>>Oh, incidentally, it ain't hard to figure out why a gain device might be inferior to a plain ol' resistor. Consider which more closely approximates the ideal for its kind: resistor or gain device. Good resistors (by which I mean your ordinary metal film critter) are pretty linear, nearly perfect in the ideal sense. Yes, there's going to be some stray capacitance & inductance, some thermal effects, etc. but damned close to the ideal. Semi's and tubes? Fuggetaboutit! << I have always liked the Leach amp with its resistor off of a zener supply as current source.Daniel Meyer of SWTPC fame, and who Leach claims inspired his front end design, offered a stripped down version of the Tiger .01 that had a resistor off of a zener instead of an active current source and a straight CFP output stage instead of the darlingon connected CFP.I bought some of all his models and thought this one sounded best.McIntosh was fond of using a resistor connected to a very high voltage supply as a current source.I remember being surprised seeing a supply of over 100 volts in a solid state pre-amp.>>In the meantime, I find it amusing to note that solid state manufacturers fall all over themselves to tell you that their designs sound 'like tubes,' but you have to search long and hard to find a tube manufacturer that would brag that his equipment sounds 'like solid state.'
I like 'em both, each for what they do well. << One thing I have noticed was as tube gear improved it tended to sound more like solid state and as solid state gear improved it tended to sound more like tubes.AtmaSphere comes to mind as having the clarity in the highs and the punch in the bass not normally heard in tube gear.Threshold comes to mind as having the midrange liquidity of a SET.I wonder what a Wiggins Circlotron would sound like with a 6H30Pi as the diff pair with a resistor pulled down to a high negative voltage driving a single pair of 300 watt IRF N-ch mosfets.I have some 10H toroids that might work as plate loads for the 6H30Pi.
I like 'em both, each for what they do well. << One thing I have noticed was as tube gear improved it tended to sound more like solid state and as solid state gear improved it tended to sound more like tubes.AtmaSphere comes to mind as having the clarity in the highs and the punch in the bass not normally heard in tube gear.Threshold comes to mind as having the midrange liquidity of a SET.I wonder what a Wiggins Circlotron would sound like with a 6H30Pi as the diff pair with a resistor pulled down to a high negative voltage driving a single pair of 300 watt IRF N-ch mosfets.I have some 10H toroids that might work as plate loads for the 6H30Pi.
Perhaps the problem with active current sources is related to their high frequency characteristics? In my recent audio designs, I have been experienceing the benefits of "going passive" in many areas, especially power supplies. As has been pointed out, passive devices often offer performance much closer to ideal when compared with active circuits. Furthermore, recent discussion seems to show a greater interest developing in the subjective effects of HF performance and other phenomena ocurring well beyond 20kHz.
Has anyone tried using inductors to improve the performance of either resistors or active current sources? If HF performance is holding back active sources, an inductor in series with the output might be just the thing.
Finally, has anyone tried using resistors in place of the active tail-current sources on the Stochino design? I'd love to hear about it, as I'm considering building something based on this design.
thanks,
Has anyone tried using inductors to improve the performance of either resistors or active current sources? If HF performance is holding back active sources, an inductor in series with the output might be just the thing.
Finally, has anyone tried using resistors in place of the active tail-current sources on the Stochino design? I'd love to hear about it, as I'm considering building something based on this design.
thanks,
djk,
There is some element of truth in what you say about tubes and solid state coming together. Note that advances in parts quality (e.g. film caps, metal film resistors, etc.) benefit both types of gain devices. (I am not sorry to see carbon composition resistors go. The idea of resistors being +-20% now is laughable...if you can keep from crying. I still remember the first time I actually held a 1% tolerance resistor in my sweaty palms--now I buy them by the handful, and regard 5% parts with grave suspicion.) The stereotypical 'tube' sound has generally been found mostly in the cheaper gear, even way back when. Folks go hear an inexpensive tube piece--then generalize the tonal qualities to include all tube gear. For whatever reason, they are less prone to do this with solid state. If they hear a midrange glare in one SS piece, they try another brand or a more expensive piece. Human psychology is a strange thing.
The Atmasphere, as an OTL design, offers an opportunity to hear tubes without the transformer and its inherent problems. OTLs have been around for years but they, too, are getting better and better. I've done a fair amount of work on an OTL circuit, but am somewhat hamstrung by the fact that my drivers are all low impedence (tweeter= 3 ohms, purely resistive, fortunately).
Be alert to the idea that inductors, although passive, are far from their ideal, largely due to hysteresis effects, although resistance and capacitance play their part, too. Now, an air core inductor might be an avenue worth exploring in that application...
C. Simpson,
I would agree that the problem with current sources is high frequency related. If the frequency were to equal zero, then we'd be talking DC, and we know that's not the problem. But at what frequency does the performance deteriorate? Is it something simple like a 6 dB/octave rolloff caused by capacitance? Lotsa possibilities, here.
Yeah, I tried an inductor on top of the current source for the front end. It didn't help. However, you might could argue that I didn't try hard enough. The inductors were just what I could lay hands on in my junk box. I don't even know the value, offhand. Perhaps more experimentation would have produced a workable variation, but I didn't keep up with it--just went on to the next current source. I didn't try a resistor & inductor combination, because the parts I had on hand would have produced a rolloff in the audible range. (R+L in series= low pass filter) If someone's got a better stock of inductors on hand (or is willing to order a few in) then try it and report back.
Grey
There is some element of truth in what you say about tubes and solid state coming together. Note that advances in parts quality (e.g. film caps, metal film resistors, etc.) benefit both types of gain devices. (I am not sorry to see carbon composition resistors go. The idea of resistors being +-20% now is laughable...if you can keep from crying. I still remember the first time I actually held a 1% tolerance resistor in my sweaty palms--now I buy them by the handful, and regard 5% parts with grave suspicion.) The stereotypical 'tube' sound has generally been found mostly in the cheaper gear, even way back when. Folks go hear an inexpensive tube piece--then generalize the tonal qualities to include all tube gear. For whatever reason, they are less prone to do this with solid state. If they hear a midrange glare in one SS piece, they try another brand or a more expensive piece. Human psychology is a strange thing.
The Atmasphere, as an OTL design, offers an opportunity to hear tubes without the transformer and its inherent problems. OTLs have been around for years but they, too, are getting better and better. I've done a fair amount of work on an OTL circuit, but am somewhat hamstrung by the fact that my drivers are all low impedence (tweeter= 3 ohms, purely resistive, fortunately).
Be alert to the idea that inductors, although passive, are far from their ideal, largely due to hysteresis effects, although resistance and capacitance play their part, too. Now, an air core inductor might be an avenue worth exploring in that application...
C. Simpson,
I would agree that the problem with current sources is high frequency related. If the frequency were to equal zero, then we'd be talking DC, and we know that's not the problem. But at what frequency does the performance deteriorate? Is it something simple like a 6 dB/octave rolloff caused by capacitance? Lotsa possibilities, here.
Yeah, I tried an inductor on top of the current source for the front end. It didn't help. However, you might could argue that I didn't try hard enough. The inductors were just what I could lay hands on in my junk box. I don't even know the value, offhand. Perhaps more experimentation would have produced a workable variation, but I didn't keep up with it--just went on to the next current source. I didn't try a resistor & inductor combination, because the parts I had on hand would have produced a rolloff in the audible range. (R+L in series= low pass filter) If someone's got a better stock of inductors on hand (or is willing to order a few in) then try it and report back.
Grey
djk,
As an addendum to the above, I seem to recall seeing someone musing in print about the convergence of tube and solid state sound. The point was that it's easy to say that tubes and solid state are closing in on the sound of music. But what if...what if the convergence is simply that both styles of gain devices are using the same passive components and the similarities are simply a reflection of the sound of those self-same shared passive components?
Take, for example, the Dale 1% resistors. They're popping up everywhere, as they're readily available, tight-tolerance, and fairly reasonably priced. For those who are into the name-dropping aspect, it's a cheap way of saying that you're using Vishay resistors (Dale being owned by Vishay); marketing departments love that aspect. In the case of commercial gear, I've seen Dale resistors in both tube and solid state equipment. What are the chances that ten years from now, we'll be sitting back laughing about our current fumblings..."Oh, remember when everything sounded the same? It was just that ol' Dale sound."
I tend to believe we're making progress, myself, but it's useful to try to stand back once in a while to make sure we're not getting lost in the trees whilst searching for the woods.
Grey
As an addendum to the above, I seem to recall seeing someone musing in print about the convergence of tube and solid state sound. The point was that it's easy to say that tubes and solid state are closing in on the sound of music. But what if...what if the convergence is simply that both styles of gain devices are using the same passive components and the similarities are simply a reflection of the sound of those self-same shared passive components?
Take, for example, the Dale 1% resistors. They're popping up everywhere, as they're readily available, tight-tolerance, and fairly reasonably priced. For those who are into the name-dropping aspect, it's a cheap way of saying that you're using Vishay resistors (Dale being owned by Vishay); marketing departments love that aspect. In the case of commercial gear, I've seen Dale resistors in both tube and solid state equipment. What are the chances that ten years from now, we'll be sitting back laughing about our current fumblings..."Oh, remember when everything sounded the same? It was just that ol' Dale sound."
I tend to believe we're making progress, myself, but it's useful to try to stand back once in a while to make sure we're not getting lost in the trees whilst searching for the woods.
Grey
This i think was the claim for The Stasis Circuit of Mr. Pass and that is why Threshold could not apply global feedback because of the Low distortion output stage. Most conventional Output stages sound better to me operated within the Loop. I have tried the other way, it's real easy to impliment into an exsisting Design.Just take the Feedback from the Second stages output, right at the input to your Flower output Circuits.
Odd diff stage connection.
The Stochinos input stage. What purpose do the R6 and C? serve(between the emitter resistors? Is is some equalizing of some sort?
I have the article in jpeg but it's too large. The size are 200k per page and there are 5 pages. EW Aug 1998. Send me a message if you want the article.
BTW: Has anyone built this amp since the thread started? Is it easy to get going?
The Stochinos input stage. What purpose do the R6 and C? serve(between the emitter resistors? Is is some equalizing of some sort?
I have the article in jpeg but it's too large. The size are 200k per page and there are 5 pages. EW Aug 1998. Send me a message if you want the article.
BTW: Has anyone built this amp since the thread started? Is it easy to get going?
CCS in LTPS!
Talking about superior perfomance from a resistor feeding tha LTP versus a CCS here it goes my opinion!
I walways use a resistor in series from the colector of the transistor of the CCS to the emiters of the LTP.
This resistor has two porpouses:
-limits the dissipation in the CCS transistor.
-and the sonicly more important it isolated the emiters of the LTP from the output capacity of the CCS transistor...this is very audible...lilke getting rid of the muttings transistors in a CD player.
With that you can have the good sound of resistor with superior perfomance of the CCS...
Regards
Jorge
Talking about superior perfomance from a resistor feeding tha LTP versus a CCS here it goes my opinion!
I walways use a resistor in series from the colector of the transistor of the CCS to the emiters of the LTP.
This resistor has two porpouses:
-limits the dissipation in the CCS transistor.
-and the sonicly more important it isolated the emiters of the LTP from the output capacity of the CCS transistor...this is very audible...lilke getting rid of the muttings transistors in a CD player.
With that you can have the good sound of resistor with superior perfomance of the CCS...
Regards
Jorge
Current Sourcing and Mirroring My take on it
To me i think that all current sources and Current Mirrors are improved with a Resistor Between it and the load. Speed is improved because the resistor Buffers the Nonlinear capacitence of the Current source/Mirror. The Dynamic impedance is increced by the additional impedance of the resistor at the frequency of use, However this impedance is most often small compaired to the Current source/Mirror's Impedance unless Substantial inductive effects are present on the resistor at the frequency of measurement, The effects of non linear capacitence are real and methods like placing a resistor between the CCS and RL not only Measure better but sound alot faster and more articulate. Futher improvement of this nonlinear capacitence by Active Methods like casscoding just add futher refinement. The value of this resistor is so chosen for the Best compromise of DC as well as AC design parrameters. I evean like this resistor in cascode circuits.
The above is true wether the load be a Diff amp a voltage Amp sutch as the second gain stage or a Current gain stage> This is also true on using a constant Current source to bias an opamp's output stage into a ritcher bias or Single ended Class A (Current dependent)
Anyway the above is just my take on the Current source/Mirror issue. you might also find my Casscode current source disscussed at http://www.head-fi.org/forums/showthread.php?s=&threadid=3254&highlight=cascode+current+source Interesting also.
To me i think that all current sources and Current Mirrors are improved with a Resistor Between it and the load. Speed is improved because the resistor Buffers the Nonlinear capacitence of the Current source/Mirror. The Dynamic impedance is increced by the additional impedance of the resistor at the frequency of use, However this impedance is most often small compaired to the Current source/Mirror's Impedance unless Substantial inductive effects are present on the resistor at the frequency of measurement, The effects of non linear capacitence are real and methods like placing a resistor between the CCS and RL not only Measure better but sound alot faster and more articulate. Futher improvement of this nonlinear capacitence by Active Methods like casscoding just add futher refinement. The value of this resistor is so chosen for the Best compromise of DC as well as AC design parrameters. I evean like this resistor in cascode circuits.
The above is true wether the load be a Diff amp a voltage Amp sutch as the second gain stage or a Current gain stage> This is also true on using a constant Current source to bias an opamp's output stage into a ritcher bias or Single ended Class A (Current dependent)
Anyway the above is just my take on the Current source/Mirror issue. you might also find my Casscode current source disscussed at http://www.head-fi.org/forums/showthread.php?s=&threadid=3254&highlight=cascode+current+source Interesting also.
Oooh, ooh, I remember those! Sansui, Kenwood and a host of others were doing commercial battle during the "Slew Rate Wars"
It was fun to look over those schematics and see the clever tricks folks came up with to try to win the war. If only that same energy and focus could have been applied to solving a number of other performance issues - as a group.... oh well. I remember having to repair a lot of those high speed amps, seems they had a bad habit of blowing fuses, output devices and drivers from common mode conduction in the output stage. This plus all the high capacitance exotic speaker cable. Nothing like that steady income in college from those amp repairs
Good thing many devices were in TO3 cans; plastic chips make dangerous projectiles!
Where are those amps now, I wonder....
..... not !
mlloyd1
It was fun to look over those schematics and see the clever tricks folks came up with to try to win the war. If only that same energy and focus could have been applied to solving a number of other performance issues - as a group.... oh well. I remember having to repair a lot of those high speed amps, seems they had a bad habit of blowing fuses, output devices and drivers from common mode conduction in the output stage. This plus all the high capacitance exotic speaker cable. Nothing like that steady income in college from those amp repairs
Good thing many devices were in TO3 cans; plastic chips make dangerous projectiles!Where are those amps now, I wonder....
..... not !
mlloyd1
Nelson Pass said:
Re: CCS in LTPS!
You have a technical point here. Stray caps down to ground steals current from the stage especially when fast inputs signals are applied and the amp is non-inverting. By reducing this stray cap you will get a much cleaner step response. I stumbled across this phenomenia when I designed my old QRO-amp (looks very much alike my monster headphone amp). When I made a hole in the ground plane around the emitter resistors in the input stage I ot more or less a perfect step response. Before that the step response was rather ugly. I'm a guy who belives that a nice looking step response is good thing sonicly.
http://www.national.com/an/AN/AN-A.pdf
Check page 11 for the theory. My amp had exactly the same waveforms as in the article.
One way to enhance the performance is to have several resistors in series in order to reduce the cap. Each resistor has 1-4 pF shunt capacitance and a collector has 2-50 pF depending of type.
Tube_Dude said:
You have a technical point here. Stray caps down to ground steals current from the stage especially when fast inputs signals are applied and the amp is non-inverting. By reducing this stray cap you will get a much cleaner step response. I stumbled across this phenomenia when I designed my old QRO-amp (looks very much alike my monster headphone amp). When I made a hole in the ground plane around the emitter resistors in the input stage I ot more or less a perfect step response. Before that the step response was rather ugly. I'm a guy who belives that a nice looking step response is good thing sonicly.
http://www.national.com/an/AN/AN-A.pdf
Check page 11 for the theory. My amp had exactly the same waveforms as in the article.
One way to enhance the performance is to have several resistors in series in order to reduce the cap. Each resistor has 1-4 pF shunt capacitance and a collector has 2-50 pF depending of type.
OK, to answer my own question: I believe that connecting to diff stages together is not very wise. A ordinary diff stage must be supplied by a single current source, even stray caps are bad. I really wonder what the positive things is to connect two different current sources this way. Anyone who has a strict technical explaination (sorry for beeing boring...)?
I must also add that my question is relevant only if maximun performance is wanted.
I must also add that my question is relevant only if maximun performance is wanted.
LOL> I rember those sansui AU-919 High speed intergrated amps and yes thay Blow-up at thr drop of a hat, I was bench testing one once and it blew output transistors when Outputing with a 200KHz 10 watt into 8 ohm Sine wave. Gee Dimond diff and all. thay did howerver employ some nice 100 MHz. Ring Emmitter TO-3 output Transistors that worked nice in Normal Amps.
The Output stage may be junk but the Transistors themselfs i have used in Other Circuits and thay did not blow, Regarding the AU-919 one would thing with all that Slew and bandwidthn that a mear 200k would me a walk in the park, After all at that same Time I tested a Technics SU-8099 under the same conditions and it still worked, Imn fact i ran Full power up to the point that the waveform turned trangler @ 120KHz. @ 29 Volts RMS into 8 Ohms, however may have been More at 100k due to resistor inductance
Getting back to the topic of this thread (now, there's a novel idea!)...
I've updated my notes on my own Stochino amplifier project, in case anyone is interested.
My original article, including the schematic, is at
http://www.soton.ac.uk/~apm3/diyaudio/Stochino_amp.html
while further construction details and comments on the sound of the amp, as well as one or two photos, are at
http://www.soton.ac.uk/~apm3/diyaudio/Stochino_progress.html
I plan to include some pictures when the whole thing is finally completed.
Alex
I've updated my notes on my own Stochino amplifier project, in case anyone is interested.
My original article, including the schematic, is at
http://www.soton.ac.uk/~apm3/diyaudio/Stochino_amp.html
while further construction details and comments on the sound of the amp, as well as one or two photos, are at
http://www.soton.ac.uk/~apm3/diyaudio/Stochino_progress.html
I plan to include some pictures when the whole thing is finally completed.
Alex
Alex,
I am happy to read that you have completed this long pending project. I also read your report on the sonics of the Stochino amplifier.
I made a stereo amp using this design about 1 1/2 years ago and gave the amp away to a friend. As I can recall, the sonic quality of this amp is second to none. Your observations about the solidity and resolution of the bass notes is absolutely on target.
However, I would recommend that you use an active preamplifier to experience the dynamics this amplifier is capable of. I have driven the Stochino amplifier Passively, through OPA604s and a Class-A preamp using MAT02, 03 that appeared in Elektor. The last one had an output impedance below 50 ohms or so, the THD was negligible ( you have to count more zeros after the decimal than any other numbers) and the slew rate was about 250v/uS. To say the least, this preamp made the amp sound fabulous.
The set up in which this was tested consisted of a Meridian CD transport, Monarchy Jitter Buster, outboard D/A converter (DPA or something), KEF floor standing speakers using the famed B139s, XLO and Venden Hull interconnects, XLO speaker cables, Ben Duncan's Pure Henry(s) between amplifier and speaker, isolation transformer, Balancing ring on CD etc., Yes the dark background that the amp lends to the soundstage and the dynamic fidelity was stunning to say the least.
Improve on your preamp and you will be even more pleased with the Stochino amplifier.
I am happy to read that you have completed this long pending project. I also read your report on the sonics of the Stochino amplifier.
I made a stereo amp using this design about 1 1/2 years ago and gave the amp away to a friend. As I can recall, the sonic quality of this amp is second to none. Your observations about the solidity and resolution of the bass notes is absolutely on target.
However, I would recommend that you use an active preamplifier to experience the dynamics this amplifier is capable of. I have driven the Stochino amplifier Passively, through OPA604s and a Class-A preamp using MAT02, 03 that appeared in Elektor. The last one had an output impedance below 50 ohms or so, the THD was negligible ( you have to count more zeros after the decimal than any other numbers) and the slew rate was about 250v/uS. To say the least, this preamp made the amp sound fabulous.
The set up in which this was tested consisted of a Meridian CD transport, Monarchy Jitter Buster, outboard D/A converter (DPA or something), KEF floor standing speakers using the famed B139s, XLO and Venden Hull interconnects, XLO speaker cables, Ben Duncan's Pure Henry(s) between amplifier and speaker, isolation transformer, Balancing ring on CD etc., Yes the dark background that the amp lends to the soundstage and the dynamic fidelity was stunning to say the least.
Improve on your preamp and you will be even more pleased with the Stochino amplifier.
Hi Sam,
Thanks for your encouragement! A couple of questions:
You said you listened to the Stochino amp using both your Elektor discrete preamp (I still have the issues of the magazine with that project in - I was tempted to build it myself, but for the absence of remote control) as well as with the OPA604-based preamp. What sonic differences were there between the preamps? My interest was piqued because my nearly-completed preamp uses OPA2604s as input and output buffers.
Secondly, why did you give the amp away? What do you use yourself that is (presumably) better?
Alex
Thanks for your encouragement! A couple of questions:
You said you listened to the Stochino amp using both your Elektor discrete preamp (I still have the issues of the magazine with that project in - I was tempted to build it myself, but for the absence of remote control) as well as with the OPA604-based preamp. What sonic differences were there between the preamps? My interest was piqued because my nearly-completed preamp uses OPA2604s as input and output buffers.
Secondly, why did you give the amp away? What do you use yourself that is (presumably) better?
Alex
Alex,
The preamp using OPA604(BurrBrown) was an adaptation of a circuit that appeared in Electronics World by Reg Williamson in which he used LF356 for the input buffer and NE5534 as the gain stage with an active volume control. He noted that in a study he conducted using this preamp configuration even with more exotic components, the difference in sonics were not notable to the listeners. He also used gyrators for bass/treble controls.
I eliminated the tone section and had OPA604s for the buffer and gain stages. I don't remember the exact values, but I made a few changes to the bias and feedback resistors of the gain stage, while retaining the active volume control configuration.
As opposed to Reg Williamson's observations, the OPAs outscored on the NE5534.
However, compared to the Elektor Class A Discrete preamp, the OPA604s had a higher noise floor and the sound stage was not as much forward. The rather laid back sound stage was too vivid with the Stochino amp but not with other amps I tried at that time. The discrete preamp also exhibited a greater degree of resolution, more neutral tone and a greater dynamic range. I guess the parameters that played a significant role were the lower output impedance, higher slew rate, absence of crossover artefacts and lower TIM, DIM and THD.
My friend who used to visit Gulf countries every month or so (he was a trader) had heard the top of the line Mark Levinsons and Krells among others. He was absolutely pleased with the sound of the Stochino and commented that it sounded slightly better in some areas as compared to stuff that he had heard. He owned a pair of B&W (CDM1, I think) speakers and an Arcam CD player (24bit 96KHz) and wanted no other amp than the Stochino amp. Hence, I gave it away.
I have tried Anthony Holton's N-channel amp and I think there is a certain magic to the sound of this amp, particularly with the mids. I have tried several other amplifiers in the mean time but am not as pleased as with the Stochino amp. However, I would prefer the sound of the Stochino amp to be slightly less metallic and more rounded for it to be as close to perfect as we can get. Maybe it is the current source on the input pair that is suspect, as has been discussed in this thread. But this is pushing it really as otherwise the sound of the amp is amazing. It is just that little extra that I would have preferred. I have about ten assembled PCBs of the Stochino amplifier. So I rigged one channel this afternoon and powered it up, albeit using a lower common voltage for the input and output stages. Yes the sound of the amplifier did not fail to impress me again.
I am thinking of completing stereo amplifiers of the Stochino topology, Anthony Holton's N-channel, Aleph-X and Andrea's Power Follower. Then I will decide on which one to listen to on long term basis.
The preamp using OPA604(BurrBrown) was an adaptation of a circuit that appeared in Electronics World by Reg Williamson in which he used LF356 for the input buffer and NE5534 as the gain stage with an active volume control. He noted that in a study he conducted using this preamp configuration even with more exotic components, the difference in sonics were not notable to the listeners. He also used gyrators for bass/treble controls.
I eliminated the tone section and had OPA604s for the buffer and gain stages. I don't remember the exact values, but I made a few changes to the bias and feedback resistors of the gain stage, while retaining the active volume control configuration.
As opposed to Reg Williamson's observations, the OPAs outscored on the NE5534.
However, compared to the Elektor Class A Discrete preamp, the OPA604s had a higher noise floor and the sound stage was not as much forward. The rather laid back sound stage was too vivid with the Stochino amp but not with other amps I tried at that time. The discrete preamp also exhibited a greater degree of resolution, more neutral tone and a greater dynamic range. I guess the parameters that played a significant role were the lower output impedance, higher slew rate, absence of crossover artefacts and lower TIM, DIM and THD.
My friend who used to visit Gulf countries every month or so (he was a trader) had heard the top of the line Mark Levinsons and Krells among others. He was absolutely pleased with the sound of the Stochino and commented that it sounded slightly better in some areas as compared to stuff that he had heard. He owned a pair of B&W (CDM1, I think) speakers and an Arcam CD player (24bit 96KHz) and wanted no other amp than the Stochino amp. Hence, I gave it away.
I have tried Anthony Holton's N-channel amp and I think there is a certain magic to the sound of this amp, particularly with the mids. I have tried several other amplifiers in the mean time but am not as pleased as with the Stochino amp. However, I would prefer the sound of the Stochino amp to be slightly less metallic and more rounded for it to be as close to perfect as we can get. Maybe it is the current source on the input pair that is suspect, as has been discussed in this thread. But this is pushing it really as otherwise the sound of the amp is amazing. It is just that little extra that I would have preferred. I have about ten assembled PCBs of the Stochino amplifier. So I rigged one channel this afternoon and powered it up, albeit using a lower common voltage for the input and output stages. Yes the sound of the amplifier did not fail to impress me again.
I am thinking of completing stereo amplifiers of the Stochino topology, Anthony Holton's N-channel, Aleph-X and Andrea's Power Follower. Then I will decide on which one to listen to on long term basis.
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