I built a sort of attenutaor box

[DeepEnd]

Not a power soak but it solves the problem. Here’s what I needed: I own a Fender FM65R guitar amp. 65 Watts, 1 X 12, Solid State. Like a lot of Fender amps, it’s loud at fairly low settings of the Volume knob like 3. Since 1 is “Off,” there’s not a lot of wiggle room. I wanted to turn the amp down and run a line to a DI box. But, on this amp, like many others, the “effects loop” consists of a “Pre Out” and a “Power In,” which means the nominal “Line Out” comes after the Volume (and “Drive” in the case of the “Drive” channel) control. I needed to turn up the output through the “Pre Out” without turning up the Volume to deafening levels.

 

I made a box that goes between the “Pre Out” and the “Power In” jacks. There’s a single 1/4" input jack, two 1/4" output jacks, and a 10K audio taper pot with a nice, big knob. One output jack is affected by the pot and the other isn’t. The output that isn’t affected goes to a DI box. The output that is affected goes back to the “Power In” on the amp. By turning down the pot, I can reduce the volume of the amp without turning down the output to the DI box.

 

The whole thing cost about $12 in parts (a tip of the hat to the folks at Gateway Electronics, BTW) plus my labor and a couple of Planet Waves 3' cables on Amazon for another $17 shipped to connect it to the amp.

 

I sketched the basic design, adapted from one on gearslutz.com, bought the parts, and started building. I drilled holes at the corners for the rubber feet and attached them with screws. No coming unstuck. I drilled holes for the jacks and pot.

 

The box is 4" long and I’m lazy so I cut half a dozen identical 5" lengths of wire. I soldered the wires and then installed the pot and jacks in their respective holes. I assembled the box and attached the knob to the shaft of the pot. As you’re facing the unit, the input is on the right side. The output that’s affected by the potentiometer is at the rear, and the unaffected bypass output is on the left side.

 

Anyway, it works like a charm. I’m happy and I heartily recommend a project like this to anyone.

 

Here's the final design and a few before and after pics:

 

 

During construction:

 

 

Completed:

 

[DeepEnd]

I had a chance to try it out this morning in worship and it seems to work well with the pot at 12 o'clock. I have no idea how much attenuation that is but it works for me. Anyway, as I said, if you'd like to invest $12 or so in parts and some labor, it's a handy little gadget.

[isaac42]

Seems to me that it ought to be 90%, or -10dB. That would make it sound half as loud.

[WRGKMC]

So it worked out for you OK. Good deal. Did you also send a signal to the PA?

[DeepEnd]

^ I haven't tried plugging into the PA yet but I'll keep everyone posted.

[DeepEnd]

Update: I discovered that the reverb didn't work with the volume knob on the attenuator box below about the one thirty position. I posted about it over in the Amp Forum and WRGKMC suggested adding a 1uF capacitor to create a high pass filter to reduce the DC bias load on the reverb circuit. I added the capacitor and now everything works as expected. Here's the revised design: