Anyone experience popping sound when switching channel?

[J M Fahey]

The stand off voltage are guaranty by design. If it is designed for certain voltage, you should really follow it.

Yes, thatīs the safe way to design.

As of your switching problems, the "universal" solution is using relays.

And for muting-while-switching, use some SS device (probably a FET) which will be faster than the relay contact (an LDR will act after the pop), and avoid high signal voltage problems by muting at a point where signal is less than 60Vpp ... or even lower.

Absolute worst case, you pad your signal to manageable levels and then reamplify it.

[Alan0354]

Just placed the order. I ordered the H11F3 Opto-FET also, just in case the Vectrol is too slow in recovering. I ordered 74HC221 together with LM555 as insurance. On top I ordered 74HC86 and 74HC132 Schmitt trigger NAND and 74HC86 EOR in case debouncing becomes a problem. These 74HCxx are very cheap, so it's worth getting as insurance to save shipping cost. Now is the waiting game.

[loudthud]

The H11F3 is only rated at 15V breakdown. The H11F1 has the 30V breakdown and lower on resistance.

[Alan0354]

The H11F3 is only rated at 15V breakdown. The H11F1 has the 30V breakdown and lower on resistance.

I double checked, I ordered the H11F1VM. Ha ha!!! You scared me. I type the wrong part number here!!! Digikey is very fast, they already shipped.

[Alan0354]

I received the Vactrol, I build and test the circuit. I can't wait for the digital ICs to arrive, so I designed another circuit using transistors. It is not simpler nor cheaper than the monostable design, but I have all the parts. It works like a champ!!! Here is the circuit if anyone is interested.



I included the timing waveform to show how I get the mute on both transitions. The 30K current setting resistor is the most important in setting the response. It needs to be this high so the LED is turned on very slightly only. If you lower the resistor to drive more current, you'll here the sound coming on very slow. it's like the volume rise up slowly and is not acceptable. Since the input signal is high impedance, I don't need the Vactrol to go very low impedance to mute the sound. I can see the switch debounce, but it is not important as the slow recovery of the Vactrol is really what set the timing.

I am sure you can find better switching transistors than what I use, I just happen to have these two.

I want to thank everyone for the help. I just never seen these opto parts before.

[loudthud]

That looks good! What kind of pulse width are you seeing at node E? With such low current in the Vactrol, you can drive it direct from a CMOS logic gate.

I went looking for an H11F1M part. There is an NTE replacement, but they don't stock it at Frys.

[Alan0354]

That looks good! What kind of pulse width are you seeing at node E? With such low current in the Vactrol, you can drive it direct from a CMOS logic gate.

I went looking for an H11F1M part. There is an NTE replacement, but they don't stock it at Frys.

It is about 1mS or something. But that is not important. I did a lot of experiment on this. The width is set by the two 0.1uF cap. As long as it is over 0.5mS, it's all good. You don't want it to be long because it will further slowing down the recovery time. The Vactrol is very slow in recovering, I started out using 1uF, it slow the recovery even more. Also if you drive too much current through the LED, you can actually hear the volume goes up as if you turn up the volume on the amp. It can be so slow that it's not acceptable. I found you just use a short pulse at "E", then adjust the 30K resistor to get the right response. I started out using very low value resistors in the whole circuit, driving the base of the transistor with over 5mA, but I kept increase the value so the circuit now draw no current static and less than 1mA during the switching.

Don' worry about the debounce at A and C, it all gets filtered out by the slow response of the Vactrol. Even 24.9K is a little too low and I can hear the volume build up. You can even increase the resistance to 36K or 40K depends on the output impedance of the preamp circuit. I put a 50K resistor in series to the output to guaranty the output impedance of at least 50K.( wrong on the schematic that shows 100K).

It is very nice, there is not a hint of pop with the circuit.

I just received the H11F1, but I don't think I am going to use it at this point. This circuit might not work for the H11F1 because it is a lot faster than the Vactrol, then you have to have a more precise pulse width. I don't exactly trust the timing using this circuit as the base current drift can change the timing. In my particular case, the response time is govern by the Vactrol, so I can safely use this circuit. The 74HC221 monostable circuit should be a better fit for the H11F1. I am going to do a Marshall build in the future, I'll experiment with this the next go around.

[Alan0354]

Well, as in the other post, the amp is in the cabinet and all tested out. Because I have a relay switching in the power amp section for separate resonance control for both clean and OD channel, I still have a very slight popping sound. But nothing loud like the relay from the preamp. I have to have it very quiet and listen for it. There's nothing I can do because the mute circuit is before the power amp and it's not easy to mute that slight pop. It's not any louder than a normal foot switch of an effect pedal with true bypass switch. So I think it's not a problem at all.

Thanks for all the help.

[okcrum]

Wow. Just put a diode backwards across the relay coil to suppress switch-off transients, and make sure the points switched by the relay contacts are at 0vdc. The latter is often overlooked. DC = pop when switched.

[Alan0354]

Read the post, those were all covered before I even start the thread.

[okcrum]

Read the post, those were all covered before I even start the thread.

Actually I did read the thread, at least up to the point where the solutions got overly complex.

This problem has been solved many times before transistors or ICs existed. Caps across DC switched relay coils are not effective noise suppression for switching transients. Switched points must remain at the same DC potential when switched or not switched, so you have to look at the transient behavior of the switched circuits. Simply loading down coupling caps with resistors is not a solution. All the noise coupling paths (and that includes layout) need to be considered, and so far none of them have been AFAICS. You should be able to copy a simple switching circuit out of a Peavey or Fender in the worst case.

[Alan0354]

Wow. Just put a diode backwards across the relay coil to suppress switch-off transients, and make sure the points switched by the relay contacts are at 0vdc. The latter is often overlooked. DC = pop when switched.

I am referring to this post, I checked the DC of the circuits and have flyback diodes across the relay coil from the get go before even posting. Gone through long testing before posting.

You need mute circuit in order to get rid of the pop just like Peavey, Fender and others. That's the whole point of this thread. I don't want to copy Peavey because when looked at the 5150, there is a problem with the J176 only able to work up to 30V. The swing in my case is up to +/-40Vpp. It's all in the thread. Obviously 5150 works for them, but I sure would not copy a circuit that by design cannot handle the voltage swing of my amp. You don't just blind copy. I studied Fender Super Sonic, they mute only one transition, they just let it pop on the quieter transition. Of cause the circuit is a lot simpler if you don't need to trigger on both transition!!! I read Bougner, they use a relay to mute, I afraid it will create a pop by itself!!!

I don't think the solution is overly complex, just different ways of getting the job done. Studying others design to make sure it work for my amp is not exactly time saving than to just designing one. The one I have works like a champ.

[okcrum]

I am referring to this post, I checked the DC of the circuits and have flyback diodes across the relay coil from the get go before even posting. Gone through long testing before posting.

You need mute circuit in order to get rid of the pop just like Peavey, Fender and others. That's the whole point of this thread. I don't want to copy Peavey because when looked at the 5150, there is a problem with the J176 only able to work up to 30V. The swing in my case is up to +/-40Vpp. It's all in the thread.

You don't need a separate mute circuit if you design the switching circuit correctly and you pick the correct points to switch. But you're got all the bases covered. Good luck.

[Alan0354]

You don't need a separate mute circuit if you design the switching circuit correctly and you pick the correct points to switch. But you're got all the bases covered. Good luck.

What do you mean by correct point to switch?

Actually the monostable multivibrator design is very simple if it is on the pcb. 1 60cents IC, 2 resistors, 2 ceramic caps, and 2 1N4148 for the control circuit. All connections are just traces.

[Alan0354]

When I looked back on the design, it can even be a little more simplified.


I can eliminate the PNP as symmetry is not important for the Vactrol at all. The mute time is totally governed by the slow Vactrol, I can just use the channel switch as the trigger for high to low transition. It's not a whole lot simpler, just eliminates one PNP, and two resistors. It's not even worth my time to open the amp to try this. If this work out, this would be simpler than the Monostable design.