I built a sort of attenuator 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:

 

[guitarcapo]

You can buy those on EBay for $15. I tried one but it sounded bad at any setting.

[gardo]

I love to tinker and build thigs too.That's cool

Your amp is fairly similar to my Princeton Chorus solidstate so I'll keep this in mind should the need arise but mainly I use a Mustang amp for anything digital

[DeepEnd]

You can buy those on EBay for $15. . . .

Try $19 shipped minimum without the bypass jack. Some of them run $40 or so shipped and probably don't work any better than my little home made gadget, and still don't have the bypass jack. For $12 in parts, some gas, and a bit of labor (and I work cheap), I have just what I needed. I doubt it would work well with a tube amp but for a SS amp like mine it's okay.

[onelife]

That's a good thing to have with the 40Watt Hot Rod Series of amplifiers from Fender as well because the Volume controls are early in the gain structure and the amplifiers are inherently noisy. The attenuator lets the player turn up the sound of the guitar to get a good signal to noise ratio then turn down the whole thing (guitar and noise) to a manageable volume with the attenuator.

 

Thanks for sharing.

 

 

 

 

 

 

 

[Verne Andru]

I built a similar box but used an L-Pad on the speaker output instead of a pot within the FX loop.

[DeepEnd]

That's a good thing to have with the 40Watt Hot Rod Series of amplifiers from Fender as well because the Volume controls are early in the gain structure and the amplifiers are inherently noisy. The attenuator lets the player turn up the sound of the guitar to get a good signal to noise ratio then turn down the whole thing (guitar and noise) to a manageable volume with the attenuator.

 

Thanks for sharing.

Thanks for checking it out. I'd just assumed it wouldn't work well with a tube amp because you wouldn't be driving the output tubes as hard and that an L-Pad or something similar would be a better idea. BTW, thanks again for your troubleshooting advice. In case you didn't see my reply in the other thread, it was a shorted jack.

I thought of using an L-Pad in my own situation but WRGKMC had already suggested the original idea of using a pot between the pre- and power amps and I just stuck with that. For what it's worth, 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.