Sadowsky bass preamp clone troubleshoot

[rankot]

I have used this schematic:

[Rob Strand]

I have used this schematic:

It's more or less OK but it has some differences to what I thought.

The main issue is there should be a 1k in series with each 50uF cap.    That will reduce the gain.

The original JFETs were 2N5457's.

Some other stuff:
- the optional parts were not present.
- the 47pF on the input wasn't present but there's nothing wrong with it.
(- the 300pF was present)
- I don't remember a 100uF on the divider.  Seems crazy large.  Maybe it should be 100nF.
- Minor stuff: Parts were 2n2 not 2n5 and 47uF not 50uF, 4k7 not 5k
- There was a cap across the power rail and a protection diode.
- There were two 12V zeners in "inverse series" at the output between the 5uF and the 1K then to ground; for protection

[rankot]

Like this? I hope I understood you well.



JFETs are doubled due to fact that I use both TTH and SMD parts. I also left trimmers on source resistors to simplify biasing.

[Rob Strand]

Like this? I hope I understood you well.

This should represent the original (at least for pre 2000),

JFETs are doubled due to fact that I use both TTH and SMD parts. I also left trimmers on source resistors to simplify biasing.

Sorry I crossed them off when I was looking at it. 

From what I remember the drain voltage should be about 5V (this was *not* measured from an actual unit).

The series Schottky diode you had is fine.

[pee-j]

hi,

I always see these warnings: "this topic has not been posted in for at least 120 days.
Unless you're sure you want to reply, please consider starting a new topic"

well, if I was opening a new one, I'd definitely link this one in... first thing...
also, this topic will be relevant as long as people are interested in building a sadowsky bass preamp...
so I venture forth
...................................

what is the conclusion?
is it worth attempting to build one?
using J201? and doing other mods?

or maybe it was a period thing which worked with the former generations (and make) of the 2N5457?

is it that it has noise and distortion issues?

how could moodysounds' still work?
they use SMD in the first place, meaning different transistors, I imagine...

anyway, what is your advice to newcomers?

[iainpunk]

welcome to the forum!

never take that 120 day warning to serious, zombie threads aren't as scary as zombie humans

smd or through hole of the same type use the same silicon bit inside, only in a different plastic mold and with longer or shorter metal pins.

i don't think the J201 will sound the same, but it will probably work, as the biassing scheme is quite robust.

i can;t answer the other questions as i havent build this exact unit, still hope this helps.

cheers

[pee-j]

thanks very much!

you know, I see the demo of the boutique "version", and sounds amazing, and I'll suspect they use different means somehow
now I know that those transistors aren't different...

if I could call a time-travel cab, I'd go back to when DIYers first built it, and would ask everyone to plz mention the transistor make,
and perhaps the hfe...

[rankot]

Build it, it sounds good!

[iainpunk]

the difference between different Jfets in such a circuit is a very marginal one.
also, Jfets don't have a Hfe/Beta, they have transconductance, but this circuit operates well within the margins of that gain limit that that parameter doesnt matter here

a thing to keep in mind is that a demo always sounds different than anything IRL.

i suggest you just try it out on a breadboard and then decide if you want to build a pedal out of this

cheers

[Rob Strand]

There is a 100k + 10k divider that eventually feeds the gates.

If you change the 10k to around 22k (maybe upto 24k/27k) it will make the circuit with J201's behave *very* much like the original.