Using Jfets for switching in tube amps - high voltage concerns

[nickb]

It's not my idea. It comes from the link below (Pops, clicks section but there's other interesting info there as well) and it's all explained. I just added the SSR. It's tested and works.

http://guitaramplifiers.prv.pl/misc.htm#Pops

It's still good idea. I didnt know optocouplers with back to back LEDS existed. It made me wonder if anyone makes an SSR with back to back LEDS. If they did then you could feed the SSR directly and that would be the simplest possible scheme.

Anyway, it did give me the inspiration for this, using diodes instad of the bi-directional opto-coupler:

[Gaz]

Can't wait to try these ideas. I will report back!

[Gaz]

It's still good idea. I didnt know optocouplers with back to back LEDS existed. It made me wonder if anyone makes an SSR with back to back LEDS. If they did then you could feed the SSR directly and that would be the simplest possible scheme.

Anyway, it did give me the inspiration for this, using diodes instead of the bi-directional opto-coupler:

[ATTACH=CONFIG]57287[/ATTACH]

Back home early from my trip for obvious reasons, and have more time to play with this to distract myself.

I tried this setup, but the LED stays on in one direction. I'm guessing I may have it hooked up wrong. Are there any other parts necessary in this schem besides a LED limiting resistor (I am using 2.2K)?

I have the relay ground going to the 470R resistor for the trigger, and the 12V power source through the 2.2K resistor to the anode of the LED. Is that correct?

[Gaz]

Back home early from my trip for obvious reasons, and have more time to play with this to distract myself.

I tried this setup, but the LED stays on in one direction. I'm guessing I may have it hooked up wrong. Are there any other parts necessary in this schem besides a LED limiting resistor (I am using 2.2K)?

I have the relay ground going to the 470R resistor for the trigger, and the 12V power source through the 2.2K resistor to the anode of the LED. Is that correct?

Nick, you crazy son of a bitch. You did it I realized the schem you drew needed no extra parts. It works great, and it seems as though you've come up with a robust mute circuit using a resistor, cap, ssr, and 4 diodes that can be used anywhere in the signal path!

The only thing I had to adjust, and maybe you can explain this is the resistor cap combo. At first the mute was quite long, and I got a short time (but long enough to silence the pops) using a 220-470R resistor and 22uF cap. Can you explain why this might be so?

Thanks again!

[nickb]

The resistor needs to be small enough to ensure the LED lights up, but not so small so at to break it. The cap needs to be big enough to just mute the pop. The original 220uF was just a conservative guess. If 22uf does it then great!

So happy you got it to work in practice rather than on paper.

[Gaz]

The resistor needs to be small enough to ensure the LED lights up, but not so small so at to break it. The cap needs to be big enough to just mute the pop. The original 220uF was just a conservative guess. If 22uf does it then great!

So happy you got it to work in practice rather than on paper.

Thanks, Nick, yeah I'm really happy with the performance, and came across something interesting. I noticed that when I got the limiting resistor down to 220R or less the click transient was silenced completely. I wasn't sure why this was so, but came across an interesting article from Vishay that mentioned faster turn on times using a peaking circuit.



With 220R and below the SSR switches so fast it's able to catch the transient completely, and since the duration is so short 50mA through the LED shouldn't be a big deal, right? The article says limit to 300mA, and the absolute peak rating for the SSR I'm using is 1A. I'm thinking

[nickb]

You are correct. Yes, the right thing to do is use the biggest resistor that give you the pop suppression you need but not so small as to nuke the SSR.