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Old 26th May 2013, 07:47 PM   #1241
Hikari1 is offline Hikari1  United States
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I have fresh batteries...12 AA's, about 19 volts.

I changed the the source side resistors to 5 ohms, and the V+ input drain resistor from 2.2K to 1K. Thats giving me about 10V across the Jfets. No more crazy distortion.

It's making music now. It sounds well...good I think.

Also, The voltage across D-S of the Jfet is 10.1V on one channel and 9.5V on the other. Does this indicae a bad match on the jfets?

It's got lots of noise If I crank up the volume without a signal. Maybe I need to sort out the wiring a bit. But it's working.

What voltage should I be aiming for across the Jfets? They are BL grade. I am starting to understand the relationship between the drain and source resistor to the distortion and voltage across the Jfets.

Also, I have a Pass f5 that I jacked up the gain by using 200ohm gain resistors instead of the stock 100 ohm. So, I have more feedback and 6db more gain than stock in the amp. maybe I should go back to the 100ohm.
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Old 27th May 2013, 01:08 AM   #1242
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That's great...almost there!

I'm running 16v with a 22 ohm on the Source side 2.2k on Drain.
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Old 27th May 2013, 01:25 PM   #1243
Marra is offline Marra  United Kingdom
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What is the smallest value cap I could use on the output? I have some Ampohm 2.2uf's would they be useable?
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Old 27th May 2013, 04:02 PM   #1244
Hikari1 is offline Hikari1  United States
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Quote:
Originally Posted by Marra View Post
What is the smallest value cap I could use on the output? I have some Ampohm 2.2uf's would they be useable?
I have seen some people suggest a 5.6ish UF cap, i am using an 8.2UF and have no DC on output.

I finally got mine sounding good by playing with the source and drain resistor values. I'd pick up an assortment of resistor values to play with for the source and drain if you don't have a lot on hand already.

Also, I had a lot of hum and noise when turned up. It was my unshielded interconnects. Never noticed it when using a passive preamp setup.
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Old 18th September 2013, 10:52 AM   #1245
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Default gain

hi,
how can I reduce the gain of the jboz starting from the original scheme?
thanks
Antonello
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Old 18th September 2013, 11:27 AM   #1246
Zen Mod is offline Zen Mod  Serbia
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ratio of source and drain resistor

increase source resistor until you hit what you want
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Old 19th September 2013, 01:41 PM   #1247
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thank you very much, I'll try as soon as possible!
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Old 27th September 2013, 06:59 PM   #1248
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Hi all, thanks for an interesting thread. I have started dabbling with solid state audio recently starting with a DCB1 and the ACA, both originating from Mr Pass (Thanks Nelson). Compared to my valve power amp (a 6L6 SE with EF86 drivers) I have to crank up the LS volume on my DCB1 to get sufficient SPL from my 90dB speakers.

Now I'm planning to build a jBOZ preamp and B1 buffer in the same case. As the two designs have have a potentiometer at their inputs I would like ask where is the best place to have the volume control: at the jBOZ input or at the B1? I am thinking of putting a 25K trimmer at the input of the other design.

Is this plan OK, and will it work? I don't want to have two volume controls on the front facia, one to control the JBOZ and another for the B1.
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Old 27th September 2013, 07:37 PM   #1249
tinitus is offline tinitus  Europe
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its difficult to understand what you are saying, or trying

but in case the jboz is input and B1 is output, I would place the attenuator between Jboz and B1
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Old 27th September 2013, 07:38 PM   #1250
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The Bride of Son of Zen article has quite something on volume control placement iirc, might wanna check the PassDIY site.
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