Circuit to switch between 3 channels

[Joss]

Hello, this is my first post in this forum. I am Spanish, sorry for my mistakes when writing in English.

I have experience making high-gain amplifiers, all with two channels. I usually use opto-isolator (VTL5C1). The circuit to control optos is simple in a two-channel amplifier, but for a three-channel amplifier I think it is more difficult and I do not know any circuit.

In each channel, can only be activated some optos and other disabled. Searching the Internet, I found the schematic of the trio. This preamp has three channels and also uses optos. I do not know if the schematic is correct or if someone can help me with another circuit.

My preamp will be similar to Framus Cobra, but with other values on components.

Best regards

[Don Moose]

Originally Posted by Joss

Searching the Internet, I found the schematic of the trio. This preamp has three channels and also uses optos. I do not know if the schematic is correct or if someone can help me with another circuit.

The circuit to do the switching is good - it uses momentary-contact normally-open (NO) switches (on the chassis and in the footswitch).

Hope this helps!

[Joss]

Thanks Moose !

I do not see the kind of transistor that is used in the schematic between IC's ( 74LS132 and 74HC00 ), what transistor can I use?

It is better to have two separate secondarys ( in PT ) to get the 5Vdc and 12Vdc?

Cya!

[loudthud]

Most any NPN transistor will work. In the US 2N3904 or 2N2222A. You don't really need separate windings on the PT because the current demand is low and the regulator chips won't get very hot.

[MarkusBass]

Joss,

It seems to me that these transistors are MPSA05: http://www.fairchildsemi.com/pf/MP/MPSA05.html but any NPN medium power transistors should work.

Mark

[Don Moose]

Originally Posted by MarkusBass

It seems to me that these transistors are MPSA05: ... any NPN medium power transistors should work.

Small-signal switching would be a better description if you're not finding the suggested types and have to search what's readily available, (MPSA05 is fine, as are the other two) but that's getting picky.

Even a small N-channel MOSFET would do nicely - something like a VN10K or 2N7002. When shopping, look for a part that can withstand at least 1.5x the voltage you need to swing, and that can handle at least twice the current you need to pull down (Vrail/Rpullup). Then look at the power you want the package to dissipate (Current.active * (Vce for bipolar, Vds for FET)) and be sure you have headroom (Watts.active.power*thermal.resistance.package(junction. to.ambient in degrees/watt) << Tmax)

Too much detail?

[Joss]

Thanks guys!

I made the order of the components to make the circuit and check its operation. I have 2N3904 at home, try them and MPS05

[Joss]

Hello!

I have all the components and I did the first tests with the switching circuit. With the values of the schematic, the circuit works fine.

If someone wants to make a three-channel amplifier, the circuit works. Finally I used the 2N3904 and MPSA05 and both are ok in this circuit

Regards

[THChrist]

does it work with any other CMOS? like CD4011?

[Don Moose]

Originally Posted by THChrist

does it work with any other CMOS? like CD4011?

A 4011 quad NAND gate does the logic function correctly, but that first gate in the design is an LS132 - a NAND gate with schmitt trigger inputs. Schmitt triggers are fine with a slowly rising edge like you'd get with a 10k/22uF RC. Regular gates can chatter a bit as the input voltage stays in the region between Vil and Vih.

There is an HC132, if that helps. Is there a particular reason you want to use 4000-series logic over 74HC?

The short answer is that you could probably get away with all CD4011s, but in an electrically noisy environment, you could get some unexpected behavior.

Hope this helps!

[THChrist]

Originally Posted by Don Moose

A 4011 quad NAND gate does the logic function correctly, but that first gate in the design is an LS132 - a NAND gate with schmitt trigger inputs. Schmitt triggers are fine with a slowly rising edge like you'd get with a 10k/22uF RC. Regular gates can chatter a bit as the input voltage stays in the region between Vil and Vih.

There is an HC132, if that helps. Is there a particular reason you want to use 4000-series logic over 74HC?

The short answer is that you could probably get away with all CD4011s, but in an electrically noisy environment, you could get some unexpected behavior.

Hope this helps!

there's no particular reason, it just happens that i'm kinda familiar with those 4000-series, just because i've seen 'em alot on marshall's and in the ToneGod page (http://www.geocities.com/thetonegod/).

In fact, the only reason i like this "3-channel switching thingy" is b'cos i don't know any other (the TLS gives me headaches). i just need a simple 3-channel switch for a dummie like me.

that means i'll need 2 LS132?

[Don Moose]

Originally Posted by THChrist

i just need a simple 3-channel switch.
that means i'll need 2 LS132?

This one's pretty simple and looks reasonably bulletproof (at least in the logic section).

Each LS132 has 4 gates, so a 3-way selector would use one LS132 and one of the HC00 - as shown in the schematic at the top of the thread. I think I'd stick with the LS132 as it is less susceptible to ESD damage than the HC132. (Coming from a PC/Server motherboard design background, I worry a lot about static discharge from people touching buttons and connectors.)

[THChrist]

Originally Posted by Don Moose

This one's pretty simple and looks reasonably bulletproof (at least in the logic section).

Each LS132 has 4 gates, so a 3-way selector would use one LS132 and one of the HC00 - as shown in the schematic at the top of the thread. I think I'd stick with the LS132 as it is less susceptible to ESD damage than the HC132. (Coming from a PC/Server motherboard design background, I worry a lot about static discharge from people touching buttons and connectors.)

nice. thanks for your help. i'll use the LS132 & HC00

edit: i forgot to mention, i'm a total idiot when it comes to CMOS. what's the difference between LS132 & HC132?

[Gtr_tech]

74LS logic is TTL, so its not sensitive to static charges like CMOS can be. There are spec differences as well.