Testing
Time was my scarcest resource lately... I haven't had the chance to put together a full report, but I'll post a short version very soon.
I have recorded each subject's (subjective) "best amp ever heard" preference. A live comparation with other commercial amps is in the cards, but it won't happen anytime soon, due to the lack of commercial high end equipment, the lack of switching equipment and the logistics required to set up such a session. I'm in contact with a few high end audio shops here in the Greater Toronto Area, trying to stir some interest in such a test - with limited results so far.
Time was my scarcest resource lately... I haven't had the chance to put together a full report, but I'll post a short version very soon.
I have recorded each subject's (subjective) "best amp ever heard" preference. A live comparation with other commercial amps is in the cards, but it won't happen anytime soon, due to the lack of commercial high end equipment, the lack of switching equipment and the logistics required to set up such a session. I'm in contact with a few high end audio shops here in the Greater Toronto Area, trying to stir some interest in such a test - with limited results so far.
Very off topic
Don't use caustic soda, just anodize aluminum. All you need is diluted sulfuric acid (10% H2SO4, 90% H2O), a stainless steel cathode and of course a power supply. Notice that some aluminum alloys are less suitable for anodizing (see the web). Optionally, use wool dye for coloring the oxide layer.
Cheers, Edmond.
Nordic said:
Don't use caustic soda, just anodize aluminum. All you need is diluted sulfuric acid (10% H2SO4, 90% H2O), a stainless steel cathode and of course a power supply. Notice that some aluminum alloys are less suitable for anodizing (see the web). Optionally, use wool dye for coloring the oxide layer.
Cheers, Edmond.
I haven't had a chance of writing down a full compilation of my notes, so here is a quick draft... As an absolute beginner in this area, I have concluded that analyzing and extracting signal from noise in subjective listening tests is actually more difficult than building amps!
Equipment:
- Mark Levinson No.32 preamp
- B&W 801 speakers (8 ohm)
- Totem Acoustic Model 1 Signature (4ohm)
- Rega Planar 5 turntable with a Dynavector MC cartridge
- Krell SACD player.
Cables:
- Speakers: 15' Monster XP Clear Jacket, AWG 12
- Audio: 3' Monster RCA Stereo Audio 300
There were four subjects (myself included, call them A, B, C, D) Each had a chance to bring his own selection of music on CD, SACD or Vinyl. It happened that two of the subjects were into the Classic genre, one into Jazz/Pop and one into Rock/Avantgarde. Here's the selection:
Classic
- Beethoven, Symphony No. 9 by Hans Sotin, Ludwig van Beethoven, Georg Solti, Chicago Symphony Orchestra & Chorus, CD, 1995
- Mozart, Violin Concertos, Julia Fischer, Yakov Kreizberg, and Netherlands Chamber Orchestra, Hybrid SACD, 2005
Jazz/Pop
- "Friday Night in San Francisco", Al Di Meola, John Mclaughlin, and Paco De Lucia, Vinyl, Live 1981
- "Live in Paris", Diana Krall, CD, Live 2002
- "Time Out", Paul Desmond and Dave Brubeck, SACD, 1999
Rock/Avantgarde:
- "Starless and Bible Black", King Crimson, Vinyl, 1974
- "The Seduction of Claude Debussy", The Art of Noise, CD, 1999
- "Up", Peter Gabriel, Hybrid SACD, 2003
Each of the subjects were interviewed on the best known power amp experience:
A - Musical Fidelity Tri-Vista kW Monobloc
B - Halcro DM58
C - McIntosh MC1201 Monoblock
D - Mark Levinson No.333
I would start with a personal satisfaction: I am not deaf (yet!). My first estimate of the sound (before the amp was installed in the chassis), as described in the web site's conclusions, were mostly confirmed.
It was unanimous that this amp is the most unforgiven piece of equipment that was ever heard. Everything, the slightest noise in the recording, background foot stomps during live performances, everything that was (probably) not intended to be listened at is there in the speakers. If this is good or bad, it is questionable. Two of the subjects characterized this behaviour as "tiresome", "distracting", "aggressive", the other two subjects mentioned "extremely detailed", "precise" and "very involving". Further discussions revealed that it's ultimately a matter of expectations. Some subjects are expecting from an amp to hide most of the background details (typically in live performances), a less grippy, authoritative and a bit softer sound, with less overall impact and dynamics. Others think that listening to a recording should be an integrated experience, so every detail is revealing and important.
During the first morning session, two of the subjects identified a faint harshness in the treble response. It took me some time to identify/hear this effect (it appeared to be more evident on tracks with very high dynamic like King Crimson's "Providence"). Strangely enough, it was located in the right channel only. When everybody went for lunch, I popped the case lid and took another look... and sure as hell, the right channel OPS had lower compensation caps (33pF/22pF instead of 47pF/39pF). I replaced the caps and the afternoon session showed that the harshness was gone.
Everybody agreed that the PGP amp has a very high harmonic accuracy. Compared to each reference amp experience, the PGP amp was excellent in preserving the distinctive timbres of voices and musical instruments. On Mozart's Violin Concertos, violins were sounding like violins, without any "synthesized" or "electronic" timbre.
The PGP delivered an amazing midband: not "euphonic", or "glazed-over", but "natural", with "unforced detail" and "sweetness". The voice on Diana Krall's "Live in Paris" sounded "grain-free" and "extended".
Dynamic was another very strong point. We were unable to hear high-level congestions, or any other limitations in dynamic range.
Once the OPS compensation was fixed, the trebles were stunning. "Friday Night in San Francisco" acoustic guitars were "tangible", with an intimate touch to the sound. In fact, all live recordings sounded suprisingly fresh, with a sense of involving never heard before.
The bass response was found as "deep", "tight", "tuneful", "thunderous dynamic", and "snappy". The Art of Noise's "Born on a Sunday" sounded "involving" and "captivating". The full palette of tonal colors were so well rendered they were "physically sensed in our chests".
Results in the 4ohm speakers were dissapointing. To make a long(ish) story short, the PGP is unable to properly drive 4ohm speakers up to it's full power of 200W/ch. The PGP OPS deliveres and estimated of 15A peak and that's definitely not enough to drive 4 ohm speakers (dipping at 2 ohm, plus the phase lag) at full power. However, up to about 100W/channel, the 4 ohm performance is comparable with the 8 ohm load performance. One to another, my conclusion is that lateral MOSFETs are not recommended for the ultimate performance in 4 ohm speaker loads. A good lesson for the "lesson learned" phase of this project.
More to come...
Equipment:
- Mark Levinson No.32 preamp
- B&W 801 speakers (8 ohm)
- Totem Acoustic Model 1 Signature (4ohm)
- Rega Planar 5 turntable with a Dynavector MC cartridge
- Krell SACD player.
Cables:
- Speakers: 15' Monster XP Clear Jacket, AWG 12
- Audio: 3' Monster RCA Stereo Audio 300
There were four subjects (myself included, call them A, B, C, D) Each had a chance to bring his own selection of music on CD, SACD or Vinyl. It happened that two of the subjects were into the Classic genre, one into Jazz/Pop and one into Rock/Avantgarde. Here's the selection:
Classic
- Beethoven, Symphony No. 9 by Hans Sotin, Ludwig van Beethoven, Georg Solti, Chicago Symphony Orchestra & Chorus, CD, 1995
- Mozart, Violin Concertos, Julia Fischer, Yakov Kreizberg, and Netherlands Chamber Orchestra, Hybrid SACD, 2005
Jazz/Pop
- "Friday Night in San Francisco", Al Di Meola, John Mclaughlin, and Paco De Lucia, Vinyl, Live 1981
- "Live in Paris", Diana Krall, CD, Live 2002
- "Time Out", Paul Desmond and Dave Brubeck, SACD, 1999
Rock/Avantgarde:
- "Starless and Bible Black", King Crimson, Vinyl, 1974
- "The Seduction of Claude Debussy", The Art of Noise, CD, 1999
- "Up", Peter Gabriel, Hybrid SACD, 2003
Each of the subjects were interviewed on the best known power amp experience:
A - Musical Fidelity Tri-Vista kW Monobloc
B - Halcro DM58
C - McIntosh MC1201 Monoblock
D - Mark Levinson No.333
I would start with a personal satisfaction: I am not deaf (yet!). My first estimate of the sound (before the amp was installed in the chassis), as described in the web site's conclusions, were mostly confirmed.
It was unanimous that this amp is the most unforgiven piece of equipment that was ever heard. Everything, the slightest noise in the recording, background foot stomps during live performances, everything that was (probably) not intended to be listened at is there in the speakers. If this is good or bad, it is questionable. Two of the subjects characterized this behaviour as "tiresome", "distracting", "aggressive", the other two subjects mentioned "extremely detailed", "precise" and "very involving". Further discussions revealed that it's ultimately a matter of expectations. Some subjects are expecting from an amp to hide most of the background details (typically in live performances), a less grippy, authoritative and a bit softer sound, with less overall impact and dynamics. Others think that listening to a recording should be an integrated experience, so every detail is revealing and important.
During the first morning session, two of the subjects identified a faint harshness in the treble response. It took me some time to identify/hear this effect (it appeared to be more evident on tracks with very high dynamic like King Crimson's "Providence"). Strangely enough, it was located in the right channel only. When everybody went for lunch, I popped the case lid and took another look... and sure as hell, the right channel OPS had lower compensation caps (33pF/22pF instead of 47pF/39pF). I replaced the caps and the afternoon session showed that the harshness was gone.
Everybody agreed that the PGP amp has a very high harmonic accuracy. Compared to each reference amp experience, the PGP amp was excellent in preserving the distinctive timbres of voices and musical instruments. On Mozart's Violin Concertos, violins were sounding like violins, without any "synthesized" or "electronic" timbre.
The PGP delivered an amazing midband: not "euphonic", or "glazed-over", but "natural", with "unforced detail" and "sweetness". The voice on Diana Krall's "Live in Paris" sounded "grain-free" and "extended".
Dynamic was another very strong point. We were unable to hear high-level congestions, or any other limitations in dynamic range.
Once the OPS compensation was fixed, the trebles were stunning. "Friday Night in San Francisco" acoustic guitars were "tangible", with an intimate touch to the sound. In fact, all live recordings sounded suprisingly fresh, with a sense of involving never heard before.
The bass response was found as "deep", "tight", "tuneful", "thunderous dynamic", and "snappy". The Art of Noise's "Born on a Sunday" sounded "involving" and "captivating". The full palette of tonal colors were so well rendered they were "physically sensed in our chests".
Results in the 4ohm speakers were dissapointing. To make a long(ish) story short, the PGP is unable to properly drive 4ohm speakers up to it's full power of 200W/ch. The PGP OPS deliveres and estimated of 15A peak and that's definitely not enough to drive 4 ohm speakers (dipping at 2 ohm, plus the phase lag) at full power. However, up to about 100W/channel, the 4 ohm performance is comparable with the 8 ohm load performance. One to another, my conclusion is that lateral MOSFETs are not recommended for the ultimate performance in 4 ohm speaker loads. A good lesson for the "lesson learned" phase of this project.
More to come...
syn08 said:
Impressive review so far!Your suggestion about the taste of details or not that it is a matter of expectations is the same as mine. But, additionally, one must not forget that recordings are very far than being perfect and one accurate sound system can reveal these recording/mix/mastering problems. In rock music it is generally worst than classical music - my observation....
Dynamic compression is probably always present in any commercial recording productions...
Regarding your conclusion of the lateral mosfet not adequate for 4 ohms pseakers are you considered these possible reasons:
1- 2SK1058 is 7A device. Other lateral devices are 10A but generally several devices can be put in parallel to get more peak current. 3 pairs only for 200W may not be enough?
2- Is the bias for the mosfets sufficient for such a high power demand (200W)?
3- Is your power supply big enough for 200W/4 ohms?
just some thoughts....
fab said:
Well, I'm not aware of any laterals, available at a reasonable price on this side of the pond, other than the 8A 2SK2221/2SJ352. To my experience, paralleling more than 3 devices starts to be a tedious job. Matching, and the current balancing on the PCB (due to long traces) is difficult. Another big problem is the parasitic capacitance that loads the amp (about 70p/device for regular Berquist silicone insulators, see the website for a discussion on this topic). The solution is to use vertical MOSFETs (2SK1530/2SJ201) but then these need some sort of protection against overcurrent which, to my experience, in a standard current limiting implementation, negatively impacts the performance.
It is currently set at about 160mA/device. I've tried higher with no measurable impact. Something to try for future audition tests, however it will be hard to hear differences without having a reference.
Good point - the power supply is also a limiting factor in the current implementation. A future version targeted at 200W/4ohm needs larger toroids (no less than 400W nominal for each channel) and perhaps 8x18,000uF (2x2x18,000uF) rather than 8x10,000uF (2x2x10,000uF) as in the current incarnation.
Thanks!
Hi Syn08,
thanks for your update. Happy you can take the time to tell the story. I appreciate the honesty of the review and the disclosure of the problems you encountered. It sounds like an amp I'd like to build.
Are all the auxilliary circuits working as expected? Did you try to create some fault conditions?
I am a little bit confused by the 4 ohms performance and it's not clear to me why it is not up to snuff. Presumably you weren't listening to 200W worth of musical program through a speaker. Do you care to elaborate on what happened? My speakers are 4 ohm MTM so this is of particular relevance to me. The transformers do look a little on the small size for the 15 amps tossing around the amp. At that kind of current the series R in the transformer would be damping the peak currents, likely.
Best Regards,
thanks for your update. Happy you can take the time to tell the story. I appreciate the honesty of the review and the disclosure of the problems you encountered. It sounds like an amp I'd like to build.
Are all the auxilliary circuits working as expected? Did you try to create some fault conditions?
I am a little bit confused by the 4 ohms performance and it's not clear to me why it is not up to snuff. Presumably you weren't listening to 200W worth of musical program through a speaker. Do you care to elaborate on what happened? My speakers are 4 ohm MTM so this is of particular relevance to me. The transformers do look a little on the small size for the 15 amps tossing around the amp. At that kind of current the series R in the transformer would be damping the peak currents, likely.
Best Regards,
Syn08,
Are you aware of Profusion's line of Exicon laterals for audio? I have used some; they aren't exactly cheap but worth a look, if you're interested.
Like this one:
http://www.profusionplc.com/pro/gex/pcatdtl0?ipartno=ECF20P20
Jan Didden
Are you aware of Profusion's line of Exicon laterals for audio? I have used some; they aren't exactly cheap but worth a look, if you're interested.
Like this one:
http://www.profusionplc.com/pro/gex/pcatdtl0?ipartno=ECF20P20
Jan Didden
janneman said:
Wow, this would be over $40 a pair, in 10's quantities, to bring these babies on this side of the pond. Unfortunately, it's unlikely to happen on my watch.
Given the current status of the power MOSFET market (with specialized audio devices at the brink of extinction), I think it should be a very interesting project to investigate what could ultimately be done (performance wise) with the regular switching pairs (IRF, FQA, etc...).
Set aside any esoteric "how does it sound" issues, the only major difference I am aware of is matching; Toshiba audio vertical devices (2SK1530/2SJ201) are matched for transconductance while IRF, Fairchild, etc... vertical devices are matched for charges. Other issues (like lower Vth in Toshiba's devices) are ultimately minor.
syn08 said:
What about the devices that were announced by Anthony Holton (The Saint on this site)? 10A devices, fairly reasonably priced (~$6??). I'm not sure if they are available yet......
See the following for announcement:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=95295
Steve.
syn08 said:
Thanks for the great review. Your point about the change in the compensating capacitors was fascinating. Can you speculate on whether the difference in capacitors made a measurable or simulatable difference in stability or frequency response that one could reasonably attribute to a change in sound? Or maybe there was a difference in stability in clipping behavior?
What was the approximate efficiency of the loudspeakers you were listening to?
Is there any chance that the amps were clipping on high-crest-factor peaks?
Thanks again,
Bob
janneman said:
wow Laterals with 16A in TO-3P device !
and transconductance between 1.4 and 4 which is double the 2SK-1058/2SJ162 devices...
Is it a double die device like I have seen somewhere but I do not remember which device...?
The price is quite high but for DIY and the idea of a super amp...
I hope you get matched devices for paralleling at that price...
Does anybody know something more about exicon? A few obvious searches doesn't bring up any of the usual websites, besides profusionplc. If it's a small specialty company, it could disappear any day in the semiconductor world.
These may very well be the ideal devices but I would much rather use Sanken or IRFs.
These may very well be the ideal devices but I would much rather use Sanken or IRFs.
Bob Cordell said:
I was unable to measure anything special on the channel with lower compensation. In fact I am pretty sure I started with the right value caps and I replaced them with lower value caps precisely for testing the stability. With 39pF/22pF the simulated phase margin is about 10degs lower. I can only speculate, but I suppose it was a stability problem.
B&W801 (8ohm) are 90dB, the Totem Acoustic (4ohm) are 87dB.
I don't think so. The Totem Acoustic speakers are rated at 120W max and we never went over that, far away from the amp clipping level. Symptoms included "muddy bass", "compressed dynamic", and a general "lack of life" in the sound field. Don't take me wrong, if it was not to be compared with the 8ohm results, the sound could probably qualify as "acceptable", however "acceptable" what was not the original performance target for this amp. Certainly, the next incarnation needs a beefy power supply and higher output current.
XLR to RCA converter
The OPA211 based XLR (balanced) to RCA (single ended) converter.
Shown below while evaluating with OPA2134 as buffers. Final implementation uses LM4562 input buffers. Chip resistors around the OPA211 are 1K 0.05%. Board is 2.8"x1.75" two layers. The bottom layer is almost entirely a (power) ground plane. All electrolytics and small film caps are power supply pins decouplings.
Sites will be updated with the full schematic/Gerbers/measurements/etc... ASAP.
The OPA211 based XLR (balanced) to RCA (single ended) converter.
Shown below while evaluating with OPA2134 as buffers. Final implementation uses LM4562 input buffers. Chip resistors around the OPA211 are 1K 0.05%. Board is 2.8"x1.75" two layers. The bottom layer is almost entirely a (power) ground plane. All electrolytics and small film caps are power supply pins decouplings.
Sites will be updated with the full schematic/Gerbers/measurements/etc... ASAP.
Attachments
Output inductance problem
Dear Edmond,
Dear Bob,
I am wondering about the following. The unknown load capacity and the output inductance form a series resonance. Using e.g. a 2 uH or larger inductance, one can easily image circumstances, where the resonance frequency falls into the region of the unity gain crossover of the global feedback loop. Although the resistor parallel to the inductance dampens this resonance, it will influence the phase margin of the amplifier.
As the listening results to the PGP (and my own experience) suggest, a phase margin change can influence the amplifier's sound, even if the unity gain crossover frequency is really high. (I would therefore also opt for a inductance as low as possible.)
[[ The engineers of Bryston probably found a nice trick. They use a quite large inductor, but also load the output with a rather large capacity of 100nF (perhaps a capacitor with high dielectric losses, providing good intrinsic damping). The unity gain crossover of their main feedback loop lies *above* this resonance. Therefore, each additional load rather improves the behaviour of the overall circuit. This also could explain the result of certain reviews that Bryston amplifiers are that well suited e.g. for planar speakers. ]]
Finally the question: did you investigate the influence of the output resonance? It puzzles me a bit, that none of the well-known audio power amplifier design books seems to further elaborate on this point.
Best regards,
Matze
Dear Edmond,
Dear Bob,
I am wondering about the following. The unknown load capacity and the output inductance form a series resonance. Using e.g. a 2 uH or larger inductance, one can easily image circumstances, where the resonance frequency falls into the region of the unity gain crossover of the global feedback loop. Although the resistor parallel to the inductance dampens this resonance, it will influence the phase margin of the amplifier.
As the listening results to the PGP (and my own experience) suggest, a phase margin change can influence the amplifier's sound, even if the unity gain crossover frequency is really high. (I would therefore also opt for a inductance as low as possible.)
[[ The engineers of Bryston probably found a nice trick. They use a quite large inductor, but also load the output with a rather large capacity of 100nF (perhaps a capacitor with high dielectric losses, providing good intrinsic damping). The unity gain crossover of their main feedback loop lies *above* this resonance. Therefore, each additional load rather improves the behaviour of the overall circuit. This also could explain the result of certain reviews that Bryston amplifiers are that well suited e.g. for planar speakers. ]]
Finally the question: did you investigate the influence of the output resonance? It puzzles me a bit, that none of the well-known audio power amplifier design books seems to further elaborate on this point.
Best regards,
Matze
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