Switchable Hi-Z input impedance, how ?

[tinitus]

found RCA tone control manual
and a Crowhurst article
looks like even I can do that

btw, consider its a 2channel/stereo
using one channel for bass, and one channel for mid/top
enables the two channels to be configured differently
like using the trick with a small bypass cap on cathode resistor, to achieve a little more high frequency gain
and having seperate attenuator for each channel further enhances sound balance control

 

[tinitus]

trying to draw curcuit, with EQ

not sure why the cathodes are bootstrapped
but seen that elsewhere

hmm, maybe only output tube should be bootstrapped

 

[tinitus]

I find it exstremely funny to read a text bit like below

 

[tinitus]

not sure why the cathodes are bootstrapped

ah, ok
by bootstrapping, the input/gain tube would achieve a bit more gain
guitar amp builders say it gives more 'grunt'
well, no real need for that here

bootstrapping the cathode output tube gives higher impedance load
and that might be of advantage, considering the EQ curcuit
well, I dont know this, but it seems logical

hope its beginning to look better

 

[tinitus]

ahh, managed to make the desired drill/router bit for doing solder pads
have been on the to do list for some time

needs a bit 'refinement', but seems to work ok
means I can get on with the solid state output (BA-3)

 

[tinitus]

needs a bit 'refinement'........

works better, smoother and much faster now
I think it will be a good tool

 

[tinitus]

and this is the way I plan to use it

seems like I will have to do some cuts for soldering directly to the ground plane, or else it takes too much heat

hmm, solder pads appears to be a bit big for some smaller components like multiturn pots with smaller legs
might have to use bigger pots

or try to build a smaller tool
well, I might take the challenge

 

[tinitus]

hmm, solder pads appears to be a bit big for some smaller components like multiturn pots with smaller legs

its close, but looks like that will work too

 

[Nigel Goodwin]

Why not just build it on plain matrix board?.

 

[tinitus]

Why not just build it on plain matrix board?.

I dont have any
only ordinary boards
old pieces, bought long time ago
why waste them

anyway, you dont find it good to have a 'free' ground plane ?

but ofcourse you are right, matrix board would be easier

 

[Nigel Goodwin]

anyway, you dont find it good to have a 'free' ground plane ?

If you were building an RF device, perhaps so - but for a low quality valve audio unit it doesn't matter.

 

[tinitus]

yeah, I know, but like I said, its free
and it also means that ground is 'available' where ever you may need it
heck, whatever, its just for fun

 

[Nigel Goodwin]

Old tobacco tins are great for building things in - it's fully screened, and the surface takes solder easily - either 'free wire' inside it, or solder tag strip inside and use that. I've built many projects (particularly preamps) in them over the years.

 

[tinitus]

Old tobacco tins are great for building things in ....

I have plenty of these small boxes
look for modems, digital receivers, etc
metal and not plastic, ofcourse

 

[Nigel Goodwin]

I have plenty of these small boxes
look for modems, digital receivers, etc
metal and not plastic, ofcourse

But presumably you can't solder to them?.

 

[tinitus]

But presumably you can't solder to them?.

I could weld

 

[Nigel Goodwin]

I could weld

But rough on the transistors though

But they are very nice looking boxes.

 

[tinitus]

hey, finished lacquering
Im happy with the result
but not so happy with the vented hole plate on front
looks a bit too dominating

might be better with 'smoked' vinyl

 

[tinitus]

not long ago I found an old B&O receiver
it gave me a nice trafo
but I also took the frontplate with me
I felt stupid, but just thought it looked nice, and might be of use, somehow

hacking off the right piece, and voila

 

[shanx]

I like that front panel look, it does make it look ''cleaner''