How to prove there is a difference between amps?

[CMonster]

As I mentioned in another thread, the KC area is hosting a pretty big HT crawl in a couple of weeks with several vendors attending and AVS Forum members flying in from across the country. The day after the main event we're planning on having a blind amp test for those interested. I'm contributing a Parasound Halo A21 and there will be three other amps including a very inexpensive Lepai t-amp. While I think most amps sound pretty much the same, I think (hope) better amps handle complex loads, such as Dynaudio speakers, better. Most of the crawl attendees are JTR fans and it's been suggested to use a pair of JTR speakers. For those unfamiliar, JTR uses high-efficiency compression drivers and their roots are in pro audio. The KC AVS Forum members are also firmly in the camp of "all amps sound the same." So anyway, I don't care if the advantage is small but I'd really like the Parasound to win. I have influence over the speakers used and some of the music. Suggestions to help me "win" - i.e. prove that there is a difference? It looks like the comp will be at another member's house so I could provide bookshelf Dynaudio C1s or (more easily) Contour S1.4s. If it's at my place then we'll use Dynaudio C2s. Maybe have both Dynaudio and JTR to show amp effect on different speaker types - would that be worthwhile? @heeman any thoughts; PSA speakers are similar to JTR. @Flint, @rammisframmis, any suggestions?

 

[Zing]

I have influence over the speakers used and some of the music.

I'd suggest the least efficient speaker and the most demanding music (low frequency extension) since there was no mention of subwoofers and crossover points.

 

[Randy]

Use Monster Cables!!!!

 

[MakeMineVinyl]

Well, all solid state amplifiers of a similar topology will sound pretty much the same when driven within their normal operating ranges.

But, there is a sure-fire way to make your amplifier sound different, and depending on the listener, music, and speaker, perhaps subjectively "better".

Its not particularly "honest" though, but given politics these days, who cares about honesty.

This is what I would do, and I would probably take the opportunity to make it into a "teaching moment", but it requires a relatively simple modification to the amplifier.

If the amplifier is single ended (i.e. if the negative terminals are grounded), open up the amplifier and place place an 8 ohm resistor of about 25 watts in series with the positive terminals. If the amplifier is balanced (i.e. the negative terminal is not grounded), place 4 ohm 25 watt resistors in series with both the positive and negative terminals.

What this will do is make the output impedance of the amplifier the same as the speaker it will be driving (if the speaker is 8 ohms), and this will do two things. First, the frequency response of the amplifier will follow the impedance curve of the speaker, and this will be audible mostly in the bass region. Second, the damping factor of the amplifier is now 1 instead of >100 like most solid state amplifiers are. This will subjectively "fatten up" the bass region.

The result is that the amplifier will certainly sound "different" and some may actually like it. At the least, I would be very interested in the "subjective" opinions of the people hearing the amp, not knowing the trick which is being played on them.

Of course, after that, I would tell what the modification was, and why the amplifier sounded the way it did.

This will either make you seem incredibly smart, or they might just kill you.....

 

[Randy]

My solution is a lot easier!!!

 

[Flint]

In my experience, it is damn ear impossible to test amps side by side effectively to start with. First off, to compare them you need to be able to switch between them instantly, which is a complex setup to stat with. As much as 1 sec of delay between amps is long enough for you to forget the prior sound because our auditory memory is very short lived. The other issue is levels... and this is often completely overlooked. Most amps have different gain levels, so getting two to produce the exact same voltage gain for the same input can be tedious if they don't have gain controls. A difference of as little as 0.2dB SPL from the speakers is perceptible when switching between amps, and most people will consider the slightly higher SPL as "better sounding" even when the lower level signal is higher fidelity.

So, two rules that must be adhered to are:

1. You need to be able to switch back and forth instantly during the auditioning
2. The output voltage must be identical between the two amps being auditioned

People who have been through ear training (or the equivalent through years of work in the audio or recording industry) can get away with not having those two rules perfectly followed, but it still helps even for them.

So, the audition is not at all definitive if those two things are not assured.

 

[MakeMineVinyl]

So, the audition is not at all definitive if those two things are not assured.

Just out of curiosity, do you think you would readily hear a difference in an amplifier which was modified as I outlined above, and what do you think would be the "differences"?

 

[Flint]

Yes, I do think it would be audible immediately to the trained ear and with repeated comparison to the lay ear.

 

[Flint]

I would also add the resulting performance characteristics of the passive crossovers on the speakers will be altered from the intended design which usually assumes a near zero output impedance on the driving amp.

 

[CMonster]

We have an instantaneous switching mechanism (so I've been told) and will take the time to do our best to level match the amps before blind auditions. I want to feel good about my Parasound purchase versus something like an iNuke. I have no problem believing the latter is perfectly fine driving a subwoofer but I'd like to believe there's a way to prove a quality "audiophile" amp, in this case a Parasound Halo, can do a better job full range with a difficult-to-drive speaker than a cheap digital amp.

 

[AndySTL]

We have an instantaneous switching mechanism (so I've been told) and will take the time to do our best to level match the amps before blind auditions. I want to feel good about my Parasound purchase versus something like an iNuke. I have no problem believing the latter is perfectly fine driving a subwoofer but I'd like to believe there's a way to prove a quality "audiophile" amp, in this case a Parasound Halo, can do a better job full range with a difficult-to-drive speaker than a cheap digital amp.

FWIW, I'm really rooting for you Chuck!

This GTG sounds like a blast. KC must have a great group of audio techies. Have fun and share the pics here if you don't mind.

 

[Flint]

Hearing a difference between amps can be difficult, especially in a group setting. When I participated in cable auditioning and amp tests back in the late 1980s and early 1990s we always made sure the listener was in a very quiet room alone and could spend as long as they wanted to compare the two items being tested. Doing the tests in double-blind setups where an ABX system was in place, the most consistent and repeatable tests where differences were found were done with the listener in isolation.

So, I recommend a mix of music, some music consisting of a single acoustic instrument, like a violin, acoustic guitar, or similar. Some solo piano music. Very dense symphony music, especially with a choir and organ included, and some dense rock studio recordings, like my favorite Supertramp's "School" from Crime of the Century and Rufus Wainwright's "Oh What A World" from Want One and the complete side 2 of Kate Bush's "Aerial". Those last three recordings are on my speaker auditioning CD disc 1.

On the simple single instrument recordings listen for the decay at the end of notes before the next note is played, it should be smooth and appear to be decaying infinitely until muted and the next note starts. Listen for the air at the edges of the harmonics. Listen for ANY sounds behind the instrument like breathing, a foot shuffling, or clothes compressing as the performer emoted while playing. Even try to tell of the performer is moving closer to or farther away from the microphone. Try to find flaws in the sound which appear with both amps.

With the dense and complex music, be sure you can pick out sounds which are subtle, like the two separate acoustic guitars in the intense and fast section of School, or the oboe in "Oh What a World" when it is at it's peak. Listen for the bass flattening out or the drums losing their hammer to the chest impact. Check that the cymbals are clean when the bass is strong.

Take notes while listening as well so you can remember what you heard in worlds. Replay little bits over and over until you are sure your impressions are real and not imagined.

And... this is important and almost always ignored in these situations... if you can, try to convince everyone to withhold ANY opinions until everyone has taken their turns and written down their opinions. Our brains, even the best of us, are easily swayed by descriptive comments of sound. So, if you sit down for your audition after being told the digital amp has better bass, you will walk out believing that's what you heard regardless of the truth.

 

[Towen7]

I want to feel good about my Parasound purchase versus something like an iNuke. I have no problem believing the latter is perfectly fine driving a subwoofer but I'd like to believe there's a way to prove a quality "audiophile" amp, in this case a Parasound Halo, can do a better job full range with a difficult-to-drive speaker than a cheap digital amp.

Since I haven't invested in an audiophile amp I'm actually hoping that your tests are inconclusive and that relatively inexpensive amps will suffice for me.

 

[Towen7]

So, if you sit down for your audition after being told the digital amp has better bass, you will walk out believing that's what you heard regardless of the truth.

Wouldn't it be best to not let the listener know which amp he was listening to in the first place?

 

[Randy]

Since I haven't invested in an audiophile amp I'm actually hoping that your tests are inconclusive and that relatively inexpensive amps will suffice for me.

Me too, I am hoping they discover purchasing a used ATI 1505 for $700.00 is the smartest move ever made in Audiphilia!!!

 

[Flint]

Wouldn't it be best to not let the listener know which amp he was listening to in the first place?

If the user ever learns which amp he is using (which in these group situations almost always occurs), and they sound pretty much the same, the listener will assign the characteristic they were told they would hear. And they will completely believe it.

If the user never learns which amp is which, but he can consistently hear a difference, the one the listener assumes is the digital amp will appear to have the better bass (using my scenario above). Even if he is wrong in the end, at the time of listening that's what they will totally be convinced they heard.

If the user cannot tell them apart and never knows which is which, they will likely randomly assign the characteristic, but likely be wrong and if doing an ABX test statistically unable to hear the difference. But the listener will walk out of the session convinced that one amp had better bass.

 

[Flint]

Even if we can hear small differences between amps, the difference between two well-made transistor amps of a good design will be minimal. I always go back to the old "how much impact does each component have on the sound?"

 

[heeman]

Chuck I have only driven the PSA's with a Parasound HCA-1000. So I really have nothing to add.

When I bought the C1's they were driven with the same HCA-1000 until I bought the A21. Did the A21 drive them any better and sound better.....................of course! But then again it was a silver "B" stock so maybe it's not as good as a Black New One!

This subjective hobby drives me freakin' nuts; hence the recent Pre/Pro exercise.

 

[MakeMineVinyl]

Me too, I am hoping they discover purchasing a used ATI 1505 for $700.00 is the smartest move ever made in Audiphilia!!!

The reality of the situation is that there are only so many transistors suitable for audio work, so many audio grade capacitors and so on. And every higher end audio manufacturer uses this relatively (actually very) limited selection of parts. There are only a few ways to design the circuitry of an audio amplifier; one design from manufacturer X is going to be very, very similar to that from manufacturer Y.

The output transistors in your 1505 are identical to those used in a very high end Mark Levinson amp of the period. The rest of the parts are also identical; Wima capacitors etc.

The transformers come from the same manufacturer, usually Noratel.

The biggest cause for a price difference between a solid amplifier made by ATI and one made by some esoteric high end manufacturer who's amp is many times the price comes squarely down to bling; the milled-from-solid-billet chassis and the other "jewelry", like this monstrosity:

http://dandagostino.com/products-momentum-mono.php

As I've mentioned several times before, the thick laser etched front plate for even moderately higher end amps typically cost the manufacturer at least $500, and the really fancy ones like the above amp undoubtedly cost the manufacturer thousands, which gets passed on to the customer, and make not one bit of difference in sound quality. None.

Them's the facts - I know, I work in the sausage factory.

 

[TitaniumTroy]

What the about the old audio myth, that an amplifier that doubles in power as impedance lowers. Like the Momentum amplifier does, is a superior amplifier compared that one that only goes up by say 1.5x instead of by 2x. Or is it just a numbers game manipulated by amp manf. to make their amp look better on paper?