transistor circuits under load which is the whole point!  Lots of manufacturers use them in power amp output stages exactly for that reason. Croft may be one, but Rega use them too.  

Alan

Aren't Bedini supposed to be great with Shahinian speakers? Them and Dynavector, if I recall.

Bedini also make an infamous CD clarifier device, which seems extremely suspect when you read about it. However, some who have used them say they do something, so I won't argue the point.