APPJ PA1501A mini tube amplifier with 6AD10 tube (black)

Tubes are not audio magic. They behave a certain way when in an audio circuit, and many listeners anjoy the sound. Many others just like the glowing tubes. They look cool. Who cares... It’s all part of the fun of playing with our respective stereo “train sets”.I had the precursor to this amp. It was fine. I rolled some NOS telefunkens in it and it drove my front mains in my home theater. All good (they were very efficient speakers). I ditched home theater for my first love - stereo reproduction, and decided to go old school, though my source remains hi-Rez digital.So, is the APPJ comparable to an Audio Research amp? No. Power cord? Supply your own. Tiny little metal feet? They slide and scrape - I have the APPJ on a cork pad. Heat? VERY HOT! I added heat sinks (it’s still hot, but the sinks are pulling quite a bit oh heat off the housing). The tubes are tilted at slightly odd angles and I can’t move them. That’s it. That’s every negative I can think of except it’d be cool to have an old Bakelite volume knob - it’d fit the aesthetic.On the positive side, because the itty bitty thing is driving old Belle Klipsch speakers with 104 dB efficiency, it’s hardly working when producing room melting sound pressure levels. With typical speakers, your peak output will be much more reserved.Peak levels don’t tell the whole story, of course. And I’ll mention also that I use a subwoofer, which is being driven by the speaker outputs of this APPJ. Yes, you read correctly - the speaker outputs. Just like Revel subwoofers suggest you do. Amazingly, this works out great! Are there phase problems and more? Possibly, but the Belles aren’t much about imaging. They’re all about dynamics. This amp can pull off great dynamics!Tonally, it’s balanced, with satisfying mids and highs. There’s plenty of air up top, and the bass is, um, reserved. Ok. The bass response could be better. There are three solutions. 1) Don’t worry about it. Seriously, just forget it and enjoy the qualities the amp does bring to the music. 2) Swap some of the capacitors as others have done (see reviews from other audiophile press sources) to bring the bass up a few dB. 3) Get a subwoofer and dial in all the bass you want! It’s working well for me. And I chose a budget sub from Parts Express.So what do we have here... My goal for this system was to find a synergy between 40 year old vintage speakers, and a modern, inexpensive, tube-based amplifier. And I did. I’ll swap in a NuForce DDA-120 and have solid state bliss when the mood hits. That amp is a bargain too. (Or was. They’re disappearing. Get one if you can.) But the APPJ tends to be the “go to” amp as it just sounds correct.Is this an amp for everyone? No. It needs space as it’s very, very hot. Power is extremely limited. The design is clean, though slightly quirky. However, if you have the right ancillary gear, you’ll get a sound that is above the amp’s price point. Again, I’m not talking about Quicksilver level performance here. Just pretty darn good tube sound. For the money, I highly recommend it.Happy listening!

Update 04/21/2019:Today I tried a different approach with the Appj PA1501A tube amp in my system. I set my Oppo UDP-203 to fixed output instead of variable output as I had been using it with the Appj PA1501A previously. Then I manually set the volume control on the Appj to a comfortable level, which has the volume knob set quite low, around 8 o'clock.To my surprise, that sounds great with no hum. It sounds as good or maybe even slightly better than with the Oppo set on variable output and the Appj's volume control turned all the way up, and the new settings have no hum.I don't understand why the sound is worse when the Oppo is set on variable output and set to a high output level with the Appj's volume control set to a similarly low position as when the Oppo is set to fixed output. Perhaps there is some impedance difference between the Oppo's output when it is set to variable output versus fixed output.The interactions between audio electronic devices are so frustratingly weird.Update 03-27-2019:I installed a Rolls "Buzz Off" between the output of my UDP-203 and the input of my Appj PA1501A. I also plugged the Appj PA1501A and Oppo UDP-203 into the same extension chord so that they are grounded together at the same electrical outlet. This reduced the hum to a level where I was able to make it inaudible with the Appj PA1501A's volume set at about 3 o'clock rather than all the way at full volume, without degrading the audio quality.An unexpected consequence of these changes was a marked improvement in clarity, definition, touch, and impact so that guitar and bass plucks are pluckier and the impacts of drum sticks tapping cymbals are better defined.After these system tweaks, I would now rate the sound quality from the Appj PA1501A as about equal to that of the Musical Paradise MP-301 Mk3 deluxe in my system.I am, however, keeping the rating at 4-stars instead of 5-stars since the Appj PA1501A still emits fairly loud squeaky chirps and gurgles when first turned on.Update 03-21-2019:I received the speaker level external volume control that I mentioned below. It is a Russound TBL-50. Just the insertion loss of the TBL-50 on maximum volume setting is enough to make the hum from the amplifier unnoticeable. However, it degrades the audio quality severely, even more than the volume control in the Appj PA1501A. With the Russound TBL-50, the stereo image is flattened and smeared out, the transients are blunted, and the bass is rolled off, muffled, and muddy. The balance also shifts as the volume setting is changed. Although it didn't work out, it was worth a shot.Therefore, for now I'll live with the low level hum between passages. I have ordered new NOS 6AD10 tubes for the amplifier to see if they lower the hum and lessen the turn-on noises.Update 03-12-2019:I keep tweaking my system with this little amp with interesting results.Setting the Oppo UDP-203 source's digital filter from Super Slow to Sharp Roll-off eliminated the remaining mid-treble sizzle and slight over sibilance. This really surprised me since my other tube amps sound better with the Super Slow setting on the Oppo UDP-203's digital filter when using it as a source.Another setting on the Oppo UDP-203 I altered next was the Down Mix setting, which I changed from Stereo to LT/RT. This made instruments and vocalists better localized in the sound stage, and more solid and palpable, and less diffuse. With my other tube amps, the LT/RT setting also did this, but dulled the reverberance and sense of space and air around the individual instruments and vocalists, but not with the APPJ PA1501A.The cumulative result of these system tweaks is that the sound of the APPJ PA1501A now rivals the sound of my MP-301 Mk3 deluxe in my system, and perhaps even exceeds it in midrange richness. This reminds me once again of the importance of component matching and synergies in obtaining the optimal sound from an audio system. It also reminds me of the adage that everything matters in audio reproduction.There are two remaining issues with the APPJ PA1501A that I have noticed so far, and which keep me from giving it 5-stars.First, with its volume control at maximum as needed for the best audio reproduction performance as discussed in my earlier update below, I can hear a low level hum between the music passages in near-field listening. I have ordered a speaker level volume control to insert between the amp and the speakers to see if I can make that hum inaudible and so I can turn up the source volume, without degrading the sound quality that I have achieved with the APPJ PA1501A.Second, when powering on the APPJ PA1501A, the speakers emit one or two fairly loud mid- to high-treble chirps or squeaks, similar to the sound made when letting the air out of a rubber balloon quickly through its pinched neck. The volume of these chirps/squeaks is independent of the volume setting on the amp. Since this sound does not recur after the initial turn on and warm up, I could live with it if I weren't worried about it possibly injuring my speakers. Hopefully the speaker volume control that I plan to install will also reduce the volume of this turn on chirp/squeak and thereby reduce the likelihood that it will injure my speakers. This chirp/squeak at turn on, however, may also be an indication that something in the amp is teetering on the edge of failure. I suppose time will tell.Update 03-09-2019:Since I wrote the original review below, I have been running the APPJ PA1501A on different volume settings. I had originally set the volume knob at 12 o'clock which allowed me to set my source (Oppo UDP-203) digital volume control above 50 out of 100 maximum. I have now, however, found that the APPJ PA1501A sounds substantially better with its volume control set to its maximum even though this requires me to set the digital volume on the source lower than 50 on most material, at least with my relatively high sensitivity Caintuck Audio Betsy open baffle speakers.Setting the volume control on the APPJ PA1501A to its maximum cures many of the ills that I had listed in the CONS in my original review below without diminishing its PROS. In particular the roll off in the frequency extremes that it had at the original volume setting is eliminated, and the bass is much tighter and more distinct. This greatly improves the pace, rhythm, and timing (PRAT) and dynamic punch. In addition, the sound stage is more expansive in depth and especially in width, with better spatial resolution. The treble is less harsh and sizzly, but still a bit more sibilant than I would like.This dramatic change in sound quality with the volume setting may indicate that the problems I discussed in my original review below were due mostly to a low quality volume control, rather than being inherent in the amplifier.With its volume control set at its maximum, the APPJ PA1501A's sound quality is on a par with that of the Kohstar Old Buffalo, the Gemtune GS-01, and Nobsound NS-03D, even though those amplifiers are more expensive. Its sound quality is not quite at the level of the much more expensive Musical Paradise MP-301 mk3 deluxe, but it isn't very far behind.I have not run the APPJ PA1501A long enough to speak to its reliability in the long haul, nor can I speak to its ability to drive less efficient speakers since I have not tried that yet, but for now, based on its sound quality when its volume knob is set at its maximum, and driving my Caintuck Audio Betsy open baffle speakers, it deserves a 4-star rating for its high performance to price ratio.***Original Review*******************************************************************This little amp is OK for the price, but it is no "giant killer."Pros: Rich and resonant midrange with lovely tube bloom and long decays.Cons: Indistinct, loose, and muddy bass. Hot, sizzly mid treble that overemphasizes sibilants and makes cymbals too clangy. Rolled off at both the low and high frequency extremes. Poor soundstage imaging lacking in depth, lateral extent, and spatial resolution. Lacking dynamic punch. Middling pace, rhythm, and timing (PRAT).Despite the cons I listed above, one has to take into consideration of the low price of only $179, hence my fairly neutral rating of 3-stars.One can get a tube amp with the listed pros and without the listed cons for about 2-3 times the price of this amp, which is still reasonably priced in my opinion.Of such reasonably priced amps that I have heard, my favorite is the Musical Paradise MP-301, Mk 3 deluxe, but the Kohstar Old Buffalo, the Gemtune GS-01, and Nobsound NS-03D also sound quite good. The improvement in sound quality of these amps over the APPJ PA1501A is worth the increased cost to me. Going much higher in price than the MP-301, however, has not been worth the increased cost in my experience. I have had amps costing about 4-7 times the cost of the MP-301, and which I have not liked as well as the MP-301.If you are seduced by the lovely rich midrange of the APPJ PA1501A without being turned off by its bass and treble problems, or need something decent for a low price just for non-critical background listening at low to moderate volumes, then the APPJ PA1501A is not a bad low cost option.