Leaf Audio PA-03 MKII Review (Tube Preampifier)

[Peternz]

Hello @SIY ,

You have designed some quality tube projects. You also have AP test gear on your bench. It would be really cool if you post some test plots of what tube equipment can do.

I did build a SET 12B4A tube headphone amplifier near the end of 2017 about the time when I drove to Oregon and picked up an APx555. Using a solid state shunt regulator power supply that cost more than the Single End Triode stage including the output transformer, for typical listening levels The 12B4A SET cleaned up pretty nice.

Thanks DT
View attachment 149909

Pretty nice? Really? Why is the level only -18dB or so?

This is what I would call nice and it is on another planet (Note that level at 1k is 0dB, not -18.dB):

 

[DualTriode]

Pretty nice? Really? Why is the level only -18dB or so?

This is what I would call nice and it is on another planet (Note that level at 1k is 0dB, not -18.dB):
View attachment 149942

Hello All,



First hats off and thanks to @amirm for posting this review.

Next Vacuum Tubes are from another time, space and generation.

I do tubes for fun and learning. Tube measurements are relative to tubes not the comparison of good better best against the current state of the art electronics.



In terms of -18dBV, I measure relative to 1 Volt not dBrA. Using dBV as the scale always puts the sound floor relative to 1 Volt. It always puts the 60hZ and power supply harmonics relative to 1 Volt. You know what to expect in terms of noise coming out of you speakers or headphones.

Back to-18dBV as I said -18dBV is a typical comfortable level (I used to feed my HD600’s at the time).



In terms of cleaning up pretty nice compared to the current state of the art electronics, see the attached FFT of an AHB2 amplifier on my bench. That is at 5 Watts into 8Ohms or +16dBV. Note the better than -140dBrA distortion.

Thanks DT

 

[CedarX]

Just curious: it is also sold on AliExpress ($496 + $187$ shipping). There are apparently a “normal” (bad?) and an “upgraded” (worse?) version

What are these German aluminum oil capacitors? Never heard of…

 

[SIY]

Mundorf is highly fashionable among those who don't understand how coupling capacitors work.

 

[eriksson]

Love the VU meters.
Remind me - why can't we have those with Hypex or Purify amps?

We want them for god sake. Why not provide them?

 

[gonzoucab]

Just curious: it is also sold on AliExpress ($496 + $187$ shipping). There are apparently a “normal” (bad?) and an “upgraded” (worse?) version

View attachment 149977
What are these German aluminum oil capacitors? Never heard of…
View attachment 149978

It is the upgraded with all the extras, the whole enchilada

 

[gonzoucab]

Love the VU meters.
Remind me - why can't we have those with Hypex or Purify amps?

We want them for god sake. Why not provide them?

TEAC sells an hypex i think so that has VU meters

 

[Toku]

Is this product an audio effector?
It's definitely not an audio preamplifier, right?
To me, this characteristic never seems like a preamp.

Looking at this product as a preamp can be very confusing, but looking at it as an audio effector makes a lot of sense. High-order distortion addition effector.
But for this kind of effect, a tube preamp for less than $ 50 is enough.
The only thing that can be evaluated with this product is that it uses a line transformer for balanced input / output. Well, it's a vacuum tube circuit, so it's natural, but this is a true balanced connection.

 

[Ralf Stocker]

They really tried hard to use good components and to make a good quality of workmanship. Unfortunately, this is of no use if you have no idea about audio circuit technology.

 

[MakeMineVinyl]

Did you measure the output impedance? The 25V spec might be into something like a 100k load.

 

[MakeMineVinyl]

Just curious: it is also sold on AliExpress ($496 + $187$ shipping). There are apparently a “normal” (bad?) and an “upgraded” (worse?) version
View attachment 149976
View attachment 149977
What are these German aluminum oil capacitors? Never heard of…
View attachment 149978

Yup, just throw a bunch of expensive capacitors at the problem.

 

[amirm]

Did you measure the output impedance? The 25V spec might be into something like a 100k load.

My measurement impedance is 200K Ohm.

 

[whazzup]

Listen to it please!! Otherwise it's just electronicssciencereview!

 

[Hiten]

I gather this will have not too much effect on measurements but. is the transformer orientation correct ? That shield looks like aluminum which will hardly block magnetic field.

 

[H-713]

The low-frequency distortion makes me wonder if you were starting to saturate the core of a line transformer. Those transformers do look pretty small.

Looks like a great platform for modding, however. You could probably build a damn good tube line stage out of it, since the hard part (sexy chassis with VU meters) is already done.

 

[restorer-john]

Love the VU meters.
Remind me - why can't we have those with Hypex or Purify amps?

We want them for god sake. Why not provide them?

It always goes full cycle with VU and big power meters. Soon, they'll be all over everything again and the "purists" will be complaining.

 

[AndreaT]

Great review: I personally avoid electronics that measure poorly. I worry they might corrupt my listening experience and waste my time, recreating a tonality, dynamics and, in the end, a psychological experience far removed from the best intentions of the composer, the musicians and the sound engineers. It is akin to reading the printed edition of a novel with missing (errors of omission) and added paragraphs (not by the original author) because of poor editorial proofing of the original manuscript. Or watching a 1950’s movie on a blue ray DVD sourced from a high generation copy of the master film, with extra cuts between the reels and on a screen with the wrong aspect ratio.
I am therefore extremely grateful to Amir because he helps me to choose the best electronics to be as close as possible to the intentions of the creators of the source material.

 

[laudio]

As bad as it measured I might still consider buying it lol. Put a nice as preamp in that package and it's a winner.

The little teac above I own, nice kit. Meters matter.

 

[FrankF]

Beautiful piece of equipment but I prefer the tubes to be visible for maximum effect. Hopefully with a little work this unit will turn over a new leaf.

 

[tomtoo]

I think the general and accurate conclusion, at least in this community is that most tubes don't measure well and at the same time bad/mediocre measurements might not easily be reflected in normal listening conditions - and as far as I know even Amir did have positive subjective impressions with certain badly measured designs (under certain conditions).

My point is that we've been having subjective impressions/conclusions besides our pristine and accurate measurements for some time now and frankly we even have rankings now. Secondly, it actually contributes a lot of value to people that visit this site. Not everyone is primarily interested in the final measurement, they also want to know how it translates to listening experiences (might be the main reason why we now have more elaborated subjective impressions that we didn't have years ago? idk) - so why not continue to do that? For example, if the distortion is completely inaudible then great. But hey, if it's more or less the same in the first case but this time you can hear it loud and clear if you use a pure 20Hz sin or with some other specific conditions then it's another great discovery. Readers that are interested in this audio piece now have concrete information and they now can decide to do what they see fit with it!


Even if we go with your cow sh!t analogy I still think there's nothing that can be worsened if we have more information about a product in different angles - which is why I think milosz has a good suggestion because it can further remove bias of confirmation (if there is any).

And lastly, you say you don't see why you should do an experiment like that, with a device most people buy to play music (or maybe as a decorative piece...), but you'd rather do an experiment with 20Hz sin wave? I mean if we look at the facts, we already know it measures badly and is quite expensive. Nobody will try to deny that, it'd just be more helpful to know how it performs in the most realistic scenarios (which is playing music).

Its @amirm's time. Iam not against it. For me personal, it would not be any bennefit.

The main job of a amp is to amplify a signal without changing it. This amp fails in its main job. I can get a cheaper amp that does its job better. So what?