[Maxx134]

and my friend used to use his two fingers to test for house 110v AC,

Ha

Wow lol.

You know the mechanic type guys with super rough callous dried out hands, lol

 

[baronbeehive]

You know the mechanic type guys with super rough callous dried out hands, lol

I'm back again after the house move!
 
What you said reminds me of the car maintenance class I went to and this old chap started up the engine and pulled out the high tension leads and proceeded to stick one finger up it and sparks flew out of his remaining 9 fingers!

 

[coinmaster]

http://spectrum.ieee.org/semiconductors/devices/introducing-the-vacuum-transistor-a-device-made-of-nothing
https://www.nasa.gov/sites/default/files/atoms/files/arc-17130-1_nanostructure-based_vacuum_channel_transistor.pdf
http://spectrum.ieee.org/semiconductors/materials/how-a-microscopic-supercapacitor-will-supercharge-mobile-electronics

 

 

[Maxx134]

Need.
More..
More testing...

 

[Mogos]

Finnaly arrived. The guy just forgot to send them after my payment . He has done it two months later after the dispute on the PayPal had been opened. It can happend but why he did not respond to my messages? 

Now the 7193 are runing and it looks like this:
 

Compared to 6C8G they are in the same league. There is no jaw dropping effect as I had encounter substituting the new production Tungs Sols with the 6C8G tubes.
The 7193 are giving more foucused and tight sound. Better sound stage imaging with very good separation of the instruments. Less spontaneous and colorfull presentation than the 6C8G but also very interesting. They need more hours and most probably the sound signature will change. But I don't know which direction. 
I have to do the mod on the driver stage resistors. I had planned to make a switch for the 6SL and 6SN tube types but I will do optimisation only for the 6SL type and it will be enought also for the 7193. What I hear now is very good so no need to go for extreme solutions 

.
 
Thank you MrCurven to pointing out the 2C22 tubes. You have mobilized me to get finnaly good tubes for the drive stage. Now I understand how mutch I had been missing till now.

 

[coinmaster]

Just don't buy the lot of 10 2C22 tubes from the italian ebay guy. He stiffed me. 

 

[Mogos]

I have got at last 2 pairs from him. But it looks like I had been lucky. PayPal helped 

.

 

[SonicTrance]

I think you got "lucky" Mogos, to at least get the tubes. Just look at the guys recent feedback.

Great that you're enjoying them as well!

 

[Maxx134]

Mogos,
Remember your stock settings on driver section are set very small/low. ..
All your tube have hidden potential.

Once you open up the bias more,
It will be the biggest improvement over any tube choice.
You will be blown away, guaranteed!


I have had some delays, and will be finishing up my amp on my Vaca next week.

 

[Maxx134]

For those interested,
I was looking into this issue of "feedback" in the mk6 & mk8 circuits. .

There is an attenuation or gain switch inside ,
Which introduces Global feedback into the overal amp design...

It seems like a more significant amount in the MK8...

Also it has been PM to me that reduction of this feedback makes the MK6 worse.
This is opposite of what normally would be assumed.


It is generally assumed that Feedback will allow and intoroduce more higher harmonics and sideband distortions that were not originally present,
while only basically lowering the 2nd harmonic to make specs look good. .

But the testing was not fully covered as it introduced low amounts of feedback...

What we have in the little dots amps are (by my assumption), relatively high amounts of feedback...

This in turn poses both an intellectual problem and a real one,
Because the amp literally sounds fantastic with the gain on low, which translated to higher global feedback. ..

So this got me to do a little searching and I immediately found this issue explained which our amps prove in actual use of higher feedback amounts...

Quote :

"...it is normal for an experimenter to experience that if you take a good-sounding zero-feedback amplifier and add 6dB of feedback, the result sounds worse. They heard that right. But had they been in a position to add 60dB, well then, suddenly they would have been confronted with a sound that is little short of magical."

Here is the link to the page for an interesting read:

http://www.soundstageultra.com/index.php/features-menu/general-interest-interviews-menu/455-searching-for-the-extreme-bruno-putzeys-of-mola-mola-hypex-and-grimm-audio-part-one


Looks like the designer of these little dot amps is still "one step ahead ",
As we discover his design goals..

Edit :
Actually I believe the primary reason for the feedback was to bring down the output impedance. .

Looks like yet another topic to experiment. ..

 

[coinmaster]

Negative feedback increases high order harmonics unless you use a lot of it. That is why adding only 6db of NFB would make a good zero feedback amp sound worse. High order harmonics are the bad stuff.

 

[Bruch]

2 stupid questions:

1) Is the negative feedback in the system the single most limiting factor in this amp - even more so than the limiting factors that the mods on the first page are trying to solve?
2) Is it even possible to achieve reasonable levels of impedance in this amp without a negative feedback loop?

 

[coinmaster]

The main purpose of the negative feedback is to lower the output impedance. The higher the output impedance of an amplifier the more the headphones imperfect frequency curves are exaggerated. Tubes all have too high of an output impedance even as a cathode follower. Negative feedback sacrifices gain for linearity, lower impedance drop, better phase alignment.
So no, negative feedback is not the most limiting factor unless you are part of the crowd that thinks all NFB is evil, which it may or may not be, I haven't built an open loop amp yet.
Also no, you can't get reasonable levels of output impedance without changing the design. Unless you use planar headphones, then output impedance doesn't matter anyway because they have a flat impedance curve.

 

[Maxx134]

The MK6 really doesn't have any problems with any headphones and I would say it actually hard to beat..

 

[Maxx134]

I had some delays both electronically and in personal life,
So ow back to refining driver stage.

So far I am liking the soundstage of the 6f8g,



But my best driver stage tubes consist of the ecc35, and the Silvana 6sn7W..


Those top choices I assume will be similar to the MK6, because the driver stage is the same..