[Maxx134]

Even in Stock mode, it has abundant soundstage potential with so much tube rolling possibility.
To me this is the nicest design because of being tube only, triode wired, and Japan output transformer for most headphone compatability.

Very interesting. Let us know what you done.

For Cathode caps,
I ordered some Elna silmic caps as they is best brand for quality and and also cheap price.

I also will be adding a second cap in parallel to help these electrolyctic caps, as explained in the first page of Little Dot SuperMod thread,
Quote:

Bypass : in order to help the Lytic cap in the areas it is weakest (treble, microdynamics, ...), we add in parallel an another cap of a different techno, smaller and faster.
After having tested various caps (Teflon, Polypro, PIO, Styroflex, ...) the best "musical" match was with some (multilayer metallized paper) PME271 used as "electromagnetic interference suppressor...



For coupling cap:
I will pick a nice coupling cap.
I like the PIO vitamin Q caps as best value for natural treble sound..
I don't like any plastic type film caps, as they can add artificial sweetness (like mundorf) to the very top end of their sound, and WIMA caps tend to be slightly too soft sounding unless you get the real huge performance type .
There is a cap review link in the SuperMod thread mentioned above.

So that's my plan, just waiting on the cathode Electrolytics costing maybe 3dollar, as I bought 3 in case I mess one up!, lol

 

[a44100Hz]

If anyone else in the States wants one of these, I have one for sale that's not in use; drop me a line.

One thing to note about this amp is that the volume pot has a bit of a channel imbalance at low volumes (as do a lot of pots, unfortunately) so it wouldn't be suitable for low level listening to something like IEMs. But that's IMO and YMMV.

 

[Maxx134]

Upon Tube rolling different tube types,
I have noticed differences usually noted with different bias changes.
Most likely because the tubes are dependent upon the amp pre selected bias points.

So, Although I did like the huge 6L6 type better than stock,
And also the fat bottle New production KT66,
I am finding that the amp seems to sound most natural with the 6V6 type, most notably these 6V6G Fivre (made in Italy, CV509 military spec) :



Link;
http://www.ebay.co.uk/itm/311574587793
Great price.


Edit: I have not tried my 6Y6 type yet..

Edit 2:
So I am in agreement with the product description stating 6V6 type as replacement...

 

[Kryl0071]

Best result for my ears Sylvania Baldwin 12AX7 and NOS Russian 6Ф6С (6F6S) "Cobra".

 

[Kryl0071]

 

[Maxx134]

Public thanks to member "Kryl0071" for helping me mod this beauty of a little amp.

This is a highly underrated beauty that I will put up against any amp once done upgrading it.
I have already tested it against my main amp and it only needed more bottom end punch and a bit more Soundstage.
The shockingly promising clue that this amp has potential,
Was both the resolution and the very quiet background.

On my amp, I see they quietly upgraded the PSU with two small caps where there was one in older designs.
Look:
Old:

Circled in red is the area of original design, along with a blue circuit board.

Now mine:

You see there are two caps now in same area,
Along with slightly different green circuit board.

Those are the only noted changes as I do not have a schematic or know if I can get one.

So, to increase both low end authority and punch, I first will change the coupling cap yet again
Stock .1uf is dismal,
And I am currently using only .2uf which is not enough for low end response.
I was able to achieve much more clarity and musicality with the change of stock coupling cap.

So if I use a "boutique" cap, I should notably increase the soundstage.
It already has resolution from tube upgrades .
I am still almost done with tube rolling , just a few more tries.
I tried alot so far.

What should be noted as to why I decided to put my efforts into this little amp,
Is because of the usage of very very heavy quality output transformers being used.
I would say 95% of the total weight of this mini amp is due to the output transformers,
Which , to me, are better than most top mid-grade amps.

So this little amp has huge potential if the upgradeling works out.
This amp has made a great and wise achievement to invest the money on output transformers, and eliminate the traditional PSU Transformer.

You don't see this in any other tube designs.
This is also how the new electrostatic amp , the " Sonoma Acoustics Model One Electrostatic Headphone System",
achieves it's high voltage for the headphones, as well as portable tube amps boost voltage,

So it is a relatively new idea usage in the tube area.
With ALmost all major tube designs being much more traditional or even excessive with tube as rectifiers.

Anyways, moving on:
The Electrolytics I also upgraded, but was still not enough punch to them.
I believe due to the type of PSU being used, and the tube bias settings.

For this "switching" PSU to be effective, I am finding out what memeber "Kryl0071" already knows, and showed me,
That it is more reliant on the caps.

So we need to boost the cathode Electrolytics more.
It's already good at 470uf, but not jaw dropping good.

Once I am done I hope to achieve a quality close to my main heavily modded amp.

The question is to be able to achieve this without much expense.
This will rely on choice of coupling cap, as other cathode caps won't cost much..

I already have it at a level where it can either **
Edit: this comment is both subjective and debatable,
But in my opinion,
it **can** match or surpass a crack or Torpedo or woo wa7 in terms of clarity, as they are all units I were familiar with or owned or borrowed.
Again, my subjective impression.

Other aspects of sound, such as dynamics or Soundstage will vary with tubes and caps upgrade.

I totally expect my own finished results to definitely do so (surpass),
So it will be fun to compare as I love tube gear in general regardless of how good it is.

So it is surprising because I only wanted a small amp like a vali2 to burn my headphones in,
So I won't burn my main amp,
but I fell in love with this little amp.


Here is it now and next to my reference amp:
.

Update , I edited this post for clarification.

 

[Maxx134]

Here is how my amp currently is,
using only .2uf as coupling, and 470uf as cathode, and a .047 as a bypass on the Electrolytic:

This was initial mod test.
Super easy upgrade.

Once I found out it actually improved significantly,
I decided to see if it could climb more.
I decided to give it the end game level boutique caps test.

So I should have it upgraded over weekend with some larger capacitance top level caps.
It will be interesting to see how good this baby can get.

 

[Maxx134]

OK, my mistake for being lazy:

I used two parallel caps in coupling cap position to boost the capacitance...
Big no-no.
The result was a thickness in the bass area which was a loss of focus in that specific area.
I mistakingly thought it was the driver tube choice.

AFTER I completed my coupling cap upgrade to a single HUGE copper foil cap,
I was quite surprised the driver tube now sounded MUCH more focused an clear.
I was quite shocked as I really thought it was the tube.

 

[Maxx134]

OK so I have finished upgrading my mini amp..

The result forced me to have to extend the bottom plate.

I had to go buy some longer metric screws and spacers for them, to extend the bottom about ALmost one inch.

The only reason was for the coupling cap.

I should have just used .48uf as recomended as the largest, as it not need more,
But instead I bought HUGE .68uf "Audyn True Copper" which were on sale almost same price.

So now I am using monster copper foil caps,
Arguably one of the best for the money as well.

I feel Audyn True Copper can achieve sonic quality on par with the other best copper foil caps.

 

[Maxx134]

Although the caps upgrades was a major improvement,
The system seems more dependent on matching driver tube with power tube.
Tube rolling is more noticable.

 

[stolikat]

I need to up my soldering skills so I can do this mod.

 

[jekjek]

I ordered my gemtune appj 1502

Another idea for the power tubes is EL33 with different heater current

Cheers

 

[Maxx134]

Best result for my ears Sylvania Baldwin 12AX7 and NOS Russian 6Ф6С (6F6S) "Cobra".

Thank you for suggestions as I ordered and will have the 6F6S"Cobra" coming in soon.
Great deal these Russian tubes!

Also,
I am finally satisfied with the outcome of my mini amp modding.

Coupling cap:
.68uf Audyn True Copper

Cathode cap:
1000uf Audio Note KAISEI Electrolytic Capacitor

Bypass cap on the Electrolytic:
.1uf Audyn True Copper

Now this baby is impressive!
Only Problem , like I said, was that I had to extend the bottom plate with long screws and spacers to make sure the pressure was in the chassis and not the board.

Will post pics soon.


So although I was excessive with my mod,
It seems the general consensus / recommended values are:


Coupling cap:
.47uf film (any preferred type)

Cathode Electrolytic:
1000uf Audio Note KAISEI

Bypass cap on Electrolytic:
.047uf-.1uf cap (film)

Cheers

 

[Maxx134]

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

...

...

...

...

...

...


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



impressive considering this amp is less than $200,
and the upgrade was around $135 in parts..

So for about $330 total plus some soldering you get upper mid-tier level sound!

 

[Maxx134]

I ordered my gemtune appj 1502

Another idea for the power tubes is EL33 with different heater current

Cheers

What I noticed is that the tube interaction with the output transformers have effect as well as the bias setting.
So although we can place in various tubes,
It is guess work unless you take these two parameters into consideration.

I will post soon on my various tube trials and most optimal suggestions for the power tubes..
Good news is I believe I found the m
Best tube type for our amp,
from member "Kryl0071"...

So big thanks to him for his help, which made the amp climb to new heights.

For the driver tube, it does have more choices that do not affect power so I'd a better place to have preference.

I still believe an 9 pin to 8 pin adapter is my preferred choice of tube type for driver,
But I will give the 9 pins another shot.

I have boxes of different tubes to try over weekend.


I will post tube review soon.