[jekjek]

OK here are some pics of my internal/external mod:

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I can safely say I can place this baby next to any amp and it will hold it's own in quality sound.
All areas of sound are now top notch.(detailing/depth/dimensionality/realism/micro¯o dynamics)

The only weakness was in blasting.
Like my 20ohm HEKV2, it did so, but did run out of gas at a earbleed levels of end game power.
I was still able to shake them good and with other cans it did have authoritive power.
I atribute this to the 1000uf cathode caps as suggested by member "Kryl0071".

Edit2:
As I am nit-picking here , I would say channel separation is not at endgame level,
I believe due to using one tube a driver for both channels..

This applies to every amp like this in my opinion.
Still very good but probably 95℅ of what it can be.

It is not fair for me to compare it to a "balanced" OTL & OCL tube amp,
But it still is quite impressive considering this amp is less than $200,
and the upgrade was $134 in parts ..

So for about $330 total plus some soldering you get near top level sound!

Hi Max,
Can you show us the soldering points you did on the other side of the board please?
I am trying to do the same mod as you
Below is the pictures of my board. Looks like i have version 1 board

 

 

[Maxx134]

Yes they are the same exact points posted in thread by others,
but I will post again:



I am trying to find the top​side pics..

 

[Maxx134]

Here is a close up of the Electrolytics and the film caps soldered on the leads.

For the square coupling cap replacement,
I used silver wire in the holes to bring wires to that area for big coupling caps..

Edit:
Go here for clear pics on the solder points on the topside / surface mount side of board:

https://www.aradiogurl.net/hhjournal/2016/06/01/gemtune-pa1502a-appj-headphone-tube-amp-mod/

 

[jekjek]

Below us my modified appj 1502
 
I would like to say thank you to @Maxx134 for his support

 
My modification is:
- wima 0.47 uf 400v
- panasonic fr 1500uf
- solen 0.1 uf
 
I have completed the modification but there is no sound on the right channel
I will need to resolder it again tonight

 

[Maxx134]

Wow that is excellent work!
Now onto your "no sound" issue.

The board is double sided.
It is also easy to rip the trace ads: were the leads go into hole.

Although you should check the right side coupling cap first,
My guess is the right side electrolytic cap not have ground connection.

That is where my trace broke when I pulled out old one,
and then it was essentially an open circuit.


So, on those holes that I pulled up the trace, I had to scrape the board to expose the copper trace.

 

[jekjek]

Wow that is excellent work!
Now onto your "no sound" issue.

The board is double sided.
It is also easy to rip the trace ads: were the leads go into hole.

Although you should check the right side coupling cap first,
My guess is the right side electrolytic cap not have ground connection.

That is where my trace broke when I pulled out old one,
and then it was essentially an open circuit.


So, on those holes that I pulled up the trace, I had to scrape the board to expose the copper trace.

Thanks Max
Its working now


I'm using EL33 with old Philips ECC83
Sounds awesome. Very smooth

EL33 is basically octal version of EL3N.

 

[Maxx134]

I never tried that ...
EL33 Hugh?
Ok now I wanna try!
Also caps need burn in..
Edit**
I just checked and EL33 is not as optimal as it will give lower output performance over 6v6 in this amp.

EL33 may still sound very good as those tube number are usually designated from Europe.

 

[jekjek]

I never tried that ...
EL33 Hugh?
Ok now I wanna try!
Also caps need burn in..
Edit**
I just checked and EL33 is not as optimal as it will give lower output performance over 6v6 in this amp.

EL33 may still sound very good as those tube number are usually designated from Europe.

Agree about the lower output however people from the felix audio elise gang loves it

Let me try and compare the EL33 vs rca 6v6 this weekend

 

[baronbeehive]

.........
That is where my trace broke when I pulled out old one,
and then it was essentially an open circuit.


So, on those holes that I pulled up the trace, I had to scrape the board to expose the copper trace.

 
He, he...... I've been there, tell me about it!
 
I just wondered if you guys would be interested in the other .....!!! APPJ ...... the Miniwatt, or APPJ PA0901A speaker amp. This amp is just so good I don't want anything else, but having already modded my LD I'm interested in pushing it to see how far it will go. I'm from the Little Dot Supermods thread along with Maxx134. I'm planning on doing the coupling and cathode caps mod to this amp also.
 
I've had the little Miniwatt for 5 years or so and am pretty awestruck with it, I can say. I'm using it with only 87db speakers yet it sure rocks. I'm planning on adding the highly rated Jupiter copper foil, paper and wax caps, and the Audio Note Kaisei's that Maxx134 has used. My alternative plan if the Jupiters produce too much bass for my set up is to use Audyn True Copper caps with a lower capacitance than Maxx134 used because the amp as it is produces plenty of bass for me and the 0.47uF Jupiters might just be too much of a good thing! While increasing capacitance for headphone amps is the thing to do to get better bass I'm not sure about doing that for a speaker amp.
 
Anyway if you are interested I will report back when I've done the mods.
 
I didn't know about this sister amp until recently, great thread guys

.
 
Edit:
Thanks to Maxx134 for the info on the mods.

 

[jekjek]

He, he...... I've been there, tell me about it!

I just wondered if you guys would be interested in the other .....!!! APPJ ...... the Miniwatt, or APPJ PA0901A speaker amp. This amp is just so good I don't want anything else, but having already modded my LD I'm interested in pushing it to see how far it will go. I'm from the Little Dot Supermods thread along with Maxx134. I'm planning on doing the coupling and cathode caps mod to this amp also.

I've had the little Miniwatt for 5 years or so and am pretty awestruck with it, I can say. I'm using it with only 87db speakers yet it sure rocks. I'm planning on adding the highly rated Jupiter copper foil, paper and wax caps, and the Audio Note Kaisei's that Maxx134 has used. My alternative plan if the Jupiters produce too much bass for my set up is to use Audyn True Copper caps with a lower capacitance than Maxx134 used because the amp as it is produces plenty of bass for me and the 0.47uF Jupiters might just be too much of a good thing! While increasing capacitance for headphone amps is the thing to do to get better bass I'm not sure about doing that for a speaker amp.

Anyway if you are interested I will report back when I've done the mods.

I didn't know about this sister amp until recently, great thread guys .

Edit:
Thanks to Maxx134 for the info on the mods.

Dig it. Show us what you have done

 

[baronbeehive]

OK, thanks. I'll let you know how the mods went when I've done them, I've got to order the parts first, the fun comes later!!
 
Forgot to say my APPJ has EL84's for power tubes instead of your 6V6's, I have Amperex Bugle Boy type power tubes and Tungsol 5751 for the 12AX7.
 
Edit:
Parts on order.

 

[Maxx134]

Caps upgrade give increase in resolution (coupling cap) and power(cathode cap).

Frequency "extension" (lower freq, not an increase in amplitude) from cap size seems optimal at .047uf on coupling cap.
As for voltage rating, there is only about 60v across it (I only measured 55v),
So any voltage 250v or higher is fine.


Transients, bass punch, and power sustain is optimized with larger Cathode Electrolytic of 1000uf.
This is due to the "larger" cathode cap value causing the effect of holding the cathode voltage constant, which keeps it at optimal gain.

As for voltage, 25v or higher is fine here,
And the Audio Note Kasie caps are recommended first,
Or also Panasonic or Elna silmic2.

WARNING:
Do not confuse the cathode caps with the PSU caps Wich actually do need high voltage ratings.
It is suggested to not alter and not modify the PSU section.


The preset autobias settings of the circuit will still be optimal with either designed tube choice, or your preferred choice,
And the point is this will not change with the cap upgrades.

For the 1502A amp, I have tried most tube types available,
and will post about them soon.
Cheers

 

[baronbeehive]

This is my PCB, very similar to yours, very neat and tidy inside:
 
    
 
And these are the finished mods:
1 - Coupling caps: Jupiter copper foil paper and wax caps, 0.47uF, 600V
2 - Cathode caps: Audio Note Kaisei , 1000uF, 25V
 

 
 
I'm also going to put in a new AMR Audio 90% Silver Alloy Fuse Tube 5x20mm (Slow Blow).
Unfortunately I can't say anything about the sound due to an ear infection but if it's even slightly better then it will be pretty amazing.
Also doing some cosmetic mods. Pics to follow....
 
Had one  scary moment,  I plugged in the power cord without realising it had switched itself on, and there were no tubes in, I quickly switched off and no harm done

.
 
Edit: Looking  forward to your tubes post Maxx134!

 

[jekjek]

  This is my PCB, very similar to yours, very neat and tidy inside:
 
    
 
And these are the finished mods:
1 - Coupling caps: Jupiter copper foil paper and wax caps, 0.47uF, 600V
2 - Cathode caps: Audio Note Kaisei , 1000uF, 25V
 

 
 
I'm also going to put in a new AMR Audio 90% Silver Alloy Fuse Tube 5x20mm (Slow Blow).
Unfortunately I can't say anything about the sound due to an ear infection but if it's even slightly better then it will be pretty amazing.
Also doing some cosmetic mods. Pics to follow....
 
Had one  scary moment,  I plugged in the power cord without realising it had switched itself on, and there were no tubes in, I quickly switched off and no harm done

.
 
Edit: Looking  forward to your tubes post Maxx134!

Nice job in a very tiny case!

 

[baronbeehive]

  Nice job in a very tiny case!

 
Thanks! Fortunately the Jupiters are smaller than the Audyns by a lot. The caps would have fitted better if I had removed one of the posts but they just squeeze in atm. Also I didn't use bypass caps for the cathode caps because the Kaisei's are supposed to be that good anyway. I will try to look out for any missing treble when I've done the listening test.