Albert Kreuzer onboard preamp -- mod questions

[pee-j]

hi,

Like many of us, I also really like Albert Kreuzer's onboard preamp,
I've been using it, too...

still I have some questions regarding possible mods...
okay here they are:

a.)    is the buffer necessary? or good to have anyway?

b.)   is it a good idea to take apart the tone control as Jack Orman did it?
      (link)  just so you have "more control" (more knobs )

c.)  would it be possible and also a good idea to (I'm no expert) bias the jfets using Vref instead of ground? as Jack Orman does it in his buffer example page, example #3 and #4
   (link)

d.)  if we use it as it is, with the buffer, wouldn't some cap and a resistor be good to the input?



---NOTES:

I'm aware that Albert Kreuzer designed this, as he explains, (link archive.org)  || the page is part of a frameset, whigc is necessary for navigation,
so here it is: (link, frameset)
so that it could be placed in a passive bass, using its original pots...

hence the buffers... (for piezo pickups, or -- also useful in case of -- different pickups who wouldn't work well together normally as a pair)

and hence the BMP tonestack, one knob...

and this is why he had no "coupling" at the input, as I guess without good knowledge in electronics

anyway, here is his big bass preamp (link to page), of which this is a cool "rip off",

The reason I'm making this post is question c, mainly
cause I see the Sadowsky preamp, "the" (the one we know), and it appears that the biasing happens using Vref,
and I thought that his "feature" could be added to Kreuzer's onboard preamp too...

just to have the maximum out of it


thanks in advance!

Peter

[antonis]

a) You need one of them for Tonestack drive and two of them in case of both pickups connected..
edit: I don't see any buffer..
T1 & T2 are, inherently inverting, Common Source amps with gain of X3 and output impedance much higher than 1/g_m..

b) If you like..
(but, IMHO,  with resistor values scaled up..)

c) By biasing Gate(s) to Vref, you have more headroom (IMHO, you don't need it.. ) but you'll have to also bias T3 in a similar way..

d) No..
(there isn't any DC, other than negligible Gate leakage current, going to coils..)

[pee-j]

thank you, Antonis,

a.)  your answer surprised me I thought that the parallel cap at T3 was what brought about the gain, and that T1 and T2 were low/no gain "boosters" (amplifiers) ... but I had no reason to believe so other than imagination -- thanks for explaining

b.) this is what I was "afraid of" (expecting): that you have to redesign it - no thanks! (saying to myself ) it really is good as is

c.) thank you for the good news! and for your expert opinion, too, that -- IYHO -- we don't need it

d.) thank you!


so, I'd draw the conclusion, if you agree, that it is a good design, works well, and there are no compromises to regret
i.e. we should use it as it is -- has been for over 20 years now..

THANK YOU!

[antonis]

I thought that the parallel cap at T3 was what brought about the gain, and that T1 and T2 were low/no gain "boosters" (amplifiers)..

As for T3, C5 (in series with R12) indeed sets particular stage gain, which is considered as the ratio of R10 and R12 in parallel with R11..             [ R10 X (R11 + R12) / (R11 X R12) ]..
As for T1 & T2, gain is the ratio of R1 and R2 & R3 and R4, respectively..

[Mark Hammer]

You do know that Albert has passed away several years ago?

[pee-j]

You do know that Albert has passed away several years ago?

yes, Mark,

when in 2019 I wanted to get the schematic from his website, which was linked everywhere, that website was down...
and google search results had it that he had died in April 2011,

I never knew him or anything, but I regard him as kind of a point of reference in time,
cause not only he disappeared but his work, his website too, and -- I don't want to be disrespectful at all -- j-fets, too...

his website is accessible at archive.org, using the "wayback time machine"... and this sort of true for so much of culture in... including guitar electronics, pedal culture, and the music that used to be there around it...

in <30 years, copper would be out of stock, globally,
tonight I placed my second order of j201-s, 12 pieces probably my last shipment

one thing, however, that will always exist is sensitive humans' affinity to beautiful music, and wanting to listen to good music, and also to play...
and that's something good, and something that Albert Kreuzer would be pleased with, for certain..

I think, it is very cool that you mentioned him

[pee-j]

I thought that the parallel cap at T3 was what brought about the gain, and that T1 and T2 were low/no gain "boosters" (amplifiers)..

As for T3, C5 (in series with R12) indeed sets particular stage gain, which is considered as the ratio of R10 and R12 in parallel with R11..             [ R10 X (R11 + R12) / (R11 X R12) ]..
As for T1 & T2, gain is the ratio of R1 and R2 & R3 and R4, respectively..

Now it came to my mind where I got the buffer idea:
a talkbass post, a bassist explains how he made a buffer back in the day,
I should have known, when he mentioned gain and that signal is louder, that it couldn't be a buffer
but it just stuck in my mind, regardless...

https://www.talkbass.com/threads/onboard-buffer-nice-one-albert-and-don.1224463/

PS:
I do know that a j-fet amplifier is a buffer --- a "separator", so to speak -- because of the jfet's high input impedance
BUT regardless, I do understand that I was wrong, cause by "buffer" I meant close to unity gain, not just high input impedance

I'm only writing this down so that people in the future reading this would not be confused (about the buffer functionality)...
and last but not least because I've just decided to put the lower gain (the Don Tillmann) amplification stage into my bass...
like that guy did it at talkbass
thanks again!

[antonis]

We could shake hands for "an inverting buffer with not so good Zin / Zout proportion"...

[pee-j]

We could shake hands for "an inverting buffer with not so good Zin / Zout proportion"...

shaking hands with you would be a privilege for me, but not in this sense, cause you're teaching and I'm learning,
you're correcting my misinterpretations, you're a master and I'm a beginner student, let there be no doubt about this

so, thank you -- and thank you also for your remark about the Zin / Zout ratio  another thing that I've learned about