How to elimate POP

[Leevi]

Any ideas how to prevent POP in the following circuit when switching form bypass to operation.
I have tried resistors over the switches but it does not fully eliminate it. Smaller resistor are better but
then it is not really bypassed any more.

http://s218.photobucket.com/albums/cc183/kz14100/?action=view&current=RikstoneReverUnit.jpg&newest=1

Leevi

[VMS]

Have you tried it like this?

[Leevi]

Thanks VMS
That solution is much better. There is still some snap but not a loud POP any more.
/Leevi

[VMS]

Here's a couple more things to try to get the snap out. First I would change the order of the first two resistors and if that doesn't get rid of the snap, then I would try a big resistor across the output.

[Leevi]

Thanks, I can not test that right now since one of the relay pins was
broken. After I have got a new relay I'll come back.
/Leevi

[Shrapnel]

Another option is use a high resistance resistor (i.e. 10M) from center to each side of the switches. This should give just enough electrical connection to eliminate the popping, and yet not bleed signal.

[dude]

I know I don't have a lot of knowledge to give but I had a pop every time I flipped on the stand-by in an Ampeg J20, they had the stand-by off the ctr tap of the PT. When I changed the stand-by off the rectifier I got this loud pop turning it on and/or off I can't remember. I saw some old Fenders had a 47uf 500v filter cap off the stand-by. This stopped the pop. I guess I could have used a smaller filter but that's what I had, I have an 5AR4 in that amp.

I've read about using a R here, maybe I should have gone that route but the filter worked great. I also notice that David Allen of Allen Amplification used a filter cap here in a lot of his Fender copies, I have one with it. That's why I did it.

al 

[Leevi]

Here's a couple more things to try to get the snap out. First I would change the order of the first two resistors and if that doesn't get rid of the snap, then I would try a big resistor across the output.

Thanks, this helped a lot. The snap is on acceptable level now.
/Leevi

[RicharD]

You say relay so I have to ask:  Do you have a protection diode across the relay coil?  Very very important.  Eliminates pop & keep the relay healthy.

[Leevi]

Do you have a protection diode across the relay coil?

No, I have normally used capacitor which is probably not the same thing.
How does the diode eliminate pop which is caused by the switches of the relay?

/Leevi

[RicharD]

Same as the ignition coil in your car. Flow 12VDC at it, break the circuit, the coil kicks to 400V.

In theory: the current in a coil can't stop instantly, just like the voltage on a cap can't decay instantly. If you break the circuit, where does the current go? It "backs up" as a high voltage, trying to find a place it can go. In a spark coil, it breaks-over at the spark plug. In a relay, it may breakover at the switch, especially if the switch is a wimpy transistor. If there is no place to breakover, in theory the voltage rises to infinity. In practice an iron-core coil rarely kicks more than 10V the former DC voltage because the iron saps some energy (spark coils do a bit better).

http://www.el34world.com/Forum/index.php?topic=8089.0

[Leevi]

Sounds promising but I believe in that after I have tested it in practice.
Thanks for the tip.

Btw. the popping is a general problem also when using mechanical toggle switches.
By replacing a relay by a toggle switch you should get rid of that problem according
to this theory because you do not have anything that "backs up" as a high voltage?

/Leevi

[RicharD]

>By replacing a relay by a toggle switch you should get rid of that problem

Yes and no.  Depends on the quality and type of switch.  A make before break switch will pop less (usually) and a break before make switch.  I do know for certain relays pop without the protection diode (forward bias, points to + across the coil) and they will fail prematurely.  Another trick is to put something along the lines of a 4M7 resistor between the secondary switch legs.  Look at a Ceriatone EF86 tone control.  They're using a 5M1 between each switch leg to shunt transients.
http://www.ceriatone.com/images/layoutPic/marshallLayout/36WEF86NewCeriatone.jpg

[Leevi]

Another trick is to put something along the lines of a 4M7 resistor between the secondary switch legs.

Yes, I agree, I have used that successfully in many amps.

By using several relays for switching you can control the switching e.g. delay the break by using a capacitor. In that way it is possible to create a working "make before break" switch.

/Leevi