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Old 7th November 2012, 02:02 PM   #691
generg is offline generg  Germany
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Quote:
Originally Posted by Zen Mod View Post
if you boys got it 98% of THD spectra , rest is in your head

I had short circ between two headphones too many times , so I know how's that

So we will do what is to do to hear no difference any more....

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Old 7th November 2012, 02:04 PM   #692
generg is offline generg  Germany
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Quote:
Originally Posted by vdi_nenna View Post
Could it be some other part you are overlooking that is effecting the sound of your J2?
Maybe it was some other choice in part(s) and not your circuit design that's having, to your ears, a negative effect or less than perfect result.

What about polarity at the speakers? What about break-in time? What about grounding scheme? Power supply? etc, etc.

Maybe you are dead on target, but just overlooking one small piece. Just a thought.
Hope you find the missing piece. Really do!

Vince
Thank you Vince!

Copycats are looking in the direction you suggested....
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Old 7th November 2012, 06:45 PM   #693
dsdjoy is offline dsdjoy  Germany
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Quote:
Originally Posted by Zen Mod View Post
if you boys got it 98% of THD spectra , rest is in your head

I had short circ between two headphones too many times , so I know how's that

Sonically after having 98% the same Spectra my J2 inspired amp sounded almost identical to the original. Without a direct A/B comparison they would be almost indistinguishable.

But what am still after is - it is only a nuance - following:

The original J2 has a bit more silkyness, while my J2-inspired version is a tiny bit more on the hard, edgy side.
As said this is a nuance, and you can argue, it is a short-circuit between two headphones

However, I tend to believe that it is due to my usage of 20mA CCS....
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Old 7th November 2012, 07:15 PM   #694
dsdjoy is offline dsdjoy  Germany
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Why, did I use 20mA then ?

Well, first I applied the mod you suggested:"fold input LTP (inner drain) to lower SJEP source".
GOOD - it brought THD from 0.015% to 0.022% - right direction.

2nd harmonic looked almost fine, but 3rd harmonic was still too low.
I found that raising CCS from 10mA to 20mA brings up 3rd harmonic - Good - right direction !

Then I began fine-tuning K2/K3 relationship by using LARGE ZenPot (in wrong place,but working for me):
J2_ZenPot.jpg

When I was happy with K2 vs K3 relationship, I replaced the pot with a
dsdjoy Butterfly(TM) resistor.

butterfly.png

A tiny bit adjustment of feedback to raise overall K2 & K3 and
I got to 98% same Spectra.

The overall process took many many days of iterations, measurements and listening sessions (repeat similar procedure for 2nd channel !).

This is where I am. Only things that bores me (translate: does not let me sleep) is that J2 sounds a bit more silky/relaxed vs. my J2-inspired amp sounds a nuance more on hard/dynamic side.

Is it the 20mA CCS that was a wrong choice ?
A bit like in a known board-game I fear I have to start all-over: Go Back to Start, Do Not Pass.

Last edited by dsdjoy; 7th November 2012 at 07:30 PM.
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Old 7th November 2012, 08:28 PM   #695
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If you are referring to the input bias CCS, then that does sound like
a bit much. I run about 8 mA.

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Old 7th November 2012, 08:58 PM   #696
Zen Mod is offline Zen Mod  Serbia
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dsdjoy

if you wanna exact copy - you need to dismantle bloody thing and measure Idss of all Jfets ........ I mean - all

then try to repeat that

and then ask Pa what he's doing when he's putting some other Idss grades in ?

OK - say that he choose always (approx.) same current through LTP ;

then it's slightly less believable that he's always choosing same Idss range for LTP itself , simply because 2SJ109 BL's aren't growing in a field (never mind that he's probably having Jfet's inventory as big as all other HiEnd makers together ) ...... so that will be just waste of good wine

same as for output Jfets - it's completely sane thinking that Pa is puttin' there spread of +/-10% Idss ....... meaning 20% of majority

tricks are there ; we are having pics of , say , several J2 specimens ; none of them are showing paralleled source resistors as seen on F5
but - even if we didn't saw them , maybe they're here in some

so - there is another trick ( which I can't share publicly ) to alter/influence Iq .... and that change will also influence OLG , so feedback , so THD spectra ..

whatever - I'm writing too much , most probably contemplating even more ....... but I'm almost positive that Pa isn't so obsessive to have all amps of one breed in same 2% of performance

considering most probably scenarios - that 100 J2 specimens will end on at least 89 different speakers ..... spread of performance will be much much higher than these 2%

conclusion - for us - it's worth chasing understanding of performance , not performance itself

if later is the case - drink glass of red , everything will be 20% better

edit - and yes - I chose 20ma in LTP , along with cascodes

I like them bleed , and shiny , too
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Last edited by Zen Mod; 7th November 2012 at 09:02 PM.
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Old 7th November 2012, 09:39 PM   #697
dsdjoy is offline dsdjoy  Germany
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Thanks a lot for good hints !

Quote:
Originally Posted by Zen Mod View Post
if you wanna exact copy - you need to dismantle bloody thing and measure Idss of all Jfets ........ I mean - all
Nah...I would need to know J2 repair price at FirstWatt facility.
....or better.....J2 will stay untouched.

Quote:
Originally Posted by Zen Mod View Post
simply because 2SJ109 BL's aren't growing in a field
I found they grow better on nutrient agar...
(matched them for a good friend)
DSC_5242.JPG


Quote:
Originally Posted by Zen Mod View Post
conclusion - for us - it's worth chasing understanding of performance , not performance itself
if later is the case - drink glass of red , everything will be 20% better
Learning is my main aim here, too. I learned how different THD and different K2 and K3 levels sound. Interesting !

Now junior wizard apprentice likes to learn more (hunting )

Last edited by dsdjoy; 7th November 2012 at 09:41 PM.
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Old 8th November 2012, 10:14 AM   #698
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Could someone suggest me how to transform power jfet with mosfet, I never see J2 schematic before
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Old 8th November 2012, 02:35 PM   #699
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Quote:
Originally Posted by Nelson Pass View Post
If you are referring to the input bias CCS, then that does sound like
a bit much. I run about 8 mA.

This sounds like 2 x 2SK270GR's
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Old 8th November 2012, 04:10 PM   #700
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that's a lot less that I would have guessed. I have 2x9mA 2SK170.
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