Congrats Paul, i'm sure you'll be very pleased with your Turnberry's. I would be very interested in your stands, that's something i was thinking about, but afaik there is nothing available commercially.Quote:
Originally Posted by Reffc
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Congrats Paul, i'm sure you'll be very pleased with your Turnberry's. I would be very interested in your stands, that's something i was thinking about, but afaik there is nothing available commercially.Quote:
Originally Posted by Reffc
Nice one my son. Great speakers!
They can really boogie!
That's the problem, so I am going to add speaker stands for the prestige (smaller range) to the RFC products. I have a cunning design penned up. Checked the timber priced this morning and (gulp) not cheap for high quality solid Walnut, but its got to look right!Quote:
Originally Posted by lewis
Nice one Paul i'm sure you won't be dissapointed , the stands look interesting and probably look a lot better than the concrete blocks i used :lol:.
If you are interested in a Pure sound 2A3 push pull give me a shout as i know for one, i was impressed when i tried it on my Tannoys
Thanks Jon
I'll stick with the Croft amps but may give Glenn a shout to see of the power amp should be optimised for the Tannoys. My thinking is quality over quantity so perhaps having work on the power amp to lower output but lift quality of power supplies etc even further.
Amps -- Hmm :hmm: -- I'll take my Mini-T amp round to Paul's once he's got his Tannoys - it sounded damn fine on 10 inch Monitor Golds in Lancaster cabs! :)
I look forward to a mini-T v's Croft bake off Jerry but suspect I know which I'll prefer....NOS valve loveliness v's op-amps? :ner:Quote:
Originally Posted by jandl100
Tee hee - maybe - maybe not!
I must confess I preferred my American solid state muscle amp to your Croft loveliness on the Harbeths in every way! ;)
Quote:
Originally Posted by jandl100
I have to agree with that Jerry. Cleaner sounding with slightly better bass definition, but not as "night and day" as I was expecting. I think that the outcome would have been the same nomatter what 50w/ch amp was up front, as bolting on a power amp with the reserves of the Parasound clearly will make a difference. Most speakers I've ever owned, even highly efficient ones, have benefited from powerful amplification. It allows better transient behaviour and headroom and the Halo has massive speaker damping ability!
The Croft amps are still a class act though;)
If the quality of the other wooden furniture on your website is anything to go by, these Tannoy stands should be worth waiting for.Quote:
Originally Posted by Reffc
Thankyou Andrew!Quote:
Originally Posted by lewis
As it happens, I'm meeting with RFC's cabinet maker this morning to run through the designs and start making some trial versions. The final ones are a few weeks off and will be worth waiting for ;)
Yes indeedy! Looking forward to seeing those :)
Regarding the Croft vs. Parasound thing, which Croft amps have you got Paul? IMO, the real gems in the Croft range are the preamps. The power amps are very good, but not quite in the same class as their (quite exceptional) preamps. I put this down to the power amps being a hybrid design, using MOSFETS with a valve input stage, rather than being out-and-out valve designs. That type of principle works very well in their preamps, but less so, IMO, with their power amps.
Quite simply, in order to compete with Jerry's Parasound 'muscle amp', in terms of transient response, dynamic impact and overall headroom, you need a big push-pull Class A valve amp, using the likes of KT88 or KT120 tubes and massive, top-notch, mains and output transformers, which combine to provide the required 'clout'! :hairmetal:
In that respect, I think that the likes of my Tube Distinctions Copper amp would be more able to give the Parasound a run for its money, in terms of the things that 'big-boy' sand amps do best, as well as also throwing some thermionic lurveliness into the equation, for good measure! If I can make the bake-off at Martin T's this weekend (where Jerry's Parasound is going up against Martin's Chord behemoth), I'll get the opportunity to demonstrate this, if I bring the Copper amp down with me :cool:
A couple of pics of the beastie in question... In situ in my listening room:
http://imageshack.us/a/img822/2935/copperamp.jpg
The last time Martin heard it in his system, along with my (heavily modified) Croft preamp:
http://imageshack.us/a/img211/1681/r...2020100228.jpg
Since then it's had a bigger mains transformer fitted, from Sowter, been upgraded from 30W to 50WPC Class A, had Clarity Cap MR power supply caps fitted, KT88s changed to KT120s and GZ34 rectifiers changed to 5U4GBs, new NOS Brimar CV1988 driver valves, Cardas solid-copper speaker terminals, Furutech phonos and IEC socket fitted, along with dual-mono variable feedback control.
Yes, it's even better now than it was before....! :eyebrows:
Marco.
I'm using the Croft Micro25 pre with the Series 7R power amp Marco. I agree with you. the Micro25, even though not the "full blown" version is about as good a pre as I've ever heard. I have tried valve rolling with it (NOS of course) but TBH there's very litle difference between any ECC83 put in it and the system is revealing enough to distinguish differences. This accords with Glenns' views I think so is a circuit design thing.
The power is very good and punchy, but lacks ultimate precision IMHO. Thats a compliment by the way as for the money, there's not a lot out there to touch the 7R.
My own preference if using all valve would be pure class A for lower distortion. The valve type may impact output but sound is something determined more by the circut design and quality of power supplies and output transformers. Big money for something really good though compared with a good SS. However, in SS format, and for the money, I still rate the Quad 909 as one of the best in class having tried one with a range of pre-amps and speakers. It was remarkably close to the Parasound. Consummate ease of power deliver with bags in reserve, very polished detail and high definition of things like the leading edge of bass notes and very high S/N for low noisefloor. Also vanishingly low distortion across the frequency band.
The Tannoys are on order and will be with me in 4 to 5 weeks. At present they are probably still in timber sheets waiting to be cut and the electronics in bits in boxes somewhere! I can see the elderly gents wearing half moon glasses and spotless blue aprons with a flat pencil behind their ears approaching the timber stacks right now...
To be fair to the Croft power amp, my Parasound is the best sounding amp I've come across in all my years of boxswapping and dozens and dozens of fine amps of all types have been heard.
It's not just about power and headroom, though, even on very low level music where just a watt or two is required the Parasound still excels, imho.
I meet up this Saturday at MartinT's place to see how the big Para does with his Ushers. Mucho looking forward to that. :)
Hi Paul,
I completely agree. Good circuit design is far more influential and important than the effects of tube-rolling. In comparison, swapping valves can only ever cause subtle changes, usually in terms of tonality, although some also allow an amp to deliver greater punch and drive.Quote:
I'm using the Croft Micro25 pre with the Series 7R power amp Marco. I agree with you. the Micro25, even though not the "full blown" version is about as good a pre as I've ever heard. I have tried valve rolling with it (NOS of course) but TBH there's very litle difference between any ECC83 put in it and the system is revealing enough to distinguish differences. This accords with Glenns' views I think so is a circuit design thing.
However, the effects of tube-rolling are rather more obvious in Croft's earlier high-end preamps, such as the Charisma X, which I use, that feature the bigger octal 6SL7 type valves. These are a different ball-game to ECC83s, and have a much bigger, richer, more 'finessed' sound. Playing around with different types of those has a rather more profound effect on the sound.
A sneaky peak inside my preamp, showing various NOS 1940s and 1950s-vintage 6SL7s, at the back, and the (superb, best I've heard) SCR Teflon Foil coupling capacitors (shown in green) at the front:
http://imageshack.us/a/img42/7541/img6055n.jpg
Again, I totally agree. For me, Class A (when done *really* well) is where its at, no matter whether we're talking about SS or valve amps, as the way in which it reproduces music is truly magical!Quote:
My own preference if using all valve would be pure class A for lower distortion. The valve type may impact output but sound is something determined more by the circut design and quality of power supplies and output transformers. Big money for something really good though compared with a good SS.
Big money? Yes, but perhaps not as much as you might think... The Copper amp (hand-built and hard-wired from scratch, featuring hand-wound transformers and the highest quality components) does all that, and it can be bought brand new for £5k ;)
Inside the beastie:
http://imageshack.us/a/img580/5280/i...copperampe.jpg
You should really come up sometime and have a listen! :cool:
Marco.
Out of my price range. I'd probably go for a big class A SS power amp at a quarter of the price ;-)
Lol - if I was going SS, I'd probably have the Usher Reference R-1.5:
http://imageshack.us/a/img545/6444/u...mp20250x72.jpg
http://imageshack.us/a/img193/3568/usher1m.jpg http://imageshack.us/a/img28/2600/usher2l.jpg
http://imageshack.us/a/img827/458/usher3.jpg
Deco Audio are selling it for £1500: http://www.decoaudio.com/deco_audio_...mplifiers.html
I've heard the beastie, and it's stunning! :eek:
Marco.
To do it properly, it needs to be a PROPER Class A, a stonking big SET, something like the big ol' 211's, no push-pull. Very dynamic sounding, great headroom. Had a few push-pull valve amps including a Lumley ST40 and a Consonance Cyber 10s which claimed to be Class A, but they were only Class A for the first Watt or so before the circuit behaved (push-pull) class AB. Whatever, they sounded good. Less interested in the circuit design (I'll leave that to those who design the things) and more interested in what they sound like.
Jerry's Parasound Halo is one of the best power amps I've come across in the sonic stakes. Neutral, massive headroom and portrays micro detail like few others.
The Quad 909 I particularly liked, despite its dissenters. Not unlike the Parasound in character but from what I can remember, more "3-D" in presentation. Not ultimately as detailed but close.
The Lumley ST40 was the very best of the valve amps I had and one of the best amps I've owned. No relation of the St70, a far better circuit design, tweaked by Ben Carter for John Jefferies who owned the Lumley Brand. It brought music alive in my system. Sold it to help pay some stock bills (even though it was one of only 10 ever built in the better mk1 guise). We all do silly things.
The Croft pre I'd describe as outstanding at the price point and would recommend it to anyone without hesitation (25R even better I'm told). The Series 7R is ok and reasonable value. It does punch above its rated output and is relatively polished (refined...low distortion, good S/N and channel separation and gives music a nice depth) but there are more refined power amps out there and you do need to be careful not to switch inputs on the pre without turning the volume (controls) down to avoid popping fuses all the time in the power amp.
Hi Paul,
I know what you mean, but you *can* have proper Class A, with a P/P amp. I've heard big 211 SET amps, and whilst they're very good, I still wouldn't swap them for my copper amp, which is also a true Pure Class A design. Read here, for more on the design of the Copper amp: http://www.tubedistinctions.co.uk/custom.htmQuote:
To do it properly, it needs to be a PROPER Class A, a stonking big SET, something like the big ol' 211's, no push-pull.
Have a read at this article too, which explains some of the common misconceptions you've alluded to: http://www.aikenamps.com/ClassA.htm
...noting this bit in particular:
:)Quote:
A class A audio amplifier can be either single-ended or push-pull. Now, you might be thinking, how can a push-pull amplifier be class A? Doesn't one side amplify half the waveform and the other side amplify the other half? Isn't this why we use a phase splitter?
These are common misconceptions. You can, indeed have a true class A amplifier that operates in push-pull mode. Amplifier class has absolutely nothing to do with output stage topology. If the output tubes on either side of a push-pull pair are biased in class A (halfway between cutoff and saturation), then the current in each side will still flow for the full 360 degrees of the input cycle, just in opposing directions. As one tube's current increases from the midpoint, or idle, bias current, the other tube's current is decreasing by an equal amount.
The output transformer sums these oppositely-phased currents to produce the output waveform in the secondary winding. As one side reaches saturation, the other side reaches cutoff, just as they would in a single-ended class A amplifier. Neither side cuts off at the full, unclipped output power of the amplifier. The output power of a push-pull class A amplifier is exactly twice the output power of a single-ended class A amplifier operating under the same conditions of plate voltage, bias, and effective load impedance.
Marco.
I know what you mean Marco and was just being provocative :ner: and purist about Class A (I do understand each of the topologies). I have owned and heard both but the sweetest was single ended. Best I heard was a Horning Sati 520 SET. 12w of SET gloriousness.Quote:
Originally Posted by Marco
Coo - that's a cool reviewlet of my amp, Paul. :thumbsup:Quote:
Originally Posted by Reffc
So the Quad 909 might be better than the Para in terms of 3D? Blimey - you should hear what the Para can do with my MBLs and my Bushmaster DAC in terms of 3D imaging! :wowzer:
Hi Paul,
Lol - yeah, now we're getting down to the difference in sonic presentation between SE and P/P, for somewhat different reasons... SE does sound 'sweeter'. I like both (when done well), but prefer P/P, as I need the extra 'balls' it gives when playing rock music at realistic levels! :eyebrows: :fingers: :fingers:
Marco.
Big sensitive speakers (100dB/1w plus) and 10w SET rocks pretty darned well! Yes, for most set ups, P-P's where it's at, agreed. SET, when played well within it's optimal operating envelope does have a sweetness few can match and very low distortion (unless pushed).Quote:
Originally Posted by Marco
Its difficult (and most probably VERY unreliable) to ever quote from memory Jerry, especially when it comes to my own! In fairness, the system using the 909 was nothing like as revealing as yours (Proac 2000 Ref8 Signatures/Rega P25/Rega preamp and Quad 909) but I compared several power amps and only the Quad gave me that :wow: moment.Quote:
Originally Posted by jandl100
I certainly can't and won't compete on the techno-babble side of things (I cherish my ignorance :eyebrows:) but from a listening pov, you do need to be careful when 'sweetness' just becomes smooth rolled-off rez-reduction. Real music is seldom 'sweet', ime, and the closer you get physically to the musicians the less sweet it gets - and I like to sit close up! ;)
Yup, quite right Jerry but on the flip side, SET has become a byword stereotype for low res, which it most certainly is not. You must have listened to a really good SET-up(doh!)? It can rock, can have the resolution but at the same time there can be something alluring about the presentation which only SET seems to manage. Not ultimately for me (I don't have pockets deep enough for a really good SET) but I have enjoyed some of the better quality SET systems I've listened to.Quote:
Originally Posted by jandl100
Sure - I had a pair of Cary SET 15W monoblocks - fook me, they rocked with any music. Very hi-rez and bundles of presence. Too much so, at times! :eek:Quote:
Originally Posted by Reffc
(there's a review in a certain webzine. ;))
But, as you say, SET to some folks is what they (erroneously) call "valve sound" - way too smooth, coloured, gentle .... :nono:
Hi All,
I would like to add my own comments on the subject of what has been discussed in the latter of this thread, i hope that's ok with you paul.
Biasing an amplifier into class A ie; setting the bias of the output devices to draw the maximum current needed for full desired output does not change the class of the amplifiers output stage, ie push-pull to single ended etc.
Unfortunetly this subject has been debated many times before, and if we allow it here, it will continue to poison an otherwise interesting and informative thread.
A...
Thank you Anthony, and yes, the chap who rebuilt my (last) valve amp said pretty much exactly the same thing to me a few years back which is what my understanding is based on. The thread has wandered slightly off course (as they do) so in the spirit of getting it back on course............................................ .................................................. ................................................T-minus 4 weeks before the Turnberrys arrive. I'd offer a bakeoff, but the thought of cramming in some lockwood majors and other suitably large Tannoys into my listening room might not be too practical:scratch:Quote:
Originally Posted by anthonyTD
Congrats Paul!
I read this from the yahoo groups site specifically regarding amps for westminsters but interesting i thought, I loved Tom's TD KT88 when he was here, i think its the nicest amp i have heard on my speakers.
I know there are many people who think that low power valve kit is the best
route to take with Tannoys but having now spent nearly 8 years with
Westminster Royals I would have to disagree.
I love valve kit and it can sound stunning and I have tried many different
valve amps including very low power SE's and much higher powered push pull
designs in my music room. They all have two thing in common. They all have a
very slight bias towards the treble end of the frequency spectrum. This in
my view tends to push the image too far out into the room which makes them a
bit 'in your face'. They are also all slightly shy in the bass and lack
control on very heavy low bass such as some 32' organ pedal notes. On some
music they are fabulous but on other large scale music they come up short.
My music philosophy is that a system should be able to cut the mustard on
all types of music and if it cannot do this then it is doing something
wrong. My listening tastes vary from chamber music through large scale
classical stuff to jazz and popular music.
One of the major strengths of the Westminster Royal is the way is produces
bass both quantity and quality, which is hardly surprising given that each
cabinet has a 15" bass unit firing down two 11' folded horns. They are only
6db at 18hz and to me it makes no sense to use an amplifier that is not
capable of fully exploiting this. After much experimentation I have opted to
use Meridian solid state amplification, specifically the GO2 dual mono
control unit and G57 power amplifier (200wpc) connected with DNM solid core
cables (Tannoys love solid core cable) terminated with WBT Nextgen RCA's and
WBT 0600 banana plugs on the LS cables. This combination works stunningly
well across all genres and can make the hairs on the back of my neck stand
on end. I have friends who are keen valve enthusiasts (mainly Audionote) who
are completely blown away by this combination.
I know that this view makes mine a siren voice and I now it is not what you
were expecting to hear, but the proof of the pudding is in the eating and
it really does work remarkably well
I'm with you there Simon as with my previous Horning Agathons, they responded far better with a muscular SS feeding them than with any valve amp. It takes a special valve amp to cleanly exploit deep bass with the proper speed, damping and transience. Cheaper route by far IMHO is to bolt on a big power amp. I am tempted to keep the Croft pre (it's a stunner) and I will try the power with the Tannoys, but would also like to try a few SS power amps with it including the 909 which I rate very highly.
I got a bit lost on this thread:doh: Who is the one talking bollocks about it not being possible for p/p amps to be class A? I have an Art Audio Quintet playing very sweetly in triode mode class A P/P as I type this. Also getting back to the question about which Tannoys.
The link to my article about the Lockwoods on Musicosis says it all. Again I have read criticism of the Majors based on the fact that their porting was devised, as with all the old Lockwood designs, before the Thiel/Small parameters and without their benefit. Quite right and that's why Lockwoods don't suffer from one note bass the way a lot of modern reflex designs do:)
I would always stick to my MGs for choice but, the new Majors with the HPDs did sound good:)
regards to all
BTW see the first of our reader comps on musicosis.co.uk
Hi Paul , may I ask what amps you heard with the agathons ? A friend who lives in Northampton also called Paul , used agathons for many years , I heard them with AN conquest monos and later a pair of Diavolo's each with border patrol psu's , he's since moved up the range , not sure of the name but the next one up anyway , they sounded fabulous with acoustic and classical music .Quote:
Originally Posted by Reffc
Hi ChrisQuote:
Originally Posted by chris@panteg
mine were the later Agathon Ultimates with twin 12 inch bass drivers around back :stalks: I used a Lumley PP40/ST40 combo to great effect (40 watts push pull 6L6GC valve amp). The next model up is the Eufrodites and mighty fine too although it does occupy a lot of space!
Hi Paul,Quote:
Originally Posted by PaulStewart
That would be Richard Dunn of Nene Valley Audio: a bollocks-talker, par excellence, who's dug himself into a very deep hole - and is still digging! :doh:
Nice one, mate. Extensive experience of listening to the above allows me to concur with your observations :)Quote:
The link to my article about the Lockwoods on Musicosis says it all. Again I have read criticism of the Majors based on the fact that their porting was devised, as with all the old Lockwood designs, before the Thiel/Small parameters and without their benefit. Quite right and that's why Lockwoods don't suffer from one note bass the way a lot of modern reflex designs do
I would always stick to my MGs for choice but, the new Majors with the HPDs did sound good
Marco.
The reason they don't suffer from "one note bass" as you call it is simply down to the very low driver Qts, this lets any power amp including low feedback valve amps control them very easily. The drivers have huge electro magnetic damping & as a result will sound clean.Quote:
Originally Posted by PaulStewart
Thiele/small parameters used in the right way & with drivers of a suitable Qts will also result in clean bass in a reflex enclosure. Just a shame that Dynaudio & many others tend to stuff high Qts drivers in reflex enclosures, for which they were patently not designed :lol:
You may well do a lot of listening, but if you don't understand the technical side of things you'll not see a correlation between driver parameters & bass performance.
Hi Mark,
Indeed! Any views on the claimed impossibility of push-pull valve amps to be pure Class A? We're looking to educate Mr Dunn, as clearly his technical understanding in this area is lacking :)Quote:
The reason they don't suffer from "one note bass" as you call it is simply down to the very low driver Qts, this lets any power amp including low feedback valve amps control them very easily. The drivers have huge electro magnetic damping & as a result will sound clean.
Marco.
I saw the locked thread earlier, so obviously I cannot comment :rfl:Quote:
Originally Posted by Marco
But yes, the man is a fool & totally wrong. While any single ended class A amp can be in theory 25% efficient (not allowing for any component losses), a push pull class A amp can in theory be 50% efficient, again not taking into account of component losses.
Where did this guy come from, the Jurassic? :eyebrows: If so I guess he stayed there :D
Fool...
This guy is mean't to be an audio expert :rfl:
Ok, so I know we didn't get along due to differences of opinion on certain aspects of amplifier protection, but this takes the biscuit.
I'm actually wondering if he gained his amplifier knowledge from a book sold by Tandy by a certain chap called (R A?) Penfold :scratch: His stuff is honestly about the same level at the end of the day.
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 ;)Quote:
Originally Posted by Reffc
Marco.
Lol... As an aside, Anthony's got an original GEC technical manual, from the 1950s, which clearly states the position in relation to KT88s, Class A and push-pull valve amplifiers, details of which he's going to post later ;)Quote:
Originally Posted by Reid Malenfant
Marco.
It's the same with solid state, bias to half the quiescent current needed & as one device gradually reduces in current, the opposite device increases.Quote:
Originally Posted by Marco
At some point cutoff will occur, though if the output stage is biased to full class A this will only occur if there is a drop in impedance.
Assuming the output stage is biased high enough, it'll operate in full class A.
Admittedly the sonic signature of push pull & single ended are different, but so is the dissipation :eyebrows:
While a single ended output stage will output mainly even order harmonics (which are musical), a push pull stage will tend to odd order harmonics. Though these aren't so musical, they'll be at a stupidly low level due to it being biased into class A...
Which is what it is all about :D
One big advantage of push pull is if it requires more current for the load it can be supplied, though it'll go into class B. A single ended stage will simply crap out (clip), as it can only supply the current it is set at on whichever side the current source is on.
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).
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! :doh:
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.
Told you.
His latest bollocks:
Getting a little flustered now, are we? Calm down, dear, and stop shouting!! Shouting doesn't make you any less wrong :DQuote:
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!!
Care to answer Mr Dunn's comments, Nick, or anyone else who's qualified?
Marco.
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!
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.
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,Quote:
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!!
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.
Hi lewisQuote:
Originally Posted by 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!
Hi Marco,Quote:
Originally Posted by 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!
:)Quote:
Originally Posted by lurcher
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...
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 ;)Quote:
Originally Posted by realysm42