Switchable Hi-Z input impedance, how ?

[tinitus]

rearranged the inside
tube board and solid state board shifted place
matches the new curcuit layout with BA3 at input instead of output

and thought I would like to see how it looks with tubes 😎

 

[tinitus]

did a search on 3PDT

under pictures it revealed a ton of info how to connect a LED in bypass
yesterday I was unable to find anything
strange world

 

[shanx]

Google Image Result for http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=11083&g2_serialNumber=2

 

[shanx]

Hi tinitus, you will want to do a ''true bypass'' where the section is switched out completely. I posted a link for the basic wiring. To avoid any ''thump'' sound when you switch over, a 1 meg ohm is sometimes added from signal line to ground on the input to that switched section. The Led occupies 1 section of the triple pole, usually switch to ground and complete the circuit. A cool option is to use a dual LED, like yellow/red and switch in either one depending on which ''channel'' or bypass selected.

 

[tinitus]

A cool option is to use a dual LED, like yellow/red and switch in either one depending on which ''channel'' or bypass selected.

😀

regarding the 1M ohm
I have seen some suggest to short the input of the bypassed curcuit
But I guessed the 'usual' 1M ohm to ground would do the trick 😕

 

[shanx]

yeah the 1 Meg will tie the input to ground even when switched over. As you are bypassing completeley that section, any small noise in that bypassed section will be also completely out of the active signal path.

 

[tinitus]

right now thinking about where to 'steal' the power for the LEDs

use one half of the +/- 18V from the jfets supply
or take it from the tube heater winding

in any case, it will ofcourse have its own regulator

or simply use a battery ?
sounds a bit 'weird'

 

[tinitus]

hmm, a very small trafo should not be any problem

 

[tinitus]

this one looks neat

 

[tinitus]

pretty cool little thing

measures 4.7Vdc, unloaded

 

[tinitus]

small trafo for the LEDs have now found a new home 🙂

and btw, it will have its own mains fuse, so that it dont take out the whole amp in case of errors

which is also part of my point with having both solid state and tube curcuit
should a tube fail, or in need of being replaced, it will still be a fuctional preamp

still need parts for the regulated +/-20V

 

[tinitus]

trying to rethink my curcuit/function layout

first, the tone control
I suppose it would optimally have a buffer on both input and output
despite the fact thats it means adding further curcuits
and that its best not to place any att in between

buffers will be placed together with the control knobs
all mounted on a small bord behind the front plate

 

[tinitus]

and, thinking about a rotary switch after the first gain stage, with a direct out option

 

[tinitus]

problems

 

[tinitus]

and a possible new front for the changed layout
good thing Im slow, sometimes 😀

 

[tinitus]

3P4T rotary switch
could be I have solved it now

pos 1 is first gain stage direct to output

pos 2 involves the tone control (toggle bypass for fast tone defeat)

pos 3 involves tube stage output

pos 4 input direct to tube stage output

 

[tinitus]

3P4T rotary switch
could be I have solved it now

shoot, no, not quite so simple
maybe better go back to the one with all bypass toggle switches
or a combination

 

[tinitus]

have found a 4PDT toggle switch with ON/ON/ON switching that might give what I want 🙂

 

[tinitus]

man, thats a tricky one

its a 4P ON/ON/ON
but with jumpers made a DP3T
read that jumpers are external and may be cut to make it 4PDT
I do need at least 3P because of the LEDs
but maybe the last 4th pole could work with leaving one of the jumpers
which would make it a mixed 4PDT/3P3T hybrid, or whatever aint switches just a lot of fun 😱😀

 

[tinitus]

and the 4P switching with both jumpers cut

it gives 3 options
and able to 'create' complicated connections
or in other words, it can do signal in/out switching and bypass at the same time 😎
and still have a free pole for LEDs
now I only need to figure out what is the reality 😀