Nige, it could be so much more than that.
Suppose you arranged two of them in a bridged configuration. I reckon each could effectively deliver up to 18V peak, which is some 40 Watts into 4 ohms. Theoretically, in a bridged configuration, you should have twice the voltage and twice the current, or 4 times the power - this is rarely quite so, but say 3 times the power should be real enough. That's still say 120 W into 4 Ohms.
At that voltage, the BD 249/250 C can deliver way over 10 Amps no problemo, using low voltage high capacity capacitors, say 22,000 uF/40V.
You might consider running it off higher voltages, say +/- 25V, and use zener diodes to regulate to say +/- 22V for the op amp, but compensating for voltage drops across the output stage.
And so forth - the point being that many opportunities arise, some of them being very interesting.
Suppose you arranged two of them in a bridged configuration. I reckon each could effectively deliver up to 18V peak, which is some 40 Watts into 4 ohms. Theoretically, in a bridged configuration, you should have twice the voltage and twice the current, or 4 times the power - this is rarely quite so, but say 3 times the power should be real enough. That's still say 120 W into 4 Ohms.
At that voltage, the BD 249/250 C can deliver way over 10 Amps no problemo, using low voltage high capacity capacitors, say 22,000 uF/40V.
You might consider running it off higher voltages, say +/- 25V, and use zener diodes to regulate to say +/- 22V for the op amp, but compensating for voltage drops across the output stage.
And so forth - the point being that many opportunities arise, some of them being very interesting.
How to use what, the Ferrograph analyzer, or the bridged amp?
As for 1 Ohm, given proper design, that should not be too much of a problem, although beside our old buddy Wayne, I am not aware of anyone else being a Member of the Sub 1 Ohm League. Normally, bridged amps have problems with very low impedance loads, I am told, but in this case, given the low voltage rails and the prodigious currents the BD pair can handle with safety, this may well not apply to you.
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I always say I am too lazy to do simulations . Usually I rush out to my shed and solder up a few things . With this one I would love Dvv to see what he comes up with . Even 7 Vrms into 1 R would be interesting . I think I would follow the advice of Douglas Self and use 0R1 emitter resistors . I would start with 2N3055/2955 and BD139/140 . From my tests the complimentary feedback pair is the only option . Ideally 3 A of standing current would be used . That would be about 200 W of heat to get rid of . In bridged mode isn't worth talking about .
Casting aside that option a conversational class AB might be interesting . I would base it on the Quad 303 . I would use the 2N3055 . The standing current is 10 mA , we can be generous and use 20 sets in bridge . 100 mA and will only be 2W of waste heat . I will now say something which is seldom said . Regardless of transistor type or any other consideration this circuit has seldom been beaten for how easily it works . It would laugh at 1 R . I suspect even better to use 2N3055/2955 are driver ( 303 is a triple ) . Gogny made an amp like this in 1967 with just 2 x 2N3055 diving the load , it was 50 W into 0.8R ( 0R8 ) . +/-18 V rails and 10A fuses as emitter resistors . This would be a loop feedabck amp . It's crossover distortion is very low and predictable . I would expect problems if " better " transistor were used .
Off to the garage now and I am late , forgive any typo's .
Casting aside that option a conversational class AB might be interesting . I would base it on the Quad 303 . I would use the 2N3055 . The standing current is 10 mA , we can be generous and use 20 sets in bridge . 100 mA and will only be 2W of waste heat . I will now say something which is seldom said . Regardless of transistor type or any other consideration this circuit has seldom been beaten for how easily it works . It would laugh at 1 R . I suspect even better to use 2N3055/2955 are driver ( 303 is a triple ) . Gogny made an amp like this in 1967 with just 2 x 2N3055 diving the load , it was 50 W into 0.8R ( 0R8 ) . +/-18 V rails and 10A fuses as emitter resistors . This would be a loop feedabck amp . It's crossover distortion is very low and predictable . I would expect problems if " better " transistor were used .
Off to the garage now and I am late , forgive any typo's .
Of course, others among us might wonder why does Nige always insist on the one output stage known to be difficult to get right without oscillating, when he could have used a nice triple Darlington emiiter follower configuration, well known for proving the best possible control of the load an amp will do even with reasonably low global NFB figures, and, MOST important, offers the lowest output impedance. This alone would suggest its use in a balanced cofiguration as the most recommended, given that whatever you have will halve in a balaced setup.
Nige, it's better to think it all through at least one scenario before you're off to solder somethig.
Nige, it's better to think it all through at least one scenario before you're off to solder somethig.
Cfbp like most old wives tales is exactly that . Op-amps oscillating when used with boosters is common regardless of output stage . OPA 604 seems very obliging . The 303 circuit is very stable . Another old wives tale was the 303 has many tweaks to get it stable , I never saw where they were . It has output tipples which I feel have never been creditor with how they completely they eliminate most of the problems . Not least the use of all NPN outputs which makes for rugged designs . BTW , The bottom half of Quasi comp is Cfbp . People dream up all sorts of reason not to use this proven arrangement , old fashioned is not valid I feel .
Because it is better ? This debate raged in Wireless World for years . Reluctantly it was agreed that an NPN with 100 % local negative feedback becomes a PNP to all intents and purposes . The addition of a cheap diode solves most of the asymmetry . Even to this day the way a PNP works is more difficult in terms of transition speed and durability . The fact the PNP's look so good is testament to the hard work done. Some say all NPN sound more alive and punchy . In the 303 and Crimson amps they show how good it can be . The Crimson was especially good .
Frankly, I don't like anything at all at 100%, such absolute values always scare me. They never seem quite true to me.
I remember hearing several Crimson amps locally, they were quite fashonable in their time. I do not recall being sonically bowled over, or even accepting them at anything special, but I do remember that their reliability as kits was quite outstanding.
They seem to be a bit of a fetish these days.
Nige, you said "a battle raged in the Wireless World)..."
THAT'S the one thing I never did and never will understand regarding audio. For one reason or another, everybody has to be very partisan about it - the RIGHT is this, and no other way can ever be THE right way.
I've never seen that as anything but petty ego problems. I know there are at least several, and more typically many ways to achieve the same result. Sure I like my way best, else I wouldn't have adopted it as mine, but someone alse might have different ideas, and will certainly have a different hearing, so for him, another approach may be better sounding.
The worst of it that very soon you realize that what someone alse thinks is bad is so merely because he's used to another approach and knows it well, while he's not intimate with your method. Insecurity, perhaps ignorance and certauinly inflated egos.
Hardly doing us all a favor in terms of audio advancement.
THAT'S the one thing I never did and never will understand regarding audio. For one reason or another, everybody has to be very partisan about it - the RIGHT is this, and no other way can ever be THE right way.
I've never seen that as anything but petty ego problems. I know there are at least several, and more typically many ways to achieve the same result. Sure I like my way best, else I wouldn't have adopted it as mine, but someone alse might have different ideas, and will certainly have a different hearing, so for him, another approach may be better sounding.
The worst of it that very soon you realize that what someone alse thinks is bad is so merely because he's used to another approach and knows it well, while he's not intimate with your method. Insecurity, perhaps ignorance and certauinly inflated egos.
Hardly doing us all a favor in terms of audio advancement.
Talking off an all NPN solution . In was forced to build an all LM317 +/- PSU ( +/-13.6 V ) . That is to take 25 V down to 13.6 and then join + to minus as if batteries . After a few problems I have to say it works rather well . The -ve very marginally worse ( 2dB ) . The noise about - 108 dB reference 13.6 V . This was preceded by 250 mA CCS using 2N2687 . This was all about using what I had to hand , the transistor mounted in the wood and used as binding posts ( LED + 3K9 + 2R = 250 mA into short cct load ) . There is a 20R series resistor between CCS and LM317 . This is for maintenance charging of lead acid batteries . To be honest I didn't do any calculations apart from the basics . It seems about right . It is almost impossible to tell when charging or not ( sound ) . A good sign for what is a fancy battery charger . Although LM 337 would have been nice I feel this design is not to be dismissed . Spectrum analyzer found nothing bad at any frequency .
I would assert that much of what is said about amplifiers addresses the wrong problems . Everyone takes about 30MHz transistors as if they barely meet the grade . Then they try to get a single pair to drive a speaker that touched 8 ohms briefly and then traveled down to 3 ohms .
This week I threw together a power supply for a friend . I used up some 2N2687's as said previously . Wanting to price them favourably I found 2N6051 . You know what they are not bad . If the bridged op amp circuit was put together using 2N6051/58 with 4 devices at 0.7A standing current we would have the basis of a good amp . As very little switching would occur my feeling is 4MHz is ten times faster than any real need . The biasing would not be very complicated as it is well into class A . I would then have 8 more devices in switchable class B/C ( simple feed-foward ) . Nasty class G is said to sound OK . B/C has to be better ? My hunch is often this amp would sail past amplifiers that claim the world . It would need tweaking naturally .
An analogy is a motorcar trying to be a locomotive . It all looks OK on paper . In reality it is not .This amp would be a locomotive . My hunch is it would sparkle also . If my other hunch is right it would in single ended still serve as a better sounding preamp . OPA 604 being the op amp .
This week I threw together a power supply for a friend . I used up some 2N2687's as said previously . Wanting to price them favourably I found 2N6051 . You know what they are not bad . If the bridged op amp circuit was put together using 2N6051/58 with 4 devices at 0.7A standing current we would have the basis of a good amp . As very little switching would occur my feeling is 4MHz is ten times faster than any real need . The biasing would not be very complicated as it is well into class A . I would then have 8 more devices in switchable class B/C ( simple feed-foward ) . Nasty class G is said to sound OK . B/C has to be better ? My hunch is often this amp would sail past amplifiers that claim the world . It would need tweaking naturally .
An analogy is a motorcar trying to be a locomotive . It all looks OK on paper . In reality it is not .This amp would be a locomotive . My hunch is it would sparkle also . If my other hunch is right it would in single ended still serve as a better sounding preamp . OPA 604 being the op amp .
Yeah, so what else is new? Remember the slew rate race in the late 70-ies? Or the tone control range in the mid 70ies? Or the who's-gonna-have-more-channels race in the 90ies?
There is always some dilly-dally to make people take their minds off the real problems, easly explained, almost always wrong, but great stuff for friends to argue endlessly about. And many woodwork scientist mercenaries to make their name, fame and fortune.
The point is this . Most amplifiers seem to me to be like a 2000 cc V8 with perhaps 15 000 rpm , the type where the tick over starts at 5000 rpm ( we seem to be heading that way ) . Lets say 500 BHP . Far better a 6000 CC engine red lined at 6000 rpm and tick over at 400 . Same 500 BHP . The difference being so relaxed and rewarding .
The analogy being the peak revs is not especially what we want . It is grunt . My amp I described probably doesn't need emitter resistors as the dumpers run in Class B/C . The prime amp does have emitter resistors and could have better devices there perhaps ? My instinct is to say unlikely it needs them . The point is if the switching comes in above 5V rms it should be fine sonically and will be robust . The Quad 405 probably came in too early . Into darlington's perhaps 16 V rms is possible from bridged OPA604 ? > 250 W @ 1 R . If the darlington's were booted to simple triples it might be even better . easy to drive and coming in later . It might be interesting to use double feed-forward if so . Darlington's usually have feed forward to help improve switching speeds . It also smooths the transition .
This section is about measured verse subjective . I would assert that an amp with grunt and safety always pleases the ear . As my friend John says , good amps happily tick away feeding 1000 W into sub woofers all day long . Power meters reading 1000 , protection lights off . Sub woofers dying , amplifier not .
Off to Malta for a week now .
The analogy being the peak revs is not especially what we want . It is grunt . My amp I described probably doesn't need emitter resistors as the dumpers run in Class B/C . The prime amp does have emitter resistors and could have better devices there perhaps ? My instinct is to say unlikely it needs them . The point is if the switching comes in above 5V rms it should be fine sonically and will be robust . The Quad 405 probably came in too early . Into darlington's perhaps 16 V rms is possible from bridged OPA604 ? > 250 W @ 1 R . If the darlington's were booted to simple triples it might be even better . easy to drive and coming in later . It might be interesting to use double feed-forward if so . Darlington's usually have feed forward to help improve switching speeds . It also smooths the transition .
This section is about measured verse subjective . I would assert that an amp with grunt and safety always pleases the ear . As my friend John says , good amps happily tick away feeding 1000 W into sub woofers all day long . Power meters reading 1000 , protection lights off . Sub woofers dying , amplifier not .
Off to Malta for a week now .
The small engine/high rev vs big engine/low rev analogy doesn't quite stand here, Nige. These days, for example you can have an engine efficiency of over 130 hp/litre with a rather mundane turbo charger.
With amps, and you should know this, simply adding output devices to give it grunt is meaningful only up to a point, after which it turns to nonsense. I experimented a lot with that and in my case, that of preferring low global NFB, adding the fifth pair brings me no addtional obvious gain, even if it does raise it current capabilites.
I think it's much more a question of what your design goals are. If you look at your goals as theoretically pure, and ask your amp to behave as a true voltage source right up to its supply rail limit, that's one thing that makes you go for a lot of material and design work, most of which is probably pointless.
If, on the other hand, you recognize the fact that even the worst of recorded material offered today does have at least a minimal dynamic range, then you could be happy with a true voltage source performance only up to one half of the nominal power, and provide for the rest with biggish supply capacitors. In which case you can dedicate more time and effort to the WHOLE signal path, rather than concentrating on the sheer, brute muscle of the output stage.
When you study the schematics of the industrial fare, you'll notice that their schematics on the whole are not half bad. You can find more than a few realistically generously made amps, and where they will differ from better fare is in the details (where the Devil lives) and of course, the overall approach to the power supply. On the whole, they use about one half of I'd use, but of course, the other approach would cost more and mess up their marketing ploy. You and I basically look at one model which would suit us best, but they have to have a line of models, typically three or four, and very possibly another up market line with also three of four models. They have to structure them very carefully, so as to have them perform as expected, but also with nicely spread along "features".
Looking at just myself, I have come to the conclusion that three pairs of series/parallel MJL 3281/1302 sould be generously above what I might ever really need. If HK 665 can deliver over 450 Watts into 2 Ohms (on impulses) with two such pairs, I should be fine with 50% more. This will probably greatly dissapoint Wayne, but it's a hard reality fact that Wayne has requirements suchas I have never before run up against. How many pairs of output devices, how big heat sinks would I need to get it to reliably run into 1 Ohm loads at high power levels for any period of time? How much should I have to pay for that which I will never ever use just so I can say I have the capability?
My feeling is that Wayne needs an amp designed from the outset for his specific needs and, I must add, wallet. Lower rail voltages, more power devices, greater heat sinks, he needs a hell of a lot of current.
One approach can never suit all.
With amps, and you should know this, simply adding output devices to give it grunt is meaningful only up to a point, after which it turns to nonsense. I experimented a lot with that and in my case, that of preferring low global NFB, adding the fifth pair brings me no addtional obvious gain, even if it does raise it current capabilites.
I think it's much more a question of what your design goals are. If you look at your goals as theoretically pure, and ask your amp to behave as a true voltage source right up to its supply rail limit, that's one thing that makes you go for a lot of material and design work, most of which is probably pointless.
If, on the other hand, you recognize the fact that even the worst of recorded material offered today does have at least a minimal dynamic range, then you could be happy with a true voltage source performance only up to one half of the nominal power, and provide for the rest with biggish supply capacitors. In which case you can dedicate more time and effort to the WHOLE signal path, rather than concentrating on the sheer, brute muscle of the output stage.
When you study the schematics of the industrial fare, you'll notice that their schematics on the whole are not half bad. You can find more than a few realistically generously made amps, and where they will differ from better fare is in the details (where the Devil lives) and of course, the overall approach to the power supply. On the whole, they use about one half of I'd use, but of course, the other approach would cost more and mess up their marketing ploy. You and I basically look at one model which would suit us best, but they have to have a line of models, typically three or four, and very possibly another up market line with also three of four models. They have to structure them very carefully, so as to have them perform as expected, but also with nicely spread along "features".
Looking at just myself, I have come to the conclusion that three pairs of series/parallel MJL 3281/1302 sould be generously above what I might ever really need. If HK 665 can deliver over 450 Watts into 2 Ohms (on impulses) with two such pairs, I should be fine with 50% more. This will probably greatly dissapoint Wayne, but it's a hard reality fact that Wayne has requirements suchas I have never before run up against. How many pairs of output devices, how big heat sinks would I need to get it to reliably run into 1 Ohm loads at high power levels for any period of time? How much should I have to pay for that which I will never ever use just so I can say I have the capability?
My feeling is that Wayne needs an amp designed from the outset for his specific needs and, I must add, wallet. Lower rail voltages, more power devices, greater heat sinks, he needs a hell of a lot of current.
One approach can never suit all.
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DVV, your writing is first rate as well as your english,your knowledge of power amp deep and profound.I even use some of your articles as a reference for power supply calculation.
I think that we, forum members , will be interested to see photos of some of your power amp built according to your electronic design.
I think that we, forum members , will be interested to see photos of some of your power amp built according to your electronic design.
Ah pillo ! You have them hidden !
I also want to see !
If you both leave the analogies to Formula One, I do not get offended...
Hi everyone , Just off to Malta this minute and the snow isn't too bad . Dvv I am going to build this thing when I get back . I have a big heat sink from A PA friend with many T03 holes .
The F1 analogy is correct . I live about 6 kM from what was Renault now Lotus . I have seen and touched the insides of that engine . The engineer for Mercedes lives about 500 metres away ( never met him ) .
The F1 analogy is correct . I live about 6 kM from what was Renault now Lotus . I have seen and touched the insides of that engine . The engineer for Mercedes lives about 500 metres away ( never met him ) .
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