Blind Test Results: Benchmark LA4 vs Conrad Johnson Tube Preamp

[DVDdoug]

Nice job on the experiment!!!

But it would be helpful if you could translate what you heard into meaningful terms. i.e Frequency response and distortion. I assume there was no audible background noise from either amplifier since you didn't mention noise.

It seems I'm constrained via this particular meter to those two options - 750 or 200 - when set to measure AC voltage.

I have a meter with a similar limitation. My meter is auto-ranging and it's OK with low DC voltages and it shows resolution of 0.1V (maybe lower with DC). But I think there's a diode for AC which means about a 0.7V loss (or 1.4V if it's a full-wave rectifier) and non-linearity and you can't read anything below the diode-drop. Just recently I bought a "better" meter.

You are right. 110Hz is not a good choice, pink noise would be much better.

110Hz should be OK unless one of the amplifiers has a dip or bump in the frequency response at that frequency. And if there is a difference.... Hey! You've found a true-difference between the amplifiers! But, you could check a couple of other frequencies. High frequencies can be "screwy" because of the reflections. I was doing some high-frequency experiments in my home office once (I think 5-10kHz) and just moving around behind the SPL meter changed the readings by several dB.

The difficulty with pink noise is that it's noise... There is randomness so readings are not constant so it's hard to get a constant-repeatable reading. You'd need some kind of longer-term averaged measurement.

(On trial two I'd initially guessed wrong, but immediately recognized the differences again between the preamps once the switching continued).

Of course it's nice to get 100%, and you have to wonder if it's worth paying more, or switching amplifiers if you can't get it right 100% of the time. But, 14 out of 15 is literally "off the chart" (less than a 0.1% chance that you are guessing).

BTW - Normally in an ABX test you are allowed to take as much time as you want and you are allowed to request "A", "B", or "X" as many times as you want before you "lock-in" your answer, or just give-up and guess.

 

[pma]

The difficulty with pink noise is that it's noise... There is randomness so readings are not constant so it's hard to get a constant-repeatable reading. You'd need some kind of longer-term averaged measurement.

DMM is a pretty integrating device. You mentioned reflections, I think he measured voltage not SPL, so what reflections? If he measured 110Hz SPL, then it would be a subject of room modes of class I quality .

 

[MakeMineVinyl]

Perhaps the multi-tone signal would be a better for level matching; not random like pink noise and it fills the entire bandwidth.

 

[Blumlein 88]

I see no advantages to pink noise over 1 kHz for level matching. And he did use spl as his voltmeter didn't have the scale needed.

 

[abdo123]

the tube pre-amplifer has a SINAD lower than 40 at 0.1 Vrms output so hardly a surprise here.

 

[MattHooper]

Thanks very much for the input everyone!

FWIW: Previous to the test I actually had been using pink noise for level matching between the LA4 and the CJ preamp. (Occasionally I used music, but usually pink noise). That was for all my past sighted listening switching between them. I was going to use pink noise again but as I mentioned I re-visited Amir's video on how to do blind testing in which he suggested using a single tone. He said make it a lower tone, suggested 200Hz, said there was nothing magical about that number, but just try not to go above it. So I selected 110Hz.

It's a shame about the voltmeter not working out for me. Though I do think that the fact that the levels matched perfectly on two different metering devices suggests it was well matched. Nothing I'd submit to a science panel though.

 

[MattHooper]

the tube pre-amplifer has a SINAD lower than 40 at 0.1 Vrms output so hardly a surprise here.

Might be a surprise to some on this thread:

If "Tube Sound" Is a Myth, Why Tubes?

Disclosure: my university education was in applied physics and signal processing, and I currently work in the software industry, so my knowledge of electrical engineering is not zero, but I'm no EE. So apologies in advance for any technical errors. This thread is inspired in part by comments...

www.audiosciencereview.com

A fair amount of skepticism in there from some members. Not of course that something that measured "badly enough" couldn't be audible, but more along the lines that the "tube sound" was something more likely to be "all in your head."

 

[MattHooper]

What is it about some audiophiles wanting a more homogenised, nicer and thicker-textured sound presentation?

Live music doesn't do this to me at least - it's immediate, strings sound 'rosinous,' trumpets can hurt, saxes make you jump with the intensity and drums will pin you to the wall behind (this on music genres I don't always listen to). To me if nobody else, the CJ is NOT a 'high fidelity' component if it's making the signals

Your position makes sense to me.

FWIW: The differences I described were subtle and the significance would vary to different listeners. For me the subtleties are subjectively significant. To my ears, yes the CJ does slightly homogenize the sound but: 1. Not to the degree instrumental timbre doesn't sound 'right' or differentiated. Specific acoustic guitars sound specific, individual woodwinds sound individual, etc. 2. It slightly homogonizes everything to make things sound a bit more like I hear them in real life, in terms of a warmth of timbre and tonality. So for me the trade-off works.

Nice job on the experiment!!!

But it would be helpful if you could translate what you heard into meaningful terms. i.e Frequency response and distortion. I assume there was no audible background noise from either amplifier since you didn't mention noise.

Thanks DVDdoug! No audible background noise that I noticed from my listening seat. But that wouldn't matter anyway since the music played continuously during the switching. There wouldn't have been any quiet parts in which to hear 'only' background noise with no music playing.

Didn't have measuring devices (but then...we'd want to see if the measurements were audible anyway in controlled listening), so descriptions are all I have for what cued me as to the differences.

BTW - Normally in an ABX test you are allowed to take as much time as you want and you are allowed to request "A", "B", or "X" as many times as you want before you "lock-in" your answer, or just give-up and guess.

Yup, I'm aware. Sometimes I switched quickly, sometimes I let the music play for a while just to listen to different aspects of the sound.

20+ years ago I tried a few high-end CJ preamps that a local dealer let me borrow against no preamp (a DAC with a digital volume control). I could also tell the difference, including in a blind test with an audiophile buddy helping me out. In the audiophile parlance, CJ preamps sounded veiled to me, while no-preamp sounded natural and transparent. I felt like the sound became muddier, thicker, denser with CJ. I've not used a preamp since.

I can imagine you would feel just the same about the difference between the LA4 and my CJ preamp. I get it.

I also don't understand how a sound can be laid back and easy on the ears and, perhaps, veiled, but also be sparkly at the same time. Once again, simply curious as to the descriptions.

Yes that's actually one of the aspects that feels surprising and sort of hard to describe. And it's exactly what I have heard from my CJ gear over the years whenever I've compared it to, for instance, solid state components. Take an acoustic guitar being played vigoursly, single notes picked hard. On the solid state presentation the high frequencies transients sound sharper, thinner, more forceful, "harder" and more vigorous. On the tube the transients sound slightly thickened, more laid back less "spikey" in terms of jumping out of the mix. At the same time there is this tonal shift I described, almost like a "golden glow" lightens up all the sound so it simultaneously sounds more "airy and in the room" and tonally vivid, yet relaxed sounding. As an exaggeration, think of playing a high quality recording of someone playing an acoustic guitar vigorously, then replace that with someone actually playing that same guitar in the room, but a bit less vigorously. One sounds a bit more "tonally right" to my ears in terms of what acoustic guitars sound like "real" not recorded.

As to that combination of "more vivid tonally yet more relaxed" for many years I had a parametric digital EQ in my system and I had tried a few times to get that sound using solid state and using EQ. I never managed it. I'm pretty good with EQ, I used it in my job, but still maybe I'm not good enough. But I never managed to get "that sound" I'd hear from the CJ gear which led me to the hunch it might be more than just changes in frequency responses but perhaps some level of distortion in the tube amp that the EQ wasn't giving me. But...hey...I dunno....but it's one reason why I've stuck with the tube stuff. I also battle tinnitus and hyperacusis sometimes which means certain tones can jump out of a track and stab my ears with pain (even at low volumes). I've found that when something is bothering my ears that way - e.g. a muted trumpet or some really sharp electric guitar, switching to the tube preamp, it's relaxed, thickening effect, helps mitigate the sharpness. I can listen to it without pain, and listen louder. (And it does so without the obvious sense of "rolling off the highs").

 

[whazzup]

A measuring mic would have been a good inexpensive device to shed more light on your findings. Gives more data on whether the two devices have a different FR or distortion profile.

To repeat my last question (to the OP or anyone with the knowledge), is it possible either of the devices have a non-linear FR (or distortion), so level matching at one frequency is sort of meaningless (without that info)?

 

[DSJR]

Your position makes sense to me.

FWIW: The differences I described were subtle and the significance would vary to different listeners. For me the subtleties are subjectively significant. To my ears, yes the CJ does slightly homogenize the sound but: 1. Not to the degree instrumental timbre doesn't sound 'right' or differentiated. Specific acoustic guitars sound specific, individual woodwinds sound individual, etc. 2. It slightly homogonizes everything to make things sound a bit more like I hear them in real life, in terms of a warmth of timbre and tonality. So for me the trade-off works.


Thanks DVDdoug! No audible background noise that I noticed from my listening seat. But that wouldn't matter anyway since the music played continuously during the switching. There wouldn't have been any quiet parts in which to hear 'only' background noise with no music playing.

Didn't have measuring devices (but then...we'd want to see if the measurements were audible anyway in controlled listening), so descriptions are all I have for what cued me as to the differences.



Yup, I'm aware. Sometimes I switched quickly, sometimes I let the music play for a while just to listen to different aspects of the sound.


I can imagine you would feel just the same about the difference between the LA4 and my CJ preamp. I get it.



Yes that's actually one of the aspects that feels surprising and sort of hard to describe. And it's exactly what I have heard from my CJ gear over the years whenever I've compared it to, for instance, solid state components. Take an acoustic guitar being played vigoursly, single notes picked hard. On the solid state presentation the high frequencies transients sound sharper, thinner, more forceful, "harder" and more vigorous. On the tube the transients sound slightly thickened, more laid back less "spikey" in terms of jumping out of the mix. At the same time there is this tonal shift I described, almost like a "golden glow" lightens up all the sound so it simultaneously sounds more "airy and in the room" and tonally vivid, yet relaxed sounding. As an exaggeration, think of playing a high quality recording of someone playing an acoustic guitar vigorously, then replace that with someone actually playing that same guitar in the room, but a bit less vigorously. One sounds a bit more "tonally right" to my ears in terms of what acoustic guitars sound like "real" not recorded.

As to that combination of "more vivid tonally yet more relaxed" for many years I had a parametric digital EQ in my system and I had tried a few times to get that sound using solid state and using EQ. I never managed it. I'm pretty good with EQ, I used it in my job, but still maybe I'm not good enough. But I never managed to get "that sound" I'd hear from the CJ gear which led me to the hunch it might be more than just changes in frequency responses but perhaps some level of distortion in the tube amp that the EQ wasn't giving me. But...hey...I dunno....but it's one reason why I've stuck with the tube stuff. I also battle tinnitus and hyperacusis sometimes which means certain tones can jump out of a track and stab my ears with pain (even at low volumes). I've found that when something is bothering my ears that way - e.g. a muted trumpet or some really sharp electric guitar, switching to the tube preamp, it's relaxed, thickening effect, helps mitigate the sharpness. I can listen to it without pain, and listen louder. (And it does so without the obvious sense of "rolling off the highs").

I'm going to make a cheap but very silly suggestion here (don't flame me please)

I'm hoping you may use RCA's for this and not balanced, so ignore me if you're balanced here

Can you try a couple of the Amazon Basics RCA cables on the solid state feeds? Definitely not 'PC' in ASR terms as they shouldn't make any difference and not PC in audiophile terms as they're so darned CHEAP, but it's a kind of niggly hunch I have...

If balanced, it'd be interesting to know what interconnect wires you use - For the subtle 'effect' you describe, I remember the Klotz MC5000 doing this, at least when newly made up...

All this is the subjectivist dealer in me that won't fully die.... And yes, I do know it could may well be a total hiding to nothing, so my sincere apologies in advance if I end up costing you or anyone else money...

 

[Blumlein 88]

A measuring mic would have been a good inexpensive device to shed more light on your findings. Gives more data on whether the two devices have a different FR or distortion profile.

To repeat my last question (to the OP or anyone with the knowledge), is it possible either of the devices have a non-linear FR (or distortion), so level matching at one frequency is sort of meaningless (without that info)?

When devices have differing frequency response you can't fully level match in any way. Using noise or multiple frequencies doesn't help. They will differ at some point. And that difference is part of what you'll hear as an audible difference.

Using 1 khz is good as it is near the middle of things in octaves, and most devices will be flat at and around this frequency. Using lower frequecies like 400 hz is usually okay too. Many cheaper voltmeters don't respond much past 400 hz though most will be flat at least to this frequency as some generators use 400 hz AC. Using very low and very high frequencies is a bad idea as this is where FR is most likely to be different.

The Stereophile test shows the C-J preamp has differing high frequency response depending upon the volume setting. Possibly enough to be audible. It also shows the C-J having audible levels of distortion at 50 hz. Most likely these combined made the C-J audibly different and were the main reasons MattHooper can hear the C-J so reliably. My guess would be listening to pink noise as a test signal the C-J would be easy peasy to hear. However until he gets better level matching it is also quite possible the levels were off enough to help.

 

[Blumlein 88]

I'm going to make a cheap but very silly suggestion here (don't flame me please)

I'm hoping you may use RCA's for this and not balanced, so ignore me if you're balanced here

Can you try a couple of the Amazon Basics RCA cables on the solid state feeds? Definitely not 'PC' in ASR terms as they shouldn't make any difference and not PC in audiophile terms as they're so darned CHEAP, but it's a kind of niggly hunch I have...

If balanced, it'd be interesting to know what interconnect wires you use - For the subtle 'effect' you describe, I remember the Klotz MC5000 doing this, at least when newly made up...

All this is the subjectivist dealer in me that won't fully die.... And yes, I do know it could may well be a total hiding to nothing, so my sincere apologies in advance if I end up costing you or anyone else money...

You make it hard not to flame you, but I won't.

I think your suggestion for a source of the difference is very, very, very unlikely however.

 

[pma]

Again, if he used mic and SPL meter, then single tone method in a room is incorrect due to reflections or room modes. Noise would be much better.

 

[DSJR]

You make it hard not to flame you, but I won't.

I think your suggestion for a source of the difference is very, very, very unlikely however.

Like I said and with apologies, it's the subjectivist dealer that won't die part of me that had this thought. The CJ response and distortion results of course wouldn't help one iota here

 

[MattHooper]

Again, if he used mic and SPL meter, then single tone method in a room is incorrect due to reflections or room modes. Noise would be much better.

I just tested levels again using both white and pink noise. I left the levels of the LA4 and CJ the same as during my blind tests. Again, using two different apps on my iPhone and also SCOSCHE spl1000 Decibel meter, the SPL levels remained matched between the LA4 and CJ, just like with the single tones.

FWIW: doing some quick back and forth I didn't find sonic differences in these noise tracks nearly as revealing as with music.

 

[MattHooper]

I'm going to make a cheap but very silly suggestion here (don't flame me please)

I'm hoping you may use RCA's for this and not balanced, so ignore me if you're balanced here

Can you try a couple of the Amazon Basics RCA cables on the solid state feeds? Definitely not 'PC' in ASR terms as they shouldn't make any difference and not PC in audiophile terms as they're so darned CHEAP, but it's a kind of niggly hunch I have...

If balanced, it'd be interesting to know what interconnect wires you use - For the subtle 'effect' you describe, I remember the Klotz MC5000 doing this, at least when newly made up...

All this is the subjectivist dealer in me that won't fully die.... And yes, I do know it could may well be a total hiding to nothing, so my sincere apologies in advance if I end up costing you or anyone else money...

With apologies, I won't be doing this any time soon. (For one thing I'm in "belt tightening mode" waiting for my next job to begin, so I'm not spending on anything. Gotta love the freelance life!).

 

[xaviescacs]

Nice work @MattHooper. Thanks.

 

[Feyire]

I see the CJ inverts polarity.

For me the thread ends right here.

I don't bother about the CJ amp switching polarity. As I understand it, that's rarely audible.

Have you actually tried and listened? I've done live switching (in the source) from non-inverted to inverted and back again, and the audible difference was not at all subtle.

 

[solderdude]

How difficult would it be to record the output from both pre-amps using the same song ?
Record in 96/24 and use the song where you heard the most differences.

We all can try to hear and null the 2 files.

 

[pma]

How difficult would it be to record the output from both pre-amps using the same song ?
Record in 96/24 and use the song where you heard the most differences.

We all can try to hear and null the 2 files.

Easy to say for a qualified person. Not that easy to make it properly without ground loops and added noises/buzz and other mistakes made by an amateur without experience. The test is then useless.