How to Remove poppings in Switching of Reverb Pots

[psychepool]

I'm going to add a digital reverb on the amplifier in make.
The reverb circuit is Box of Hall.
I want to put it into the active loop.
To be specific, I planned to located between the return jack and the loop circuit return input.
When external stompboxes are connected to the loop, the built-in reverb will be at the rear of the effect chain.
And I want to switch the reverb pot when channel is switched.
The purpose is to use different reverb settings for different channels.

I make and test it, and I found some problem.
There's no problem in sound but has a functional problem.
There's popping noise when bypass on/off and reverb pot switching.

Switching is done with a relay attached to the board.
The strange thing is, the popping noise does not always occur.
It seems to occur about 50% of the time.
They're not putting it in an amplifier yet, but they're testing it on temporary wiring.
I wonder if it will disappear if you clean up the wiring well.
Or do I need to do something else?

Below is the circuit diagram. The part marked with the red box is the part of the switching.
As such, only the reverb pin2 is switched while the other part is fixed.

box_of_hall_schematic_v1-1.jpg

If the reverb setting is left at zero, there is not much difference between the bypass status and tone, so the reverb bypass can be omitted, but I really want to apply the channel change.
Please give me advise.

[wpaulvogel]

You can put large value restistors across the contacts. 22 Meg should work like Dumble uses across relay switch contacts. It’s enough resistance to mute. It’s worked for me. Look at a Dumble schematic.

[psychepool]

You can put large value restistors across the contacts. 22 Meg should work like Dumble uses across relay switch contacts. It’s enough resistance to mute. It’s worked for me. Look at a Dumble schematic.

Do you mean do like this?

20191016_205425.jpg

[pdf64]

Yes, but...
Who is doing this work, you or someone else? If someone else, are you paying them?
Solving such issues, and avoiding them in the first place, is basic stuff. So if you’re paying someone to do the work I’d be concerned about their competence.

[psychepool]

Yes, but...
Who is doing this work, you or someone else? If someone else, are you paying them?
Solving such issues, and avoiding them in the first place, is basic stuff. So if you’re paying someone to do the work I’d be concerned about their competence.

I don't understand your comment perfectly.(Sorry for my poor language skill)

It is my DIY tube guitar amp project just for hobby.
I didn't pay someone to make it.

I didn't start with a perfect production plan, so a number of additional options are being added along the way.
I apply the options if it has good sound with proper performance, otherwise cancel.

This reverb is also part of a number of options being tried. If the popping noise is not overcome, I will cancel the plan.

[pdf64]

Ok, my apologies for the misunderstanding
The likely issue with the circuit is that all electrodes of active devices, be they tube or solid state, must have their dc conditions maintained whilst switch flips from one state to the other.
As it is, at the moment of switching, IC1D +input loses its dc path to VB.
The solution suggested should fix that.
Good luck

[wpaulvogel]

To answer you about the resistors. Yes, exactly like that. You will have to play with different values to get the correct results. 10 meg might be the right value. The lower value will eliminate the pop but may bleed some of the signal. The high value may have a little pop but no bleeding. Get 22 Meg and 10 Meg and see what works best. Resistors are inexpensive. 1/2 watt are acceptable.

[psychepool]

To answer you about the resistors. Yes, exactly like that. You will have to play with different values to get the correct results. 10 meg might be the right value. The lower value will eliminate the pop but may bleed some of the signal. The high value may have a little pop but no bleeding. Get 22 Meg and 10 Meg and see what works best. Resistors are inexpensive. 1/2 watt are acceptable.

Following the advice, I successed to remove the popping noise with insert 22M resistance. Thank you very much!!

But despite of your advice, I decided to give up to add a digital reverb.
In the text, I wrote that this circuit called "Box of Hall" was transparent, but when I tested it again, the tone distortion was very severe.
There was also a serious distortion even reverb sets zero.
There's much highcut and lowend is booming and overall volume boosts. It seems to be a characteristic of this reverb.
The sound itself was sweet and attractive, but it showed the worst combination with high-gain Sound.

I found another circuit that uses the same module because I felt sorry to give up the reverb.
I found a circuit called "Rub A Dub". It was only the difference between using PT2399 and the reverb module, and it seemed to ensure transparency because the Deep Blue Delay and the buffer circuit were completely the same.
If there is enough transparency, I thought using the tail-bypass would give me a natural feeling with no popping.

Tests showed only little difference from the bypass tone, as expected, and the tail-bypass worked well.
But it had too awkward a sound compared to the sound of the box of holes. It's like shouting, "I!! am!! Spring Reverb!!!!"
I decided not to use it because it is an awkward sound that doesn't naturally get buried, but is making a distracting bounce.

Finally, there is one more circuit that I want to test left, but since it will be equipped with Active FX Loop anyway, I think it is most likely to use external effects.
Anyway, thank you for your advice!