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:
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:
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 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:
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:
There is nice absence of power supply noise in both which is good. Also good is signal to noise ratio:
There is no good news after this. Here is our frequency response:
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:
Remember that IMD has dual tones: one at 60 Hz and one at 7 kHz. Let's do a THD+N sweep versus frequency:
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:
Yes the waveform on the left supposed to be sine wave.
Company advertises 25 volts output without distortion. Let's test that:
OK, it misses it by half but still darn good for a pre-amp to produce 13.5 volts.
Crosstalk is poor:
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:
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.....
-----------
As always, questions, comments, recommendations, etc. are welcome.
Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
This is one absolutely gorgeous looking and feeling piece of audio gear:
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:
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 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:
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:
There is nice absence of power supply noise in both which is good. Also good is signal to noise ratio:
There is no good news after this. Here is our frequency response:
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:
Remember that IMD has dual tones: one at 60 Hz and one at 7 kHz. Let's do a THD+N sweep versus frequency:
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:
Yes the waveform on the left supposed to be sine wave.
Company advertises 25 volts output without distortion. Let's test that:
OK, it misses it by half but still darn good for a pre-amp to produce 13.5 volts.
Crosstalk is poor:
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:
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.....
-----------
As always, questions, comments, recommendations, etc. are welcome.
Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/