Which Tannoys, folks?

[lurcher]

Its very very simple

Class A: Device conducts for full signal cycle
Class B: Device shut off for some of cycle, but conducts for more or equal to half the cycle
Class C: Device conducts for less than half the cycle.

For push pull, As long as the signal level is such that neither valve goes into shutoff then its class A, once one valve is off then its B. Its possible to bias the valve such that neither valve shuts off with full input signal, Class A. Bias so that both are on for some of the time but as the signal increases one shuts off, then its AB, Bias it so at idle both are shutoff, and they are never on together, but never both off when there is a signal, then its Class B. Bias it so there is a dead zone where both are off its Class C.

(the above is equally true for transistors as valves).

If no grid current flows at any time, its A1, B1, or C1 (the 1 is normally omitted). If grid current flows for some or all the time, its A2, B2 or C2.

Its all In RDH (but if you know what that is, you already know the above).

[Marco]

Thanks, Nick, for the clarification. Hopefully Mr Dunn has learned something now, particularly as he's always respected and considered you as someone who knows what he's talking about, regarding electronics. He's so pig-headed though, that no doubt he'll not accept that he is WRONG - instead he'll continue to claim in vain that everyone else is wrong, bar him!

The fact is that not one single person, who understands and builds electronics, has come to his defence and sided with his argument, which for me, says it all.....

Quite simply, if he continues spouting his misguided tosh, in reference to Class A valve amps, then he'll only make himself look even more like a fool. There's a time to hold your hands up and admit you've made a mistake and are wrong, whilst you still have some technical credibility left - and for Richard Dunn, that time is now...!

Marco.

[Marco]

Told you.

His latest bollocks:

Well Lurcher knows what he is talking about, which is unusual on that forum, BUT he doesn't mention class AB and that is what these push pull amps are = highly biased class B's = AB. On a test rig perhaps the amps stays biased for most of its gain range, but under load - no way.

The only circuit that stays in class A *ALL THE TIME* is single ended, and then it runs out of steam and clips, these pseudo class A's revert to class B *SO THEY ARE CLASS AB* - FULL STOP!!

Getting a little flustered now, are we? Calm down, dear, and stop shouting!! Shouting doesn't make you any less wrong

Care to answer Mr Dunn's comments, Nick, or anyone else who's qualified?

Marco.

[lewis]

Hi Paul,
Just curious, but when you listened to the Turnberry's, you mentioned that you could hear the Tannoy upper-mid honk. Were the speakers toed in facing the listening position, or firing straight down the room?

Very interesting reading regarding amplification with the Tannoys. I'm currently driving mine with a Unison Research Sinfonia, a very nice sounding 30w single-ended pure class a integrated, but can't help thinking that the Turnberry's could do with a bigger kick up the arse!

[lurcher]

Well, I have no dog in this fight, but I was just trying to offer some definitions. But it seems to be getting confused about just what is what.

The only circuit that stays in class A *ALL THE TIME* is single ended, and then it runs out of steam and clips, these pseudo class A's revert to class B *SO THEY ARE CLASS AB* - FULL STOP!!

I don't mention AB as it was not needed when describing the classes. Strictly speaking AB is not a class. its just a example of B,

A is always conducting
B is conducting part of the time, but more than half the time
C is less than half the time.

Ignoring shared cathodes components (for a push pull amp) any output stage can be regarded as any class depending on the level of signal its fed.

If you take a SET as a example which is being quoted as the defacto standard of a class A amp, and if the driver stage has the headroom you can drive the output valve into shutoff. Its (in that state) a class B amp, drive it harder still and it will be shutoff more than half the time. Its now a class C amp. All classes with a single output valve. So what type of amplifier is it, A?, B? or C? Well of course its all of them, the only thing that decides is the level of the input signal. The same is true of a push pull amp, but in that case, its possible to select the combined idle point. If the idle current is high, then it will be able to spend a lot of time with both valves conducting, its only in class A, but push it harder one will shutoff as was the case with a SET, then its in B.

You can't just look at a output stage and decide that because it can be driven into B or C, its a B or C amp, it entirely depends on what power is needed from it. The SET will sound horrible in B or C, but thats not the point. Single ended class C driver stages are often used in RF designs with a tuned circuit following to fill in the remainder of the time.

Its entirely possibly to design a output stage such that the driver stage clips before the output stage is driven into B, in that case, that amp can only be A, not AB, not B.

As a final example, I am experimenting (still, been some years now) with a DAC with a transformer coupled push pull output stage, just like a little push pull amp. I can say for certain that its a push pull output stage that will never leave A, because I know for certain what the max signal from the DAC chip will be, so I can choose operating conditions such that it will remain in A. So that simple example disproves "The only circuit that stays in class A *ALL THE TIME* is single ended".

Sorry for the long repeating post, but I nave not said anything that wasn't in the first one, just tried to explain what it means in context,

If I knew the op points for Marco's amp, and the max signal levels he runs it as I could say for certain if its A all the time, or B some of the time. I do know how loud a single 211 (A2) will go through Tannoys, I can well believe that a couple of kt88's will stay in A for most of the time.

[Reffc]

Hi Paul,
Just curious, but when you listened to the Turnberry's, you mentioned that you could hear the Tannoy upper-mid honk. Were the speakers toed in facing the listening position, or firing straight down the room?

Very interesting reading regarding amplification with the Tannoys. I'm currently driving mine with a Unison Research Sinfonia, a very nice sounding 30w single-ended pure class a integrated, but can't help thinking that the Turnberry's could do with a bigger kick up the arse!

Hi lewis

I listened to them with an Air Tight EL34 amp (unsure of output but guess at 40 watts?) and were slightly toed in listening about 2m away (near field-ish). Every Tannoy I've heard has benefited from additional power and I intend to use mine with at least a 150w SS power amp bolted onto the valve pre!

[Reffc]

Oooh, nice one, dude. I can sense your excitement! Can I come for a listen when the Turns arrive? If you want, I'll even bring my 'kid-on' Class A P/P valve amp along for a giggle

Marco.

Hi Marco,

they'll need 50 to 100 hours to bed in but after that if you'd like to bring your amp, then you'd be welcome to come and listen. Of course, it's all dependant upon the Harbeths being sold first!

[anthonyTD]

Its very very simple

Class A: Device conducts for full signal cycle
Class B: Device shut off for some of cycle, but conducts for more or equal to half the cycle
Class C: Device conducts for less than half the cycle.

For push pull, As long as the signal level is such that neither valve goes into shutoff then its class A, once one valve is off then its B. Its possible to bias the valve such that neither valve shuts off with full input signal, Class A. Bias so that both are on for some of the time but as the signal increases one shuts off, then its AB, Bias it so at idle both are shutoff, and they are never on together, but never both off when there is a signal, then its Class B. Bias it so there is a dead zone where both are off its Class C.

(the above is equally true for transistors as valves).

If no grid current flows at any time, its A1, B1, or C1 (the 1 is normally omitted). If grid current flows for some or all the time, its A2, B2 or C2.

Its all In RDH (but if you know what that is, you already know the above).

The ridiculous thing about all this is; the only reason RD is even debating this [and getting his thongs in a knot in the process] is because of his constant obsession with Marco, and nothing to do with me, but because Marco uses equipment that was made by me, i get brought into his silly games time after time, and its starting to wear thin now, Lurcher [among others]have made it quite clear to understand the different classes of bias needed to obtain a certain class of operation, ie; Class A, B, c etc, now RD is going on about class Ab1, what he is describing is an output stage that is mainly biased into class A, but can go outside of the parameters of class A for the remainder of its power cycle, most traditional push-pull amplifiers circuits when biased into class A will go outside of its class A region when pushed to their limits of usable grid signal etc,but how much will depend on a few factors, these include power supply voltage Sag etc.
Marco's amplifier produces its full stated power of 50 watts per Chanel whilst staying in its Class A region.
I really, really hope he gets this now and leaves me out of any further debates or silly games he may have planned for Marco, lets hope.
Anthony,TD...

[realysm42]

I know I'm walking into a long standing thing here but what's the issue; even if Marco were wrong (and I'm not intimating he is, I don't understand all of the technical stuff but even a fool can tell all the techy people are agreed) why can't the other guy just laugh about it and move on?

[Reffc]

I know I'm walking into a long standing thing here but what's the issue; even if Marco were wrong (and I'm not intimating he is, I don't understand all of the technical stuff but even a fool can tell all the techy people are agreed) why can't the other guy just laugh about it and move on?

Perhaps better addressed on the new thread that Marco has posted? This one is confused enough now as is