Very High Quality Audio Switching

[helgrind]

Hi all,

I'm attempting an auto-recall patchbay project similar to Air Studios at Lyndhurst Hall patchbay with automated recall at Air on Twitpic. However, I have learned that they use the unused ground/shield connection and line in the patchcord for sensing - this can introduce noise as well as possibly lack of screening (depending on the circuit).

At present I see two options - one is to physically detect the presence of a jack, the other to switch out the audio and flash through the jacks with a dc signal. I prefer the latter as I can then store routes rather than just a series of inserts - and even write the connection names on an LCD. The former has been used before - there is a patent to use optical sensors - but it would have to be constantly recording and interruptions in power and or sequence throughout the session could cause major problems.

So, I need a very high quality audio SPDT or DPDT switch, with very low THD and crosstalk (if in a multiple package). I originally suggested doing it all electronically and using analog crosspoint matrices but this was rejected due to the above conditions - plus "Air doesn't do it that way"! I have though of relays, but apparently even gold-plated sealed ones degrade rapidly as they use 'dry' contacts. The audio must not be touched in any way either - so DC biasing is out of the question. I can only think of reed relays or solid state possibly...

Any thoughts would be greatly appreciated!

Laurence

 

[mbarazeen]

i didnt fully understand you post, though if your requirement is to switch audio, you can use ICs such as 4066.

 

[MrAl]

Hello guys,

I've used the 4066B and 4051B for several applications in the past. Another issue you have to be aware of is the switching transient that gets injected into the signal (audio) when the switch is turned on or off. This may or may not be a problem depending on how often you have to switch. There are better analog switches out there too though with a price tag to match, so you should probably go over the spec's and see what looks good for your application.
BTW the 'B' package chip 4066B is a little better than the original chip that has no suffix 4066.

 

[gootee]

You could also use analog optical isolators, like the Perkin Elmer / Vactec VTL5C series or the Silonex products. They are made by encapsulating an LED and a photocell in a light-tight enclosure. The photocell, which would be the signal path, is basically just a pure resistance, which in some VTL5Cx models can vary from under 50 Ohms to megohms, as the LED current is changed from 40 mA to 0 mA. I am not sure what speed you would need for switching. That would be something to keep in mind when evaluating these devices.

See:

https://www.electro-tech-online.com...4-3429APP_AnalogOpticalIsolatorsAudioApps.pdf

https://www.electro-tech-online.com/custompdfs/2010/08/analogoptoisolatorintroduction.pdf

**broken link removed**

Or you could use solid state relays. Or maybe a bi-directional MOSFET switch (google "transmission gate").

 

[audioguru]

Maxim have some audio switch ICs with very low distortion. They avoid a switching "pop" by detecting a zero-crossing of the audio signal and then making a silent change-over.

 

[canadaelk]

For audio switching I love the Analog SSM2402. Unfortunately, soon to be discontinued