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Old 3rd December 2005, 12:27 AM   #21
steenoe is offline steenoe  Denmark
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Quote:
will you try some oneways some day?
Yep, I have a pair of Coral Flat6 that is supposed to be driven by the darn F2 I am working on!! I am sure it will play in short time

Steen
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Old 5th December 2005, 09:33 AM   #22
Buhl is offline Buhl  Denmark
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Hello Steen - and others....

Its Ok that you donít have anything to complain about - neither do I, BUT - I have built 3 Pearls in the last couple of months, and the all sounded different from each other, so there are definitely some parameters that you can change, and it will affect the sound, maybe to your liking, maybe not.

Supply noise - I have a inefficient set of Proac clones, just like you - on them, there are almost no noise - switching to my Snell E II (+5dB in sensitivity)- there are definitely noise to be heard, and more noise than ex. with the Ono. Hence, I build a version with an even more overkill PSU, with 80000 uF in the PSU (plus the 43000 uF on board) - and added two extra RC filters - the result was even less noise, but more pronounced was the reproduction of space - the room 'grew' in some way. It is quiet, but ex. the Ono is quieter......but its ok for me.

I have also builded one in a wooden box, and one in a metal box - there werenít more noise in the wooden one, but the "metal" had more bass, and more pronounced bass - why I donít know.

Have built it with and without battery, and there were no obvious difference in sound - except its easy to hear when the battery runs down, and that happens once a month......

I donít have any trouble with it - builded it just like Wayne in his article - have tried a lot of different groundings - about 3 hours with the soldering iron, and the RIAA turned on, to find the grounding that made the least noise - and it was the "wayne way".

I donít think that you can say what is best for you, if you have not heard them all - i have not heard them all, therefore I experiment.

I wont just drop the source resistors, donít worry ;- ) - but I recall that nelson suggested that one could lower the value to 18 ohms, given that the devices was matched well enough.


Cheers !
Buhl
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Old 5th December 2005, 09:45 AM   #23
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Allthough dependent or your specific set of 2Sk170's , but you won't run in to problem if you drop the source resistors. The bias point will change offcourse but there is room enough for that. Transductance will be somewhat higher (good for MC) en noise will be somewhat lower (again good for MC) .. THD won't change much , since this is primairily set but the output stage.
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Old 5th December 2005, 09:59 AM   #24
Buhl is offline Buhl  Denmark
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Hello tschrama
Ok - that must be tried - but what do you mean with "your specific set of 2Sk170's" - all my three kits are from promitheus - 2sk170BL - is it the type - BL or not, or the matching ?

Cheers !
Buhl
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Old 5th December 2005, 10:11 AM   #25
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Default GR maybe for no source resistors

The 2SK170 came in three grades, GR,BL, and V. The differences are in "on resistance" or current flow. If you replace the BL with V, the current maybe too high. The current through GR would be low in this circuit. Tied straight to ground they would run along fine.
The 170's are low current fets. No resistors will also make matching them up more critical.

George
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Old 5th December 2005, 10:17 AM   #26
steenoe is offline steenoe  Denmark
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Hans, after reading your last post, I realise that I might have been to fast, out of the gates I never heard a better RIAA than the Pearl (on my system), thats why I will think twice about modding on it. Your findings tells us, that maybe something could be gained anyway
If you didn't read them yet, here is a couple of nice articles about J-fets. They say a lot about biaspoint and Idss limiting via the source resistor and so on. "J-fet's, the new frontiers" are the ones.
Before anyone starts to fiddle with the resistor values, remember that the SK170's in Pass's Q-pack's were not matched. (Or so I was told at least)

Steen

http://www.borbelyaudio.com/special_articles.asp
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Old 6th December 2005, 08:17 AM   #27
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Hi !

Now this thread has come out of the sauerkraut and back to the technical. So Iīll try again.

Here is an idea I got from an article by Jean Hiraga:
Try lowering the voltage over the FETs ( and increase it over the bipolar ). You can go as low as around 3 volts. This reduces Igx , excesive gate current. It worked well for me in a Monster. Gave a more natural sound with more wood in wood instruments , more brass in the brass etc.

Any experiences or comments ?
Thorsten ( another one )
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Old 6th December 2005, 11:05 AM   #28
Buhl is offline Buhl  Denmark
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Quote:
Originally posted by thorstenlarsen
Hi !

Now this thread has come out of the sauerkraut and back to the technical. So Iīll try again.

Here is an idea I got from an article by Jean Hiraga:
Try lowering the voltage over the FETs ( and increase it over the bipolar ). You can go as low as around 3 volts. This reduces Igx , excesive gate current. It worked well for me in a Monster. Gave a more natural sound with more wood in wood instruments , more brass in the brass etc.

Any experiences or comments ?
Thorsten ( another one )

Hello Thorsten
Sorry if it was me that brought the sauerkraut into this thread - bu, having chosen Computer Science, instead of EE - I lack very fundamental knowledge about electronics.....
How - do you lower the voltage over the Jfets, and how do you do that ? By higher value of the source resistors ?
And the bipolars - I expect those to be the N-channel (eg. ZTX450) that are used as cascoding and regulating devices - how do you raise the voltage here - by lovering their collector value ?

I sorry, but you have to "cut this one out in cardboard" to anglophile a well known danish expression ;-)

Cheers !
Buhl
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Old 6th December 2005, 12:12 PM   #29
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Like Thorsten, I would recommend lower the JFETs voltage too, it seems to lower noise a bit..
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Old 6th December 2005, 02:40 PM   #30
AuroraB is offline AuroraB  Norway
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Now... I have 4 PCBs for Ono an 2 for a Pearl.....for me and my brothers....( we probably will have to draw tickets when I'm all done..)

- and I have a bucket of SK170 GR.. judging from the above, I wil do fine by shorting the source resistors... but wouldn't lowering them so -say 1-5 ohms instead help the balancing between them..??
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