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Old 12th June 2007, 09:28 PM   #161
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by Nelson Pass
It really helps if you have any kind of distortion analyzer
for setting this up. There is a specific bias voltage/current/
gain/load sweet spot, and the figures I gave are approximate
due to part variations.






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Old 12th June 2007, 09:35 PM   #162
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Quote:
Originally posted by Nelson Pass
It really helps if you have any kind of distortion analyzer
for setting this up. There is a specific bias voltage/current/
gain/load sweet spot, and the figures I gave are approximate
due to part variations.

Thank you very much Mr. Pass.

It is realy a great pre.
I'am currently hearing the Folia by Jordi Savall, and there are some Castagnette playing. Trust me, it is so realistic that you could guess out which Wood essence they are made...

Unfortunately I don't have this equipment to test ( Not long ago I ebayed aScope, still learning how to use it).
As for the sweet pot, it is amazing how the changes suggested by Zen Mod made the difference.

But for now I'am very happy.

Please Mr. Pass, may I call you Papa, please just this time.

manuel

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Old 12th June 2007, 09:36 PM   #163
Manu is offline Manu  Europe
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Quote:
Originally posted by Zen Mod



send my hello to her
what's her name ?

Nadija.
But I will not post a photo. She is too beautiful.

manuel
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Old 12th June 2007, 09:43 PM   #164
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by Manu


..........

Unfortunately I don't have this equipment to test ( Not long ago I ebayed aScope, still learning how to use it).
.......................

if you don't have siggene you can use any sine source you can find ....little pc utils from net,burn that to cd or directly from (presumably dreky ) sound card to DUT..........

then-observing current and voltage across sayed jfet ,crank up volume on input (toss entirely that volume on output) and look for symetrical clipping ;to achieve that ....tweak current through stage and voltage across........

there is yours sweet spot.


regarding Nadija....
is it Nadija or Nadja .........?

send Zdravo to her from Sasha


and-keep that photo away of all these old farts
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Old 12th June 2007, 09:55 PM   #165
Manu is offline Manu  Europe
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Quote:
Originally posted by Zen Mod



if you don't have siggene you can use any sine source you can find ....little pc utils from net,burn that to cd or directly from (presumably dreky ) sound card to DUT..........

then-observing current and voltage across sayed jfet ,crank up volume on input (toss entirely that volume on output) and look for symetrical clipping ;to achieve that ....tweak current through stage and voltage across........

there is yours sweet spot.


regarding Nadija....
is it Nadija or Nadja .........?

send Zdravo to her from Sasha


and-keep that photo away of all these old farts
Zrado from Nadija (the i make this name so beautiful - No I am not Breton (wimpy) and she's not Nadja) to you.
I have to thank you very very much for your help.

I will try what you suggested with the scope ( the scope scares me a little - the last time I tested my Aleph 5 with is it ended with 5 blown Mosfets and a nice source resistors light show). May be I will need some help, but you're here no?

Manuvic
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Old 12th June 2007, 10:35 PM   #166
Vix is online now Vix  Yugoslavia
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Congratulations Manu! Your experience with Jfet Boz will be helpful.

Tonight I just collected almost all the necessary parts...well, I discovered that there's no small 10 ohm resistor in my junkbox. But I have 27 and 22 ohm ones. So I think I am going to use two 27 ohm ones in parallel. I also bought "eau de toilette" I needed just a metal can. And it has a nice aroma!

Regards,

Vix
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Old 12th June 2007, 10:36 PM   #167
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Old 12th June 2007, 10:56 PM   #168
Manu is offline Manu  Europe
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Hi Vix, it was a great day indeed... Thanks the help of Zen Mod I have found a sort of sweet pot with my system. If a can manage it I could certainly find the ultimate sweet point...
But I am now enjoying...
As Nelson Pass says the pre need a fine adjustement to your system ("There is a specific bias voltage/current/
gain/load sweet spot"), and then, I can confirm it is worth the effort. It is a remarquable pre.

For recall my setup is now:
Source res: 22R
PSU 17 V
May be the 2K2 hare to be adjusted.

Please build it and post your impressions.
manu
PS (Twitchie): Every time I see the name Toronto It reminds me of Glenn Gloud, my master, the greatest Musician ever. Really.

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Old 12th June 2007, 10:56 PM   #169
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Indeed, thanks for leading the way Manu - I mocked up the circuit with a protoboard to make sure my values were correct and all I'm getting is alot of distortion as well - the music is also present, but at very low volume (compared to the noise).

I measured 6.33V across the jfet and a few others (didn't record them though) - although I'm playing into a LM1875 gainclone for testing ... probably not the best for high-gain circuit.

I'll try other Rs values and see if 22 is the magic number for me too

I'll be sure to post some pictures when I get it running.

Stephen
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Old 13th June 2007, 01:49 AM   #170
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I found that I could eliminate all the 'noise' but not all the distortion by switching to a 9V battery instead of a cheap regulated supply (LM337).

I also find that the 20K pot I have on the input does not have any effect on the volume

Any ideas? I tried 10 ohm and 20 ohm Rs and going to 10, attenuates the output slightly (is that supposed to happen?)

Thanks in advance

Stephen

Update: I measured voltage across the jfet again and since I switched to the 9V battery, it's very low, so I swapped the 2.2K for 1K and now it's beautifully clear , looks like (as Mr Pass already explained), it will take quite a bit of tweaking to get it right for any given application

Does anyone have a schematic for a very nice and quiet regulated supply? Thanks
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