Review: First Watt Aleph J Power Amp

jdjohn

I first posted about this amp as a Christmas present to myself. Now that I have some playback time with it under my belt, I thought I'd share a few thoughts. This was a DIY build that I purchased from the original builder/owner, with the design originating from Nelson Pass. 'diyAudio' has a LOT of information about building an Aleph J. In the end, the builder of this unit decided that he preferred a tube amp, so he elected to sell this. Lucky me, since he invested about $1,000 in parts with it, and eventually sold it to me for $700 shipped.

Below is some summary information about the amp's design. This is a copy/paste from Nelson Pass's design notes. @heiney9 posted this same info in another thread a while ago.

The Aleph J carries on in the tradition of the Pass Labs Aleph series, combining those elements that were particularly right about the Aleph 3 and 30, and re-thinking those areas open to improvement. Unlike its First Watt predecessors the F1 and F2, the Aleph J is a voltage source amplifier – a regular sort of amplifier like the ones you already know and love.
There are differences between the Aleph J and its predecessors:
1) Improved power supply filtration with about 20 dB less voltage ripple
2) Reduced gain on the active current source, giving better overall performance into 8-16 ohm loads
3) Input stage using high quality matched JFETs
4) Much higher input impedance and vanishing capacitance
5) 15 dB less negative feedback.
6) Even greater stability, operating without lag compensation
7) 15 dB less noise
8) No electrolytic capacitor in the signal path
Some things have remained the same – the Aleph J has the same basic 2-stage topology and uses output MOSFETs operating in single-ended Class A mode. It’s distortion character is still 2nd harmonic, and it’s sound is still natural and liquid. It is still very reliable. I don’t know of a load that can damage it.

Summary of the nominal specifications:
Measured at 120 V AC with an 8 ohm load:
Input Impedance 242 Kohms (RCA input)
Damping Factor 20
Output power 25 watts @ 1% THD 1KHz; 30 watts @ clipping
Gain 19.6 dB
Input for 25 watts output 1.5 volts
Maximum output voltage +/- 21 volts
Maximum output current +/- 2.5 amps
Frequency response - 3 dB @ 6 Hz, 80 KHz
Noise 100 uV unweighted, 20-20 KHz
Power consumption 200 watts
Fuse 3AG slow blow, 4 A (120VAC); 3AG slow blow, 2 A (240 VAC)

Below are some pics of it, inside and out, from the original sale ad.
Pretty plain Jane front...just the one LED top-left...it's red when illuminated.

In the next pic, you can see this particular unit only has XLR inputs...fine with me. However, having the on/off switch on the rear panel would not be my first choice.




Not the biggest transformer, but sufficient for my needs. Total weight of the amp is ~25 lbs, or so.

The preamp used was a Benchmark HPA4, which proved to be a very good impedance/gain match, with fully balanced outputs/inputs between the Benchmark preamp and First Watt power amp.

Full disclosure: I was not 'on the hunt' for this amp. I originally saw the ad on FB Marketplace, and just kept an eye on it for several weeks, if not months. I eventually contacted the seller, and he pointed me to his USAM ad. We chatted back-and-forth many times, and finally sealed the deal.

I would say build quality is good - not great. My only two nits to pick relate to the rear panel. The panel itself is only secured on the sides, with no attachments in the middle to the top or bottom, so it bends a little when pressed. That in-and-of-itself might not be a problem, except that the IEC socket and power switch are in the middle of the panel, so when pressing the power cord plug into the socket, the panel bends a little. The power switch being on the rear panel is my other issue...it's not exactly convenient back there.

I'd never tried a low-wattage, pure Class A amp before, and I did have some preconceptions/reservations, which have largely now been dismissed. First, the bass: I didn't expect such a low-wattage amp to provide such powerful bass. I really don't even feel the need to use my sub-woofer while using this amp. Next, the detail and PRAT. I had a preconception that pure Class A would sound syrupy and slow, but this amp does not...perhaps others do. This Aleph J is nimble and quick, with lots of detail coming through, especially in the mids and lows.

True to form for Class A (I think), it is on the warmer side (sound and temperature), which basically equates (at least in this case) to a roll-off in the upper highs. There is still detail in the highs, but absolutely no shimmer or glare. Cymbal crashes are less forward and have less splash, but the decay is still present, if that makes sense. I'd say that is where I'm still a bit on the fence, since I'm typically a guy who might reach for the treble knob...if one is present. I probably need to do some more critical listening before making definitive statements.

One example I can give is Eva Cassidy. If you've listened to much of her music, there always seems to be an excess amount of ambient/room noise in the background, which is initially kind of neat, but then when she hits those high notes, it can get to be a little much, depending on what gear is in the chain at the time. I often use some of her songs as test tracks in that regard when evaluating new gear. With the Aleph J, the ambient background noise is gone, and her voice is never in danger of going too far.

For classical music, jazz, and acoustic music, there is a real fullness to the sound that is really, really nice. Rock and pop is where the bass can seem a bit heavy, and/or some energy is missing in the upper registers...at least, compared to what I'm used to. But, perhaps that is closer to the original than I realized? It probably comes down to personal preference in that area. I've typically preferred a high level of detail in the higher frequencies, so this is a change for me. But, there is so much detail and texture coming through in the mids and lows, I don't feel cheated, since the overall dynamics are still very present. It has me thinking about how I might fine-tune other elements in my system in order to bump the highs up a bit (e.g., cables, phono cartridge, DAC, etc.). As mentioned earlier, it pairs really well with my Benchmark HPA4 - good impedance match, and no problem with gain.

Having said that last bit about gain, I can say that eventually, if you crank it up enough, those 25 watts can top-out, where a diminishing amount of return happens with turning the volume knob further. I haven't experienced clipping, or things falling apart in the soundstage, but it has a limit that I just don't want to challenge. I don't listen at insane volumes, but some guys might be left wanting more with this amp, depending on speakers. By the way, it drives my Mezzo Utopias just fine, although they can certainly handle more.

Bottom line: this Aleph J got me curious about other Nelson Pass designs, but for the money, I think this amp hits a good sweet spot. A potential buyer might want to study some of the various design aspects, and see which model strikes their fancy, but I think a person can scratch their Class A itch for not a lot of coin with one of these DIY builds.

WagnerRC

nice review and this amp really surprised me too. fun times . I also have the pass labs xa30.5

heiney9

What speakers are you running? The Alpeh J is 25 watts into 8 ohms and 13 wpc into 4 ohms. What Pass Labs amp is in the background? That runs class A up to a point so to say you've never heard a class A amp isn't true. That's either an X-150 or XA30 in the background.

Aleph J is a First Watt product not designed to run with large, power hungry, low ohm speakers. Probably why it sounds rolled off.

The transformer and heat sinks look undersized for an Aleph J. The DIY unit isn't the same as the real deal. Kind of like a kit car isn't the real car.

But, I'm glad you're enjoying it. I bet if you try it in a smaller room on more efficient and 8 ohm speakers it would sound much different and probably better.

Keep us posted.

H9

P.S. I am selling my Pass Aleph 30 if you want to experiment with a more robust (can run more speakers and lower load) single ended class A amp. No rolled high, no syrup. I promise

EDIT, sorry I was looking at WagnerRC and the Pass amp in the background, thinking it was yours....my bad

jdjohn

WagnerRC wrote: »

nice review and this amp really surprised me too. fun times . I also have the pass labs xa30.5

Thanks, and very nice Cary/Pass mix you have there! Do you have any comments comparing the Aleph J to the XA30.5?

jdjohn

heiney9 wrote:

What speakers are you running? The Alpeh J is 25 watts into 8 ohms and 13 wpc into 4 ohms. What Pass Labs amp is in the background? That runs class A up to a point so to say you've never heard a class A amp isn't true. That's either an X-150 or XA30 in the background.

Aleph J is a First Watt product not designed to run with large, power hungry, low ohm speakers. Probably why it sounds rolled off.

As mentioned in my original post, my speakers are JM Lab Mezzo Utopia. They are rated at 92.5dB efficiency, so relatively efficient.

heiney9 wrote:

The transformer and heat sinks look undersized for an Aleph J. The DIY unit isn't the same as the real deal. Kind of like a kit car isn't the real car.

That is an interesting comparison, that I can't realistically address. However, the orientation of the output PCBs (horizontal vs vertical) comes into play when looking at real estate inside the chassis. Visually, the orientation of those PCB output boards comes into play when trying to evaluate overall spatial dimensions inside the chassis.

heiney9 wrote:

But, I'm glad you're enjoying it. I bet if you try it in a smaller room on more efficient and 8 ohm speakers it would sound much different and probably better.

Keep us posted.

H9

P.S. I am selling my Pass Aleph 30 if you want to experiment with a more robust (can run more speakers and lower load) single ended class A amp. No rolled high, no syrup. I promise

EDIT, sorry I was looking at WagnerRC and the Pass amp in the background, thinking it was yours....my bad

Thanks for your advice regarding your Pass Aleph 30. At this point, I'm more inclined to invest in a Pass Labs XA25, as you did.

billbillw

Years ago, I did a Pass DIY Pearl phono stsge with help at DIYaudio. Still have it in my system 15+ years later.

heiney9

jdjohn wrote: »

At this point, I'm more inclined to invest in a Pass Labs XA25, as you did.

It's a really, really nice sounding amp. This is my end amp (unless Nelson comes up with something different in the next 5-10 years).

H9