Switchable Hi-Z input impedance, how ?

[AndrewT]

Tin,
you are still showing the BJT buffer without a DC blocking cap on the input.

Without that necessary cap, anything you attach to the front end will corrupt the BJT biasing you have shown.

Look again at that 2002 pre-amp.
C1, C4, C7, C16, C17, C8, C14, C18, C19, C20 are all DC blocking caps.

 

[tinitus]

Tin,
you are still showing the BJT buffer without a DC blocking cap on the input.

yah, I know....but right now Im working on the jfet section only
you may notice I removed output resistors
so the jfet output dc blocking cap would connect directly to the BJT buffer

but that BJT thing is just for fun
output buffer for the final preamp project will different, and have symmetric power supply
unfortunately no time for that right now
but until then I need to stay fit, and on my toes

 

[tinitus]

all wired up, and ready to roll
for the third time
it worked ok yesterday, after a few corrections
even the tone control seemed quite good

 

[shanx]

Hi Tinitus, Yup that last layout looks very useable.
I noticed that your cabinet has quite of bit of free space...maybe are you planning to build a complete power amp in there?

 

[tinitus]

hey....it really works

 

[tinitus]

I noticed that your cabinet has quite of bit of free space...maybe are you planning to build a complete power amp in there?

you just gave me an idea
maybe it would be 'convenient' to have just a small power amp built in
to use just for 'silent practice'
it could also have optional high pass filtered output

 

[tinitus]

next project .... small late night practice 'combo'

from lesson learned here, I would say all that it takes is a single jfet, and a small solid state amp

 

[tinitus]

but since power amp muscle is plenty, and more coming in soon.....

I decided to try with a just hi-z jfet buffer in front of the BJT buffer

 

[shanx]

Hi tinnitus,
Any updates for your project? Have not seen any posts for a while. Anyways I hope you keep experimenting and have fun! I am still working on some guitar projects for fet preamps..not quite done yet but getting there.

 

[tinitus]

Hi tinnitus,
Any updates for your project? Have not seen any posts for a while.

hi shanx
havent changed a thing, and its still rocking

well, one small change
I now use only one channel to drive my 3way speaker

if I continue with 2-channel preamp, the second channel will be for another instrument, like a guitar

hey....it really works

 

[tinitus]

Anyways I hope you keep experimenting and have fun!

status quo of my big power amp project

 

[shanx]

Glad your enjoying the preamp as it is, simple is good. Now for that power amp project of yours,
those heatsinks look like it's ready to put out some serious wattage. Do you have that build going on another thread?

 

[tinitus]

Do you have that build going on another thread?

no, not yet
but its from apexaudio's '1000watt Simple PA Amplifier'

well, I really dont need it, but since I already got most parts, why not try it
besides, it might be fun to have such a power monster

 

[shanx]

Yes that is some serious wattage there!! Good luck with it. Maybe you will post the build online?

 

[tinitus]

Good luck with it.

I may need it, thanks

yeah, I suppose there will be more to post later

 

[tinitus]

sure hope it will work again, later

need to search a bit on this stuff

 

[shanx]

Hi Tin, I actually thought you mounting your fet preamp into your bass to make it active. But saw from your other post that it is some pickup rewiring.

 

[tinitus]

sorry, I got busy, and was confusing

broke one coil wire, but managed to fix it, and it works ok again, in parallel

nah, I hate batteries, and prefer passive

 

[tinitus]

like said, it works fine again
and I like the parallel pickups too
but had to change tone control cap
or else it was way too bright

found a wire had been jammed by magnet
and I broke one coil wire
I suppose it burned from too many solderings, when testing the different configurations
not all worked well
(as a warning if you try this)

 

[shanx]

Hi Tinitus, yes those really small wires can be tricky. I avoid touching them if at all possible. If I do I rewire the other end of the cable connections with a switch. In my case it's a 5 way switch for strat style 3 pup. While you have the pickups out you may want to look at the shielding inside the cavity of the bass. Get some copper tape and line the insides, as well as the cover, and connect to your jack ground. Should be a big improvement to reducing hum and interference.