Mark Johnson Opamp Evaluation
I received some evaluation opamps from Mark Johnson a few days ago. Wasting no time, I replaced my M2x IPS6 cards with my IPS7 cards and began listening evaluations on the 3 samples he sent. They had their part numbers painted out and color coded (Red, Blue and Green), presumably to prevent "data sheet bias" and to provide a 'single blind' test environment. My reference standard opamp for the IPS7 is the OPA1612 dual/OPA1611 single. The OPA1611/12 was decided on some time ago as a result of listening to a half dozen or so forum-recommended opamps. I compared the blind study opamps to each other. I also compared them to the OPA1612 and the IPS6. Tech note: I added two sockets to the bottom of each of Mark's opamps to facilitate quick swapping during the tests.
I listened for tonal balance, clarity, smoothness, detail, imaging and depth and something I'll call the smile factor, i.e., does it raise any goosebumps and is it a fun and exciting listening experience.
I'll I try to assign a number scale of 1 to 5 (5 best) to the following characteristics:
T - Transient Response (a combination of high slew rate and low transient intermodulation distortion)
D - Depth (a combination of low noise and low total harmonic distortion)
B - Balance (a combination of wide bandwidth and flat frequency response)
Evaluation opamps, in order of preference:
#1 BLUE - T3, D3, B4; Balanced overall. Clean but not harsh. Moderate smile factor. Noticably preferable to RED or GREEN.
#2 RED - T2, D2, B3; Very smooth and non-fatiguing. Soft overall, and a bit veiled and 2-dimensional sounding. Did not handle female vocals well. Not exciting. No smiles.
#3 GREEN - T2, D3, B2; Very bright, translating to a bit more low level detail than BLUE or RED but lacking imaging and sound stage depth. Not exciting. No smiles.
Reference devices, in order of preference:
#1 IPS6 - T4, D5, B5; Basically creates a studio monitor version of the F6 amplifier (T5, D4, B5), different but equal with the F6 holding the edge in the smile department and the M2x/IPS6 having the edge in the detail department.
#2 OPA1612 - T4, D4, B5; None of the 3 new opamps sounded as good to me overall as the OPA1612, which itself is outperformed by the IPS6.
System components:
Source: Yamaha CD-S300-RK CD player in 'Pure Direct' mode
Preamp: Wayne Colburn BA2018 with Whammy linear power supply (LED reference, +/-17.3VDC)
Crossover: Nelson Pass LX Mini Active Crossover Network customized for 450Hz loudspeaker biamplification
Mid-Hi Power Amp: M2x with 400 watt linear power supply
Bass Power Amp: Behringer A800 Class-D 400w/ch
Loudspeakers: Mid-1980s ADS L980 12" 3-way studio monitors, biamplified, crossed at 450Hz
Primary CD material:
Kevin Mahogany "Another Time Another Place" acoustic jazz: male vocals, saxophone, piano, bass, drums, Track 2
Stanley Clarke "The Stanley Clarke Band, featuring Hiromi" electric jazz: bass, piano, synthesizers, drums, Track 9
Paul Simon "Songs From The Capeman", doo-wop, rock 'n' roll and Puerto Rican rhythms, Track 13
Final caveat: I built an F6 long before I built an M2x and I tweeked the slopes, levels and crossover points in the Pass ACN using my F6 as reference amp for the mid-highs. I did not readjust the ACN for any changes the M2x might introduce.
I received some evaluation opamps from Mark Johnson a few days ago. Wasting no time, I replaced my M2x IPS6 cards with my IPS7 cards and began listening evaluations on the 3 samples he sent. They had their part numbers painted out and color coded (Red, Blue and Green), presumably to prevent "data sheet bias" and to provide a 'single blind' test environment. My reference standard opamp for the IPS7 is the OPA1612 dual/OPA1611 single. The OPA1611/12 was decided on some time ago as a result of listening to a half dozen or so forum-recommended opamps. I compared the blind study opamps to each other. I also compared them to the OPA1612 and the IPS6. Tech note: I added two sockets to the bottom of each of Mark's opamps to facilitate quick swapping during the tests.
I listened for tonal balance, clarity, smoothness, detail, imaging and depth and something I'll call the smile factor, i.e., does it raise any goosebumps and is it a fun and exciting listening experience.
I'll I try to assign a number scale of 1 to 5 (5 best) to the following characteristics:
T - Transient Response (a combination of high slew rate and low transient intermodulation distortion)
D - Depth (a combination of low noise and low total harmonic distortion)
B - Balance (a combination of wide bandwidth and flat frequency response)
Evaluation opamps, in order of preference:
#1 BLUE - T3, D3, B4; Balanced overall. Clean but not harsh. Moderate smile factor. Noticably preferable to RED or GREEN.
#2 RED - T2, D2, B3; Very smooth and non-fatiguing. Soft overall, and a bit veiled and 2-dimensional sounding. Did not handle female vocals well. Not exciting. No smiles.
#3 GREEN - T2, D3, B2; Very bright, translating to a bit more low level detail than BLUE or RED but lacking imaging and sound stage depth. Not exciting. No smiles.
Reference devices, in order of preference:
#1 IPS6 - T4, D5, B5; Basically creates a studio monitor version of the F6 amplifier (T5, D4, B5), different but equal with the F6 holding the edge in the smile department and the M2x/IPS6 having the edge in the detail department.
#2 OPA1612 - T4, D4, B5; None of the 3 new opamps sounded as good to me overall as the OPA1612, which itself is outperformed by the IPS6.
System components:
Source: Yamaha CD-S300-RK CD player in 'Pure Direct' mode
Preamp: Wayne Colburn BA2018 with Whammy linear power supply (LED reference, +/-17.3VDC)
Crossover: Nelson Pass LX Mini Active Crossover Network customized for 450Hz loudspeaker biamplification
Mid-Hi Power Amp: M2x with 400 watt linear power supply
Bass Power Amp: Behringer A800 Class-D 400w/ch
Loudspeakers: Mid-1980s ADS L980 12" 3-way studio monitors, biamplified, crossed at 450Hz
Primary CD material:
Kevin Mahogany "Another Time Another Place" acoustic jazz: male vocals, saxophone, piano, bass, drums, Track 2
Stanley Clarke "The Stanley Clarke Band, featuring Hiromi" electric jazz: bass, piano, synthesizers, drums, Track 9
Paul Simon "Songs From The Capeman", doo-wop, rock 'n' roll and Puerto Rican rhythms, Track 13
Final caveat: I built an F6 long before I built an M2x and I tweeked the slopes, levels and crossover points in the Pass ACN using my F6 as reference amp for the mid-highs. I did not readjust the ACN for any changes the M2x might introduce.
Wow!! Grateful thanks and powerful congratulations to avdesignguru!
@avdesignguru, thank you for an incredibly thorough and thoughtful review! Clearly you invested a large amount of time, carefully listening and then beautifully summarizing your conclusions. I'm certain your ratings and explanations will be hugely beneficial to M2x owners when we finally drop the kimono, and show the opamp part numbers & where they can be purchased.
The chart of colors and device IDs is attached below as an encrypted .zip archive. When all reviews are complete and have been posted here, I'll provide the password. This makes it hard to "cheat" by waiting to see which color was best-liked and then falsely claiming, after the fact, that the best-loved one was OPAMP-X, which my daughter designed while consulting for Ersatzco Semiconductors.
{reminder to self: the password is the third word in the nickname of that hilarious guy in Dallas: JOHN KIRKLAND WORD3}
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@avdesignguru, thank you for an incredibly thorough and thoughtful review! Clearly you invested a large amount of time, carefully listening and then beautifully summarizing your conclusions. I'm certain your ratings and explanations will be hugely beneficial to M2x owners when we finally drop the kimono, and show the opamp part numbers & where they can be purchased.
The chart of colors and device IDs is attached below as an encrypted .zip archive. When all reviews are complete and have been posted here, I'll provide the password. This makes it hard to "cheat" by waiting to see which color was best-liked and then falsely claiming, after the fact, that the best-loved one was OPAMP-X, which my daughter designed while consulting for Ersatzco Semiconductors.
{reminder to self: the password is the third word in the nickname of that hilarious guy in Dallas: JOHN KIRKLAND WORD3}
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One of the joys of having 8 different IPS cards to try, is that different people will have different favorites. Since September there have been several people who love and sing the praises of IPS7 (single or dual opamp, socketed), several others who love Love LOVE IPS6 (matched, discrete J113 FETs), and several others who think Cederburg (twitchy racehorse AD797 opamp) is the best of them all.
Each one of those people is 100 percent correct, of course.
Each one of those people is 100 percent correct, of course.
There are video buffer ICs available today, which viciously kick asszs upon the ancient HA-5002 used in Norwood. SPICE model in 1991 means first production in 1990. The thing is over 30 years old, no surprise that others have caught up and surpassed it by a wide margin.
Flop out two or three PCBs with two or three newer video buffer chips, and experiment with TurboNorwood V.1 and V.2 and V.3 . You'll have smashing great fun. Be sure to provide Moderator 6L6 with progress reports and listening evaluations. He really, really likes line level circuits which include video buffer ICs. He even loved the Azul HPA @ Burning Amp 2019, which used extremely ancient LH0033 video buffers to drive headphones. Gulp!
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Flop out two or three PCBs with two or three newer video buffer chips, and experiment with TurboNorwood V.1 and V.2 and V.3 . You'll have smashing great fun. Be sure to provide Moderator 6L6 with progress reports and listening evaluations. He really, really likes line level circuits which include video buffer ICs. He even loved the Azul HPA @ Burning Amp 2019, which used extremely ancient LH0033 video buffers to drive headphones. Gulp!
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Marconi118
Yes, I prefer the F6 to any IC opamp I've heard so far in the front end of the M2x (the OPA1612 does come very close for me). The F6 must be biased up to at least 0.575 volts drop or higher across the source resistors or that comparison falls apart.
But then I also prefer a Burson Classic V6 fully discreet component 'opamp' to any of the IC opamps as the front end to my Whammy headphone amplifier (again, the OPA1612 does come very close for me).
Yes, I prefer the F6 to any IC opamp I've heard so far in the front end of the M2x (the OPA1612 does come very close for me). The F6 must be biased up to at least 0.575 volts drop or higher across the source resistors or that comparison falls apart.
But then I also prefer a Burson Classic V6 fully discreet component 'opamp' to any of the IC opamps as the front end to my Whammy headphone amplifier (again, the OPA1612 does come very close for me).
Both F6 and M2X have a buffer at the input to drive a transformer
Maybe M2X with J74/K170 jfets (ishikawa) input buffer would sound almost the same as the F6?
or maybe the other way around how would an F6 with OP amp input (IPS6 IPS7) would sound?
We could imagine an F6X using the same daughter cards as M2X ?!
Maybe M2X with J74/K170 jfets (ishikawa) input buffer would sound almost the same as the F6?
or maybe the other way around how would an F6 with OP amp input (IPS6 IPS7) would sound?
We could imagine an F6X using the same daughter cards as M2X ?!
Matching JFETs Ishikawa
My M2x boards are on the way, so in preperation I decided to match two sets of N and P Jfets. I had previously sorted my fets by IDSS so finding a pair should not be difficult. I had purchased a Mega328 tester ( 6L6 recomendation ) so I decided to test the jfets again. The Mega328 gives the Id and Vgs the pin-out and the type ( J or P channel ). It was interesting to note that the measurement tracked well with the Idss. By matching the Vgs I was able to match those Jfets much closer than simple Idss matching. In a simple prototype board with 10 ohm source resistors and a bipolar 24 volt supply I was able to get a 10 MV offset at the output. My question is ; do I need the capacitor between the Jfets and the transformer ? or is 10 mv too much.
My M2x boards are on the way, so in preperation I decided to match two sets of N and P Jfets. I had previously sorted my fets by IDSS so finding a pair should not be difficult. I had purchased a Mega328 tester ( 6L6 recomendation ) so I decided to test the jfets again. The Mega328 gives the Id and Vgs the pin-out and the type ( J or P channel ). It was interesting to note that the measurement tracked well with the Idss. By matching the Vgs I was able to match those Jfets much closer than simple Idss matching. In a simple prototype board with 10 ohm source resistors and a bipolar 24 volt supply I was able to get a 10 MV offset at the output. My question is ; do I need the capacitor between the Jfets and the transformer ? or is 10 mv too much.
marconi118
F6 and M2x will probably never sound the exactly same. The transformers have different core materials and are used in completely different ways. The M2x has complementary push-pull output devices, the F6 uses the transformer to reverse phase to one of two identical output devices and create the push-pull. For at least those two reasons, the harmonic distortion signatures are slightly different.
F6 and M2x will probably never sound the exactly same. The transformers have different core materials and are used in completely different ways. The M2x has complementary push-pull output devices, the F6 uses the transformer to reverse phase to one of two identical output devices and create the push-pull. For at least those two reasons, the harmonic distortion signatures are slightly different.
I just learned that the same underlying circuit idea in daughter card IPS7, was patented in Great Britain by inventors Sandman and Mohapatra, 41 years ago. Since British patents have a lifetime of 20 years, this one is definitely past its expiration date. Still, it's fun to read their discussion of the advantages and disadvantages. Check out Figure 5: they have the cojones to connect "N" number of supply bootstraps in series. Boggle!
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