[baronbeehive]

Could someone please point out in the schematic where the coupling caps and cathode caps are?

I haven't got the schematic but this is where they are on the board, coupling caps are the white rectangluar caps, cathode caps are the brown round caps.

 

[Haidar]

Thanks baron!

 

[Pratt99]

Sorry to hear about your amp! That's a shame because it looks like you had done some good cap upgrades and have a good tube combo for best soundstage and resolution. The only thing you could have done to top all of that off is fit cathode caps which would have increased power reserves resulting in more dynamics, and the tonality of the amp could be changed depending on which caps you used also.

I will try as best as I can to compare the two amps, bear in mind my APPJ is the speaker version and I prefer to listen through speakers rather than headphones because I feel the sound is more real and natural.

Also bear in mind it will depend on what equipment you have, mods etc., and I have to remember what my impressions were prior to modding them

In unmodded form both amps sounded great, I preferred the APPJ for the reasons above. The APPJ is a faster amp which means that bass is tighter, treble had a bit more sparkle. Whereas the LD had a smoother more relaxed, richer more refined sound and great soundstage, both amps had great tonality. I would say the LD was slightly more tubey sounding whereas the APPJ was more neutral.

The mods bring the level of both amps up to compete with top level amps I believe. I wanted to try to cancel out the weaknesses of both which I more or less managed. The LD became more lively, tighter, transparent resolved, great treble and bass more like the APPJ and the APPJ more resolved punchy airy soundstage, more like the LD.

I did however use top quality caps in the mods so nothing was spared in the APPJ and I believe that was what really bumped up the level of the amp in soundstage in particular, which has a nice separation of instruments and a wide, fairly deep soundstage. I don't know if this is due to the speakers you would have to ask others on this thread some of who have experience of the 2 amps also.

I have to say that it was way easier to mod the APPJ, not much needed to be done whereas it took a lot of work to get the LD to get to the top level, and a lot of the time it was trying to keep up with the APPJ in some respects.

If you were to change amps I don't think you would get a better performing amp, unless you spent well into the thousands, what would be different is the flavour of the amp, do you want more tubey sound, more transparent sound and so on.

I wouldn't change my APPJ except for an absolute top level amp and probably not even then. Why would I when I love the flavour of both amps now LOL!

@baronbeehive Thanks much for your time and patience. This makes me reconsider my decision to try something else. The reason I wanted to look around is I am not sure how to or where to go to fix this amp. I am located in the USA and I did a google search on "tube amp repair" and I got some results on people who work on guitar amps. So I need to figure this out, if someone located in USA have some info on this please share.

Another option is to order a new amp from china (costs around $200) since I already have the tubes and caps, but I got the same question "what if I run into issues , where do I go to fix it?"

 

[rdale]

@rdale I remembered you have the speaker and headphone APPJ's and I wondered if you could do a comparison of these, it would be interesting to see how they differ!

Yes I have both the PA1502A and a Miniwatt N3 speaker amp.

They are a great visual match and look really good sat next to each other - I posted a picture of them earlier in this thread. I've replaced the feet on them with 3M Acoustifeet and sat them on SSC Mini Bases (I got both of these items from MCRU in the UK). It is very difficult to compare the sound of the headphone amp driving Audeze LCD-3s with the Miniwatt driving modified Tandy LX5 speakers with Linaeum ribbon-like tweeters. They both sound very transparent and 'electrostatic-like'. The Miniwatt works best with Psvane valves, and I preferred Psvane EL84s to Genelec Gold Lion Reissue EL84 valves that I use in my other small single ended speaker amp, a Glow Amp One. I use cryo treated Gold Lion Reissue 6V6s in rthe PA1502A with a Psvane 12XA7 input tube. I use Duelund speaker and interconnect cable all my systems and I think that adds to the tonal richness that valves amps have.

In comparison to the Glow Amp One, the Miniwatt N3 has slightly faster more lit up treble where the Glow was more on the rich side, although the Minwatt bass was less extended. I haven't noticed a lack of bass extension with the LCD-3s/PA1502A compared with my Chord Hugo driving the Audezes. I didn't really hear what the Audezes/Nordost Heidall 2 cables were capable of until I heard them with the PA1502A.

 

[baronbeehive]

@baronbeehive Thanks much for your time and patience. This makes me reconsider my decision to try something else. The reason I wanted to look around is I am not sure how to or where to go to fix this amp. I am located in the USA and I did a google search on "tube amp repair" and I got some results on people who work on guitar amps. So I need to figure this out, if someone located in USA have some info on this please share.

Another option is to order a new amp from china (costs around $200) since I already have the tubes and caps, but I got the same question "what if I run into issues , where do I go to fix it?"

No worries I enjoy being boring about amps!

Re: your APPJ I don't want to influence you in any way regarding keeping or changing it if that's what you want, it's just my view.

What I've done if I need help in the past is to take it to a local electronics repair engineer. It probably doesn't matter if they specialise in tube amps, all that's needed is someone who can test an electronic circuit and usually anyone such as TV repairs and such like would be able to troubleshoot and repair it. It's probably something happened to the mods you did affecting the circuit.

Edit: I would not use it again until it's been repaired before any damage is done!

 

[baronbeehive]

Yes I have both the PA1502A and a Miniwatt N3 speaker amp.

They are a great visual match and look really good sat next to each other - I posted a picture of them earlier in this thread. I've replaced the feet on them with 3M Acoustifeet and sat them on SSC Mini Bases (I got both of these items from MCRU in the UK). It is very difficult to compare the sound of the headphone amp driving Audeze LCD-3s with the Miniwatt driving modified Tandy LX5 speakers with Linaeum ribbon-like tweeters. They both sound very transparent and 'electrostatic-like'. The Miniwatt works best with Psvane valves, and I preferred Psvane EL84s to Genelec Gold Lion Reissue EL84 valves that I use in my other small single ended speaker amp, a Glow Amp One. I use cryo treated Gold Lion Reissue 6V6s in rthe PA1502A with a Psvane 12XA7 input tube. I use Duelund speaker and interconnect cable all my systems and I think that adds to the tonal richness that valves amps have.

In comparison to the Glow Amp One, the Miniwatt N3 has slightly faster more lit up treble where the Glow was more on the rich side, although the Minwatt bass was less extended. I haven't noticed a lack of bass extension with the LCD-3s/PA1502A compared with my Chord Hugo driving the Audezes. I didn't really hear what the Audezes/Nordost Heidall 2 cables were capable of until I heard them with the PA1502A.

Thanks for that, very interesting! I'm lucky in that I've managed to get the sound of both the speaker amp and the headphone amp to sound pretty much the same, quite an achievement considering the different equipment involved!

Yes they both looked good in the picture you posted!

I remember reading about the Glow One a while back and they were comparing it to the Miniwatt N3 and on that basis I decided on the Miniwatt.... and I'm glad that I did!

 

[corbimatic]

Welp, I’m hooked. The stock tubes took the entire side 1 of Houses of the Holy to warm up, but by side 2 the sound was pretty impressive. Clarity was good, bass was there, vocals could get a little harsh at times but that’s also probably partly Robert Plant’s fault. Next I listened to Axis: Bold as Love and interestingly, the first track (EXP) when the grungy distorted guitar is swirling around your head - there was almost a discreet step between left, right, and center. I’m new to HiFi headphones, so I’m not sure if I’m just used to it sounding much more blended as sounds move from left to stereo to right channel. Anyway, I didn’t pick up on it as much or at all on the remaining tracks that rip sound all over the soundstage in your head, and generally was impressed with the amp. I am willing to admit that after spending as much time shopping as I did, I’m prone to confirmation bias here, so I’ll give it a critical listen again but my first impression is: this is a very good amp for the money.

Oh, and I think I need to ground the chassis of my turntable to it. I got just a slight zap when I touched both with my hand at the same time. Didn’t notice any of the tell-tale humming of an ungrounded magnetic cartridge, so not too concerned, but I assume it can’t hurt.

Question - my headphones are 64ohm Sonys. At high gain, they sound great and plenty loud at maybe 45/50% volume on the dial. On low gain, they sound great at 85/90%. Is there any reason to think I might get better or worse long-term tube performance at different volume settings? Said another way - Navy jet engines in the 60s were designed to operate best when wide open, so my (now) 95 year old neighbor who was a test pilot they nicknamed “Speedy” never flew anywhere at less than max velocity. Samesies? By the way, Speedy still takes his tiny 12’ boat with the way oversized engine out in 5-7’ swells in the middle of the lake and calls it surfing.

Question 2 - how do I post pictures? This thing doesn’t like my setup pics.

 

[baronbeehive]

Welp, I’m hooked. The stock tubes took the entire side 1 of Houses of the Holy to warm up, but by side 2 the sound was pretty impressive. Clarity was good, bass was there, vocals could get a little harsh at times but that’s also probably partly Robert Plant’s fault. Next I listened to Axis: Bold as Love and interestingly, the first track (EXP) when the grungy distorted guitar is swirling around your head - there was almost a discreet step between left, right, and center. I’m new to HiFi headphones, so I’m not sure if I’m just used to it sounding much more blended as sounds move from left to stereo to right channel. Anyway, I didn’t pick up on it as much or at all on the remaining tracks that rip sound all over the soundstage in your head, and generally was impressed with the amp. I am willing to admit that after spending as much time shopping as I did, I’m prone to confirmation bias here, so I’ll give it a critical listen again but my first impression is: this is a very good amp for the money.

First impression is always important, I tend to find that the impression improves with time as you get to appreciate the amp.

Probably more of a headphone thing than to do with the amp. I know some headphones have that weird presentation where there is a well defined place for right, centre, and left, much like the old recordings used to put drums on the left stage, keyboards on the right etc. If you were to get to modding... and who wouldn't... then I would suggest good quality caps will improve soundstage. With my.... expensive.... Jupiter caps the soundstage has increased and become much more open, airy and seamless on my headphone amp.

...my (now) 95 year old neighbor who was a test pilot they nicknamed “Speedy” never flew anywhere at less than max velocity. Samesies?

I'm hoping you're not thinking of listening at max volume all of the time LOL! Be kind to your ears…. as well as tubes!

I don't know if it would harm the tubes long term, but that's not practical listening!

Question 2 - how do I post pictures? This thing doesn’t like my setup pics.

Copy and paste is the simple way.

This was copied and pasted from Paint:

This was uploaded from a folder:

 

[rdale]

Question 2 - how do I post pictures? This thing doesn’t like my setup pics.

I had the same problem when I first registered for Head-Fi - I think you might need to have done a minimum number of posts or maybe someone has to confirm you're not a robot. But it suddenly started working for me.

 

[Pratt99]

No worries I enjoy being boring about amps!

Re: your APPJ I don't want to influence you in any way regarding keeping or changing it if that's what you want, it's just my view.

What I've done if I need help in the past is to take it to a local electronics repair engineer. It probably doesn't matter if they specialise in tube amps, all that's needed is someone who can test an electronic circuit and usually anyone such as TV repairs and such like would be able to troubleshoot and repair it. It's probably something happened to the mods you did affecting the circuit.

Edit: I would not use it again until it's been repaired before any damage is done!

@baronbeehive Thanks again! Will check with my local electronics repair shop then. Since the sound went thin I assumed this should be a powersupply issue and someone with knowledge on tube biasing will be a better source to ask for help. Will update if I manage to get this fixed.

 

[corbimatic]

Question on the high/low gain switch - my guess is that on the high gain setting nothing is actually happening, and that the low gain is just adding a resistor in series to increase circuit resistance for use with lower impedance headphones. If that’s the case, that would help me answer the question on whether to run on high at 40% or low at 80% for normal listening volumes. Anyone take a close look at the switch? I’m not ready to crack mine open quite yet.

Second question for folks who have switched out capacitors - has anyone hooked this up to a oscilloscope to see what the stock low-end frequency response within 3db is? I get how the coupling capacitor might be acting as a high-pass filter in this circuit, but wondering if we can put some real numbers on it. Mine seems to have pretty good low frequency response, as best I can tell it’s getting pretty far to the low-end of the range and I can’t detect any of the tell-tale signs of a diode thirsting for current when the bass drum thumps. Wondering if this was something done primarily by people powering speakers with this little guy?

Second listening session was Diver Down and by the time I got to Little Guitars (which is an excellent track) the amp was definitely warmed up and sounding great. A good record for checking out the range, in my opinion, because you have a lot of very loud things going on, sometimes all together, and sometimes not. Everything sounded very accurate and I got really nice clarity. I followed that up with 77, which is an excellent pop record but is the least demanding from a post-production/engineering/cross-fading/stereophonic standpoint of what I’ve listened to so far. That proved to be a good test in and of itself, as David Byrne’s range might be limited but his voice is distinct and was very well represented and clear, and sounded natural. Last record was The Bends, and while they certainly mellowed out and became much more prog/alt/art-rock with OK Computer, this is a record that is still very much guitar-god-alternative-grunge and yet uses production/engineering to move things around the sound stage. The amp again, represented things well and gave a nice, full-range, clear representation of the record.

So that’s probably it for posts using the stock tubes. They sound great, for what they are. I question if the 6N4 is the reason I hear discreet steps on certain highly engineered tracks like EXP on Axis: Bold as Love. It could also be that I’m not used to headphones and for the first time I’m hearing the hurried overnight work of Chas Chandler et al after Hendrix lost the side 1 master tape when he left it in a taxi. It only really showed up on that one track, which is admittedly the most demanding of what I’ve heard so far. I would say this whole tube amp thing is outrageously fun and new and exciting for me, and while I don’t think that’s clouding my judgement too much, I would also readily admit that I miss having many several thousand watts of multi-channel power shaking my whole house. We just moved, but in the old place it was a source of pride for my wife to come home and find that I’d popped another retrofit recessed light out of the ceiling with sonic power emanating from coils driving magnets shaking massive diaphragms. Oh well. Time to grow up anyway, right?

I’ve got reissue Genalex matched 6V6s and a 12AX7 on order and will keep rolling through the reissues I can get on Amazon Prime. From what I can see on there now, I can get matched 6V6s and a same-branded 12AX7 (or similar) from: Electro-Harmonix, Tung-Sol, Telefunken, JJ Electronics, Mullard, and Fender’s Groove Tubes (not really a reissue on that last one I guess...) One of the many reasons I settled on this amp was the ready availability of the reissued stuff. After that I might maybe possible start digging a hole in my wallet with some of the NOS options. The 1960s RCA 6V6G does look pretty rad, after all.

 

[baronbeehive]

@baronbeehive Thanks again! Will check with my local electronics repair shop then. Since the sound went thin I assumed this should be a powersupply issue and someone with knowledge on tube biasing will be a better source to ask for help. Will update if I manage to get this fixed.

OK. It could be the SMPS as you say but I think that's more likely to go suddenly..... and would be accompanied by smoke lol, so perhaps it's the driver tube socket because the driver tube feeds both power tubes. The socket gets a lot of use with tube rolling and could have worked loose.

 

[baronbeehive]

Oh I see... I thought you had actually been consigned to the cupboard under the stairs lol!

Question on the high/low gain switch - my guess is that on the high gain setting nothing is actually happening, and that the low gain is just adding a resistor in series to increase circuit resistance for use with lower impedance headphones. If that’s the case, that would help me answer the question on whether to run on high at 40% or low at 80% for normal listening volumes. Anyone take a close look at the switch? I’m not ready to crack mine open quite yet.

I see you have the updated APPJ with the gain switch, nice!

You are correct and it wouldn't harm the circuit to run at those settings, I don't know what the effects are on tubes is in the log run though.

Second question for folks who have switched out capacitors - has anyone hooked this up to a oscilloscope to see what the stock low-end frequency response within 3db is? I get how the coupling capacitor might be acting as a high-pass filter in this circuit, but wondering if we can put some real numbers on it. Mine seems to have pretty good low frequency response, as best I can tell it’s getting pretty far to the low-end of the range and I can’t detect any of the tell-tale signs of a diode thirsting for current when the bass drum thumps. Wondering if this was something done primarily by people powering speakers with this little guy?

You are correct again, but no i don't have an oscilloscope. I'm the only one here with speakers apart from rdale.

This is why we decided to put high capacitance cathode caps in for that very reason. Also this is why I made 3 options in my earlier post for replacing them. The actual power output, 3.5W in my case though quite low is not so important for the operation of the amp, more important is recovery from clipping in transients. If this is super effecient then you could probably make do with only 1W of power. We settled on 1000uF capacity for the cathode caps so that there was plenty of power in reserve for recovery. The problem is that electrolytics are slow, what is really needed is fast acting film caps but these are very large and expensive so what we went for is a compromise of high capacitance electroytics but with small faster bypass caps to aid those higher frequencies. The higher you go with capacitance the higher the power reserves but the longer the charge-discharge cycle which will adversely affect the higher frequencies.

Clipping is not usually heard over the music because the ear just thinks what it is listening to is a continuous stream of music, and if recovery from transient clipping is good it would not be heard, but if recovery was poor then the music would sound pretty bad.

Oh well. Time to grow up anyway, right?

Possibly, yes!

1000Watts seems a good idea until you realize that circuits with that much power have associated problems with damping down the frequency response to get the desired output impedance, and need to use massive amounts of GNFB which has negative effects on SQ.

How would you say your APPJ compares to your 1000W monster, apart from all that power?

Very interesting observations in your review, keep us posted!

Edit: I only have experience of the TS and JJ reissues, and I liked the JJ's which have a good reputation. However reissues in general.... nope, not really!

 

[corbimatic]

Ah, that makes sense. I have the headphone-only version of the amp, the APPJ PA1502A, and so far I’m really impressed with the sound quality when pushing my headphones, which are reasonably priced but audiophile enough for me (the Sony MDR 7506.) I think you have the APPJ PA1501A, and so I get why you might potentially experience clipping and might have trouble reaching very low frequencies without upgrading your coupling capacitors to something that can hold a lot more farads when you try to push speakers. I said I was done with reviews of the stock tubes, but for reference I’ll add that I listed to DMB’s Big Whiskey and the GrooGrux King, which is a nice test because Dave’s voice is singular, and Carter’s drums are almost more melody than rhythm and Dave’s guitar is almost more rhythm than melody, and the amp did a really nice job recreating the entirety of the soundstage with great clarity. I followed that with Meddle, which is a great test album for the stock capacitors as the entire B side is basically one long homage to low frequencies and sonic experimentation by Waters and Gilmour. From what I can tell, zero issues hitting and sustaining and recovering from very low notes at pretty loud volumes. I think for anyone considering getting a dedicated headphone-only amplifier with pure tube amplification (not hybrid) this little guy is an excellent choice, even with the stock tubes in.

My other setup is my home theater, which is a completely solid state Dolby 7.1 setup with the speakers all built into the walls and ceiling. The comparison is somewhat difficult, because with all that digital processing the soundstage separation is going to be extreme by comparison, but at the same time my vinyl is a stereo source at best. In the past I would run the 3 front channel speakers and subwoofer (a Monitor Audio IWS-10 pushed by an IWA-250) and quite franky, it’s just not an apples-to-apples comparison. It makes movies with Dolby Atmos or 5.1 or whatever advanced digitally processed source sound pretty cool, and for music it’s... pretty effen good, too, but again, hard to compare. Headphones have such dramatically lower total harmonic distortion than even the world’s most expensive speakers that it’s just not apples-to-apples. Also I never once plugged headphones into my receiver, although I suppose I could do that and get back to you. I’d say the primary difference is that I don’t feel the bass anymore. I certainly hear it and it’s represented with perfect clarity, but the couch and walls aren’t also vibrating and things aren’t rattling on the shelves.

The reissue Genalex Gold Lion 12AX7s and matched 6V6s show up today, if the approaching snowstorm doesn’t stop the delivery. This is Chicago, so a few inches of snow shouldn’t be an issue. Everything I’ve read tells me the reissue 12AX7 is a worthy reissue, so I’m excited to see what it can do. I think the 6N4 is potentially limited in its ability to process tracks that move things around the soundstage in rapid, loud fashion (see also: Jimi Hendrix.)

I also have to admit that I couldn’t hold off buying NOS tubes for as long as I intended. I found a matched pair of smoked glass 1950s RCA 6V6GT aka VT-107A and a 1960s RCA 12AX7A on nostubestore.com and pulled the trigger. I asked for the low-cost shipping method which will take a few weeks coming from Europe, so I’m telling myself that means that I actually waited awhile before diving into NOS world, but if I’m being honest with myself I jumped in head first and plunked down a chunk of money before the reissue experimentation even began... And so it goes.

 

[baronbeehive]

Ah, that makes sense. I have the headphone-only version of the amp, the APPJ PA1502A, and so far I’m really impressed with the sound quality when pushing my headphones, which are reasonably priced but audiophile enough for me (the Sony MDR 7506.) I think you have the APPJ PA1501A, and so I get why you might potentially experience clipping and might have trouble reaching very low frequencies without upgrading your coupling capacitors to something that can hold a lot more farads when you try to push speakers. I said I was done with reviews of the stock tubes, but for reference I’ll add that I listed to DMB’s Big Whiskey and the GrooGrux King, which is a nice test because Dave’s voice is singular, and Carter’s drums are almost more melody than rhythm and Dave’s guitar is almost more rhythm than melody, and the amp did a really nice job recreating the entirety of the soundstage with great clarity. I followed that with Meddle, which is a great test album for the stock capacitors as the entire B side is basically one long homage to low frequencies and sonic experimentation by Waters and Gilmour. From what I can tell, zero issues hitting and sustaining and recovering from very low notes at pretty loud volumes. I think for anyone considering getting a dedicated headphone-only amplifier with pure tube amplification (not hybrid) this little guy is an excellent choice, even with the stock tubes in.

Yeah! I have the speaker version, the APPJ PA0901A, or Miniwatt, which I always mention to avoid confusion because the Miniwatt threads died out a while ago whereas this thread is still going strong, despite having to be given the kiss of life a while back... and it was touch and go! APPJ's continue to be made and you have the latest upgrade with the gain switch so this is the place to come for information about it. I enjoy reading about members experiences, which are mostly positive.

Headphones have such dramatically lower total harmonic distortion than even the world’s most expensive speakers that it’s just not apples-to-apples. Also I never once plugged headphones into my receiver, although I suppose I could do that and get back to you. I’d say the primary difference is that I don’t feel the bass anymore. I certainly hear it and it’s represented with perfect clarity, but the couch and walls aren’t also vibrating and things aren’t rattling on the shelves.

…...no neither are your brain and eyeballs!

Yes, no beating headphones for accurate reproduction compared even with the most expensive speakers, no room acoustics to consider at all, just the shape of your ears!

Some headphones are capable of real bass heft, even sub bass, and bass drum reverberation but mostly its a question of accurate definition.

The reissue Genalex Gold Lion 12AX7s and matched 6V6s show up today, if the approaching snowstorm doesn’t stop the delivery. This is Chicago, so a few inches of snow shouldn’t be an issue. Everything I’ve read tells me the reissue 12AX7 is a worthy reissue, so I’m excited to see what it can do. I think the 6N4 is potentially limited in its ability to process tracks that move things around the soundstage in rapid, loud fashion (see also: Jimi Hendrix.)

I also have to admit that I couldn’t hold off buying NOS tubes for as long as I intended. I found a matched pair of smoked glass 1950s RCA 6V6GT aka VT-107A and a 1960s RCA 12AX7A on nostubestore.com and pulled the trigger. I asked for the low-cost shipping method which will take a few weeks coming from Europe, so I’m telling myself that means that I actually waited awhile before diving into NOS world, but if I’m being honest with myself I jumped in head first and plunked down a chunk of money before the reissue experimentation even began... And so it goes.

Don't we all!

Keep us posted on your observations, I am interested in those Gold Lions.

With NOS you should get better all round SQ frankly, soundstage etc. should all go up a level there are plenty of recommendations going back a few pages or so, or you can ask of course.