A homebrew FM3 + PS170 combo amp

Watt McCo

Member
I posted some pics of my FM3 setup in the "show me your rig" thread, and one of the mods suggested I start a dedicated thread with more details. I'll go ahead and start it with the pics I have, and might add a few more detail shots once the rain clears out later this week.

Executive summary is that I made a 1x12" cabinet with a compartment to hold an FM3 and a Seymour Duncan Powerstage 170 poweramp to turn the FM3 effectively into a Fractal combo amp. Yes, it means the 3 buttons on the FM3 are for the most part unused. There are 2 cutouts in the "brain" compartment, one of which lets me see the FM3 screen so I know what preset I'm on and can use the tuner, the other gives access to the four knobs of the PS170. The lid of the brain compartment is easily removed to allow editing of the FM3 if needed. The wet weight is 40 pounds, and total size is roughly 20" tall, 22" wide, 10.5" deep. The speaker is a Weber Silver Bell 50 watt ceramic.

The first pic below shows the core structure of the box, with the lid and speaker grill cloth frame removed. It's basically just a 1x12" cabinet with the sides extended upward an additional ~3" and the FM3 and PS170 placed on the top of the cab. The second pic shows the rear view of the cabinet with the lid in place (but not attached), speaker grill cloth frame still removed. Again, you can see it's basically just an open backed 1x12" cabinet with sides that extend further upwards. The back of the compartment that holds the FM3/170 remains open even when everything is in place, so I can still easily get to XLR jacks, USB jack, power switches. The output volume knobs are fairly easy to adjust even sitting in front of the amp, though for the most part I just use the PS170 controls to handle volume adjustments and any slight EQ adjustments needed to compensate for the room, the spot on the F-M curve current volume is at, different guitar, etc. The FM3 and PS170 are both stuck down with dual lock, There is also a hole cut in the top panel of the cabinet directly under the bottom vent of the FM3.

The second picture giving the rear view also shows that a Line6 G10 is attached to the internal side of the cab. At first I intended to run a short ~1.5-2 foot instrument cable from the receiver to the FM3, but after using it for a week think I'll stick with the 15' cable that is currently in there coiled up in the back of the cab. That way if anything happens to the wireless system, I can just unplug the instrument cable from the wireless and plug it into my guitar.

You can also see where power is centralized in this rear-view image. I bought one of those multi-outlet boxes designed to plug into a wall outlet. It has 6 3-prong ports, 2 USB-A ports, and 1 USB-C port. I use one of the USB-A ports to power the G10 wireless. The USB-C can charge my phone...but doubt I'll ever use it. I glued this to the inside top back door panel with WeldIt, using an additional spacer block to inset it far enough into the cab the extension cable that plugs into it doesn't poke out so far. So The whole system only requires one IEC cord plugged into the wall to run. I considered using a power strip with its own power switch so there would only be one power switch, but there will be plenty of times in my studio/office that I run the FM3 without turning on the PS170, so for now I just reach around the back and turn each unit on once the power cord is plugged in. The FM3 switch is easy to get to; the PS170 switch involves a moderate amount of awkwardness. Awkward enough that I'll probably eventually add something to make that situation easier.

The third picture shows the cabinet with speaker grill cloth frame (but no grill cloth) attached and the top removed. The grill cloth frame will not generally be removed now that the whole thing is complete. In this mode, the whole thing still works fine - nothing has changed about the speaker enclosure by removing this top lid - but you can access all the controls of the FM3 if editing is needed. You can see the threaded posts sticking up onto which the lid attaches. If I had it to do over again, I would have done T-nuts or threaded inserts inside the cab so I inserted threaded bolts through the lid once in position to attach rather than sliding the lid over the threaded posts for inserting.

The fourth picture shows the lid now attached. As you can see, there are decent sized knurled thumb nuts that screw onto the threaded posts once the lid is on place to hold it there. You can also more clearly see the side vent Fractal-logo cutouts in the rear portion of the cab sides in the "brain" compartment -- there is one on the FM3 side, corresponding to its side vent and one on the PS170 side...for symmetry. With the hole underneath the FM3s bottom vent, the side vent, the cutout above the FM3 screen, and the open-back nature of the brain compartment, I'm not too worried about heat build-up at this point. In use so far the fan on the FM3 has only kicked on once.

The final two pictures are after finishing and attaching the grill cloth. Materials-wise, the cab bottom/top/side/lid panels are all made from decent-but-not-amazing-quality 5/8" thick baltic birch ply. There are a few voids in it, but I would be really surprised if using actual void-free cabinet grade ply would make a sonic difference on a cab of this size that is so well braced. The baffle, speaker grill-cloth frame, and back door panels are made from similar grade 1/2" ply. The baffle is glued around its entire perimeter to full-length cleats attached to the inner-side-walls of the cab. The grill cloth used for speaker and Fractal-logo cutouts is cain material from Speaker Builder Supply. Handle is also from them (its a great handle and it actually came with screws/t-nuts for installing which a lot of other vendors do not include). The finish is a few coats of milk paint with some sanding, followed by a couple coats of a tung-oil finish and some wax. Because this thing is likely to take plenty of hits, I wanted a finish that would live well with dings and/or be really easy to repair, so its a little distressed looking, which is fine. I don't have the patience/desire to do tolex.

For control, I'm just using a simple two-button footswitch as stand-in for FC switches 7 and 8. I have those set up so the right button turns boost on/off on tap and tuner on hold. The left button switches between channel A and B of the amp block on tap and tremolo on hold. All of the presets I use through the cab are bare-bones: drive -> trem -> spring reverb -> amp. When playing through the cab, I just view it as a really great sounding boutique 2-channel combo amp with built in boost, trem, and reverb. Mostly various Fender amp models, occasional JTM45. I leverage a lot more of the FM3s power when playing direct through studio monitors/recording, which I can easily do without having to remove the thing from the combo amp since the XLR jacks are easily accessed.

Thanks for checking it out. Happy to answer any questions.

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Very nice build. I build my own speakers cabs as well. Not trying to troll, I'm genuinely curious. I'm sure you have a reason, but why would you not want to be able to access the FM3? I can see have the amp set up like you do, but I would think being able to use the buttons on the FM3 would be wanted?
 
Very nice build. I build my own speakers cabs as well. Not trying to troll, I'm genuinely curious. I'm sure you have a reason, but why would you not want to be able to access the FM3? I can see have the amp set up like you do, but I would think being able to use the buttons on the FM3 would be wanted?
When playing live/with other people, I'm a simple, simple man. 9 times out of 10 I don't need anything more than one boost button and a single channel amp. I also hate setup. Amp in one hand, guitar on back, put the amp down, plug it in, pull the guitar out of the gig bag, grab the wireless transmitter out of the back of the cab and ready to go. Plug the dual footswitch in the back and drop it down if I need it, but half the time I don't even need that.
 
I posted some pics of my FM3 setup in the "show me your rig" thread, and one of the mods suggested I start a dedicated thread with more details. I'll go ahead and start it with the pics I have, and might add a few more detail shots once the rain clears out later this week.

Executive summary is that I made a 1x12" cabinet with a compartment to hold an FM3 and a Seymour Duncan Powerstage 170 poweramp to turn the FM3 effectively into a Fractal combo amp. Yes, it means the 3 buttons on the FM3 are for the most part unused. There are 2 cutouts in the "brain" compartment, one of which lets me see the FM3 screen so I know what preset I'm on and can use the tuner, the other gives access to the four knobs of the PS170. The lid of the brain compartment is easily removed to allow editing of the FM3 if needed. The wet weight is 40 pounds, and total size is roughly 20" tall, 22" wide, 10.5" deep. The speaker is a Weber Silver Bell 50 watt ceramic.

The first pic below shows the core structure of the box, with the lid and speaker grill cloth frame removed. It's basically just a 1x12" cabinet with the sides extended upward an additional ~3" and the FM3 and PS170 placed on the top of the cab. The second pic shows the rear view of the cabinet with the lid in place (but not attached), speaker grill cloth frame still removed. Again, you can see it's basically just an open backed 1x12" cabinet with sides that extend further upwards. The back of the compartment that holds the FM3/170 remains open even when everything is in place, so I can still easily get to XLR jacks, USB jack, power switches. The output volume knobs are fairly easy to adjust even sitting in front of the amp, though for the most part I just use the PS170 controls to handle volume adjustments and any slight EQ adjustments needed to compensate for the room, the spot on the F-M curve current volume is at, different guitar, etc. The FM3 and PS170 are both stuck down with dual lock, There is also a hole cut in the top panel of the cabinet directly under the bottom vent of the FM3.

The second picture giving the rear view also shows that a Line6 G10 is attached to the internal side of the cab. At first I intended to run a short ~1.5-2 foot instrument cable from the receiver to the FM3, but after using it for a week think I'll stick with the 15' cable that is currently in there coiled up in the back of the cab. That way if anything happens to the wireless system, I can just unplug the instrument cable from the wireless and plug it into my guitar.

You can also see where power is centralized in this rear-view image. I bought one of those multi-outlet boxes designed to plug into a wall outlet. It has 6 3-prong ports, 2 USB-A ports, and 1 USB-C port. I use one of the USB-A ports to power the G10 wireless. The USB-C can charge my phone...but doubt I'll ever use it. I glued this to the inside top back door panel with WeldIt, using an additional spacer block to inset it far enough into the cab the extension cable that plugs into it doesn't poke out so far. So The whole system only requires one IEC cord plugged into the wall to run. I considered using a power strip with its own power switch so there would only be one power switch, but there will be plenty of times in my studio/office that I run the FM3 without turning on the PS170, so for now I just reach around the back and turn each unit on once the power cord is plugged in. The FM3 switch is easy to get to; the PS170 switch involves a moderate amount of awkwardness. Awkward enough that I'll probably eventually add something to make that situation easier.

The third picture shows the cabinet with speaker grill cloth frame (but no grill cloth) attached and the top removed. The grill cloth frame will not generally be removed now that the whole thing is complete. In this mode, the whole thing still works fine - nothing has changed about the speaker enclosure by removing this top lid - but you can access all the controls of the FM3 if editing is needed. You can see the threaded posts sticking up onto which the lid attaches. If I had it to do over again, I would have done T-nuts or threaded inserts inside the cab so I inserted threaded bolts through the lid once in position to attach rather than sliding the lid over the threaded posts for inserting.

The fourth picture shows the lid now attached. As you can see, there are decent sized knurled thumb nuts that screw onto the threaded posts once the lid is on place to hold it there. You can also more clearly see the side vent Fractal-logo cutouts in the rear portion of the cab sides in the "brain" compartment -- there is one on the FM3 side, corresponding to its side vent and one on the PS170 side...for symmetry. With the hole underneath the FM3s bottom vent, the side vent, the cutout above the FM3 screen, and the open-back nature of the brain compartment, I'm not too worried about heat build-up at this point. In use so far the fan on the FM3 has only kicked on once.

The final two pictures are after finishing and attaching the grill cloth. Materials-wise, the cab bottom/top/side/lid panels are all made from decent-but-not-amazing-quality 5/8" thick baltic birch ply. There are a few voids in it, but I would be really surprised if using actual void-free cabinet grade ply would make a sonic difference on a cab of this size that is so well braced. The baffle, speaker grill-cloth frame, and back door panels are made from similar grade 1/2" ply. The baffle is glued around its entire perimeter to full-length cleats attached to the inner-side-walls of the cab. The grill cloth used for speaker and Fractal-logo cutouts is cain material from Speaker Builder Supply. Handle is also from them (its a great handle and it actually came with screws/t-nuts for installing which a lot of other vendors do not include). The finish is a few coats of milk paint with some sanding, followed by a couple coats of a tung-oil finish and some wax. Because this thing is likely to take plenty of hits, I wanted a finish that would live well with dings and/or be really easy to repair, so its a little distressed looking, which is fine. I don't have the patience/desire to do tolex.

For control, I'm just using a simple two-button footswitch as stand-in for FC switches 7 and 8. I have those set up so the right button turns boost on/off on tap and tuner on hold. The left button switches between channel A and B of the amp block on tap and tremolo on hold. All of the presets I use through the cab are bare-bones: drive -> trem -> spring reverb -> amp. When playing through the cab, I just view it as a really great sounding boutique 2-channel combo amp with built in boost, trem, and reverb. Mostly various Fender amp models, occasional JTM45. I leverage a lot more of the FM3s power when playing direct through studio monitors/recording, which I can easily do without having to remove the thing from the combo amp since the XLR jacks are easily accessed.

Thanks for checking it out. Happy to answer any questions.

78giEZF.jpg


zl3XTcq.jpg


lvhEocu.jpg


waud2g9.jpg


v7Iq91U.jpg


5yVJWz2.jpg
Smart set up man! If that works for your needs, I think it’s genius! Well done!
 
Very cool!!

I built a cabinet like this at one point (still in my basement). It's a 1x12 sealed cab with a 4 space rack above it. Had it telexed to look pro.
It sounded outstanding. Just stopped using it when I went to Fractal/FRFR.
 
Very cool!!

I built a cabinet like this at one point (still in my basement). It's a 1x12 sealed cab with a 4 space rack above it. Had it telexed to look pro.
It sounded outstanding. Just stopped using it when I went to Fractal/FRFR.
Yeah, this is effectively a homebrew version of those old Atomic Reactor things - not a terribly new idea. But the FM3 sounds a heck of a lot better than anything that could be docked in those, and I prefer the look of old beat up tweed amps :) Now if they can just get perform page ported over to the 3 it really will have a combo amp feel to it.
 
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