Jfet BOZ

[juma]

... so this pre amp is not suitable where you need to swing voltage up to 2v into a lowish gain amplifier ??

If you don't mind 5% THD at 2V output, you'll be fine.

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.

I suppose you mean JBOZ. If that's so, 17V p2p is 6V RMS. JBOZ puts out 2V with 5% THD at 16V PS. I don't know how much THD you'll get with 27V PS at 6V RMS output, but if you like the sound, everything is fine.

If you mean the old BOZ (with MOSFET) that's another pair of socks...

 

[TB]

Hello,
Is it possible to use 1.2k input resistor instead of 1k and 470 Ohm output resistor instead of 475 one without ill efects?
I want to build original pre based on schematic posted by Mr. Pass in post #2 with 16 Volts PSU.
Thanks

 

[Roscoe Primrose]

Absolutely... And I'm in Nova too, why don't I know you ;-)

Roscoe

 

[TB]

Hello Roscoe,
Thanks for the answer.
Where are you located in Nova?

 

[Roscoe Primrose]

Out near Warrenton. We have a DC area DIY group that gets together about monthly. Unfortunately most of them are in MD, we could use some more in VA ;-) We're going to have two rooms at the Capitol Audio Fest this year . See HiFi Heroin for commentary on our room from last year.

Roscoe

 

[TB]

Hello Roscoe,
I am in Arlington. Warrenton is nice and higher altitude is better for HiFi sound 🙂

 

[tfender]

Very Good

 

[tinitus]

hey, I can report that I have got a simple jfet boz test amp up and running for my bass guitar

+17.5V before Drain resistor
7.1V measured over it (1250ohm)
-82mV measured over source resistor (15ohm)
carbon film resistors
signal resistors are metal film

needs volume att and buffer

 

[6L6]

How are you using it? To put the instrument into your stereo? As a gain pedal? Driving a amp? (Combo or head) ?

Just curious. 🙂

 

[tinitus]

How are you using it?

only one jfet so far
so its just mono, but split to 2 outputs/RCA going to a 2 channel stereo preamp

but hope to have more of them later 😉

dont know if this is of any use to you guys
but for my particular project its clear to me that every gain stage must have its own attenuator to control the gain, and as a result, additional buffer

so to those who have a B1, but desperately needs the additional gain, just put the simple jfet in front of the B1
could be there will be minor grounding issues to deal with
or could just a small ad-on with its own battery supply( I think Nelson also suggested battery)

 

[Zen Mod]

not exactly on par

B1 and JBOZ are just having context and goals , so final quality is different

 

[mhouston]

@tinitus: After building both the B1 and quite a number of BoZ the B1 sounds better but I need gain to for my low gain tube power amps. So BoZ works for me. But BoZ (or my BoZSE) is an excellent sounding dead simple jFet preamp.

 

[tinitus]

I increased the drain res to 3K2ohm
source res is still 15ohm
now I measure 16V over the drain
and measure over source res, it circles around -1mV and +1mV

totally different values
now it sounds like fresh running water 😀

 

[mhouston]

With my BoZSE and a 24V supply I can get 17V swings with no clipping into 10K.

 

[tinitus]

I increased the drain res to 3K2ohm

turned into a very nice distortion machine 😀

back to 1K5 drain res, and 15ohm source

shows the input is very easy to overdrive
I have 850K to ground, and cant go any lower
1M is probably 'safer'

maybe gate/series res could be increased 😕

 

[tinitus]

related power supply
well, I never tried those little 1ohm series resistors, and thought this might be a good moment for it
and I can only say ouch
this happened yesterday, before any of my posts here
I didnt notice at first, but the downwards slide had begun, hunting other 'sound improving' adjustments
which probably gave me a clown award
but also learned something very interesting

fortunately that sweet sound I had experienced earlier came back instantly when I removed the series resistance
it may lower noise, and some claim quite a lot
but to my ears it definately kills this little curcuit, and what it does best
for me personally, series resistors are out, sorry

 

[juma]

With my BoZSE and a 24V supply I can get 17V swings with no clipping into 10K.

I suppose it's 17V peak-to-peak i.e. 6V RMS ?

 

[mhouston]

@Juma: Yes peak to peak.

 

[tinitus]

I have seen a se output buffer with jfet and a bjt inserted in the drain, and connected to source(out)
dont know what its called
thought it might be worth a try since i found some older BC547

 

[tinitus]

searching, but not much to find, other than it looks like a ccs turned backwards
and bjt appears to be biased through the jfet drain resistor