AMP A / B COMPARISONS

[milosz]

I made a little box with 2 headphone cables coming out of it with standard 1/4" phone plugs on them, a DPDT switch, and a single female headphone jack.
 
This allows me to directly compare 2 different amps with the flip of the switch.
 
The headphone cables I used are pedestrian, just some OFC extension cables I got from Parts Express, from which I cut off the female ends to allow me to wire the cables to my DPDT switch.  OK, so they are a compromise here but the SAME type of cable is used for each amp so the differences in the amps, if any, should still show up/
 
I put the thing in a little Hammond plastic project case.
 
NOTE:  THIS IS NOT A SCIENTIFIC TEST.  Not by any means.  But I found it interesting just the same.
 
I just finished this switch box today and only had a few hours to do some A / B listening, so I only have 2 amps compared so far.
 
I used a Cambridge Audio  DAC Magic as the source, fed by SPDIF from a Squeezebox III.  I used the RCA outputs of the DAC Magic, with RCA splitter cables. (Again, a compromise, but the same cable type is used for each amp under test.)
 
I listened with Audeze LCD-2 and then Sennheiser HD800 phones.
 
Today I compared a 3-channel Beta 22 and an M³ amp.  The Beta 22 has the Sigma 22 power supply; the M³ uses a 24 volt Elpac wall wart.  The M³ uses[size=small] AD843 op amps.[/size]
 
I carefully matched the volume levels of the two amps using a 1000 Hz tone.
 
I listened to a variety of music. 
 
RESULTS:
 
LCD-2
I was very hard pressed to hear ANY difference between the Beta 22 and the M³ on the LCD-2's. MAYBE a touch better bass control on the Beta 22 but then again maybe not.  I would NOT bet money on me being able to tell these two amps apart in a blind test with the LCD-2.
 
HD-800
With the somewhat exaggerated highs of the HD800's  I began to hear a subtle difference between the two amps.  The highs on the M³ sounded a tad bit harsh.  Also, the "separateness" of various instruments on a track was better with the Beta22. But these differences were quite subtle.
 
MY CONCLUSIONS
 
1. I was surprised that I didn't immediately hear incontrovertible differences between these amps. I was expecting a fairly obvious difference in their sounds.
2. These are both good amps- they both sounded pretty wonderful.

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The Beta 22 and M³ amps have things in common-  MOSFET output stages, 3-channel "active ground" design- maybe this is why any differences I may have heard were so subtle.
 
This makes me want to A / B others amps.  I also urge anyone reading this post who owns more than one headphone amp to build their own A / B box and report on your tests.
 
I expect I will hear more noticeable differences with other amps - such as Cavilli-Kumisa  vs. Beta 22, and also Beta 22 vs various tube amps in my collection.

 

[LostOne.TR]

that's a mighty selection of amps you have at hand.  I look forward to your impressions, especially with the CK2III.

 

[milosz]

Second A / B comparison:  Beta 22 & CK²III
 
Same everything as above, except this time a CK²III.  AGAIN- THIS IS NOT A SCIENTIFIC TEST.
 
LCD-2:  Very hard to tell the difference.  Both sounded great.
 
Sennheiser HD-800: Audible differences but VERY slight. The bass on the Beta-22 had more weight, seemed to go a little deeper. Highs on the Beta-22 sounded just a tiny bit cleaner.  Depth of soundfield, midrange clarity, etc., no differences heard. CK²III had a tiny bit of AC hum audible when the music was paused.  Hard to hear, at the very borderline of inaudibility, but present.  (Actually quieter than the hum from my refrigerator two rooms away as heard through the open-air Sennheisers... I had to take some pretty serious measures to get dead silence in the room I was in to hear it.)
 
CONCLUSIONS:  
 
1. I REALLY expected to hear MAJOR sonic differences here. But that was NOT the case, such differences as I could hear were very subtle.
2. I found it SUPER important to get REALLY close level matching between the amps.  I perceived any tiny difference in level as a difference in QUALITY, and NOT as a difference in level!  So I matched the output across the headphone in test using a VOLTMETER to within .005 volts RMS for both amps.
3. As with the first round of A / B comparisons, these are BOTH great amps, and they BOTH sounded beautiful on these two world-class headphones.  I had a slight preference for the Beta 22, especially on the HD800's.
4. The Sennheisers seem to be sensitive to the type of amp used, whereas the LCD-2's seem much less picky about amps.

 

[tisb0b]

I'm not exactly surprised by your results but should be interesting to see as you go through your amp collection. 

 

[milosz]

Third A / B comparison:  Beta 22 & RSA Hornet
 
Same everything as above, except this time a Ray Samuels HORNET portable amp.  AGAIN- THIS IS NOT A SCIENTIFIC TEST.
 
Note: In some ways, this is apples-to-oranges.  The RSA Hornet is a PORTABLE battery-operated amp roughly the size of a matchbox weighing 4.5 ounces (128 grams) with it's lithium battery, and the Beta-22 is a desktop amp- actually a fairly large desktop amp; mine weighs about 12 lbs (5,440 grams)
 
The HORNET gain switch was set to MEDIUM for this test.
 
LCD-2: I could immediately hear that the upper octaves were slightly rolled off using the HORNET.  Operative word here is slightly.  However, even this very slight rolloff was plainly audible.  Bass was fairly comparable between the two amps, with the Beta-22 having a tiny edge in control and depth.
 
HD800:  The high frequency rolloff was much less noticeable on the Sennheisers than the LCD-2's. It would seem, then, that the rolloff is possibly related to the lower impedance of the LCD-2's.  The very upper registers from the HORNET were a tiny bit recessed on the HD800s compared to the Beta-22, but the difference between the highs using Beta-22 vs the HORNET were much easier to hear on the LCD-2s.  Bass from the HD800s also seemed to go a little deeper with the Beta-22.  On the HD800s it also sounded like the stereo image was a little bigger with the Beta-22, as if it's stereo separation was a bit better. The highs from the HORNET seemed also to have a little more "grain" than the Beta-22, but this was subtle.
 
CONCLUSION:  At last I heard some audible differences that were pretty easy to pick out.  But for this I had to go from a big tabletop amp to a tiny portable amp. Even so, this rolloff was NOT enough to make the HORNET dull or dark sounding on the LCD-2s.  It was a small rolloff, but easy to detect.
 
Again, both of these amps sounded great, really.  The HORNET drove either sets of phones very well and the sound from it was definitely "high end audio" though not quite as "high end" as from the Beta-22.  And of course, you wouldn't tote the  Beta-22 along with you on a trip, etc.
 
More to come.

 

[milosz]

 
Fourth A / B comparison:  Beta 22 & Audio_GD  FUN

 

Same everything as above. AGAIN- THIS IS NOT A SCIENTIFIC TEST.

 

I SHOULD MENTION that in all these tests, the Squeezebox is being fed 44.1 / 16  FLAC files. I ripped my cd collection using dBPowerAmp Batch Ripper, and all the tracks I used in the test were checked by that software for the correct AccurateRip checksum - in other words, the ripping process was accomplished with ZERO errors.

 

NOTE:  FUN used here through LINE inputs, DAC not used. FUN is a "Version A"  with Wolfson [size=x-small]WM8741 DAC (although the DAC is not used for the test) the "Moon"  OPA module (not sure if that's in the LINE IN circuit or not) and the Diamond buffer output stage.[/size]

 

[size=x-small]LCD-2: Very subtle difference in bass was audible, with the Beta 22 sounding a little tighter and possibly a little more extended.  Highs from the Beta 22 might be a tiny bit more extended too.[/size]

 

[size=x-small]HD800: Similar bass character difference as heard on the LCD-2's, the bass seemed to "hit" a little harder through the Beta 22. On the high end the extreme upper register seemed a little more extended from the Beta 22, and there was a tiny bit of high frequency roughness from the FUN.  Maybe.   [/size]

 

CONCLUSION:  These differences were very subtle. In particular, the differences in the highs between the two amps seemed to be JUST BARELY perceptible. (I wonder if what I was hearing was the FUN'S  "MOON" OPA module, which Audio_GD describes as "Sounds a bit tube-like, that is, a little soft, warm and musical.")

 

Both of these amps sounded GREAT, really.  The differences were VERY minor.  When you consider that the FUN is about $350 and includes a VERY FINE DAC and preamp outputs, you can really see it's value in how well it compared to the Beta 22 which tends to sell for about $2 thousand.

 

All these solid-state amps I've tested sound so similar as to be NEARLY INDISTINGUISHABLE, and I am moving on to comparing the Beta 22 to tube and hybrid amps next which - according to conventional wisdom -  should show a greater contrast in sound.

 

[Mad Lust Envy]

So what did I gather from this? That for a slight/minor improvement, it's not worth paying a ridiculous amount of money for amps when something worth anywhere between 50-90% less gives you 95% of the performance.
 
 
I'll stick to my E9 for now, lol.
 
I wonder how the E9 would stack up to these solid state amps...

 

[Oddworld]

I too would like such a comparison

 

[swifttal]

Nice! Construction pics?

 

[milosz]

Quote:

Nice! Construction pics?

Pics of what?  The various amps' insides?
 
Yeah I could do that, sure- are you interested in that?

 

[PFKMan23]

Not to get heavy into the science of it, but, if they are not already, I think your tests would be much more beneficial if the amps were volume level matched by an SPL meter.

 

[Oddworld]

I want pics too!!
Electrical engineer over here

 

[milosz]

Fifth A / B comparison:  Beta 22 & Yamaha A-700 Integrated amplifier headphone jack (!)
 
Same everything as above. THIS IS NOT A SCIENTIFIC TEST.
 
NOTES:

1. The A-700 was produced by Yamaha in the mid 1980's. Mine is black, but there was a silver model also.
2. Rated 100 watts / channel RMS 20 Hz~20 kHz  at 0.005% thd
3. Can be switched to run in Class A up to 5 watts then runs class B. Normal changeover to Class B is less than 1 watt. ( "Auto Class A" switch)
4. Headphone jack is typical practice, it has series resistors between the headphones and the amp's output stage.
5. Spec sheet states: "Headphone jack 0.81 V / 270 ohms 0.05% THD

 
I got this in 2007 for $29 on eBay.  I haven't used it much. AudioKarma has a number of posts praising this amp's sound, calling it "Yahama's best-sounding integrated" and so on.  Apparently, it has a reputation for sounding pretty good.  I bought it when I was looking for cheap, low-power class-A amplifiers to use to power a ribbon tweeter in a tri-amp DIY speaker. 
 
INTERESTING: The line (AUX) input stage clipped like crazy when I fed the signal from my DACMagic into it.  At the level that the Beta-22 and all the other amps were comfortable, this amp's line stage clipped like crazy. The AUX / TAPE / TUNER  inputs have a rated sensitivity of 150 mV and 47k ohm impedance. This is pretty standard for integrated amps of this era; nowadays, 300 mV or so is more common.  Still, I had to pad the inputs down by 12 dB with an attenuator to get a signal that wouldn't clip the line stage.  
 
There is a "DIRECT" button on this unit that disables tone controls, subsonic filter and loudness EQ.  I performed the test using this "DIRECT" setting to disable all the tone controls, etc.
 
LCD-2:  The Yamaha A-700 showed some differences compared to the Beta-22.  Bass from the Beta-22 had somewhat more solidity, greater impact. The overall mids and highs sounded clearer from the Beta-22 though not by a huge amount. Vocals and piano sounded more natural through the Beta-22 and there was a slightly fatiguing quality to the highs though the Yamaha.
 
HD800:  Similar to the LCD-2, the bass though the Beta-22 sounded a little more solid and punchier than the Yamaha.  Upper highs sounded rolled off a tiny bit through the Yamaha and in general the mids and highs sounded more natural and cleaner through the Beta-22. Again, the highs from the Yamaha had a slightly fatiguing quality. Transient detail through the Beta 22 was better- audience claps in time with the music from Patricia Barber's Companion cd were rendered with greater clarity though the Beta-22-  individual claps stood out as sounds distinct from one another and from the music and with with more realism with the Beta-22.  With the Yamaha the individual audience members clapping in time to the song sort of merged into one rhythmic sound.
 
CONCLUSION:  First of all, let me say that the headphone jack of this old Yamaha sounded better than I expected.  After all- there's no fancy capacitors or ultra-regulated power supplies in the Yamaha, and the phones are connected to the amplifier stage through resistors which should destroy any damping by the amp. The A-700 does seem to have a reputation of being a cut above the typical wash of 1980's Japanese mid-fi, but even so I expected really dreadful sound.  I didn't get dreadful from the Yamaha, but what I got from the Beta-22 was certainly better. 
 
I could live with the bass from this Yamaha, series resistors and all. What I don't think I could tolerate is the "slightly fatiguing quality to the highs though the Yamaha."  This was starting to give me a bit of a headache as I did my test. I have heard this same thing before, when using miscellaneous mid-fi amps to run ribbon tweeters in my tri-amp DIY speaker experiments. I heard a harshness I found really objectionable, and I found that using a class A amplifier on those ribbon tweeters was the answer. This Yamaha runs class AB at the listening levels I was using, and I think I heard that. (Operative word here is THINK; I'd have to run a double-blind test to really sort this out.)  But anyway, the Beta-22 is class A and to me it sounded great and with no fatigue from the highs, whereas the A-700 is AB and had that fatiguing sound.
 
If I removed the series resistors and switched the Yamaha to "Auto Class A" it's possible I could get better sound from the headphone jack, but as this  "Auto Class A" switch does not limit the Yamaha to class A ONLY (as the class A switch in some earlier Yamaha amps did) there would be something like 28 volts available at the headphone jack at full output.  This is right at the rated maximum for the LCD-2s and probably enough to burn out the HD800s.  Not worth the experiment.
 
I did try switching the A-700 to "auto class A"  but I could hear no difference in sound. I was probably listening at levels above the A-700's 5 watt Class A limit, what with those series resistors and all.
 
SIDE NOTE:  This A-700 has a phono preamp in it, and of course line-level outputs. I'll have to compare it to some high-end phono preamps I have at some point, but that is for another forum.
 
MY BETA 22 INNARDS

 
Yamaha A-700 under the hood:

 

[milosz]

Quote:

Not to get heavy into the science of it, but, if they are not already, I think your tests would be much more beneficial if the amps were volume level matched by an SPL meter.

OK.  
 
I set the gain of the amps to produce the same voltage +/- 0.005 volts across the headphones using a 1000 Hz tone, as measured with my Fluke meter. Since the amps are both delivering near exactly the same voltage to the headphones, the headphones will produce the same level of loudness from each amp.  .1 volts into a pair of HD800s from amplifier X  will produce the same loudness as .1 volt from amplifier Y into the same headphones. 
 
But I did check with my SPL meter, and verified that when set with my voltmeter, both amps produced the same volume from the headphones.

 

[miyinan]

Very good job on the comparisons, milosz.