Crackling tone

[Leevi]

Any ideas what could be a reason for a short crackling tone
when switching from stand-by to operation. This does not happen if
the amp is warm. I have built several amps but never heard that before.
/Leevi

[dude]

I've had this before. Some Fenders had a filter (500v 30uf) off the stand-by to prevent a popping noise when going on and off standby.

I've seen Allen Amplification use a filter here and it did stop the popping, crackling if this is what you mean.

dude

[GroundhogKen]

It can also be a simple matter of dirty tube pins and sockets.


Ken

[Leevi]

I have done the following changes without success:
- changed the power tubes
- tried an extra electrolytic after the rectifier
- changed a ceramic cap to polyester in the stand-by switch
- re-soldered the wires in the power tubes

Tube sockets are new, OT is new.

It must come from the sector OT, power tubes, power supply.
PI is out of this. I have master vol in the power amp and I can
hear it even when the master is off. I stated wrongly that it doesn't
come if the amp is warm. I occurs always when switching from stand-by to operation.

/Leevi

[simonallaway]

Is the switch beefy enough for that part of the circuit? i.e. is it arcing when switched?

[plexi50]

I have the same problem right now with a Peavey amp when switching the standby off. As the switch is flipped off there is a loud POP! I have checked everything as well in my amp and am going to replace the standby switch. My switch is a cheap cheesy plastic switch and i am thinking it is arching as well. Only changing it will tell /

[Leevi]

Thanks for the tip Simon. However the root cause is probably not the stand-by switch.
The crackling occurs even when I switch the power on and the stand-by is off (=operation).
/Leevi

[Leevi]

Could it be related to the twisted wires? I have twisted both plate wires and
the B+ wire to one bundle which goes partly outside the chassis.
/Leevi

[simonallaway]

Could it be related to the twisted wires? I have twisted both plate wires and
the B+ wire to one bundle which goes partly outside the chassis.
/Leevi

Can you move those safely and try flipping the switch?

[bigdaddy]

It sounds like arching. Use a new Carling's switch and bend the contacts out a bit, run the wires inside and maybe use some shrink wrap. If that doesn't help try a 470R 5watt resistor or higher. that should block the DC voltage when the switch is off.

I had that with some fender amps and some did not do it. I must have owned about 100 of them dating into the 1950's all the way to reissues. Some of the BF amps did it.

I now have the switches on my amps right after the rec tube or diodes as per recommendation by a web site I cannot remember or find in my favs. they also recommended the resistor trick. I tried a 220k and still got some bleed but I think 470 or higher would do the trick. I still might put one in all my amps anyway eventually. I'm a bit tired and the pain meds are kicking in, good luck man.

[The_Gaz]

Sorry, but where does the 5W resistor go? Thanks.

[bigdaddy]

Across the leads on the switch so when the switch is open it still is giving voltage but the large resistor chokes it off. When the switch closes, it bypass's the resistor.

[Leevi]

Is that a true stand-by any more?
/Leevi

[bigdaddy]

Sure since you are getting NO voltage to your B+.

I found the web site, they say use a 47K I forgot I tried that and you need a 470K+ to turn it off the 220K did not work. I was feeling sick when I wrote that. I wrote R instead of K.

http://www.freewebs.com/valvewizard1/standby.html

I'm not really buying into what they say using a 1 or 2 watt and it's true the resistor might get very hot if left on standby for a long time. I'll just keep it the way I have. Since I put the standby right after the Rectifier I have never had a pop yet. I also put the wires in-between the lugs so there is less chance of arching, shrink wrap will also help.

[Jack1962]

I have experienced this problem a few times , most of the time it was either a bad switch or the switch wasn't rated for the proper current (2amp min.)

                                                   Rock On

[Leevi]

The crackling is still there.
- I have changed both stand-by and power switches to Carling.
- the 470K resistor over the stand-by switch didn't help
- I have re-wired the B+ but it didn't help
The tone is not a loud POP but a short (1-2 second) crackling.
The stand-by switch is placed directly after SS rectifier (2 diodes not a bridge)
and there is 47 Ohm resistor before the first filter cap which is big (680uF).
/Leevi

[jojokeo]

I use the "soft start" stand-by switch bigdaddy recommended and like it. Merlin says 100k/1Watt or 220k/1/2watt should be fine since not much current is going through it therefore dissipation is not much at all. It helps with the main resivoir cap to slowly charge up so that when you flip the switch off standby, there ins't such a large pull on your recifier due the internal resistance of the cap and circuit load combination.

I would like to suggest that you touch up all of the components on your tag board and tube sockets as much as possible. It shouldn't take you very long, especially after all of your other efforts and can't hurt either way but, I suspect a bad solder joint and they can be very hard to locate. Hope you find it.

[bigdaddy]

UR using a 680uf filter cap or is that 68?

[Leevi]

It's 680u , the idea is just to get a stable B+.
/Leevi

[bigdaddy]

680u is 68 mfd...right?

You might want to try a 20mfd at the rectifier then a 68mfd after the dropping resitor.

[Leevi]

It's really 680uF. I have used these successfully in several amps without
any crackling. I know it is extreme high capacitance for filter but it works fine
especially what comes to hum and keeping the sound clean. I recommend to try.

I have tested already 22u after the rectifier, which didn't help.

/Leevi

[bigdaddy]

I've heard of people using those high values before, mostly for pure recording amps to eliminate any hum and noise.

Any other crackling noise I ever got was from either a bad plate resistor or an arch from 2 points on a power tube if I remember correctly. Like I said I have had those problems with some BF fenders I have owned many years ago. Those days I just lived with it and played on.

[plexi50]

I moved my standy today right after the recto diodes and just before my filter caps and 220K bleeder resistors

The first pic is what i originally had in my amp

The second diagram is what i now have / Makes much more sense.  My Peavey did not originally have a choke in it

When i installed  the choke i did not think of voltage fly back as it was wired in the standby circuit

Sweet and quiet. No more Pop shutting standby off now. I learned something today!

[bigdaddy]

That's how I do it and I now never have any problems with a pop or crackling noises.

[Leevi]

I tried this as well but it didn't help in my case.
I don't have the choke and use a resistor instead. Could that be the reason
this solution doesn't work in my case?
/Leevi

[birt]

if something has arced there might be some carbon residue. then it will arc a lot easier. even if you changed things. i would use a listening amp and poke around to find exactly where the crackling is coming from