Jfet BOZ

Zen Mod · 2007-06-12 4:25 pm

Babowana said:
If you adjust the value of R-Source, the bias current would be changed in amount accordingly. This would change the DC-voltage at the Drain, and might affect the target symmetrical amplitude of the AC-swing. If the AC-swing is symmetrical at the voltage gain you want to have, that would be the good result. Otherwise, we should recheck the values of R-Source, R-drain, other resistors, symmetrical swing and the voltage gain in total once again . . . and repeat the process till we get all of them.

If we should consider one more factor. It will be distortion.

(ya funny Serb with gigglewiggle eyes)

Babowana · 2007-06-12 4:25 pm

Manu said:
Thx for your hints. Should I let the drain res at 2K2 if I reduce the Source res to may be 6R?

If you adjust the value of R-Source, the bias current would be changed in amount accordingly. This would change the DC-voltage at the Drain, and might affect the target symmetrical amplitude of the AC-swing. If the AC-swing is symmetrical at the voltage gain you want to have, that would be the good result. Otherwise, we should recheck the values of R-Source, R-drain, other resistors, symmetrical swing and the voltage gain in total once again . . . and repeat the process till we get all of them.

If we should consider one more factor. It would be the distortion.

:darkside:

Zen Mod · 2007-06-12 4:27 pm

how's this...........

my quote of preceding post is suddenly before that preceding post?

ZM Blond

Babowana · 2007-06-12 4:30 pm

Zen Mod said:
how's this...........

Magic

Manu · 2007-06-12 5:07 pm

Zen Mod said:
hehe

seems that hot weather is cause of confusion..........

anyway.......better than me- I'm confused all the time......

again........increase them,to increase local degeneration - feedback- so stage clipp later

(You may be right : with 6R I got only distortions, ahem)
I think I need a
:drink:

Manu

Manu · 2007-06-12 6:02 pm

17 V PSU
15R Source Res
Same as before :bawling:

I need some more
:drink:

I'am too stupid for the Job, I'am afraid.
Manu.

Babowana : Thank for Your post.

mpmarino · 2007-06-12 6:38 pm

As Choky stated earlier:

Zen Mod said:
when you use that sort of three legged fuses,you always must use pot on input,just because any not-attenuated signal will drive little bstrd in saturation and output sig will be more than clipped.
just look at bias voltage present between g-s and compare it with blabla 2V from CD out..........

Manu, I recall your using attenuation at the pre amp output -

Could this be the trouble? -or part of trouble....

Manu · 2007-06-12 7:15 pm

mpmarino said:
As Choky stated earlier:

Manu, I recall your using attenuation at the pre amp output -

Could this be the trouble? -or part of trouble....

I will check that, but without pot at the output I get some very dangerous noises.

After changing all connectors, the things improves somewhat, but still much to much distorsions.

I will try with some better pots at the input.

Again , I'am too incompetent for the job, and I don't wan't to give the impression that there is something wrong with the JFET BOZ.

Manu

Manu · 2007-06-12 8:14 pm

So I think I give up for today. Have to cook something for my (beautiful) bosnian girl-friend.
Wok with broccoli and cashew nuts I think.
Zen Mod
Now you got me.
:devilr:

manu (too incometent to give up)

steenoe · 2007-06-12 8:16 pm

Manu said:
I will check that, but without pot at the output I get some very dangerous noises.

After changing all connectors, the things improves somewhat, but still much to much distorsions.

I will try with some better pots at the input.

Again , I'am too incompetent for the job, and I don't wan't to give the impression that there is something wrong with the JFET BOZ.

Manu

Manu dont despair, you are doing great.
Do you have a picture of the board with the resistor values you used on it? The layout seems correct, but it would be nice to see the values.
Another thing, did you try and measure the actual bias current to see if it is as its supposed to be? If not; then measure the voltage drop across the source resistor and divide the value you get with the source resistor value to get the bias current. I=V/R

Steen

Manu · 2007-06-12 9:14 pm

steenoe said:
Manu dont despair, you are doing great.
Do you have a picture of the board with the resistor values you used on it? The layout seems correct, but it would be nice to see the values.
Another thing, did you try and measure the actual bias current to see if it is as its supposed to be? If not; then measure the voltage drop across the source resistor and divide the value you get with the source resistor value to get the bias current. I=V/R

Steen

Thx for your kind words. I don't despair realy but I don't want to be unjust to the JFET BOZ.
THe values are the same as in Nelsons posts. I only tried some different PSU volage values 20V 17V and 14V
With 20V and 10R Rs I had about 7mA through Rs. Voltage drop across 2K2 was 15V
With 17V ,15R Source res. -> 13,7 Volt. drop accr. drain Res. and about 6,3 mA through Rs
JFet are BL with about 9mA Idss

Manu

Manu · 2007-06-12 9:18 pm

Forgot the pic :

Zen Mod · 2007-06-12 9:26 pm

Manu said:
Thx for your kind words. I don't despair realy but I don't want to be unjust to the JFET BOZ.
THe values are the same as in Nelsons posts. I only tried some different PSU volage values 20V 17V and 14V
With 20V and 10R Rs I had about 7mA through Rs. Voltage drop across 2K2 was 15V
With 17V ,15R Source res. -> 13,7 Volt. drop accr. drain Res. and about 6,3 mA through Rs
JFet are BL with about 9mA Idss

Manu

in that case try to shoot 5mA as target current
leave at least 5-7 volts across jfet

steenoe · 2007-06-12 9:37 pm

The board seems okay. What are the +/- desigantions at the output? Looks like you have them exchanged.

Steen

Manu · 2007-06-12 9:40 pm

steenoe said:
The board seems okay. What are the +/- desigantions at the output? Looks like you have them exchanged.

Steen

Is the circuit not inverting?
:xeye:

manu

Zen Mod · 2007-06-12 9:59 pm

Manu said:
Is the circuit not inverting?

manu

nope ;
but hot end is always hot end ;
you can unhotttttt him only with xformer ;

mebbe hot isn't so important ,as gnd is :devilr:

Manu · 2007-06-12 10:10 pm

Zen Mod said:
in that case try to shoot 5mA as target current
leave at least 5-7 volts across jfet

Are you a magician, master?
:worship:

With 5mA (22R Source Res), The distortions are almost gone (bnot entirely though).But Yipiii.
I will reduce 2K2 to get 5-7V accross Jfet (now its about 4V) as you said captain.
The sound approve a lot...
The live character of this pre is amazing. Even with studiorecording.
Enjoying (My beautiful bosnian girl enjoy too)
Manu

Nelson Pass · 2007-06-12 10:17 pm

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.

Manu · 2007-06-12 10:23 pm

Zen Mod said:
nope ;
but hot end is always hot end ;
you can unhotttttt him only with xformer ;

mebbe hot isn't so important ,as gnd is

And nobody trust me when I say I am stupid.

Reconnected hot to hot and : Oh Lord!!! This sound. Plenty, full, seductive, and cristal clear.

Danke Meister
Danke Steenoe.

It is realy great.

(But I have to crank the volume allthe way up
:devilr:

)
manu

Zen Mod · 2007-06-12 10:27 pm

Manu said:
.............. (My beautiful bosnian girl enjoy too)
Manu

send my hello to her

what's her name ?

Jfet BOZ

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