Switchable Hi-Z input impedance, how ?

[juma]

Voltage doubler is OK (since power consumption of the gain stage is very small, couple of mA max) but gain stage has very small PSRR so it's recommended to use the clean PS.

 

[tinitus]

I decided to focus less on scrap from now on
since this is beginning to look better I will buy two small print board trafos
one 2x 12V, and one 24V( or another 2x12V)
up to 5VA they don't cost much

 

[tinitus]

picking up the pieces
this have taken a slightly different turn, and I decided that the original box will be a stereo preamp, with two optional outputs
2 channels tube output, and another 2 channels balanced output with BA-3
might need this later for planned tube amp project

since its now a balanced BA-3 I need more space
cut a small piece off the previous tube 'board', and turned it 90 degr

 

[tinitus]

possible layout for the 2 channel SE-balanced output with BA-3

because its to some extend is exposed to radiated heat from the tubes Im trying make it even for all parts of the curcuit, and hopefully not have too much drift

 

[tinitus]

and the instrument high-Z input, low pass/high pass with EQ, a tour'de'france, the full route

 

[tinitus]

I might do another box
the height is better suited for any possible tube experiments
need a frontplate

and was lucky to get a Salas custom designed +30V reg

 

[tinitus]

nicely vented lid, but where is the rest

 

[shanx]

Hi Tinitus,
Nice to see your continuing development. I have been checking your updates. Just thought I should send a quick post, I didn't have much to add to previous progress. Looks like you are pretty close to final for the Fet preamp.

 

[tinitus]

I have a small C-core trafo I hope will work
the regulated +/-12V from the 2x 24V, +30V from one 0-28V

 

[tinitus]

when ordering parts for my Salas reflektor I found theres a higher voltage LM317HV
will start out with that one, until I get the more complicated reflektor done
thats from the 28Vac down to +30Vdc

and I might also use 2x LM317HV as pre regs for 2x TO92 regs, to get the 2x 24Vac down to the +/12V I also need
the TO92 will be with the buffer

but man this is looking 'costly'

 

[tinitus]

got the 2sk117 today

what else are they good at ? suggestions welcome

 

[tinitus]

power supply...maybe

 

[tinitus]

thinking about dumping the LM regulators
and run the 'sensitive' single j310 gain stages directly from caps smoothing only
at least I won't have to worry about 'unstable' power supply

and the TO-92 regs might just be able to bring it down to the other needed +/-12V

or... would it still be better to use two different print trafos, and dump all regs entirely
but those small trafos ? I dont know....with their 'different regulation' it could be tricky without regulator
at least I know the voltage on the C-core I already have
and with its 1.5A rating it won't change voltage one bit

 

[tinitus]

and there might be one big advantage without the LM regs
reason, the HV positive regs all the way made my ground appear...problematic

and the advantage without, I can use seperate diode bridges
I suppose thats a very good thing if you have 'sensitive' curcuits

and maybe especially in this case, mixing SE and symmetric curcuits
and I will only need to buy one type supply cap, 50 small ones are cheaper

 

[tinitus]

another box in the works

 

[tinitus]

and its a match

 

[tinitus]

look here what I just found

 

[tinitus]

and using the big hammer.....nah, fits like a glove

 

[tinitus]

got a few needed parts today
making square holes in back panel
and its much easier than most think

 

[shanx]

look here what I just found

Attached Thumbnails

Hey I could use that, if you are throwing it away!