analogue switching

[Little Monster]

Hi all,

I'm building an external tone/vol stack (aka the Insect - it's got six
feet and is a pain in the bum) for a Leak Stereo 20 valve amp I restored
some time ago. At the moment the amp is connected only to a tuner, via a
20k dual pot to act as a volume control since niether the amp nor the
tuner have their own vol/tone controls. The Insect has four inputs, so I
can connect other separates to it at some point in the future.

I decided it would be funky to use logic switching between inputs using
those little clicky buttons (of which I have a lot of reclaimed ones)
and led indicators, for the 4 inputs. I designed a circuit to handle the
analogue side using an npn transistor in common-base mode connected to
each input. Each channel (ie, left & right) having 4 tranistors, and each
group of 4 sharing a collector load and output coupling capacitor. My
existing 20k pot could then be used as a load resistor, and function as
the volume control. The bases of the transistors are then connected to the
switching logic. On paper, it seems like a reasonable circuit, giving an
output better suited to feed the amp's 1M-ohm input, via a baxandall
circuit, than if I did similar using a common emitter arrangement.

Then I discovered the 4066 analogue switch, of which I have 2 in my very
limited junk box - just the right number. Now the question is,
considering it is supposed to be a hi-fi controller, would I be better to
use these, or the bi-polar circuit I have designed? Given I have no
means, apart from my own hearing, of testing the result (and I'm not an
audiophile), and if I were to use the 4066's, they would still need some
kind of impedance matching. Or should I just abandon the idea and use a 4
way switch.....?

Thanks in advance,
Monster
--
Of course I can! I'm British.

www.the-monstruum.co.uk

 

[Richard Crowley]

"Little Monster" wrote ...

Then I discovered the 4066 analogue switch, of which I have 2 in my very
limited junk box - just the right number. Now the question is,
considering it is supposed to be a hi-fi controller, would I be better to
use these, or the bi-polar circuit I have designed? Given I have no
means, apart from my own hearing, of testing the result (and I'm not an
audiophile), and if I were to use the 4066's, they would still need some
kind of impedance matching. Or should I just abandon the idea and use a 4
way switch.....?

It seems unlikely that any of the solid-state circuits (whether your
own bipolar design, or the 4066 FETs) would give the low-distortion
switching function that a good metal-on-metal mechanical switch does.
But if you are "not an audiophile", then maybe that doesn't make any
difference to you. I'd poke around the WWW for example circuits
where commercial equipment uses 4066s to switch audio. Of course,
the manufacturer's own data sheets and application notes are a must-
read.

 

[Little Monster]

On Sun, 22 Feb 2004 09:20:23 -0800, the world was enlightented by Richard
Crowley, unto whom the words are attributed:

"Little Monster" wrote ...
Then I discovered the 4066 analogue switch, of which I have 2 in my very
limited junk box - just the right number. Now the question is,
considering it is supposed to be a hi-fi controller, would I be better to
use these, or the bi-polar circuit I have designed? Given I have no
means, apart from my own hearing, of testing the result (and I'm not an
audiophile), and if I were to use the 4066's, they would still need some
kind of impedance matching. Or should I just abandon the idea and use a 4
way switch.....?

It seems unlikely that any of the solid-state circuits (whether your
own bipolar design, or the 4066 FETs) would give the low-distortion
switching function that a good metal-on-metal mechanical switch does.
But if you are "not an audiophile", then maybe that doesn't make any
difference to you. I'd poke around the WWW for example circuits
where commercial equipment uses 4066s to switch audio. Of course,
the manufacturer's own data sheets and application notes are a must-
read.

Mmm, thanks, that's sort of what I thought. Good job I got the switch,
just in case then

Monster
--
Of course I can! I'm British.

www.the-monstruum.co.uk

 

[CWatters]

Could always try relays?

"Little Monster" <root@localhost.localdomain> wrote in message
news:4f493651e741ebf0ed01cf56a8c4c1ba@news.teranews.com...

On Sun, 22 Feb 2004 09:20:23 -0800, the world was enlightented by Richard
Crowley, unto whom the words are attributed:

"Little Monster" wrote ...
Then I discovered the 4066 analogue switch, of which I have 2 in my
very
limited junk box - just the right number. Now the question is,
considering it is supposed to be a hi-fi controller, would I be better
to
use these, or the bi-polar circuit I have designed? Given I have no
means, apart from my own hearing, of testing the result (and I'm not an
audiophile), and if I were to use the 4066's, they would still need
some
kind of impedance matching. Or should I just abandon the idea and use a
4
way switch.....?

It seems unlikely that any of the solid-state circuits (whether your
own bipolar design, or the 4066 FETs) would give the low-distortion
switching function that a good metal-on-metal mechanical switch does.
But if you are "not an audiophile", then maybe that doesn't make any
difference to you. I'd poke around the WWW for example circuits
where commercial equipment uses 4066s to switch audio. Of course,
the manufacturer's own data sheets and application notes are a must-
read.

Mmm, thanks, that's sort of what I thought. Good job I got the switch,
just in case then

Monster
--
Of course I can! I'm British.

www.the-monstruum.co.uk