Any opinions / reviews on Gemtune APPJ PA1502A

Discussion in 'Headphone Amps (full-size)' started by mortus, Sep 6, 2015.
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  1. baronbeehive
    Re: my comment about the pot mod on the miniwatt, I have just seen a comment by someone that carried out this mod and they said that it further improved the sound quite a lot. Of course anyone who has a preamp could hook it up and use the volume control of the pre to bypass their APPJ's volume pot to see what effect this has.
    I haven't got a preamp but if anyone has it would be interesting to see what happens to the already fantastic sound! The only drawback would be that you are adding in another stage to the system which might adversely affect it soundwise. A review on tnt-audio said about using a pre on the main system...."there is a slight trade-off inserting another stage but I would say that it is worth a very slight loss of transparency for the extra 'weight' and scale that is gained." On the second smaller system they said..... "Now things were getting really serious. There was a real kick to the bass and it sounded deep too (deeper than the claimed response of 30Hz to 20kHz within 1 db). The sound was ' fuller' and that lean sound on some tracks was gone too. The speed which was already good got even better...." I've already said that I don't need a pre on the modded amp as the mods have increased the weight of the sound output anyway.

    BTW does anyone know if the APPJ uses negative feedback, because if it doesn't that could explain the clarity of this amp.

    Re: my suggestion to try using an active volume controller, ie a preamp to see what the effects on sound are by bypassing the pot on the APPJ, the other way might be to try a passive volume controller which would not introduce any further gain stage and so should be sonically purer. However I don't think I will explore this any further because although it would bypass the APPJ's pot, it could just as easily degrade SQ as improve it because of all the additional factors that need to be taken into consideration. As usual nothing is easy!
    Last edited: Oct 1, 2017
  2. Maxx134
    I just tried a tung-sol 14AF7 and I have to agree that this is just a top notch sounding tube....

    That makes me interested to try the 14F7 as well.

    So I am finding the 14AF7 to a have top notch realism/clarity with a bit more depth or Soundstage,
    Which is great because it is still clear.
    I find my 12SL7 silver plates a bit more forward and brighter and less dimensional.

    Looks like I have a new favorite with the 14AF7, although I like my trebels, they now seem more neutral.
    Very good tube!
    I may try an RCA next, but I doubt I would surpass the Tung-Sol.
    Actually what I cannot find is a Sylvania which would be desirable.

    I am also finding the 14AF7 does not run as hot as any of the others,
    So I checked and the heater only use 0.15ampere..
    Last edited: Oct 5, 2017
  3. DavidK35
    Glad I could help you get closer to Nirvana LOL!
    Years back I read that all the loctals were mae by Sylvania but just badged differently,
    dont know if thats true or not.
  4. Maxx134
    Yes I heard that about some loctals made by Sylvania for other companies, but not sure about these as there are a lot of philco ones out and these are older tubes in general.
    Last edited: Oct 3, 2017
  5. baronbeehive
    OK, so it looks like I will have to try the 14AF7 on my amp...... one 14AF7 duly ordered! I still can't see it replacing my 5751 though, we will see.

    May be the last tube I try, I've tried examples of the main types, although there are always different versions: 12AX7: RCA - OK, does the basics well, Amperex - good, nice warm sound, Telefunken - not my favourite type of sound, cold and accurate but boring, 5751: Sylvania JHS, quite good, bright, not my type of sound, JJ ECC83S, good new issue tube, smooth, open sound, like Raytheon 6SN7 that I tried on my other amp and similar to the Raytheon 5751 according to some reviews, Tungsol, my choice, clear, detailed, open, beautifully smooth yet dynamic, 12SL7, Tungsol, good, lovely flowing sound but not very dynamic, GE, good but bright, quite harsh, flat, accurate frequency response, like Sylvanias.

    One tube that gets good reviews is the Mullard ECC33, I'm quite curious about this one, don't think I will try though.
    Last edited: Oct 6, 2017
  6. CZ4A
    Not sure if it's been discussed here already, but the octal base equivalent of the 14AF7 is the 12AH7GT. It will need its own adapter because the plate and cathode pins are flipped compared to a 12SN7. Probably better going with a 14AF7 and loctal-to-octal adapter, since you can also try 14F7 (loctal 12SL7) and 14N7 (loctal 12SN7), which have the same pin out.

    ECC33 is only available with 6V heater. You won't want to use it in the PA1502A since the filaments will prematurely wear out from overheating.
    Maxx134 likes this.
  7. baronbeehive
    Re: ECC33, my mistake, I meant ECC83!

    Yes, thanks, I have a 14AF7/14F7 adapter on order.

    Edit: Of the 2 versions I decided to go for the adapter with enclosed pin sockets rather than the exposed ones, (I would rather only the tube lights up, not myself).
    Last edited: Oct 7, 2017
  8. baronbeehive
    Incidently of the tube types I've tried above they were all the top versions apart from the RCA and GE. If anyone is interested who doesn't already know, the RCA type have a version which is quite different and better than the common one, very open with great soundstage but it's supposed to be slightly fatiguing to listen to, and the GE version of the 5751 is also done in a cryoed version by watfordvalves which is supposed to improve every aspect of the sound, detail and soundstage, but as I'm not into that type of bright sound I won't be trying it.
  9. Maxx134
    I did also see that and was disappointed about the pin order being switched,
    Because I could not find an adapter for it,
    Which means one would have to make one
    Edit found one but didn't bother.

    Haha yes I went for the exposed cheaper adapter just in case, as I didn't believe the tube would be better than what I already had,
    But the slight increase in Soundstage with more neutral trebles makes them a top choice.
    Now I will have to cover the exposed adapter with something nice and pretty lol.
    Last edited: Oct 20, 2017
  10. Pratt99
    @baronbeehive My favorite pre-amp tube for this amp is TS 5751 as well, so will be looking forward for your impressions. Have ordered the 6BG6G RCA tubes based on @DavidK35 and @Maxx134 reports, upgrading from JJ 6v6 tubes.
  11. Maxx134
    Ok so as you can see I have the cheapo adapter that is all exposed in middle here:
    So you can have a shockingly good time touching it to pull it out...

    So I improvise with some special tape :

    Easy peasy.
    Last edited: Oct 9, 2017
  12. baronbeehive
    .....clever stuff!! I imagine it revolves round and lights up disco ball fashion with multi colours in time to the music lol.

    The alternative version is a funny shape anyway, I don't know why they've made it like that.
    Last edited: Oct 9, 2017
  13. Maxx134
    Good info,
    So based on this, I went for a 14F7, as being an "SL" equivalent, it should have more gain like my 12SL7 type .

    Looking over the 12AH7 types, I determine they are post war period and so not as old and so not as good, and they have very clear glass and little getter flash which to me is more newer and so at a time when more mass produced (possibly less quality)
    I have not looked in thier specs yet but not interested anyways.
    They are a few year older (3-4) but not made as rigid quality of metal base.
    Odd to see so little flash inside.

    So I just tried a Sylvania 14F7,
    And I did get back more gain.
    I am not sure which manufacturer you tried, but I am getting a more lively presentation over the "AF" type, and it sounds great.
    I seem to have replaced the slight relaxed nature of the "14AF7" tube, with a bit more "live" factor, while hearing more depth.
    So now these 14F7 are my favorites! Lol
    I probably need to try a Sylvania in the 14AF7 type..
    Last edited: Oct 20, 2017
  14. Mshenay Contributor
    So I'm having some sound stage issues with my Stock Pair... I finally worked out the freaking 6v6 Tubes I had and Adapters for those sockets are a must... those stock ones are hell to get in and out. I think my tubes weren't even situated correctly for one!

    sound wise I might get a 14AF7 for schiit's and giggles what adapter do I need? Price on it seems pretty good, $15 for two, an extra is always nice

    I'm also having a small issue with the Middle Socket as well... as it's lop sidded... how would I go about replacing that middle Tube Socket, I've yet to mod this but I'm getting there... got a ton of Product's to review but I've also got some PTO in November... so I figured while I'm modding for improved sound quality maybe I should fix that lopsided socket too... maybe even do what @Maxx134 has done and have it situated completely atop the amp... don't plan on using anything OTHER than Octal/Loctal tubes anyways
  15. baronbeehive
    For the adapter you need one of these:
    The last one is what you saw on Maxx's amp but I wouldn't advise it as it could be dangerous!

    To resolder the middle tube socket would be tricky to do, I haven't attempted it because a special tool might be needed to solder all the pins at once, so expert help may be needed there.
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