Popping Fender Prosonic Amp

[navdave]

Got me a nice Fender Prosonic amp but it pops when switching channels.
Wouldn't a diode across relay two's power supply help stop some of this?
Also these 24V relays look just like the ones Doug sells. Zinky says that
the relays are the main problem being 24V and all. Couldn't I mod the power
supply and drop in some 5V's from Doug?

[PRR]

> it pops when switching channels.

I'd be looking for a leaky cap.

The 24V is not a big problem.

[navdave]

Well I found that someone had modified the the footswitch circuit by swapping out a 9.1k resistor (R19)  that keeps the relays always a little open with a 27k
and a 10uf cap across the switch jack. I new I could hear overdrive bleeding into the clean channel. Gonna put it back to stock. Ya know PRR alot of people complain about this amp
popping when it switching channels could so many people have bad caps?

[navdave]

Wanted to chime in, even with the clean channel volume all the the way down switching from overdrive to clean causes a loud pop.
I removed R19 the 9.1k resistor in series with the footswitch because I could hear the overdrive bleeding into the clean seems to
have done the trick unless I dime the gain on the overdrive. Any suggestions?

[malt]

Hi, I have a tone master that does the same thing. My amp is of the first models, think they made a fix on the later models. Remember reading some thing about this but cant remember exactly what it was, but i think you are on to some thing. Think it was in an interview whit the man ho constructed these amp's.   

[FYL]

Got me a nice Fender Prosonic amp but it pops when switching channels.

This is a known problem on early models. Here's a copy of the relevant Fender Tech Notes with mod suggestions.

[navdave]

Thanks FYL unfortunately that mod has been performed on this amp already.
Here's a vid of this thing in action.

Got me a nice Fender Prosonic amp but it pops when switching channels.

This is a known problem on early models. Here's a copy of the relevant Fender Tech Notes with mod suggestions.

[xenrelic]

For anyone still struggling with pop issues on these amps:

They should have the relay power using a separate 12v 450mA transformer not tied into the bias supply winding and have that power a 1A 1000v bridge rectifier filtered with a 1000uF 50v capacitor with the + output going to the input of an LM7812 12v regulator with the 12v output filtered with another 1000uf 50v cap.

Then replace the two relays with Omron G5V-2-H-DC12 relays obtained through Mouser or Digikey. Disconnect the power going to the relay switch contacts on Relay #2 that activate the channel switching LED by cutting that trace on the pcb that bridges the relay power to the switch contact, cut the trace between Relay #2's coil output pcb pad and the channel switch trace and relocate the Channel LED (minus the 8.2k resistor) to be in series between the channel switch side of Relay #2's coil and the channel switch trace, so that the 960ohm Relay coil activates and powers the channel switch LED at the same time when the Channel switch is engaged. Lastly, install a .1uf capacitor over the Channel switch (SW303) contacts and a .1uF capacitor over the Channel footswitch contacts.

Remember to remove R19 and jumper R401 if they are installed.

If you want an LED on the footswitch side as well, just rewire the footswitch jack with a stereo switching jack and have RLY1's coil output disconnected from RLY2's coil output with RLY1's coil output connected to the ring on the new stereo switching footswitch jack with a stereo plug and cable going to the footswitch, then install a Red LED between the ring wire and the footswitch contact that the tip's wire connects to, so that Relay #1's 960ohm coil drops the voltage to the 2nd LED and activates Relay #1's coil at the same time when the footswitch is engaged. For the onboard channel switch to engage both relays without the footswitch plugged in, just have the ring's switch on the new Stereo Switching jack bridge over to the Tip's switch, so both relays engage when the onboard channel switch is engaged.   

This would be really simple to implement in this amp and you could follow the Dumble 183 schematic available online for reference on how to build the power supply.