Transistor arrays for switching audio?

[iampoor]

Hi

Does anyone know of any SMD transistor arrays that would be suitable for switching audio signals? Most of the arrays I have found seem to have protection diodes to protect from inductance (Im assuming when used with an electromagnet)?

[David_AVD]

You'll need to detail exactly how you intend to use a transistor to switch audio first I think.

[iampoor]

You'll need to detail exactly how you intend to use a transistor to switch audio first I think.

Gotcha. I will draw a small schematic/diagram!

[dannyf]

Does anyone know of any SMD transistor arrays that would be suitable for switching audio signals?

Anything can be suitable, depending on your particular implementation.

One low-tech approach is to use the transistor as a leg on a T-network of resistors: saturating the transistor mutes that channel it is on.

[zapta]

Hi

Does anyone know of any SMD transistor arrays that would be suitable for switching audio signals? Most of the arrays I have found seem to have protection diodes to protect from inductance (Im assuming when used with an electromagnet)?

Does it have to be a SMD transistor array? How about switches like this one?  http://pdf1.alldatasheet.com/datasheet-pdf/view/26850/TI/CD4016B.html  (there are many others).

Tell us what you want to achieve. This way you will get better answers.

[Paul Price]

You could use a transfiguration diode driving unwanted audio signals into the bit bin with careful biasing.

[iampoor]

Okay thanks for all the suggestions so far.

Basically I want to build a Pic controlled switching array. Instead of using regular switches Im using rotary encoders and a pic. I want to be able to select inbetween 10 different values of resistors and switch individual resistors into the circuit. In this particular application I am using it as a primitive gain control. I want to try using it in an opamp feedback loop, and as an attenuator after amplification). Voltage's will range inbetween 9v and 30v. My number 1 design priority is to minimize additional noise (which will really come mostly down to circuit board layout I believe) and to eliminate noise while switching resistor values.

I know there are other ways to implement this with premade IC chips, but I am really looking to do this as a learning expierement....

[David_AVD]

What have you tried so far?  How did it work out?

[iampoor]

What have you tried so far?  How did it work out?

I havent tried anything yet, in the brainstorming phase right now. HOping to try a few different topologies and compare them in person, since each seems to have significant drawbacks so far.

The bank of resistors goes from 100 to 1000 ohmns, so Im concerned that the bilateral arrays might interfere on the lower values.

[David_AVD]

I think you should experiment with just a couple of gain ranges to start with then scale up from that.

[nctnico]

I'd recommend a digital potmeter or 74HC4316 analog switches. The resistance seems a bit low. I'd choose 1000 Ohms for the smallest resistor.

[dannyf]

DC biased diodes are fairly good as switches too.

[David_AVD]

Voltage's will range inbetween 9v and 30v.

Is this the signal amplitude or supply rail?

[zapta]

Will a digital volume control works for you? There are many, here is an arbitrary one http://www.ti.com/lit/ds/symlink/pga2310.pdf

[iampoor]

Finally had a chance to revist this.

Im not looking to go the Digital Volume control route, I want to find a solution that can span across multiple applications, and that route is too limiting right now.

Ive een looking at using switched resistor ladders, since Ive realized most of the controls I want to simulate are logarithmic. Ive also realized that my initial idea was far too complex. Seems like a digitally controller resistor ladder will maximize components.

http://www.eijndhoven.net/jos/attenuator-calculator/index.html

Now these usually use relays, but Im interested in simulating this with transistors. I was thinking of using NPN switching pairs to simulate the "on-on" relays. Thoughts? Im still looking for an IC transistor array with 8 transistors without diodes on the collector!

Thanks for all your help!  And yes David, going to start simple :-)

[minime72706]

Audiophiles (cringe) tend to like using signal relays to make variable gain (or attenuation, if you will) systems. http://twistedpearaudio.com/control/jt.aspx
This probably isn't helpful, but it took very little effort on my part to write these sentences.

[iampoor]

Audiophiles (cringe) tend to like using signal relays to make variable gain (or attenuation, if you will) systems. http://twistedpearaudio.com/control/jt.aspx
This probably isn't helpful, but it took very little effort on my part to write these sentences.

Im thinking aout implementing a similar resistor ladder, albeit with Transistor Arrays. Not sure if a suitable part exists... (Im a noob). I have found many transistor arrays with 8 common collector darlington pairs, but Im wondering if an array with 8 transistors with no common collector exists. I have found one with 3, but that doesnt help too much...

[edavid]

Im not looking to go the Digital Volume control route, I want to find a solution that can span across multiple applications, and that route is too limiting right now.

So use a digital pot.

Now these usually use relays, but Im interested in simulating this with transistors. I was thinking of using NPN switching pairs to simulate the "on-on" relays. Thoughts?

My thought is that using NPN transistors to switch audio is hopeless.

Im still looking for an IC transistor array with 8 transistors without diodes on the collector!

There isn't one.

[iampoor]

Im not looking to go the Digital Volume control route, I want to find a solution that can span across multiple applications, and that route is too limiting right now.

So use a digital pot.

Now these usually use relays, but Im interested in simulating this with transistors. I was thinking of using NPN switching pairs to simulate the "on-on" relays. Thoughts?

My thought is that using NPN transistors to switch audio is hopeless.

Im still looking for an IC transistor array with 8 transistors without diodes on the collector!

There isn't one.

Okay

Why is it hopeless? Please, eat my newie rain into a pulp, Im so lost! 

Thanks you! Just wanted to make sure I am not missing something.

[David_AVD]

Using transistors is not going to work very well at all.  I suggest a simple experiment with one transistor to confirm.

[Whuffo]

You could use FETs to shunt signal to ground; low RDS on parts have on resistances less than an ohm.

[c4757p]

Using transistors is not going to work very well at all.  I suggest a simple experiment with one transistor to confirm.

I've done this before and it works pretty well.

V3/R4 bias the collector positive when switched off so the negative dips don't forward bias the B-C junction. You can even use a transistor array (with the diodes) without problems. You'll probably want resistor arrays as well for the collector bias and base resistors.

If you want something generic to switch signals in and out rather than simple attenuation, you'll need something more complicated of course.

[minime72706]

I think what people are worried about is unexpected effects on the input audio signal - you can probably kiss fidelity goodbye. I suppose if the resistor value swamps the transistor effect, it might work okay. Discrete transistor circuits are still somewhat of a weak point for me.

[c4757p]

Try it then. You probably wouldn't do it in an "audiophile-grade" system, but with the right parts you could probably make it work quite well at a consumer grade or a bit above.

[edavid]

Why is it hopeless? Please, eat my newie rain into a pulp, Im so lost! 

Distortion.  Why fight it when you could just do things the right way in the first place?