BTW. Quad 405 was less than 300 VA as the transformer ( I was told ) for 2 x 100 watts rms 8 R. On paper that is fine as the creast factor should be 1/6 or 1/3 if Techno music ( Class D guys says 1/10, No way ) . Being very unfair lets say 50 % efficient ( 67% more likely if 220 V). That is 2/3 of 300 VA = 200 watts. Yes it is correct. My design is conservative as I have 90 watts x 2 using 500 VA. The 405 was often said to be very poor compared with the hype and the 303 vastly better. Correct. Some say the 405 had awful current limiting. It was very reliable. 606 was far better. If you look at 606 there is nothing in it except a big transformer. Sadly Quad were not well liked by then and were too late in the game to be noticed. They were very good at winning technical debates. Alas that won them very few of the friends you need. Customers that is. Lets be clear they were very sucessful. With some better understanding of people that might have been 3 times more sold.
Good to hear there's a plan B, Nige. I REALLY was worried you'd fall short of what I consider to be reasonable power for home use (where reasonable means problem free). As I gather from your latest post, that to you is a bit like my Otala/Lohstroh Mk.2 is to me, paying off an old debt created by my own stupidity. Remember, I sold off mine for no good reason at all.
The reasonable limit for PSU voltages is, I think, +/-56V or so for the current stages, as this keeps you in the still reasonably priced 63V capacitor class. Yet it's still high enough to allow transient ("music") power of about 180/360W into 8/4 Ohms, and there aren't many speakers which can swallow that and live through it. I would advice 3 pairs of Motorola 250W devices per side, quite enough for even evil 3 Ohm loads. I won't have any problems with less, but then I have an exceptionally well behaved speaker load, but unfortunately not everyone is as lucky.
My initial analysis of a classic fully complementary all BJT amp, built around 2SC2240/2SA970, 2SC3503/2SA1382 for VAS and predrivers, MJE 15030/15051 for drivers indicates that I can have an open loop bandwidth of just above 70 kHz, global NFB od 20 dB (I don't need more), and THD of less than 0.04% 20...20.000 Hz into 4 Ohms, with a slew rate of better than 100 v/uS. I believe that with some development work, it could really come on song. So much so that I've bought the required heat sinks already. I already have 26+26 MJ 21195/21196.
The point is, if you like, if you think it's something to worth doing, we can do it together. No obligation, mind you, if memory serves you are not a big fan of all complementary designs. But, all in good time. Do what you feel you ust first.
The reasonable limit for PSU voltages is, I think, +/-56V or so for the current stages, as this keeps you in the still reasonably priced 63V capacitor class. Yet it's still high enough to allow transient ("music") power of about 180/360W into 8/4 Ohms, and there aren't many speakers which can swallow that and live through it. I would advice 3 pairs of Motorola 250W devices per side, quite enough for even evil 3 Ohm loads. I won't have any problems with less, but then I have an exceptionally well behaved speaker load, but unfortunately not everyone is as lucky.
My initial analysis of a classic fully complementary all BJT amp, built around 2SC2240/2SA970, 2SC3503/2SA1382 for VAS and predrivers, MJE 15030/15051 for drivers indicates that I can have an open loop bandwidth of just above 70 kHz, global NFB od 20 dB (I don't need more), and THD of less than 0.04% 20...20.000 Hz into 4 Ohms, with a slew rate of better than 100 v/uS. I believe that with some development work, it could really come on song. So much so that I've bought the required heat sinks already. I already have 26+26 MJ 21195/21196.
The point is, if you like, if you think it's something to worth doing, we can do it together. No obligation, mind you, if memory serves you are not a big fan of all complementary designs. But, all in good time. Do what you feel you ust first.
Nigel,
My understanding is that you are discussing your proposed version of the Quad 303 and that it will deliver 90 watts times two using a 25-0-25 a.c. secondaries voltage transformer rated at 500 V.A. It is important to know what is your intended speaker load. While you have mentioned it in a post in previous pages it is a job of work to know find this out.
In this post your discussion starts with the Quad 405 and moves almost seamlessly onto" my project" without introduction, Class D, and the Quad 606 etc.
Nigel,
I remember one of the "new age" Hi-Fi magazines included a 405 in an amplifier group test and slated it with a comment that it "squawked it's way to 100 watts". That was in the 70's when there were a lot of brash people making self promoting noises about themselves. Pretty much in tune with the way popular music was heading at the time.
When proper tests were done (Stan Curtis - HiFi Choice 1982) it was found that the 405 outputs met the specification of 100 watts into 8R two channels driven; 87-95 watts depending on frequency singly into 4R but only 56 watts singly into 2R.
Stan Curtis observed the 405 needed to be matched to easy loudspeaker loads and it gave good results with the right speaker. It was not suited for such as the Linn Isobarik. The Gale 401 from that era would be another.
Forgetting about the limiter the Current Dumping aspect of the 405 aroused a lot of interest in Wireless World when it was introduced. It did away with the finicky business of having to set the output stage quiescent current.
The technical discussions in the last respect could not be regarded as hype, to my mind that was more likely to be seen in advertising and it is something common to selling any product in any market from disposable nappies and toilet paper to luxury motor cars or whatever.
In my experience, Quad 405 always struggled with more difficult loads, such as AR speakers. It could not meet its 8R output voltage spec into anything less than 8R. That to me is a catastrophic failure, because I believe 8R loads do not really exist outside the test labs. Another notorious model from that time was Yamaha's M-1000 monitor, a truly hard load to drive.
Thus, the Quad failed in its most basic reaquirement, to act as a true voltage source, at least up to a point. Indeed, some way better built and more expensive amps failed the test as well, such as the Studer/reVox A740 amp, but it did deliver 100/175W into 8/4 Ohms. I think it worthwhile to mention at this point that amps with triple output stages (predriver-driver-output stage) fared best in this respect, and I include such designs as the Lecson cyliner amp desinged by Bob Stuart, which was quite advanced for its day and sounds good even today. 17 kHz open loop bandwidth, relatively low overall NFB factor, well dimensioned stages, yet simple in design, fully complementary (not often seen from UK).
There are documents floating around the Internet clearly stating that a modern power amplifier should be able to cope with 2 Ohm loads, if not RMS, then at least in short term peaks. That current has to come from somewhere, which is why I advocate multiple output pairs, fully aware of the problem of device matching - BUT, there are techniques for that as well.
This is why I suggest Nige uses two pairs of output devices even in his smaller amp, something has to kick all that current. The bugbear of the designer is that he never knows what's the load to be driven like, what it is today and what it might be tomorrow, so I think it wise to assume the worst case, in full knowledge that this will cost more money. Better to invest additional 10% of the price than compromise the initial 90% of it.
Thus, the Quad failed in its most basic reaquirement, to act as a true voltage source, at least up to a point. Indeed, some way better built and more expensive amps failed the test as well, such as the Studer/reVox A740 amp, but it did deliver 100/175W into 8/4 Ohms. I think it worthwhile to mention at this point that amps with triple output stages (predriver-driver-output stage) fared best in this respect, and I include such designs as the Lecson cyliner amp desinged by Bob Stuart, which was quite advanced for its day and sounds good even today. 17 kHz open loop bandwidth, relatively low overall NFB factor, well dimensioned stages, yet simple in design, fully complementary (not often seen from UK).
There are documents floating around the Internet clearly stating that a modern power amplifier should be able to cope with 2 Ohm loads, if not RMS, then at least in short term peaks. That current has to come from somewhere, which is why I advocate multiple output pairs, fully aware of the problem of device matching - BUT, there are techniques for that as well.
This is why I suggest Nige uses two pairs of output devices even in his smaller amp, something has to kick all that current. The bugbear of the designer is that he never knows what's the load to be driven like, what it is today and what it might be tomorrow, so I think it wise to assume the worst case, in full knowledge that this will cost more money. Better to invest additional 10% of the price than compromise the initial 90% of it.
So you have a whopper of a trafo. Fine, that's an excellent starting point. But using just one pair of output devices is compromising that insofar that your output stage may not be able to pass along what it is offered by the PSU. Why compromise the already spent 40 pounds by "saving" another 4-5 pounds for a second pair? Not to even mention that a second pair would naturally improve your damping factor and your distortion results due to sharing of the workload. It's just a bit more of extra work, after all is said and done.
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That's very much correct. The maths look about right and offer more than the commersial Quad 303 version. 405 and 606 examples of to me a failiure and a sucess from the company boss. The sucess also failed as it came too late. 405 and 306 are penny pinched. The class D quote was to say I don't agree with their crest factors. My ears say the Hypex needs exactly as large a PSU as a Quad. If not bass speed suffers. However it needs even less heat sink than maths suggest. Perhaps in the latter the crest factor is valid. I really liked the Hypex. As I was determined not to, that's not bad. Open and slighly glassy. The Hypex should be dull as it rolls of before 50 kHz. It isn't because I guess the internal parts are fast. I have a feeling if my speakers were used and 303 verese Hypex people would get it wrong. If anything the 303 sounds more alive. In truth they are very similar. No nonesense about filtering etcetera please. Most filtered amps sound awful. That's because they have defects. These two don't.
The load I use is 4 ohms pure resistive. I will measure it sometime. It will have a few mH. My VAS is 2N5551 at 3.5 mA . If I ask it to do 110V DC fixed by the regulator it is just inside what is possible. The BC109 ( 30 V ) has been uprated to BC337-40 if wanting to explore the limits. MJ15015 will take the voltage also. More so as Quad ran 60 V 3055's at 67V . On-semi list 3055 on the same page as MJ15015. I suspect the fall outs are graded 3055 ? The MJ 15015 is vastly better so if one could be sure an excellent 3055. If I was to push the voltage MJ15015 Cob improves. It's SOA the opposite. I was very surprised to see Cob stated. I can see why transitor people get confused by MOS FET's . What they fail to see is the MOS FET requires much less current even though seemingly a worse load. Effectively a MOS FET is like a tripple in how little driving it needs. 3.5 mA will easilly drive a FET of the better type ( Exicon ) . If you read Quad's technical data it says consider the output tripple they use as a super NPN PNP pair. In 1965 when I guess they started to design 303 this must have seemed journies end. My hunch is they were right. Even today NPN are slightly the better output device ( PNP as input ). My conjecture is love of the all NPN output might be that it's defects are pleasent. The NPN PNP we now use might have a smalll blandness about it. This is like an overly controlled person. Great in a court of law, not so great down the pub.
In history Ford bolted together two 4 in line engines to make the Flat head V8. From very modest parts a very good engine. Someone said in a modern chassis it still will impresss. It will drink fuel more than modern eninges. The balance factor of the in line 4 is moderately good, as is the V . However there are two main types of 90 degree V8 ( below ). As with amplifiers these balancing of forces have plus and minus arguements. The sound of the American V8 is possibly now regardless of advantage the sound it " must "make. Harley should do a 55 degree 8 for cars. The sound would be interesting. The 55 V is a disaster. It is the better type to replace a single in a 1920's design. It is now required it should be that. Triumph made a 55 paralell twin that was not to be sold outside of the USA as far as I know. That is so the sound was like the Harley. How dreadful is that? It had a balance shaft to compensate for this engineering abomination. Twins of the purests type are 180 or 360 types. Both are sections of a 4 split in half. Personally I prefer 360 with balance shaft. The in line 8 is a monster, rather nice all the same. In line 6 a great design. In line 3 and 4. I think I prefer 4. My sample of that is too small when a 3. Interesting as on paper 3 looks better. 330 cc was a 1920's Citroen calculation as to best piston displacement. Seems to be true today.
V8 engine - Wikipedia, the free encyclopedia
In British libraries Marine Diesel engines is right next to electronics in section 621. I have found reading these books very interesting. Diesel engines make the vibration worse as 1 in 4 sine wave peaks is badly squared off. Even when a V engine the harmonics are very large. To read petrol heads you would think the layout of the engine made the vibration. No, it is the fuel.
My 303 clone is not a V8. It might be a flat 4. If I change the drivers a flat 6 looks very possible. That would suit 2R resistive or 4R typical reactive. The Quad 303 16 R reactive if so.
Jay, if there is such a thing as the main gate key, for a loudspeaker that would be its crossover. When developig my own speakers, the friend I was doing it with and I spent a solid 6 month period trying to get the crossover just right. It's a hell of a job, you adjust one thing and another goes crazy. However, that crossover will make the amp's job hard or harder or easy or easier, so the time and trouble are well worth it. I believe that 99% of all loudspeakers today do not have proper crossovers. People pay far too much attention to details like which cap to use, using which technology, and so forth that they lose sight of the whole. A well designed crossover will do wonders for any speaker, and the better components you use the better sound you'll get. If the crossover does not marry these components well to the amp, all is lost. Trust me on this.
Unless you stretched your amp too far, it should not have blown in any case, may have had a funny sound, but no burnouts. The good thing I can say about all my output stages is that while I am prhaps too generous with them, I have never once had any of them burn out driving anything calles a speaker, and in fact had to try very hard to make them burn out. I always do that, the fate of the first sample is to always burn out, something which I must do to learn where the ultimate borderline is, perhaps correct something, even rethink something if need be.
Unless you stretched your amp too far, it should not have blown in any case, may have had a funny sound, but no burnouts. The good thing I can say about all my output stages is that while I am prhaps too generous with them, I have never once had any of them burn out driving anything calles a speaker, and in fact had to try very hard to make them burn out. I always do that, the fate of the first sample is to always burn out, something which I must do to learn where the ultimate borderline is, perhaps correct something, even rethink something if need be.
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Do that and I promise to call you Dr Ferdinand.Dejan. I suspect within a year this will be pulled apart. That is assuming I can get it to fly. The Quad is horribly complex in some ways.
As I watched some dreadful 1976 film it came to me. My 0 - 55 0 - 55 2000 VA will give about 90 VDC if at 243V if used 0 - 55. I also have 1000 VA that would be better. These are best in the world type designs. E & I types that hardly hum and do not bust fuses. They are I guess 100 lbs for the 2000 VA. I had asked Sowter, they give up at 600VA. These are to this quality. As luck would have it I didn't have to pay for them. I would hate to think how much they might cost. Someday they guy who asked me to do it might remember.
The film was Don't look now. I swear Donald Sutherland said about on the Internet! At college we were shown in 1974 how we could connect with another large computer somewhere . Cambridge I think ? No one said Internet although the concept was hinted at.
I could not buy from Rapid electronics a 3 pF cap. So I bought a 2 to 5 pF COG trimer with 5 mm spacing. It costs 20 pence. Did the celestial engineer make me do that? Serriosly, will be fun to see if it makes a difference. John Ellis is not my friend John. I suspect they would get on very well. J E used 2 pF. J D ( Deans ) is responsible for many LP's you own as he was at SSL mixing desks. J D didn't think them the best. They were the best TV mixing desk. He also worked with Brian Ferry and other 80's people.Punk Rock mostly. If you are near Oxfordshire and want a first class sound man with more microphones than is possible John is very affordable and a very nice man. He is slightly above PHD in electronics so a useful friend ( that is, he is time served also ). Not quite as harsh as DF 96, close. Both of them are OK with me on that as it saves me much effort not to think that deeply. John's famous quote about his now work is " don't ask as I would have to kill you ". As far as I can tell his sound business is that the money it earns buys new things. Hence the 007 day job.
As I watched some dreadful 1976 film it came to me. My 0 - 55 0 - 55 2000 VA will give about 90 VDC if at 243V if used 0 - 55. I also have 1000 VA that would be better. These are best in the world type designs. E & I types that hardly hum and do not bust fuses. They are I guess 100 lbs for the 2000 VA. I had asked Sowter, they give up at 600VA. These are to this quality. As luck would have it I didn't have to pay for them. I would hate to think how much they might cost. Someday they guy who asked me to do it might remember.
The film was Don't look now. I swear Donald Sutherland said about on the Internet! At college we were shown in 1974 how we could connect with another large computer somewhere . Cambridge I think ? No one said Internet although the concept was hinted at.
I could not buy from Rapid electronics a 3 pF cap. So I bought a 2 to 5 pF COG trimer with 5 mm spacing. It costs 20 pence. Did the celestial engineer make me do that? Serriosly, will be fun to see if it makes a difference. John Ellis is not my friend John. I suspect they would get on very well. J E used 2 pF. J D ( Deans ) is responsible for many LP's you own as he was at SSL mixing desks. J D didn't think them the best. They were the best TV mixing desk. He also worked with Brian Ferry and other 80's people.Punk Rock mostly. If you are near Oxfordshire and want a first class sound man with more microphones than is possible John is very affordable and a very nice man. He is slightly above PHD in electronics so a useful friend ( that is, he is time served also ). Not quite as harsh as DF 96, close. Both of them are OK with me on that as it saves me much effort not to think that deeply. John's famous quote about his now work is " don't ask as I would have to kill you ". As far as I can tell his sound business is that the money it earns buys new things. Hence the 007 day job.
Very right. I love the Fiat 124 sports. In engineering we must not convert Fiat into Lada. The Lancia Beta had a lovely twin cam engine which is said to be loosely speaking the 124 unit except the cam. The Lada Niva can show even Land Rover how to do things in first principles engineering. The Beta would rust inside two years in the UK. So you put the Beta engine in the Niva. The fact Lada corrupted a Fiat makes it easier. You could buy a Beta for <£200 that was less than 100 000 kM. Fantastic car.
Forgive using engine mass and amplifer internals as analogy. The sound is the thing. I do defeat my own arguement as to sell a sound is hardly the worst thing we can do ? Cosworth and Norton did an engine based on the DFV. Sadly it was underfunded. Loricarft Audio ( Garrard 501 ) is linked to Cosworth as the engineer was also with Keith Duckworth in Marlborough. Funny small world! I never met Keith, could have done if I wanted to I guess. Dave Garman was the enginneer. Still works for him I think or his brother Brian? Aircrafts these days.
Just one thing important to me. My Quad 33 303 FM3 was given to me by my old boss Julian Mason. He was very distressed to take it in part excahange. The lady's husband had died and she could not stand to own it. She had an Arcam system to replace it. Julian assumed I would want the Quad more than I did. Knowing it was special to someone it is intended to go to the grave with me. I suspect my brother did work on it as it looks like his work inside. Thus as he is no longer with us it is special to me.
My understanding of hi fi was always enough to do repair work. Gradually I understood the really difficult things. I now look for windows of the possible. As something to pass the time I asked could the Quad really sound as bad as it usually does and spec so well? The sound can be excellent if it is adapted to work correctly. One should try to meet it half way and not ask the impossible. Recently I have started to feel it is better than most things. The one doubt is the terrible current limit. Even so it is better sounding than it should be. That is because it mimics valve clipping. Thus to > double the current seems worth trying. I have a much greater limit if I want as 16 amps if only 33.5 V to each device is about possible. I have no need so won't. If I did a reactive 4 ohms load is possible with full power.
The Quad is symbolic of all learning. It is not about right or wrong. It is best use of things that matters. People also. The best companies make the best use of their people. If so everyone is a little boss.
My understanding of hi fi was always enough to do repair work. Gradually I understood the really difficult things. I now look for windows of the possible. As something to pass the time I asked could the Quad really sound as bad as it usually does and spec so well? The sound can be excellent if it is adapted to work correctly. One should try to meet it half way and not ask the impossible. Recently I have started to feel it is better than most things. The one doubt is the terrible current limit. Even so it is better sounding than it should be. That is because it mimics valve clipping. Thus to > double the current seems worth trying. I have a much greater limit if I want as 16 amps if only 33.5 V to each device is about possible. I have no need so won't. If I did a reactive 4 ohms load is possible with full power.
The Quad is symbolic of all learning. It is not about right or wrong. It is best use of things that matters. People also. The best companies make the best use of their people. If so everyone is a little boss.
I have read the notion that the modern amplifier should be about to cope with 2 ohm loads but see that as a matter of needing a four wheel drive vehicle such as a Land Rover which you are never going to drive off road and use for the specific purpose of going to the supermarket or dropping off the children at school.
It is a classic "mine is bigger than yours" scenario characteristic of many New Zealand drivers. It was started in rural farming areas and spread to cities everywhere. It looks completely strange to tourists and was noted by my brother-in-law who lives in Canada as a complete nonsense. We don't have autobahns here and the speed limit on the open road is 100 k.p.h with a zero tolerance over the Christmas holiday period and speed camera sites everywhere.
One cannot go any significant distance without having to slow down to go through some township or village community the main highway route passes through. Fuel whether gasoline or petrol as we might call it here is cheap and the same for diesel although there are distance charges with the latter.
Despite all of this it is fashionable to have a high performance four wheel drive or sports utility vehicle with the acceleration superior to many everyday cars.
What this is really all about is a display of affluence. The local newspaper here features a weekly review of new models of motor vehicles many of which are beyond the budgets and needs of the majority of people.
This is not too far removed from a lot of audio reviews that were done in the 70's.
With regard to 2 ohm loads there were some pretty nasty cross over designs around before the days of computer modelling. There was not too much fuss about raising loudspeaker designers raising the bar in this way that I can remember. I believe computer modelling has aided the design of more ideal and sensible crossover networks.
I often visit an acquaintance who deals in used Hi-Fi and listen to some of his stock. He has had Yamaha NS1000 and AR94 there and I have heard them. I would not rave about them.
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Re: mine is bigger than yours. I understand your point, but I feel the comparison is way off base. The amp designer has no idea what his will be asked to drive, so he has to think in worts case terms whenever possible. Even worse, any speaker's STATIC impedance will change under dnymic conditions, as the drivers heat up, etc. And the rice premium one needs to pay to provide for excellent current reserves is relatively low for the benfit of the security it brings.
It's more a thing of the basic design than whopping big capacitors, etc. Practical example: Harman/Kardon 680 integradted amp. Nominally sold as 85/130W into 8/4 Ohms, which is ridiculously conservative. It's a dual mono design (one trafo with dual outputs), each channel possessing its own full wave bridge rectifier backed up by 8,200 uF caps. No big deal, right? Yet, when pushed, it will deliver impulses of 530 Watts into 2 Ohms (t=20mS). But that trafo is rather big, no less than 500 VA, and 600 VA would not surpise me.
Re: AR 94. True, not the world's best speaker ever, not even AR's best ever, but a very fine speaker IF driven by a competent amp. AS most ARs, it's not an easy load. It will be superbly driven by Marantz 170 DC power amp, or 1152 DC integrated amp from the same series, by all H/K amps, but Sansui won't be happy with them, internally X balanced and all. Oddly enough, the small Toshiba SB-420, nominally just 40W/8 Ohms, with a dinky little trafo and funny little 6.800 uF caps won't mind. But when you get it right, they are very lively and engaging speakers, despite a slight tonal imbalance towards the upper midrange-lower high range (a bit on the bright side), and I should add fully refreshed with new Xover caps, in parallel, polypropylene, and pure silver wiring inside. Most pleasant to listen to.
Re: modern speaker loads. You are definitely wrong on this point. Take say B&W or Focal printed ads and you will plainly see impedance declared as 8 Ohms nominal, minimum 3/3.3 Ohms respectively. It is very likely that the worst case phase shifts will occur around the place of impedance fall, so can you sear it won't be combined with a phase shift of say -60 degrees, requiring TWICE the current? And if nothing good happens, who is blamed, a mismatch between amp and speaker, or the amp designer?
It's more a thing of the basic design than whopping big capacitors, etc. Practical example: Harman/Kardon 680 integradted amp. Nominally sold as 85/130W into 8/4 Ohms, which is ridiculously conservative. It's a dual mono design (one trafo with dual outputs), each channel possessing its own full wave bridge rectifier backed up by 8,200 uF caps. No big deal, right? Yet, when pushed, it will deliver impulses of 530 Watts into 2 Ohms (t=20mS). But that trafo is rather big, no less than 500 VA, and 600 VA would not surpise me.
Re: AR 94. True, not the world's best speaker ever, not even AR's best ever, but a very fine speaker IF driven by a competent amp. AS most ARs, it's not an easy load. It will be superbly driven by Marantz 170 DC power amp, or 1152 DC integrated amp from the same series, by all H/K amps, but Sansui won't be happy with them, internally X balanced and all. Oddly enough, the small Toshiba SB-420, nominally just 40W/8 Ohms, with a dinky little trafo and funny little 6.800 uF caps won't mind. But when you get it right, they are very lively and engaging speakers, despite a slight tonal imbalance towards the upper midrange-lower high range (a bit on the bright side), and I should add fully refreshed with new Xover caps, in parallel, polypropylene, and pure silver wiring inside. Most pleasant to listen to.
Re: modern speaker loads. You are definitely wrong on this point. Take say B&W or Focal printed ads and you will plainly see impedance declared as 8 Ohms nominal, minimum 3/3.3 Ohms respectively. It is very likely that the worst case phase shifts will occur around the place of impedance fall, so can you sear it won't be combined with a phase shift of say -60 degrees, requiring TWICE the current? And if nothing good happens, who is blamed, a mismatch between amp and speaker, or the amp designer?
I understand where you are coming from with your stance on triple output stages, stopper resistors in the feed lines of the transistors in each output half, the value of cross coupling the emitters of the driver and pre-driver with a resistor to drain out stored charges in transistor bases on opposite voltage swings. With regard to adding extra pairs in the final stage it is commonplace in high power applications.
In so far as I can see there are a couple of other advantages you will have noted have not emerged namely that the heat dissipation of a high powered amplifier should be uniform and multiple power devices will do a better job across a long heat sink. Also with sharing reducing the current each power device has to handle will allow a higher frequency before the final stage of the triple starts to run out of gain. The output stage can run a larger quiescent current.
Some years ago I built an Leach low TIM amplifier - full complementary symmetry throughout and a Locanthi triple output stage.
It is an early version and it has had an output transistor failure since when it has lain on a shelf in my garage. I have a stash of transistors but it really needs to be rebuilt and housed in a proper case. It was actually cheaper to buy second hand than to get out my soldering iron and do a rebuild.
One of these subjects is a Technics Class AA with MOSFETs, a special transformer and smoothing capacitors. My garage is where I do a lot of listening and it lives there with my other home built speakers and other equipment. I have a coastal holiday property 160 km away and have another Technics Class H amp there.
At one time I was offered a Quad 33/303 combination by a friend who had done with solid state amplifiers and bought and built a kit from Audio Note to match some Lowther based horn speakers he had built - his house is a villa so room is not a problem. He said I could keep the Quad if I had liked it. There are a number of reasons why I freighted it back to him 1. I had too many amplifiers to justify accepting it, I would have felt obliged to offer him some cash had I done so and did not see this a worthwhile investment 2. It was 30 years old and in probable need of a capacitor replacement 3. The DIN connectors needed to hook it up to the rest of my system. I made up some makeshift ones to listen to for a reasonably extended period but I could not tear myself away from the Leach.
It is interesting to see that the T-Circuit devised by Bart Locanthi in 1966 is in widespread use in the 21st Century.
With regard to the Lecson amplifier that you mention as having been designed by Bob Stuart, you may be interested to know that Stan Curtis who reviewed the Quad 405 in Choice in 1982 was responsible for designing the Lecson AP4 which later became a popular project in the English edition of Electronics Today International. It is pretty much a "pre Krell" Krell.
Curtins was a consultant designer on the British Hi-Fi scene and became Chairman of Quad before the Chinese buyout. If you are interested in big and Class A you might like to check out his website Stan Curtis, Engineer, introduction to my website
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Re: Stan Curtis. Been there, seen that. That's one smart cookie, Stan is.
Re: B&W, Focal. I am simply saying that there are still a few honest manufacturers around left alive and that this is what you SHOULD expect and be happy if you don't meet in person. My global advice to anyone designing a power amp is: design for nominal 4 Ohm impedance, and assume a phase shift of at least -45 degrees. It's the ONLY way to play it relatively safe without going overboard.
Output devices are cheap nowadays, so adding then in parallel is what any idiot can do, ecept for the ultra idiots who don't do even that. If anyone doubts, just pick up a few mags and look at what they measured as the actual working impedance. Unfortunately, that's all they can see, and all too often they are not told that most crossovers are mostly sources of trouble because their makers couldn't be fagged with developing them as far as they could and should have. If you analyze the marlet carefully, you will find that most of Britain's speaker makers of good repute or better in fact use pretty much the same drivers as the others, but do their crossover network homework much better and with more attention to details. THIS is what really separates them from the run-off.the-mill crowd.
Development time costs money and time, so many are only to happy to slap together something that looks like a crossover and appears to work somewhat. That's called "being efficient" these days of mass produced junk.
Re: B&W, Focal. I am simply saying that there are still a few honest manufacturers around left alive and that this is what you SHOULD expect and be happy if you don't meet in person. My global advice to anyone designing a power amp is: design for nominal 4 Ohm impedance, and assume a phase shift of at least -45 degrees. It's the ONLY way to play it relatively safe without going overboard.
Output devices are cheap nowadays, so adding then in parallel is what any idiot can do, ecept for the ultra idiots who don't do even that. If anyone doubts, just pick up a few mags and look at what they measured as the actual working impedance. Unfortunately, that's all they can see, and all too often they are not told that most crossovers are mostly sources of trouble because their makers couldn't be fagged with developing them as far as they could and should have. If you analyze the marlet carefully, you will find that most of Britain's speaker makers of good repute or better in fact use pretty much the same drivers as the others, but do their crossover network homework much better and with more attention to details. THIS is what really separates them from the run-off.the-mill crowd.
Development time costs money and time, so many are only to happy to slap together something that looks like a crossover and appears to work somewhat. That's called "being efficient" these days of mass produced junk.
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