Jfet BOZ

[marconi118]

I will follow juma bs170 loaded with bs170 based gyrator

 

[indra1]

Wise choice for your initial step.

 

[citationfan]

Is it possible to take K246 instead of k170?
I have two oldstock to hand.

 

[Zen Mod]

for easy load , just go for it

 

[maouna]

Hello Juma.I built Jboz with J310. I am using 24V Power supply. one channel draws 10mA with 16.34V at the drain and the other 9.5mA with 16.76V at the drain.Are the drain voltages correct or should they be half the supply voltage ?

I also found a small series shunt PSU you posted on an other forum.Is there a any updated version of it or is it final?I would like to build it.

 

[juma]

Hello Juma.I built Jboz with J310. I am using 24V Power supply. one channel draws 10mA with 16.34V at the drain and the other 9.5mA with 16.76V at the drain.Are the drain voltages correct or should they be half the supply voltage ?

12-14V is the target, but J310 have their Idss in wide range so you should use 1k or so for R3. That will give a bit more gain and higher Zout (mainly determined by value of R3) - or you can lower R5 (to increase the Id) but that will increase Pd in J310 (up to 200mW without the heatsink is OK). I would go for Id of about 15mA at Vds of 12V.

Test and find the compromise that suits your JFETs and ears.

If you have DC offset at the input (gate leakage ) lower the R2.

I also found a small series shunt PSU you posted on an other forum.Is there a any updated version of it or is it final?I would like to build it.

It works all right, just take care that Vout depends on R2/R3 (R10/R12) ratio - see TL431 datasheet.

 

[marconi118]

how would perform a j111 instead j310 in JFET BOZ?

It seems to me thet J111 could have a bit more Yfs?

 

[marconi118]

what about bf862 for the jfet BOZ?

 

[vdi_nenna]

Anyone know how to add Schade feedback to the original schematic in post #2?

 

[indra1]

A schade feedback will have low input impedance, hence it is best to have a preceding buffer. Cascoding the jfet will give lower distortion and higher output voltage capability and an output transformer will reduce turn on and off thump. Attached sim shows 2.98 ppm THD, 46.1 Vpp Max with Zout < 200 Ω.

 

[vdi_nenna]

R6 and R11 form the Schade feedback loop?

If the inter-stage transformer needed?

 

[indra1]

R6 and R11 form the Schade feedback loop?...

R6 / R21 form the Schade Feedback.
Transformer is my preference, you can go RC but there will be somewhat loud turn on and off thump.

 

[vdi_nenna]

I usually turn on a preamp before a power amp and always leave the preamp on. But it's good to know.

 

[Tyimo]

Hi!

What about to use LU1014 in such a circuit like the BOZ?

 

[Ian Greenhalgh]

I think BF862 is the most likely candidate to replace 2SK170 in the JFET BOZ.

 

[Nikos a]

Hi
I have made a JFET boz to drive a sewa v1 amp. I followed the original schematic, using a 2k2 resistor on drain of the jfet and 10 ohm on source.The JFET (2SK170) that i used has an Idss of 8.1 mA.
I supplied it with 16.3V , but the distortion was very high. I measured the voltage on the drain pin of the jfet and it was 3.4V. I replaced the 10 ohm resistor with a 22 ohm one, the distortion was reduced a bit but it is still too much.
Does anyone have any advice on this matter ?

Thanks

 

[Zen Mod]

use 24Vdc supply

it's starved

or change drain resistor to 1K

 

[ralf]

which resistor values for optimal gain for Ciuffoli power follower amp

Dear all,

perhaps you can help me out
i hav no idea how to setup this pre, but want to try it out...

since i use an amplifier without gain (Ciuffoli)-
how setting the optimal values?

thanks a lot

 

[Zen Mod]

in that case JFet Boz most likely will not have enough swing , to drive power follower

make it as shown on schematic , and if combo is loud enough , you're good

if not loud enough , make some other preamp

 

[ralf]

further JFET BOZ question
dear all,
i just build a JFET BOZ and connected it directly to input of Hiraga LeMonstre- without pot, for getting about 6-10 db more gain..

but now it has way too much gain.

can it be reduced?

or can i fix it with input voltage devider with two resistors?

what values should these resistors have for geting about 6 db?

thanks a lot

best
Ralf