SS Switch For Komet Fast Gradual

[marketleader]

I noticed in researching the PS7141-2A SS switch that Mark Huss uses in his "MOSFET Audio Switch", here's the link to Mark's switch:

http://mhuss.com/18watt/schematics/MosfetSwitch1_1.gif

There is another version of the SS switch, PS7141-1C, which is the same switch, only containing a normally open (N.O.) contact and a normally closed (N.C.) contact on the output . . . compared to the two normally open (N.O.) contacts of the PS7141-2A.

Looks like it should require fewer components to implement a SPDT like you would need in the Komet fast/gradual switch using the PS7141-1C.

Mouser stocks them, however they are slightly more expensive than the PS7141-2A.

I'm a newbie to this technology but it looks like you could eliminate the 2N5087 transistor, 290r & 5k1 resistors and 1N914 diode . . . anybody?

Mark Huss are you around?

[Structo]

I'm not sure I follow.

The PS7141-2A has a normally open and normally closed switch.

[img:827:578]http://mhuss.com/18watt/schematics/MosfetSwitch1_1.gif[/img]

Did you see the Trex as well?

[img:976:826]http://mhuss.com/18watt/schematics/MosfetSwitchTrex.gif[/img]

[Structo]

BTW, I just looked up the PS7141-1C and it is obsolete.

The PS7141-1C-A replaces it.

Can you show what you mean by eliminating the other parts?


I wonder if I could use something like this for switching a cathode cap in and out of a preamp stage?

I don't really understand all the ratings on it.

[marketleader]

You're correct that the Huss circuit implements a 1 normally open, 1 normally closed dual switch but requires the transistor, voltage divider and a diode to make it work since the PS7141-2A-A is a 2 channel 1a + 1a output part. Both channels of the PS7141-2A-A are the same . . . No input current present on the input means the FET switch on the output is nonconductive, or “open.” To make it work you need current on one input and no current on the other.

With the PS7141-1C-A it looks like we could do the same thing with fewer parts . . i.e implement the SPDT (one switch open and one switch closed) function, which reverses when you close the footswitch . . . apply current to both inputs or cut current to both inputs.

It looks simple but was hoping someone with better design chops might comment. Need to make sure not to exceed the voltage and current rating of the inputs.


Here is the link to the mfg data:

http://www.cel.com/parts.do?command=load&idRootPart=254

There's a link at the bottom of that page for their "Optocouplers Brochure " which is also helpful.

The PS7141-1C is a 2 channel type 1 a + 1 b output, one switch is normally open, one normally closed. Current applied to both channels inputs would cause them to change state/reverse, which is what you would want as a SPDT switch . . . Just need to make sure not to exceed the voltage and current rating of the chip.

I see that Mouser shows the PS7141-1C as "on order", guess I'll have to wait to get my hands on one to try it out. I'll draw up my idea to modify the Huss circuit and post for comment.

[marketleader]

Here's a quick drawing

[marketleader]

No need to parallel the inputs to the switch, series should be fine

[Allynmey]

You mean like this?

[Structo]

What are you switching Allyn?

[soma_hero]

that's dana and allyn's board for switching. I believe this is the Fast/Grad switch he's switching. Posted it in a previous topic, and it actually makes the function usable apparently.

[marketleader]

Yes, switching the Fast/Gradual on the Komet is the application. Was thinking the change to the Huss circuit using a different opto would work and require fewer components . . . the opto, a resistor, a cap and a diode. Anyone see problems with the simpler circuit?

[soma_hero]

You can treat these just like regular LEDs in terms of how you light them. I don't know how you'd figure out a current limiting resistor though, it's probably somewhere in the datasheet. But I think yes, you should just be able to use a switch if the two mosfets are permanently in opposite state. Should be very easy!

I believe Dana and Allyns boards use an inverter chip just because Dana had a bunch lying around. Transistor works fine here, and is needed since the two mosfets are in the same state. For this new chip, to transistor should be needed.

[Allynmey]

Actually Dana was talking to Mark a year or so ago when we were working on a switcher idea. Dana designed the PCB's. After a couple of tweaks to fix popping sounds, we came up with these.

Allyn

[Structo]

Could this switch be used to switch a cathode capacitor in and out on a preamp tube?

That would be a usable boost function on an amp I am working on.

[soma_hero]

For sure. You could use the single channel chip since you only need an SPST switch. Or to go between 2 values you could use the 2 channel chip for SPDT switch. If you added another stompswitch that cut DC voltage to the chip then you could remove the switching and have no boost. That might be pretty sweet little setup. Boost on / Boost off and then Boost High / Boost Low.

[Structo]

So having the cathode voltage on the chip to switch wouldn't pose any problems?

I have to admit I don't know squat about these SS switches.

Seems like a nifty way to switch things though.

Look Ma, no relays!


Is there a working schematic for this device on this forum?