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Leaf Audio PA-03 MKII Review (Tube Preampifier)

amirm

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This is a review and detailed measurements of the Leaf Audio PA-03 MKII tube preamplifier. It is on kind loan from a member. It is only sold on ebay and such with prices going from $500 to $840.

This is one absolutely gorgeous looking and feeling piece of audio gear:
Leaf Audio PA-03 MKII Review Tube Preamplifier.jpg


Switchgear feels wonderful and relays clicking on your actions reassuring. The detents on the volume control are a bit coarse though and there are none on the tone controls.

On the inside is apparently an implementation of Audio Research LR LS22 preamplifier. The audio historians need to chime in and educate the rest of us on why that is prized enough to be cloned.

The back panel is almost as nice looking as the front:

Leaf Audio PA-03 MKII Review back panel Tube Preamplifier.jpg


The whole thing weighs a ton. I thought at first it was a power amplifier -- it is that heavy and solid!

FYI the AC/DC switch which is for the tube filament doesn't do anything (it says so in the specs and I tested it as such).

VU meter is hyper sensitive which is nice for playing music but for testing, it would constantly peg to the max. Wish it had a sensitivity switch.

Here is a picture of the guts of one (not sure if it is this version or not):
Leaf Audio PA-03 MKII Review teardown Tube Preamplifier.jpg


Leaf Audio PA-03 MKII Measurements
I always start with unity gain in testing preamplifiers. For balanced ones, this means 4 volts in, 4 volts out. The detents were too coarse to get that exact voltage and snapped instead to 4.3 -- close enough:

Leaf Audio PA-03 MKII Measurements Tube Preamplifier.png


What can you say other than distortion factory? And no, it is not all "good second harmonic." There is plenty of that but then there is a strong spray going to as high an order as you can imagine. Your low frequency notes will happily trash your higher frequencies where your hearing is most sensitive. High fidelity it is not.

I tested unbalanced output and got similar results:

Leaf Audio PA-03 MKII Measurements  RCA Tube Preamplifier.png


There is nice absence of power supply noise in both which is good. Also good is signal to noise ratio:

Leaf Audio PA-03 MKII SNR Measurements Tube Preamplifier.png


There is no good news after this. Here is our frequency response:

Leaf Audio PA-03 MKII Frequency Response Measurements Tube Preamplifier.png


With tone control defeated, you get that wavy response in blue. I tried to correct it with the tone controls and got the upper set of graphs. You best not have good hearing or the high frequency peaking at 20 kHz will bother you. As it is with tone controls defeated, it will have mid-range emphasis.

IMD graphs were horrendous and made no sense until I measured the unit more:
Leaf Audio PA-03 MKII IMD Measurements Tube Preamplifier.png


Remember that IMD has dual tones: one at 60 Hz and one at 7 kHz. Let's do a THD+N sweep versus frequency:

Leaf Audio PA-03 MKII THD+N vs Frequency Measurements Tube Preamplifier.png


Aha! See how low frequencies get distorted badly? That is impacting the first tone in IMD causing it to rise so fast. Lowering the volume (shown in black) helps but doesn't fix it.

Here is the output of 20 Hz by the way when output is 4.3 volt:

Leaf Audio PA-03 MKII 20 Hz Measurements Tube Preamplifier.png


Yes the waveform on the left supposed to be sine wave.

Company advertises 25 volts output without distortion. Let's test that:
Leaf Audio PA-03 MKII THD+N vs Level Measurements Tube Preamplifier.png


OK, it misses it by half but still darn good for a pre-amp to produce 13.5 volts.

Crosstalk is poor:

Leaf Audio PA-03 MKII Crosstalk Measurements Tube Preamplifier.png


So if you think your soundstage is getting better with this amp, I suggest thinking again.

The unit uses an ALPS27 volume control which seems to have excellent channel matching:
Leaf Audio PA-03 MKII Channel Balance Measurements Tube Preamplifier.png


Conclusions
What a shame that one of the most gorgeous looking and feeling pieces of audio gear has such horrid performance under the hood. Someone needs to take the guts out and build a solid state unit inside and can have my money! This thing would have looked good even in the golden era of 1970s and 1980s audio!

Anyway, if you have to use it, keep your volume low, adjust the tone controls to get as flat of a response as you can, and maybe it produces decent sound.

I am going to highly recommend the Leaf Audio PA-03 MKII as a decorative item. Hook up a spare output to it and have its VU meters dance around. When visitors come, tell them it is actually doing its thing. No sense in being honest with them and ruin the fun. And watch then praise the liquid mids and wonderful soundstage of tube preamp.....

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As always, questions, comments, recommendations, etc. are welcome.

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Drengur

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Looks good, produces questionable output. There is a joke to be made about an ex or something. What would happen to a woofer if it was made to play that 20hz "signal"?
 
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amirm

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I guess I could test that when I wake up (going to sleep now). Given the rich spectrum of every frequency from 20 Hz to infinity, it would sound anything but a 20 Hz sine wave.
 

SIY

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Does anyone have a schematic? This might be easy to fix, depending on what they've done. Just looking at the results, it suggests they did the same cut-and-paste pseudo-SRPP that seems to be mandatory in any tube equipment coming out of China.
 
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amirm

amirm

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Does anyone have a schematic? This might be easy to fix, depending on what they've done. Just looking at the results, it suggests they did the same cut-and-paste pseudo-SRPP that seems to be mandatory in any tube equipment coming out of China.
If the owner is willing, do you want me to send it to you for some surgery/optimization? The case is so gorgeous that if performance can be improved, it would be well worth it.
 

Vini darko

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If this was a pwm amp I'd say the duty cycle was way off. How is a linear AB amp doing that? :facepalm: bias shot to hell prehaps.
Thanks for the review Amir would be very intresting if SIY could get to the bottom of this one.
 

Koeitje

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That's a good looking turd.
 

milosz

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Did you ever listen to the thing? Most of us use audio equipment for listening, rather than just testing....

I am curious with all that measured distortion- could you HEAR that? I feel that people are much less sensitive to distortion than they think they are. It would have been good if you had listened to it before you ran your tests, so not to be biased.
 

tomtoo

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Did you ever listen to the thing? Most of us use audio equipment for listening, rather than just testing....

I am curious with all that measured distortion- could you HEAR that? I feel that people are much less sensitive to distortion than they think they are. It would have been good if you had listened to it before you ran your tests, so not to be biased.

With a 20Hz sin there is absolutly no problem to hear it. What that thing makes out of the waveform is so rich on harmonics, you hear it.
 

abdo123

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This is so bad, that I was thoroughly entertained reading it.

the only time i saw a downward sloping noise floor in an FFT is with phono stages. I wonder if the S/N would be much better if it was A-weighted.
 

Madjalapeno

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But it's got VU meters. :p
 

bunkbail

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This is one of those reviews that you really want Amir to have a listen to them. The measurements look so bad that it wouldn't even matter if you have an AB switcher or not, the differences *should* be very obvious.
 
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