My recent audio concentration areas are (1) the tonearm in the main system (now, based around the Hafler 9300), and (2) the surround sound system in the kitchen.
It was the latter that inspried me to get an ATI 1502 amplifier, to better handle my current hungry Revel M20 speakers than my Yamaha HTR-5790 receiver (which was getting awfully hot, and heating up my 4x4 matrix switch above it terrible, both situations dramatically improved by a 1/4 inch foam board I installed very securely just below the matrix switch...the suspicion that the foam board is even making the Yamaha cooler has me thinking there was kind of a reinforcing "oven" effect with the bottom metal panel of the matrix switch). The Revels are 6 ohm speakers, and the Yamaha nominally can only handle that by flipping a special power-reducing switch--which I don't believe I've done as some experts believe that unless you're out of control levelwise, you get better performance leaving the switch in the 8 ohm position. I didn't tell you that.
I figured the ATI to be the "perfect" AV amp, very solidly made, low noise and distortion, etc. And at 150W, sufficient power for the Revels if not the Acoustats (which I was not, really, buying it for).
One thing, however, is that the ATI does NOT have DC trigger. That led me to think maybe I'd move the ATI into the bedroom system (which has no trigger, and I keep the amp running all the time for several reasons) and move the Parasound HCA-1500A in the bedroom to the kitchen.
And I've long admired Morris Kessler for many reasons: he's time tested in Audio having designed great amplifiers with other contributors (like James Bongiorno, for awhile at SAE) and by himself (the SAE XXXXII was apparently his own design, and one loved most by J Gordon Holt of Stereophile). He believes in making reliable products--and right here in the USA in my home state of California. My hero Sigfried Linkwitz was a reliable user of ATI amplifiers; he loved the multichannel ones for his multi amplified speaker systems and highly recommended them to others.
I visited a friend's friend who was selling an ATI amp about 10 years ago, and it sounded good to my friend George and I might almost have bought it except for the flickering light on the power switch...which the unit I have now also suffers from, now not surprising in a 25 year old amplifier.
But, does Kessler make amplifiers equal to the designs of John Curl, whose used amplifiers like the 1500A are often even available (though at slightly higher prices) than the "equivalent" ATI amplifiers. Curl certainly has more mindshare among high end audiophiles, while Kessler may be better known on the Home Theater circuit nowadays.
I decided to have an "Amplifier Clinic" both to test my new amplifier and ensure it is up to snuff, and to see how, objectively, it compares with the Parasound HCA-1500A. The 1500A is, btw, a design favored by Curl himself over the original cheaper models (like the HCA-1000A) and which is very similar to the Halo and JC amplifiers in basic design, with JFET inputs and MOSFET drivers and bipolar outputs. It's also almost contemporaneous with the ATI 1502, both coming from the early to mid 1990's (I think the ATI was a few years earlier, maybe). I believe the ATI may be an all-bipolar design, Kessler designs being like that. Curl uses bipolar outputs, but FETs in other locations.
I'm very surprised at how little power this amp uses at idle, 40.3 watts after a few hours "warmup" (if you can call it that) idling. It started at 38.9W, showing incredibly stable bias, but also very low bias, almost "Class B" operation, something I'm predisposed against.
It also made some chassis hum, but about the same as the Parasound HCA-1500A in a different location, as far as I could tell.
For some reason, my first day of measurements using my (personally calibrated) Sound Technologies 1700B and my Hantek scope and my recently purchased 500W-2000W 2 ohm to 16 ohm loads went badly awry. I wrongly measured the max output on the ATI which seemed to be only about 27V into 8 ohms (100W), and from then on every measurement I made seemed to confirm the amplfier wasn't that good.
Then I measured the Parasound, which I had often worried about because I leave it running all the time, and it measured basically fine.
Then I compared the numbers...and in many cases they were identical. Something was wrong here.
I determined several errors in my measurement technique. Including that I cannot simply turn up the analyzer voltage leaving it on some lower scale. Somehow that pre-distorts the output. I discovered to better measure amplifier clipping on the ATI like most amplifiers I need to use the 100V measurement scale on the Sound Technology. Then it was clear the ATI was clipping at 41V, equivalent to 210W, only a little less than the Parasound which went to 45V or 253W. The Hafler 9300 clips at about 40.5V.
After that, the distortion and noise numbers are generally so similar that anyone would be hard pressed to say they make a definitive audible difference, despite the distinctly different circuit designs, parts, and philosophies. Generally the Parasound measures slightly lower distortion, and slightly more so at higher frequencies, but so similar it could be measurement error (I've often made much larger errors--such as my first time around measuring the ATI!). Curiously, on my very consistent Meguro noise meter, the wideband AND "A Weighted" noise of the two amplifiers is almost identical but slightly in favor, strangely enough, of the lower bias ATI.
Update: By the following weekend, I had obtained my second Hafler 9300. This was supposedly "upgraded" but reading the fine print, it's more like just being refurbished. The original 20,000uF caps per channel per side were replaced with pairs of 10,000uF caps. Even doing this replacement is difficult in the small Hafler chassis. I measured this refurbished 9300 and also my original "museum quality" NOS 9300. They measured identically, which is evidence the refurb (which also included the replacement of some small transistors) was done well. I put the refurbished 9300 into my system, and decided I might like the sound better, having more punch from the new capacitors.
Wideband Noise:
Parasound (Channel not clear maybe both) 0.12mV wideband
ATI Ch1 0.052mV Ch2 0.056mV
Hafler 0.028mV (both channels)
Hafler Wins, then ATI
(Hafler also has widest bandwidth...so this is a surprise)
A Weighted Noise
Parasound (Channel not written down) 0.039mV
ATI CH1 0.030mV CH2 0.035mV
Hafler 0.0026mV
Hafler Wins, then ATI
Distortion at 0.01V output
Parasound 0.075%
ATI 0.046%
Hafler 0.08%
ATI Wins! (looks like error, though, Hafler should be best because lowest noise)
Distortion at 0.03V
Parasound was 0.075%, curiously identical to 0.01V, measurement error???
Hafler 0.023%
ATI not measured.
Hafler Wins!
Distortion at 0.3V
ATI 0.05%, slightly higher than 0.01V (higher???)
Hafler 0.023%
Hafler Wins!
Distortion at 1V (which, btw, corresponds to 0.125 watts)
Parasound: 0.025%
ATI: 0.055%
Hafler: 0.026%
Parasound wins! Finally it seems the lower static noise of the ATI has been exceeded by some kind of dynamic noise in the ATI that starts appearing just below 1 watt--crossover notch??? Parasound
has also pulled ahead of the Hafler, they are but neck and neck.
Distortion at 3V (about 1.25 watt)
Parasound: 0.008%
ATI: 0.023%
Hafler 0.0094%
Parasound wins by a significant margin over ATI, but ATI still only 0.023% distortion, below
the rated level. This, nevertheless, is the comparatively "worst" point for the ATI, probably a result of crossover notch distortion. At higher levels, the ATI catches up again. The Hafler is still almost as good as the Parasound, just slightly worse.
Distortion at 10V (12W)
Parasound: 0.0049%
ATI: 0.01%
Hafler: 0.0068%
Distortion at 30V (125W)
Parasound: 0.0045%
ATI: 0.0055%
Hafler: 0.0073%
By the time you get to 125W, the ATI has nearly caught up with the Parasound in THD, and the Hafler has fallen further behind--but these are tiny levels way below rated THD and close to my measuring residual and greater differences can be caused by my 1700B during warmup, so the apparent differences here might be 100% measurement error and I wouldn't take them too seriously. The Parasound and ATI give their best measurements at 30V but the Hafler shows its best measurement at 10V curiously. But the distortion numbers are consistently small, showing that all 3 amplifiers are very well designed transistorized Class AB amplifiers performing like new despite average age of 25+ years old (!!!).
At 10kHz, near ATI full power, the superiority of the Parasound is most clear:
Distortion at 30V (125W) at 10kHz
Parasound 0.023%
ATI 0.13%
But, 0.13% distortion still probably isn't audible (and certainly not at 10kHz) and 125W at 10kHz is pretty extreme (though I use such measurement as proxy for probing more complex things)... At more realistic levels the amps are again virtually indistinguishable:
Distortion at 1V, 10kHz
Parasound 0.026%
Distortion at 3V, 10kHz
ATI 0.023%
I should also point out this is getting very close to the rated power of the ATI, while it's quite far from the rated power of the Parasound. As one gets to rated power at high frequencies, distortion in most amplifiers goes way up. (And in very many cases, such as amps I looked at this week in Stereophile, distortion at 10kHz goes far higher than 0.1% at lower levels than 125 watts). To be completely fair, the Parasound ought be compared, say, at 175W, which is relatively the same to rated power (and also, to actual hard clipping).
Into 4 ohm loads, the Parasound tended to clip at 40V instead of 45V, and distortion numbers generally higher above 1V, but still below 0.016% at 1kHz:
Parasound into 4 ohms, 1kHz
30V 0.016%
10V 0.006%
3V 0.013%
1V 0.027%
.1V 0.075%
.01V 0.075%
My sighted listening suggests the ATI a tad brighter sounding on the M20's, but that might suit the bedroom acoustic anyway, with the Parasound better on the M20's in the bright sounding kitchen.
I don't at all believe these amps would be distinguishable in level matched blind tests.
Update 3/18: I put shorting plugs into the ATI in the bedroom, and the output is dead silent. I had to double check the power switch. I've taped all lights except the clip indicators with electrical tape--crude but effective. So the front face, now pulled fully forward in my bedroom rack is "out there" providing limited warmth (not much) to my cat, who was disappointed not to find his warm Parasound last night, only an amp deep in the rack bottom which was covered in dust.
The Parasound stated idling at 31 watts but quickly started rising at first, then slowly after an hour or more to 59 watts, pretty much my predicted "+50%" from the ATI.
Update 3/22: Later did reach 60 watts.
Others DO say the ATI is on the brighter side of neutral, fwiw, but also beautifully transparent, revealing instrument tonaties as well as any amp. I have not measured damping factor vs frequency which would be the most revealing in these regards. Frequency response either but we can assume it's quite flat to 20kHz for both amps (and from what I remember from the specs about 100kHz in both cases, or maybe 60kHz).
I am beginning to think both Parasound and ATI amps have too much chassis hum for continuous operation in the bedroom. In the deepest night, the hum can be heard. I believe it was that way before, I always blamed the neighbors A/C compressor, which is less than 10 feet from the bedroom exterior wall.
But finally I did turn the ATI, now pressed into the cabinet a bit for more help, totally off. And the late night silence was staggeringly different.
I am now beginning to believe what Benchmark says about switching power supplies (not to be confused with digital class amplifiers). Switching power supplies are quieter and induce less magnetic effects from leakage. (And, they're regulated too!) In principle, and the good ones moreso.
But I'm sure both amplifiers would benefit from capacitor replacement, as the old capacitors probably leak far more than brand new ones, and that leakage requires more current through the transformer, and hence more physical vibrations.
For 24 hours after the second weekend of amplifier clinic, I tried to integrate the ATI 1502 into my bedroom system.
The first challenge was the physical hum level. Intial impressions were wrong, it does appear this unit has more physical hum vibration than my other amps. But since it is fairly thin front-to-back, it could be pushed all the way back in my wood rack-cabinet. It can also be angled various ways. I tried both, and it always seemed I was making progress, but after a few hours it was the same old.
Even when it doesn't seem like you can hear the hum directly from the unit, it's energizing the room some other way, and you can still hear it.
This motivated me to finally add a remote Insteon on/off module to control the amplifier. I found a spare on/off unit in the laboratory. I figured I could add the amplifier to the same button on the bedside insteon controller that controls the Meural picture. I would only turn either on when I was not trying to fall asleep.
That problem being worked-around, I focussed on the very slight buzz I could hear from the right speaker. I thought I had heard a little of that previously with the Parasound, but not as much.
I first tried making sure the two digital EQ's, which are grounded, were plugged into the same outlet strip as the amplifier. Well, the amp was plugged directly into the Brickwall surge protector, so I managed to plug the EQ's in near it, though I couldn't plug both into the same duplex outlet on the Brickwall as the amplifier itself.
That didn't seem to help much. I also tried different interconnects from the EQ's to the amplifier, including a new pair of very well shielded Blue Jeans interconnects, which didn't help either. I was beginning to think the hum was in the output of the Behringer EQ's themselves. So I did an upgrade I'd been planning to do for years. I wired in one of the two Denon DVD 5000's as the dac driving the amplifier for the main speakers. The 5000's use dual differential 1704's and digital inputs, and I purchased 3 of them so I could have triamplification using all 1704's before I decided the 5000's just didn't sound wonderful on the living room system. So then I put two of them in a pile in the bedroom, thinking they'd be good enough for the bedroom amp and subwoofer. There they sat for two years until now.
This took some work, but was successful in reducing the electronic hum coming from the left speaker significantly. Not total elimination, but close enough I thought.
Then I listened for awhile to the living room FM tuner through Sonos on the bedroom stereo. Perhaps it's largely because I've gotten used to the much better sounding kitchen tuner (which now has an outdoor antenna), I was not liking the sound. It was too noisy and also bright and edgy, almost unpleasant to listen too. Well this was a combination of the slight edginess I had always thought the 5000's have (along with a crystaline clarity that often makes you overlook the edginess) and what appears to be the slight added brightness of the ATI 1502, a match made in hell. But there was one other thing.
One of the things I had overlooked in the amplifier replacement was the 12dB Harrison Labs attenuators. I just put those aside, assuming incorrectly I had not been using them correctly. But it turns out these attenuators, or something like them, are ESSENTIAL in the bedroom system, otherwise the DACs are only using a fraction of their dynamic range, with the signal strength meters on the Behringers only blinking the bottom light. Unless corrected (which I didn't discover I needed to do for years when I first started using the Behringers) the sound becomes very coarse and grainy.
I first measured the Harrison Labs attenuators, to ensure they are designed for plugging into the destination for a signal. They are: the top of the attenuation network is connected to the female RCA hot connection where you plug the signal bearing cable in. It would not be good to plug them into an output signal RCA jack, AND they would have been worse had they been designed to be used that way because then a resistor would be in series with driving the cable.
The Harrison Labs attenuators greatly improved the sound by restoring the digital resolution available from the DAC. And also reduced the buzz even more. But I was still not liking the sound.
So finally I decided on a different plan. I returned the Parasound HCA-1500A to the bedroom, and decided to use what used-to-be my living room amplifier, my original NOS "minty" Hafler 9300 in the kitchen, and the new refurbed 9300 (which has more punch, it seems) in the living room. This repurposes the ATI 1502 as nothing more than an emergency spare for now. Something I didn't really need to buy (though...perhaps it is the magical "black swan" amplifier which measures fine but sounds bad enough to be different on blind tests...?).
This decision was not at all based on scientific proof that there was anything audibly wrong with the 1502, except for the chassis hum, and also when I plugged the Parasound into the now improved bedroom system (with the upgrades I had done to try to make the 1502 acceptible) the Parasound had virtually no electronic buzz compared to the trace of buzz still remaining with the 1502.
I did feel the sound was more pleasant on the noisy FM radio, using the Parasound. Later as the evening slipped by, there were patches of greater noise on the radio, and I wondered just how true it was that the Parasound made the FM noise sound less objectionable. Maybe it was just a larger than average patch of noise that happened just as I had hooked up the ATI. Perhaps it had just been bad luck for the ATI. But I felt very happy about my new amplifier lineup. Also I had made several long postponed upgrades to the bedroom system:
1) Using 1704 based DAC instead of Behringer DEQ output for the main speakers.
2) High end teflon cable between DAC and amplifier.
3) Remote On/Off switch on the amplifier.
4) Verified correct use of the Harrison Labs attenuator.
5) DAC and amplifier plugged into same duplex outlet on the surge supressor.
It might be better yet using the Integra Research DVD player instead of the Denon 5000. The Integra Research also uses 1704's, but is somehow better sounding I've felt, and I was using it on the living room system for over a year. A Denon 9000 might be better sounding still, but I feel they run too hot for being left on all the time.
It was the latter that inspried me to get an ATI 1502 amplifier, to better handle my current hungry Revel M20 speakers than my Yamaha HTR-5790 receiver (which was getting awfully hot, and heating up my 4x4 matrix switch above it terrible, both situations dramatically improved by a 1/4 inch foam board I installed very securely just below the matrix switch...the suspicion that the foam board is even making the Yamaha cooler has me thinking there was kind of a reinforcing "oven" effect with the bottom metal panel of the matrix switch). The Revels are 6 ohm speakers, and the Yamaha nominally can only handle that by flipping a special power-reducing switch--which I don't believe I've done as some experts believe that unless you're out of control levelwise, you get better performance leaving the switch in the 8 ohm position. I didn't tell you that.
I figured the ATI to be the "perfect" AV amp, very solidly made, low noise and distortion, etc. And at 150W, sufficient power for the Revels if not the Acoustats (which I was not, really, buying it for).
One thing, however, is that the ATI does NOT have DC trigger. That led me to think maybe I'd move the ATI into the bedroom system (which has no trigger, and I keep the amp running all the time for several reasons) and move the Parasound HCA-1500A in the bedroom to the kitchen.
And I've long admired Morris Kessler for many reasons: he's time tested in Audio having designed great amplifiers with other contributors (like James Bongiorno, for awhile at SAE) and by himself (the SAE XXXXII was apparently his own design, and one loved most by J Gordon Holt of Stereophile). He believes in making reliable products--and right here in the USA in my home state of California. My hero Sigfried Linkwitz was a reliable user of ATI amplifiers; he loved the multichannel ones for his multi amplified speaker systems and highly recommended them to others.
I visited a friend's friend who was selling an ATI amp about 10 years ago, and it sounded good to my friend George and I might almost have bought it except for the flickering light on the power switch...which the unit I have now also suffers from, now not surprising in a 25 year old amplifier.
But, does Kessler make amplifiers equal to the designs of John Curl, whose used amplifiers like the 1500A are often even available (though at slightly higher prices) than the "equivalent" ATI amplifiers. Curl certainly has more mindshare among high end audiophiles, while Kessler may be better known on the Home Theater circuit nowadays.
I decided to have an "Amplifier Clinic" both to test my new amplifier and ensure it is up to snuff, and to see how, objectively, it compares with the Parasound HCA-1500A. The 1500A is, btw, a design favored by Curl himself over the original cheaper models (like the HCA-1000A) and which is very similar to the Halo and JC amplifiers in basic design, with JFET inputs and MOSFET drivers and bipolar outputs. It's also almost contemporaneous with the ATI 1502, both coming from the early to mid 1990's (I think the ATI was a few years earlier, maybe). I believe the ATI may be an all-bipolar design, Kessler designs being like that. Curl uses bipolar outputs, but FETs in other locations.
I'm very surprised at how little power this amp uses at idle, 40.3 watts after a few hours "warmup" (if you can call it that) idling. It started at 38.9W, showing incredibly stable bias, but also very low bias, almost "Class B" operation, something I'm predisposed against.
It also made some chassis hum, but about the same as the Parasound HCA-1500A in a different location, as far as I could tell.
For some reason, my first day of measurements using my (personally calibrated) Sound Technologies 1700B and my Hantek scope and my recently purchased 500W-2000W 2 ohm to 16 ohm loads went badly awry. I wrongly measured the max output on the ATI which seemed to be only about 27V into 8 ohms (100W), and from then on every measurement I made seemed to confirm the amplfier wasn't that good.
Then I measured the Parasound, which I had often worried about because I leave it running all the time, and it measured basically fine.
Then I compared the numbers...and in many cases they were identical. Something was wrong here.
I determined several errors in my measurement technique. Including that I cannot simply turn up the analyzer voltage leaving it on some lower scale. Somehow that pre-distorts the output. I discovered to better measure amplifier clipping on the ATI like most amplifiers I need to use the 100V measurement scale on the Sound Technology. Then it was clear the ATI was clipping at 41V, equivalent to 210W, only a little less than the Parasound which went to 45V or 253W. The Hafler 9300 clips at about 40.5V.
After that, the distortion and noise numbers are generally so similar that anyone would be hard pressed to say they make a definitive audible difference, despite the distinctly different circuit designs, parts, and philosophies. Generally the Parasound measures slightly lower distortion, and slightly more so at higher frequencies, but so similar it could be measurement error (I've often made much larger errors--such as my first time around measuring the ATI!). Curiously, on my very consistent Meguro noise meter, the wideband AND "A Weighted" noise of the two amplifiers is almost identical but slightly in favor, strangely enough, of the lower bias ATI.
Update: By the following weekend, I had obtained my second Hafler 9300. This was supposedly "upgraded" but reading the fine print, it's more like just being refurbished. The original 20,000uF caps per channel per side were replaced with pairs of 10,000uF caps. Even doing this replacement is difficult in the small Hafler chassis. I measured this refurbished 9300 and also my original "museum quality" NOS 9300. They measured identically, which is evidence the refurb (which also included the replacement of some small transistors) was done well. I put the refurbished 9300 into my system, and decided I might like the sound better, having more punch from the new capacitors.
Wideband Noise:
Parasound (Channel not clear maybe both) 0.12mV wideband
ATI Ch1 0.052mV Ch2 0.056mV
Hafler 0.028mV (both channels)
Hafler Wins, then ATI
(Hafler also has widest bandwidth...so this is a surprise)
A Weighted Noise
Parasound (Channel not written down) 0.039mV
ATI CH1 0.030mV CH2 0.035mV
Hafler 0.0026mV
Hafler Wins, then ATI
Distortion at 0.01V output
Parasound 0.075%
ATI 0.046%
Hafler 0.08%
ATI Wins! (looks like error, though, Hafler should be best because lowest noise)
Distortion at 0.03V
Parasound was 0.075%, curiously identical to 0.01V, measurement error???
Hafler 0.023%
ATI not measured.
Hafler Wins!
Distortion at 0.3V
ATI 0.05%, slightly higher than 0.01V (higher???)
Hafler 0.023%
Hafler Wins!
Distortion at 1V (which, btw, corresponds to 0.125 watts)
Parasound: 0.025%
ATI: 0.055%
Hafler: 0.026%
Parasound wins! Finally it seems the lower static noise of the ATI has been exceeded by some kind of dynamic noise in the ATI that starts appearing just below 1 watt--crossover notch??? Parasound
has also pulled ahead of the Hafler, they are but neck and neck.
Distortion at 3V (about 1.25 watt)
Parasound: 0.008%
ATI: 0.023%
Hafler 0.0094%
Parasound wins by a significant margin over ATI, but ATI still only 0.023% distortion, below
the rated level. This, nevertheless, is the comparatively "worst" point for the ATI, probably a result of crossover notch distortion. At higher levels, the ATI catches up again. The Hafler is still almost as good as the Parasound, just slightly worse.
Distortion at 10V (12W)
Parasound: 0.0049%
ATI: 0.01%
Hafler: 0.0068%
Distortion at 30V (125W)
Parasound: 0.0045%
ATI: 0.0055%
Hafler: 0.0073%
By the time you get to 125W, the ATI has nearly caught up with the Parasound in THD, and the Hafler has fallen further behind--but these are tiny levels way below rated THD and close to my measuring residual and greater differences can be caused by my 1700B during warmup, so the apparent differences here might be 100% measurement error and I wouldn't take them too seriously. The Parasound and ATI give their best measurements at 30V but the Hafler shows its best measurement at 10V curiously. But the distortion numbers are consistently small, showing that all 3 amplifiers are very well designed transistorized Class AB amplifiers performing like new despite average age of 25+ years old (!!!).
At 10kHz, near ATI full power, the superiority of the Parasound is most clear:
Distortion at 30V (125W) at 10kHz
Parasound 0.023%
ATI 0.13%
But, 0.13% distortion still probably isn't audible (and certainly not at 10kHz) and 125W at 10kHz is pretty extreme (though I use such measurement as proxy for probing more complex things)... At more realistic levels the amps are again virtually indistinguishable:
Distortion at 1V, 10kHz
Parasound 0.026%
Distortion at 3V, 10kHz
ATI 0.023%
I should also point out this is getting very close to the rated power of the ATI, while it's quite far from the rated power of the Parasound. As one gets to rated power at high frequencies, distortion in most amplifiers goes way up. (And in very many cases, such as amps I looked at this week in Stereophile, distortion at 10kHz goes far higher than 0.1% at lower levels than 125 watts). To be completely fair, the Parasound ought be compared, say, at 175W, which is relatively the same to rated power (and also, to actual hard clipping).
Into 4 ohm loads, the Parasound tended to clip at 40V instead of 45V, and distortion numbers generally higher above 1V, but still below 0.016% at 1kHz:
Parasound into 4 ohms, 1kHz
30V 0.016%
10V 0.006%
3V 0.013%
1V 0.027%
.1V 0.075%
.01V 0.075%
My sighted listening suggests the ATI a tad brighter sounding on the M20's, but that might suit the bedroom acoustic anyway, with the Parasound better on the M20's in the bright sounding kitchen.
I don't at all believe these amps would be distinguishable in level matched blind tests.
Update 3/18: I put shorting plugs into the ATI in the bedroom, and the output is dead silent. I had to double check the power switch. I've taped all lights except the clip indicators with electrical tape--crude but effective. So the front face, now pulled fully forward in my bedroom rack is "out there" providing limited warmth (not much) to my cat, who was disappointed not to find his warm Parasound last night, only an amp deep in the rack bottom which was covered in dust.
The Parasound stated idling at 31 watts but quickly started rising at first, then slowly after an hour or more to 59 watts, pretty much my predicted "+50%" from the ATI.
Update 3/22: Later did reach 60 watts.
Others DO say the ATI is on the brighter side of neutral, fwiw, but also beautifully transparent, revealing instrument tonaties as well as any amp. I have not measured damping factor vs frequency which would be the most revealing in these regards. Frequency response either but we can assume it's quite flat to 20kHz for both amps (and from what I remember from the specs about 100kHz in both cases, or maybe 60kHz).
I am beginning to think both Parasound and ATI amps have too much chassis hum for continuous operation in the bedroom. In the deepest night, the hum can be heard. I believe it was that way before, I always blamed the neighbors A/C compressor, which is less than 10 feet from the bedroom exterior wall.
But finally I did turn the ATI, now pressed into the cabinet a bit for more help, totally off. And the late night silence was staggeringly different.
I am now beginning to believe what Benchmark says about switching power supplies (not to be confused with digital class amplifiers). Switching power supplies are quieter and induce less magnetic effects from leakage. (And, they're regulated too!) In principle, and the good ones moreso.
But I'm sure both amplifiers would benefit from capacitor replacement, as the old capacitors probably leak far more than brand new ones, and that leakage requires more current through the transformer, and hence more physical vibrations.
Epilogue
For 24 hours after the second weekend of amplifier clinic, I tried to integrate the ATI 1502 into my bedroom system.
The first challenge was the physical hum level. Intial impressions were wrong, it does appear this unit has more physical hum vibration than my other amps. But since it is fairly thin front-to-back, it could be pushed all the way back in my wood rack-cabinet. It can also be angled various ways. I tried both, and it always seemed I was making progress, but after a few hours it was the same old.
Even when it doesn't seem like you can hear the hum directly from the unit, it's energizing the room some other way, and you can still hear it.
This motivated me to finally add a remote Insteon on/off module to control the amplifier. I found a spare on/off unit in the laboratory. I figured I could add the amplifier to the same button on the bedside insteon controller that controls the Meural picture. I would only turn either on when I was not trying to fall asleep.
That problem being worked-around, I focussed on the very slight buzz I could hear from the right speaker. I thought I had heard a little of that previously with the Parasound, but not as much.
I first tried making sure the two digital EQ's, which are grounded, were plugged into the same outlet strip as the amplifier. Well, the amp was plugged directly into the Brickwall surge protector, so I managed to plug the EQ's in near it, though I couldn't plug both into the same duplex outlet on the Brickwall as the amplifier itself.
That didn't seem to help much. I also tried different interconnects from the EQ's to the amplifier, including a new pair of very well shielded Blue Jeans interconnects, which didn't help either. I was beginning to think the hum was in the output of the Behringer EQ's themselves. So I did an upgrade I'd been planning to do for years. I wired in one of the two Denon DVD 5000's as the dac driving the amplifier for the main speakers. The 5000's use dual differential 1704's and digital inputs, and I purchased 3 of them so I could have triamplification using all 1704's before I decided the 5000's just didn't sound wonderful on the living room system. So then I put two of them in a pile in the bedroom, thinking they'd be good enough for the bedroom amp and subwoofer. There they sat for two years until now.
This took some work, but was successful in reducing the electronic hum coming from the left speaker significantly. Not total elimination, but close enough I thought.
Then I listened for awhile to the living room FM tuner through Sonos on the bedroom stereo. Perhaps it's largely because I've gotten used to the much better sounding kitchen tuner (which now has an outdoor antenna), I was not liking the sound. It was too noisy and also bright and edgy, almost unpleasant to listen too. Well this was a combination of the slight edginess I had always thought the 5000's have (along with a crystaline clarity that often makes you overlook the edginess) and what appears to be the slight added brightness of the ATI 1502, a match made in hell. But there was one other thing.
One of the things I had overlooked in the amplifier replacement was the 12dB Harrison Labs attenuators. I just put those aside, assuming incorrectly I had not been using them correctly. But it turns out these attenuators, or something like them, are ESSENTIAL in the bedroom system, otherwise the DACs are only using a fraction of their dynamic range, with the signal strength meters on the Behringers only blinking the bottom light. Unless corrected (which I didn't discover I needed to do for years when I first started using the Behringers) the sound becomes very coarse and grainy.
I first measured the Harrison Labs attenuators, to ensure they are designed for plugging into the destination for a signal. They are: the top of the attenuation network is connected to the female RCA hot connection where you plug the signal bearing cable in. It would not be good to plug them into an output signal RCA jack, AND they would have been worse had they been designed to be used that way because then a resistor would be in series with driving the cable.
The Harrison Labs attenuators greatly improved the sound by restoring the digital resolution available from the DAC. And also reduced the buzz even more. But I was still not liking the sound.
So finally I decided on a different plan. I returned the Parasound HCA-1500A to the bedroom, and decided to use what used-to-be my living room amplifier, my original NOS "minty" Hafler 9300 in the kitchen, and the new refurbed 9300 (which has more punch, it seems) in the living room. This repurposes the ATI 1502 as nothing more than an emergency spare for now. Something I didn't really need to buy (though...perhaps it is the magical "black swan" amplifier which measures fine but sounds bad enough to be different on blind tests...?).
This decision was not at all based on scientific proof that there was anything audibly wrong with the 1502, except for the chassis hum, and also when I plugged the Parasound into the now improved bedroom system (with the upgrades I had done to try to make the 1502 acceptible) the Parasound had virtually no electronic buzz compared to the trace of buzz still remaining with the 1502.
I did feel the sound was more pleasant on the noisy FM radio, using the Parasound. Later as the evening slipped by, there were patches of greater noise on the radio, and I wondered just how true it was that the Parasound made the FM noise sound less objectionable. Maybe it was just a larger than average patch of noise that happened just as I had hooked up the ATI. Perhaps it had just been bad luck for the ATI. But I felt very happy about my new amplifier lineup. Also I had made several long postponed upgrades to the bedroom system:
1) Using 1704 based DAC instead of Behringer DEQ output for the main speakers.
2) High end teflon cable between DAC and amplifier.
3) Remote On/Off switch on the amplifier.
4) Verified correct use of the Harrison Labs attenuator.
5) DAC and amplifier plugged into same duplex outlet on the surge supressor.
It might be better yet using the Integra Research DVD player instead of the Denon 5000. The Integra Research also uses 1704's, but is somehow better sounding I've felt, and I was using it on the living room system for over a year. A Denon 9000 might be better sounding still, but I feel they run too hot for being left on all the time.
Post Epilogue
Several days later I got motivated to check the time alignment between subwoofers and monitors. I had only guessed the latency added to the monitor side by putting the DVD-5000 in the signal path. So I started playing the dirac pulse from the polarity checker app on the bedroom system. I noticed that the 6 inch woofers on the Revel M20's were really popping out. That wasn't supposed to happen on this system, the M20's are crossed over at 60Hz. Looking at the Behringer RTA for the monitors, once actually set to the digital output (as going to the 5000), I could see there was no rolloff in the bass.
After the Bedroom Tact preamp died, I had figured out how to get along without it. I'm running the digital signal directly from Sonos into one of the two Behringers, and then, while that Behringer is putting out the high passed or low passed analog signal, it is also putting out a flat digital signal for the other Behringer.
With this arrangement, it's clear that the "last" Behringer is the only one that can put out a high passed or low passed signal. If the signal goes through the monitor Behringer first, then it will be putting out a flat digital signal and not a highpassed one.
As it turned out, I was putting the digital signal from Sonos into the subwoofer Behringer first, then taking the flat digital from there for the monitor Behringer. But, not remembering that I had done it this way, and thinking I was putting the Sonos signal into the monitor Behringer first, I had set the digital output to flat on both Behringers. And when you set the digital output for the coax output on the Behringers, it applies to the optical output as well.
So, after trying other things then figuring this out, I fixed the problem merely by changing the digital output on the monitor Behringer to the highpassed output. I also plugged the toslink cable into THAT Behringer, instead of the subwoofer one. These were the mistakes I made when first setting up the DVD-5000 so I could get less hum out of the ATI amplifier.
And this could explain why I thought the sound of the ATI amplifier wasn't right. It was not getting the highpassed signal, and the noisy FM radio signal has lots of bass modulation noise which is causing much more woofer excursion than the monitor speakers should have had.
Then, after switching back to the Parasound, I had expected the situation to improve, and it seemed to at first, but later not so much, both in the quality of the sound (a bit rougher than expected) and the chassis and electrical hum levels, which seemed to increase significantly after the Parasound had been turned on for a few hours.
Thus, my judgement about the ATI not sounding quite as good is now fully called into question. Not only was it a useless non-blind snap judgement listening to a highly variable source, but I had things set up incorrectly in such a way as to cause the slightly off sound I thought I was hearing.
This sort of mistake happens all the time to me, and I suspect other audiophiles make mistakes also.
The still unadjusted lack of time alignment could be a factor also.
The still unadjusted lack of time alignment could be a factor also.
No comments:
Post a Comment