Hi,
The theories Sushurin refers to are actually quite similar to what others like Matti Otala, Jean Hiraga and a bunch of others have been saying for many years in their own way, namely that we've been looking at distortion figures in the wrong way.
It's not so much the amount, in percentage if you like, of distortion but how it is spread and what it contains that seems to matter.
If you look at the approach of designers such as Kondo, Sakuma you will see a similar approach.
Applying this to OTL design can be done as the NFB loop acts in a different way than if it would entail OPTs but it sure isn't all that easy.
Some people preach the vitrues of iron for its musicality for instance, personally I think you can achieve the same and more without any iron at all....Which is why I and many others chose that inroad, I presume.
Cheers,
The theories Sushurin refers to are actually quite similar to what others like Matti Otala, Jean Hiraga and a bunch of others have been saying for many years in their own way, namely that we've been looking at distortion figures in the wrong way.
It's not so much the amount, in percentage if you like, of distortion but how it is spread and what it contains that seems to matter.
If you look at the approach of designers such as Kondo, Sakuma you will see a similar approach.
Applying this to OTL design can be done as the NFB loop acts in a different way than if it would entail OPTs but it sure isn't all that easy.
Some people preach the vitrues of iron for its musicality for instance, personally I think you can achieve the same and more without any iron at all....Which is why I and many others chose that inroad, I presume.
Cheers,
Hi,
As long as the distorsion in a driver stage is much lower then it is in the power stage it will contribute very little to the total distorsion, yes, distorsion from different stages in an amplifier is cumultative but as long as the phase difference between the stages is more or less constant it is just a question of vectorial addition, (or cancellation) and the contribution is miminmal, I can agree however that if you tried to drive a very good power stage with a bad driver, (maybe a bipolar CE without feedback?) then the driver would contribute to the total distorsion but why would you want to design the amplifier like that?
Given what I written above the diffrence in distorsion between an OTL using a resitance coupled phase splitter and one using a transformer based one is minimial or none.
I dont think the comparison with speaker distorsion holds, distorsion in speakers is very much dependent on frequency and level and there are many speakers available with very low distorsion in the mid range, much lower then what is possible to hear.
I myself is convinced that one of the main reasons of being able to hear differences between different amplifiers is not due to differences in THD but due to differences in IM especially IM between 2 high frequency signals. That it is possible to hear differences between amplifiers even though maybe speakers give higher THD should then be because amplifiers and speakers doesn't produce the same kind of distorsion especially not in midrange, however if the speaker is bad enough it will not be possible, (according to my experiences) to hear the differences between different amplifiers as long as the amplifiers are reasonably good.
I still fail to see that any possible advantage using a transformer phase splitter should outweigh the well known disadvantages, (intrisinic distorsion, limited bandwidth, excessive phase shift), especially when used in an OTL amp.
Hans
As long as the distorsion in a driver stage is much lower then it is in the power stage it will contribute very little to the total distorsion, yes, distorsion from different stages in an amplifier is cumultative but as long as the phase difference between the stages is more or less constant it is just a question of vectorial addition, (or cancellation) and the contribution is miminmal, I can agree however that if you tried to drive a very good power stage with a bad driver, (maybe a bipolar CE without feedback?) then the driver would contribute to the total distorsion but why would you want to design the amplifier like that?
Given what I written above the diffrence in distorsion between an OTL using a resitance coupled phase splitter and one using a transformer based one is minimial or none.
I dont think the comparison with speaker distorsion holds, distorsion in speakers is very much dependent on frequency and level and there are many speakers available with very low distorsion in the mid range, much lower then what is possible to hear.
I myself is convinced that one of the main reasons of being able to hear differences between different amplifiers is not due to differences in THD but due to differences in IM especially IM between 2 high frequency signals. That it is possible to hear differences between amplifiers even though maybe speakers give higher THD should then be because amplifiers and speakers doesn't produce the same kind of distorsion especially not in midrange, however if the speaker is bad enough it will not be possible, (according to my experiences) to hear the differences between different amplifiers as long as the amplifiers are reasonably good.
I still fail to see that any possible advantage using a transformer phase splitter should outweigh the well known disadvantages, (intrisinic distorsion, limited bandwidth, excessive phase shift), especially when used in an OTL amp.
Hans
phase splitting
The conventional phase splitter has always seemed to me a compromised design. Not the least detrimental aspects of these splitters are differing output impedances and, depending on the design, differing frequency-dependent output voltages and phase in the two legs. I don't doubt that low IM distortion is important to preserving signal fidelity. Perhaps equally important is distortion linearity and stability at differing output powers and loads? Our hearing is most sensitive to waveform accellerations and decelerations, which perhaps implies our ear can hear through distortions that remain steady. One might analogise to vision: spotting a stationary object can prove practically impossible; once the object moves, it is seen instantly. Distortion might be similarly perceived in that non-steady-state distortion products draw attention to themselves by the simple fact they are moving. Steady state distortion (ie, white noise) is more easily ignored.
Lynn Olson has commented on these subjects as follows:
"I am beginning to suspect the ear compensates for amplifier distortion if it is simple in nature and stable (which is another reason for the excellent subjective quality of SE circuits), but does not like distortion that is constantly changing. Unfortunately, conventional phase-splitters have asymmetric output impedances, an asymmetric Miller capacitance, or sensitivity to B+ voltage, so the cancellation of the even-harmonic distortion terms (2nd, 4th, etc.) bounces up and down with the program material. The instability of the distortion characteristic is very likely the source of the usual PP "fog" and vagueness compared to the more direct and immediate SE sound."
I don't quote Olson for his vote for SE sound, which isn't the issue here. And he perhaps overstates by saying phase and distortion variance in a phase splitter is "the" source of fog and vagueness ... I could name crossover distortion as another. But his observations otherwise sound valid, to me.
These considerations surely are of marginal value as OTL amplifiers, done well, already sound fantastic. We're into subtle details trying to improve this sound. Transformer phase splitting might be a step in that direction.
The conventional phase splitter has always seemed to me a compromised design. Not the least detrimental aspects of these splitters are differing output impedances and, depending on the design, differing frequency-dependent output voltages and phase in the two legs. I don't doubt that low IM distortion is important to preserving signal fidelity. Perhaps equally important is distortion linearity and stability at differing output powers and loads? Our hearing is most sensitive to waveform accellerations and decelerations, which perhaps implies our ear can hear through distortions that remain steady. One might analogise to vision: spotting a stationary object can prove practically impossible; once the object moves, it is seen instantly. Distortion might be similarly perceived in that non-steady-state distortion products draw attention to themselves by the simple fact they are moving. Steady state distortion (ie, white noise) is more easily ignored.
Lynn Olson has commented on these subjects as follows:
"I am beginning to suspect the ear compensates for amplifier distortion if it is simple in nature and stable (which is another reason for the excellent subjective quality of SE circuits), but does not like distortion that is constantly changing. Unfortunately, conventional phase-splitters have asymmetric output impedances, an asymmetric Miller capacitance, or sensitivity to B+ voltage, so the cancellation of the even-harmonic distortion terms (2nd, 4th, etc.) bounces up and down with the program material. The instability of the distortion characteristic is very likely the source of the usual PP "fog" and vagueness compared to the more direct and immediate SE sound."
I don't quote Olson for his vote for SE sound, which isn't the issue here. And he perhaps overstates by saying phase and distortion variance in a phase splitter is "the" source of fog and vagueness ... I could name crossover distortion as another. But his observations otherwise sound valid, to me.
These considerations surely are of marginal value as OTL amplifiers, done well, already sound fantastic. We're into subtle details trying to improve this sound. Transformer phase splitting might be a step in that direction.
Hi,
There are many different type of phase splitters with different performance, I prefer the split load type as that has less problems than most others. The output impedance of the split load is equal on both outputs as long as the load is constant which is the case if the power tubes does not draw grid current e.g A1 or AB1, or if the phase inverter is loaded by driver tubes. For very high frequencies the output voltages start to differ but this is in the MHz range and can easily be compensated for if needed. the split load phase inverter is unfortunately one of the most misunderstood circuits used and there are many well known text books and papers where the analysis of this circuit is plain wrong.
If distorsion linearity is how distorsion changes with output power push-pull amps is not any different than SE amps except for the total magnitude of distorsion, push-pull amps as well as SE amps will have distorsion that is reduced almost in a linear manner at lower power levels. There is no difference in this behavior between an amp using an ordinary phase splitter and one using a transformer as long as both types is designed in a competent manner.
Without speculating on if Lynn Olson is right or wrong, (I BTW don't agree with his view that SE amps are superiou) we can go trough his statements one by one and compare a split load phase inverter with a transformer based one.
1 asymmetric output impedances, as I described above this is not valid for the split load type and shouldn't be valid for a good transformer either.
2 asymmetric Miller capacitance, this is true for the split load but only affects frequencies in the MHz range and can easily be 100% compensated for if needed, a good transformer will have no problem either.
3 sensitivity to B+ voltage, the split load is almost completely insensitive to changes in B+ voltage, changes in B+ affects the max available output voltage but it has almost no effect on gain, and no effect on balance, an ordinary transformer coupled phase splitter stage will however change gain if B+ is changing.
I still fail to see that there are possible advantages of using a transformer as phase splitter in an OTL amp that would outweigh the disadvantages.
Regards Hans
There are many different type of phase splitters with different performance, I prefer the split load type as that has less problems than most others. The output impedance of the split load is equal on both outputs as long as the load is constant which is the case if the power tubes does not draw grid current e.g A1 or AB1, or if the phase inverter is loaded by driver tubes. For very high frequencies the output voltages start to differ but this is in the MHz range and can easily be compensated for if needed. the split load phase inverter is unfortunately one of the most misunderstood circuits used and there are many well known text books and papers where the analysis of this circuit is plain wrong.
I dont know what you mean by distorsion linearity but why do you believe that balance , distorsion or stability will be better using a transformer as phase splitter? there is actually every reason to believe otherwise.
If distorsion linearity is how distorsion changes with output power push-pull amps is not any different than SE amps except for the total magnitude of distorsion, push-pull amps as well as SE amps will have distorsion that is reduced almost in a linear manner at lower power levels. There is no difference in this behavior between an amp using an ordinary phase splitter and one using a transformer as long as both types is designed in a competent manner.
Without speculating on if Lynn Olson is right or wrong, (I BTW don't agree with his view that SE amps are superiou) we can go trough his statements one by one and compare a split load phase inverter with a transformer based one.
1 asymmetric output impedances, as I described above this is not valid for the split load type and shouldn't be valid for a good transformer either.
2 asymmetric Miller capacitance, this is true for the split load but only affects frequencies in the MHz range and can easily be 100% compensated for if needed, a good transformer will have no problem either.
3 sensitivity to B+ voltage, the split load is almost completely insensitive to changes in B+ voltage, changes in B+ affects the max available output voltage but it has almost no effect on gain, and no effect on balance, an ordinary transformer coupled phase splitter stage will however change gain if B+ is changing.
I still fail to see that there are possible advantages of using a transformer as phase splitter in an OTL amp that would outweigh the disadvantages.
Regards Hans
All valve phase splitters work by swinging the same AC current into two loads so that one produces an inverted output, and the other a non-inverted output. As a consequence, they are always sensitive to load impedance, whether they are split load, Schmidt, or differential pair with CCS. The solution is to buffer the phase splitter from unpleasant and changing loads (like output valves).
A transformer doesn't have the previous problems. It has problems all of its own. The impedances required of an inter-stage transformer make its design extremely difficult.
I'll stick with a buffered phase splitter.
A transformer doesn't have the previous problems. It has problems all of its own. The impedances required of an inter-stage transformer make its design extremely difficult.
I'll stick with a buffered phase splitter.
fdegrove said:
Hello Frank, I was going to say that since OTLs use cathode followers, the load capacitance should be very low, but it occurs to me that because they drive a low impedance load, their gain is very low, so they are unable to bootstrap Cgk very effectively, resulting in a rather higher load capacitance than might have been expected.
More to the point, OTL output stages are almost inevitably Class AB, so the phase splitter needs to be buffered.
Yes, but most of them except split load is also dependant on that 2 tubes are matched, this is an added advantage for the split load.
This is only a problem at clipping or a power stage that draw grid current, even at clipping a split load phase inverter can be designed to behave quite well by keeping Ra and Rk low.
Why? if it is AB2 yes but not if it is AB1.
Maybe so but the load capactance is still much lower than for instance when compared to an ordinary anode loaded output stage, using a split load phase inverter with it's very low output impedance give very wide bandwidth and it is not a problem to drive multiple output tubes, the only problem is still at clipping but this can be handled.
Regards Hans
Agreed, the split load phase splitter does not require matched valves, although a CCS in the tail of a long-tailed pair pretty well enforces symmmetry.
Capacitances change as the output devices switch on and off (Class AB), changing the loading. Agreed, they're quite small, but because an OTL needs lots of feedback, this doesn't help stability.
I'm aware that the classic OTL design drives the output stage directly from a modified split load phase splitter, but I'm wondering if cathode followers between the two would help. I should say that I haven't built an OTL, so this is speculation.
Capacitances change as the output devices switch on and off (Class AB), changing the loading. Agreed, they're quite small, but because an OTL needs lots of feedback, this doesn't help stability.
I'm aware that the classic OTL design drives the output stage directly from a modified split load phase splitter, but I'm wondering if cathode followers between the two would help. I should say that I haven't built an OTL, so this is speculation.
a CCS does not help to cather for differences in u or differences in loading, gain from each output i is still dependant on u and load for each tube.
Triodes in class AB never switch completely off which is actually a problem in itself as it gives odd order distorsion.
The gain of each tube changes I agree but it has a very small effect on the loading as the input capacitance is Cgp + (1-A)Cgk, so even if the gain is changing the total capacitance change is small, an example with 6C33C Cgp 31 pF and Cgk 30 pF, max gain as CF in OTL amp typically ~0.4 which gives Cin = 31 + 30*(1-0.4) or ~ 49pF, min gain ~0.15 at very negative grid voltage giving Cin = 31 + 30*(1-0.15) ~35.5 pF, not that much of a difference. The output impedance of a split load phase inverter is very low so the pole given by the output tube input capacitance is at very high frequency giving a minimum of problems with stability, I have both calculated and measured this and calculations and measurements agree very well.
Introducing cathode followers helps to take care of clipping and make it possible to drive the output tubes into AB2 if needed, I can report that it has no practically measureable or noticeable effect whatsoever if the output tubes doesn't clip.
Regards Hans
T8 v Ciuffoli
For those that may be interested, we have had the chance to test empirically both the T8 OTL as found in audio reality book and the ciuffoli 8.2 OTL. The theoretical arguments for and against each design can be found in this thread for anyone interest in following. The results are as follows:
It appears that the Ciuffoli design far surpasses the T8 in quality of sound, bass, mids and highs and this is also evident from the frequency range shown at the respective tests of each design's website. I'd say marketing did its trick again and we should all try to promote Ciuffoli's design as it is really excellent. It proves once again that simple and elegant designs are better since they have less chance to distort the sound.
For those that may be interested, we have had the chance to test empirically both the T8 OTL as found in audio reality book and the ciuffoli 8.2 OTL. The theoretical arguments for and against each design can be found in this thread for anyone interest in following. The results are as follows:
It appears that the Ciuffoli design far surpasses the T8 in quality of sound, bass, mids and highs and this is also evident from the frequency range shown at the respective tests of each design's website. I'd say marketing did its trick again and we should all try to promote Ciuffoli's design as it is really excellent. It proves once again that simple and elegant designs are better since they have less chance to distort the sound.
Question, did you build the Ciuffoli design exactly according to the schematic? The reason I ask is that I know some people that have had problems with the original design.
Otherwise I am not so blunt as you condemning the T8 design but I think it has been established reasonable doubts if the patented design really solve the problem it is said to solve and if these doubts are correct maybe the patent is more of marketing hype than anything else?
Regards Hans
A friend of mine has built the ciuffoli and has followed so far as I know the schematic to the detail... I guess the driver section could be reworked a bit...
registering a Patent is not that difficult, especially in the US. What is frustrating is the use of the registration as an argument for superiority of design, which is utterly ill founded. A registrable design is no guarantee of superiority despite how one likes to use this.
registering a Patent is not that difficult, especially in the US. What is frustrating is the use of the registration as an argument for superiority of design, which is utterly ill founded. A registrable design is no guarantee of superiority despite how one likes to use this.
T8 patent
Well, it seems to me that YOUR remarks regarding the T8 are ill-founded, and singularly unkind. The fact that there are many satisfied owners of the T8 all over the world, both factory-built and scratch-built (I'm in the latter category), is eloquent testimony to the effectiveness of its design.
Have you ever tried to obtain a U.S. patent?--it's not that easy, at least in the electronics field. And it takes a lot of time and money. I think you're talking through yer **** on this one, pal!
I have no experience with the Ciuffoli OTL, so I can't comment on it. However, I have yet to meet up with anyone here in the States who has built one, and it is not a very popular design at AudioAsylum, either. Apparently two people at AA have built one (I just did a search), compared with over a dozen or so who have built the T8. There are also (6) reviews of the T8 at AA (all positive), but none for the Ciuffoli.
If it's such a great design, why have so few people attempted it, or at least written about it?
Well, it seems to me that YOUR remarks regarding the T8 are ill-founded, and singularly unkind. The fact that there are many satisfied owners of the T8 all over the world, both factory-built and scratch-built (I'm in the latter category), is eloquent testimony to the effectiveness of its design.
Have you ever tried to obtain a U.S. patent?--it's not that easy, at least in the electronics field. And it takes a lot of time and money. I think you're talking through yer **** on this one, pal!
I have no experience with the Ciuffoli OTL, so I can't comment on it. However, I have yet to meet up with anyone here in the States who has built one, and it is not a very popular design at AudioAsylum, either. Apparently two people at AA have built one (I just did a search), compared with over a dozen or so who have built the T8. There are also (6) reviews of the T8 at AA (all positive), but none for the Ciuffoli.
If it's such a great design, why have so few people attempted it, or at least written about it?
Hi Guys,
A couple of points on the BR patent: I had a bit of an email argument with Broskie regarding this, and I've spent alot of time just thinking it over. Anyway, one of these day's I'll take my T8's back to the shop, disconnect the negative feedback and take a look at the output. Broskie maintains that this will prove the BR circuit to be BS. At first I thought I had a very good handle on the circuit theory, and Broskie was simply missing the point. I must say that now I'm comming around to his way of thinking. The more I analyze the circuit theory, the more I think the only way to make it work as advertised is to drive the CF bootstrapped buffer from a balanced input refereced to the output, which would require a complete redesign of the driver stage. If this turns out to be the case I will owe Frank an appology. I suspect that BR may have done something like this in his T16 design, but at present I still haven't managed to get a look at the schematic. I can say that in a rather cagey manner, BR has been pushing the T16 and downplaying the T8 for quite some time now, and I think he's discontinued the T8 as a comercial product.
One interesting aside, even if the bootstrapped CF in the design does not function as BR claims, there are buffers between the phase splitter and the output stage, which may improve the design over the classic Futterman as the previously stated advantages of a buffer here would suggest.
On the distortion front, Earl Geddes has published an AES paper regarding the human perception of various types of distortion and he prescribes a new distortion metric based on this research. I haven't read the paper yet, but in discussions on the BASSlist and having read his book, IIRC it is related to distortion at various frequencies and levels where human perception seems to be more sensitive to distortion. I can say with relative confidence that he has found the current IM and THD measurements to have little correlation to percived sound quality.
A couple of points on the BR patent: I had a bit of an email argument with Broskie regarding this, and I've spent alot of time just thinking it over. Anyway, one of these day's I'll take my T8's back to the shop, disconnect the negative feedback and take a look at the output. Broskie maintains that this will prove the BR circuit to be BS. At first I thought I had a very good handle on the circuit theory, and Broskie was simply missing the point. I must say that now I'm comming around to his way of thinking. The more I analyze the circuit theory, the more I think the only way to make it work as advertised is to drive the CF bootstrapped buffer from a balanced input refereced to the output, which would require a complete redesign of the driver stage. If this turns out to be the case I will owe Frank an appology. I suspect that BR may have done something like this in his T16 design, but at present I still haven't managed to get a look at the schematic. I can say that in a rather cagey manner, BR has been pushing the T16 and downplaying the T8 for quite some time now, and I think he's discontinued the T8 as a comercial product.
One interesting aside, even if the bootstrapped CF in the design does not function as BR claims, there are buffers between the phase splitter and the output stage, which may improve the design over the classic Futterman as the previously stated advantages of a buffer here would suggest.
On the distortion front, Earl Geddes has published an AES paper regarding the human perception of various types of distortion and he prescribes a new distortion metric based on this research. I haven't read the paper yet, but in discussions on the BASSlist and having read his book, IIRC it is related to distortion at various frequencies and levels where human perception seems to be more sensitive to distortion. I can say with relative confidence that he has found the current IM and THD measurements to have little correlation to percived sound quality.
cbrodersen
Better stick to what you know, and it seems you dont know much. Ciuffoli is not an "inventor' and his design is not prorpietory , he is using the Technics' variation of the Futterman design, heard of these two ?? So it is not very illogical that these designs, which I might add, have stood the test of time of errr 50 years now are worth something. Well another note, BR's design is based on the Futterman design, so much for ingeniuty.
Indeed I dont know anything about Patents, I only register a few every month for clients, sorry how many did you register recently? But you said you are an expert!
Next time you attempt to pick on one, try one of your limited brain capacity.....
Better stick to what you know, and it seems you dont know much. Ciuffoli is not an "inventor' and his design is not prorpietory , he is using the Technics' variation of the Futterman design, heard of these two ?? So it is not very illogical that these designs, which I might add, have stood the test of time of errr 50 years now are worth something. Well another note, BR's design is based on the Futterman design, so much for ingeniuty.
Indeed I dont know anything about Patents, I only register a few every month for clients, sorry how many did you register recently? But you said you are an expert!
Next time you attempt to pick on one, try one of your limited brain capacity.....
Ciufolli OTL
You didn't answer the question--if the Ciuffoli question is so great, why are there so few of them around, at least on the Internet? Why is there no info, no reports from people who have built one (other than on the Ciuffoli website)? Not very encouraging.
Two more points--the original Futterman design has NOT stood the test of time--I have one friend who owned a pair, used them to drive Quads. He got rid of them because they were so unreliable. And I have heard other similar reports from people who have owned the Futtermans.
The T8 is NOT based on the Futterman--it is fundamentally different, due to the biasing of the output stage, among other things.
You didn't answer the question--if the Ciuffoli question is so great, why are there so few of them around, at least on the Internet? Why is there no info, no reports from people who have built one (other than on the Ciuffoli website)? Not very encouraging.
Two more points--the original Futterman design has NOT stood the test of time--I have one friend who owned a pair, used them to drive Quads. He got rid of them because they were so unreliable. And I have heard other similar reports from people who have owned the Futtermans.
The T8 is NOT based on the Futterman--it is fundamentally different, due to the biasing of the output stage, among other things.
Sorry, let me be more succinct.
The Ciuffoli design is simply a cut down version of other great designs. You wont find it anywhere becuase the person is not interested in marketing it but the technic's variation of the Futterman is found in many other designs out their as well as the Futterman circuit itself, enter Transcendent Sounds. The real intuition was the Futterman design not the three zeners. Lets be fair to humanity than anything else.
As for the unreliability issue, one should be compare like with like ie designs of today with other designs of today. Perhaps the T8 is more reliable than the Atma-Spheres or the Graafs? Dont think so. What bothers me most is not the design but the designer's attitude who claims quite arrogantly to have the most perfect design, which allegedly sounds remarkable, being the most reliable blah blah. Atma-Shpere has been around three times longer and have not made any such high horsed claims. I wonder why..
As for many people "loving" the T8, two units were on audiogon's list, the cheapest units of all out there. and the only ones which have not been sold...
The Ciuffoli design is simply a cut down version of other great designs. You wont find it anywhere becuase the person is not interested in marketing it but the technic's variation of the Futterman is found in many other designs out their as well as the Futterman circuit itself, enter Transcendent Sounds. The real intuition was the Futterman design not the three zeners. Lets be fair to humanity than anything else.
As for the unreliability issue, one should be compare like with like ie designs of today with other designs of today. Perhaps the T8 is more reliable than the Atma-Spheres or the Graafs? Dont think so. What bothers me most is not the design but the designer's attitude who claims quite arrogantly to have the most perfect design, which allegedly sounds remarkable, being the most reliable blah blah. Atma-Shpere has been around three times longer and have not made any such high horsed claims. I wonder why..
As for many people "loving" the T8, two units were on audiogon's list, the cheapest units of all out there. and the only ones which have not been sold...
OTLs
I don't care about manufactured or marketed designs--I was looking for a DIY design with a track record, and the T8 fit that description. I would be VERY hesitant about attempting the Ciuffoli (as a first-time project, at any rate), simply because there seems to be so little support for it on the Web. It may be as great-sounding as you claim, but it seems to me to be a risky project for anyone (like myself) who doesn't possess extensive circuit-designing or troubleshooting skills.
Reliability is reliability, whether it is an old or new design. And my T8s, along with those belonging to several others I've corresponded with, ARE reliable--they work, and conitnue to work, in part due to the minimal heat load (for an OTL).
I'm sorry that the attitude of the designer (BR) bothers you, but you could level the same charge against any one of several "high-end" designers out there. I don't let that kind of thinking influence my DIY decisions.
So what? I 've seen ARC and CJ units sit on the Audiogon site for just as long. Does that prove that they're undesirable, too?
I don't care about manufactured or marketed designs--I was looking for a DIY design with a track record, and the T8 fit that description. I would be VERY hesitant about attempting the Ciuffoli (as a first-time project, at any rate), simply because there seems to be so little support for it on the Web. It may be as great-sounding as you claim, but it seems to me to be a risky project for anyone (like myself) who doesn't possess extensive circuit-designing or troubleshooting skills.
Reliability is reliability, whether it is an old or new design. And my T8s, along with those belonging to several others I've corresponded with, ARE reliable--they work, and conitnue to work, in part due to the minimal heat load (for an OTL).
I'm sorry that the attitude of the designer (BR) bothers you, but you could level the same charge against any one of several "high-end" designers out there. I don't let that kind of thinking influence my DIY decisions.
So what? I 've seen ARC and CJ units sit on the Audiogon site for just as long. Does that prove that they're undesirable, too?
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