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Old 16th January 2012, 07:20 PM   #1111
6L6 is offline 6L6  United States
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If you have a clean output from the JBOZ, the next question is how much gain do you need? 3.6v will get most 'normal' amps well past full output. You might be done.
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Old 16th January 2012, 07:21 PM   #1112
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FLG...

I noticed that you have a springer spanial...Looks just like ours...
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Old 16th January 2012, 07:53 PM   #1113
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She was a Treeing Walker CoonHound. Similar to the American Foxhound. But, she's gone I lost her back in June to an ear infection that spread to her brainstem/spine. I should change my avitar.
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Old 16th January 2012, 08:08 PM   #1114
ramallo is offline ramallo  Europe
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A two tips for the jim's board (A copy of Manu board)

-Change R1 to 1,5K Ohm
-The mosfet on the power supply drops 4V, for 16V on R7, you need set the zenners to 20V. But with 9,7mA Idss, I would try with 20V (24V before mosfet)
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Old 16th January 2012, 08:29 PM   #1115
juma is offline juma  Germany
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Quote:
Originally Posted by audionut View Post
...Onset of clipping is now 3.6volts and is symmetrical. The input signal to the pre amp is .3 volts. These voltages are measured by a meter so they are rms. ...
You can not expect that much usable output from this circuit.
According to Nelson's measurements (post #58 of this thread) the THD at 2V is 5%
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Old 16th January 2012, 08:34 PM   #1116
mjf is offline mjf  Austria
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QUOTE
with power supply at 18.5 volts and drain resistor set to 1000 ohms, the voltage on the drain of the jfet is 9.4 volts (measured between drain and ground). Onset of clipping is now 3.6volts and is symmetrical. The input signal to the pre amp is .3 volts. These voltages are measured by a meter so they are rms. The current through the drain is 8.6ma.

yes.....symmetrical clipping, drain res around 1k.........should work.
with a drain res = 2,2k psu at 18v is too low.........34v as shown in the pass schematic will fit.
here is an example - sim:
input sinus 200mv red, output = green
with 18v ........and with 34v
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Old 16th January 2012, 10:28 PM   #1117
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very cool...thanx
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Old 16th January 2012, 10:34 PM   #1118
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Quote
"You can not expect that much usable output from this circuit.
According to Nelson's measurements (post #58 of this thread) the THD at 2V is 5%"


But I thought that line level is up to 2v...

so this pre amp is not suitable where you need to swing voltage up to 2v into a lowish gain amplifier ??
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Old 16th January 2012, 10:40 PM   #1119
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Quote:
Originally Posted by juma View Post
I presume your JFET has the Idss of 9.7 mA. With 10 Ohms source degeneration the Id will be about 7-8mA.
2k2 x 7mA = 15.4V - This means that your JFET works with very low Vds and that's where the early clipping comes from.
Reduce the Drain resistor to get about 8 Volts at the Drain, but don't expect to get more than a few Volts of clean swing from that design.
My BoZ and BoZSE produce 17V p2p of swing before any degeneration of sine wave. I run mine on 27V. I'm using the BL series of jFets.
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Old 17th January 2012, 05:13 AM   #1120
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Hi,

I have an orginal BOZ driving a SE MosFet Power Follower amp (which has effectively no gain). The combination provides more than enough volume on my ancient Whatmough 202 speakers of 86dB sensitivity.

My question is: Will the JFet BOZ be able to provide similar dive capability as the older BOZ? The power follower amp needs about !0V RMS to drive it.

Joe
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