That makes two of us
I just ran a quick test, half an inch is not enough of an airgap. Testing 1.5" now...
1.5" works so the concept is good but that much space looks a little goofy IMO. I'll leave the fine tuning to Mr. Beardy
That's great info Nelson!
A little stand that sits at least 1.5" above the F5m Redux should be easy to procure/build and opens up space for all sorts of neat stuff to sit atop.
I measure the heights of the amp(s) at 125mm (~5"), so one needs the bottom of a stand to be at least 6.5" if my arithmetic is properly functioning this evening.
Edit: I also must add. I still am loving these amps. I listen to them more than anything else I have since I got them up and running.
A little stand that sits at least 1.5" above the F5m Redux should be easy to procure/build and opens up space for all sorts of neat stuff to sit atop.
I measure the heights of the amp(s) at 125mm (~5"), so one needs the bottom of a stand to be at least 6.5" if my arithmetic is properly functioning this evening.
Edit: I also must add. I still am loving these amps. I listen to them more than anything else I have since I got them up and running.
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Apologies Nelson. I had seen references to a `Neal Brock' and assumed incorrectly.
Yours confused as always, Beardy.
For context I was thinking of the upcoming NC-434 desktop speaker from Scott Hinson that will be featured at this year's BAF. if one could extend the four columns upwards to provide the necessary air gap you could use each amp as an `active speaker stand' to minimise total system footprint and it brings the tweeter up closer to head height.
Yours confused as always, Beardy.
For context I was thinking of the upcoming NC-434 desktop speaker from Scott Hinson that will be featured at this year's BAF. if one could extend the four columns upwards to provide the necessary air gap you could use each amp as an `active speaker stand' to minimise total system footprint and it brings the tweeter up closer to head height.
Stability testing will be required, but this is how I interpreted the question
Nelson, would the feet be better placed on the inner standoffs? This would have less stress on the PCB.
Sorry for the long answer to a simple question. In short, yes, supporting at the inner standoffs puts less stress on the board but I don't think it's enough to worry about so I prioritized how it looks.
The engineering answer to "is this better?" is "it depends on how you define better". I like "is this sufficient?" as a question because it implies criteria or requirements that can be met and leaves room for other considerations. I see this project, and Redux Kits in general, as an opportunity to poke around in the (visual) design space. I don't know all the right terms but I'm going to try to explain my thinking. The decision you're asking about started with the fan, which I chose in part because of the mounting arms that taper to the standoff locations. From an engineering perspective, M4 standoffs are plenty strong to support the fan, and that's what I started with. However, the visual weight of the fan on comparatively thin legs looks unbalanced or top heavy and there is an abrupt transition in "line thickness" where they meet. Bulking up the standoffs by putting sleeves over them fixes both visual issues. Now the fan mounts flow smoothly into the upper standoffs and down toward the PCB. At the PCB there are two options, end the standoffs here or continue down to the ground / table. I found that the board wasn't really thick enough to terminate that line in a satisfying way and that the whole unit looked a little top heavy if I went with the inner standoffs. Using the outer standoffs and sleeves gives a more stable and grounded appearance. Either would be structurally sufficient. The board is clamped to the (very stiff) heatsink so the stress and strain are primarily in the outer "arms" of the board, away from the components.
That's enough of that, so now onto the good news, design is subjective. You can and should build your projects however you think is best. I'm providing a kit and instructions, but at the end of the day that's just a box of parts and a suggestion for how they could go together. If you would like to add feet to the inner locations you'll need M3 x 20mm M-F standoffs.
Nelson, are these boards made of the same material you used for the ACA Redux? Very sturdy stuff to my eyes.
Same material, the usual fiberglass, epoxy, and copper sandwich, but I went for 2mm thickness instead of the standard 1.6mm
Design is very important and your design/concept really impressed me (so much so that I am copying it). My concern was the board flexing, but as you pointed out there are no components in the area that could flex and you have gone for a 2mm PCB (that's not flexing). Have a look at Silicone T-Hole Stoppers or Hole Plugs for feet.
It's perfect visually the way it is. Anyone worried about stress on the board can install feet on the inner standoffs as well, n'est ce pas?
To chime in on the "stress/strain" issue brought up if you stacked a speaker on top of the F5m Redux build as Nelson Brock showed in his picture...
Assuming the plastic M4 hex risers are true "columns" in equal loading, the board technically sees ZERO bending moment as long as there is no column buckling. If you were worried the taller plastic M4 hex standoffs were in a buckling mode, then some structural bending moment may be technically applied to the board, but I think that it would require a significant load (way more than a small speaker) to put these into any real buckling scenario that would lead to failure. That failure will be at the standoff screw interface (the narrower screw portion of the standoff would fail, not the fiberglass PBC board). In a perfect world, all the speaker load weight is transmitted in compression to the surface the amp is sitting on top of (a desk). The amp board PCB sees no significant loads at all. Nothing is a perfect world of course, but the point is the PCB is not the failure point regardless of thickness. The failure is at the standoff interfaces that screw together.
I suspect if one used brass M4 hex standoffs instead of the plastic from the board interface all the way up to where the speaker sits atop, I could put a flat board over them with pockets for the standoffs to sit in and put my entire 200lb body weight on top of the entire amp. If there was a failure, it would be a buckling failure where the screw interface exists on the stacked standoffs. The board sees compression across it's thin plane only until failure of the standoff/screw interface, at which point they (the standoffs) would collapse and snap off where they screw together (not the amp PCB). A simple free body diagram shows what I'm talking about here. Rest assured one could easily design a a stand out of this to hold desktop speakers.
The real issue I see with this approach is the "tip-over factor" if you bump the speaker that's sitting up high on top of this stack. This is why my first thought went to a separate stand that sits over-top of the amps that has a wider base for stability.
I continue to enjoy these amps every single day as my go-to listening. I'm so impressed that it's hard to swap them out with another option.
Assuming the plastic M4 hex risers are true "columns" in equal loading, the board technically sees ZERO bending moment as long as there is no column buckling. If you were worried the taller plastic M4 hex standoffs were in a buckling mode, then some structural bending moment may be technically applied to the board, but I think that it would require a significant load (way more than a small speaker) to put these into any real buckling scenario that would lead to failure. That failure will be at the standoff screw interface (the narrower screw portion of the standoff would fail, not the fiberglass PBC board). In a perfect world, all the speaker load weight is transmitted in compression to the surface the amp is sitting on top of (a desk). The amp board PCB sees no significant loads at all. Nothing is a perfect world of course, but the point is the PCB is not the failure point regardless of thickness. The failure is at the standoff interfaces that screw together.
I suspect if one used brass M4 hex standoffs instead of the plastic from the board interface all the way up to where the speaker sits atop, I could put a flat board over them with pockets for the standoffs to sit in and put my entire 200lb body weight on top of the entire amp. If there was a failure, it would be a buckling failure where the screw interface exists on the stacked standoffs. The board sees compression across it's thin plane only until failure of the standoff/screw interface, at which point they (the standoffs) would collapse and snap off where they screw together (not the amp PCB). A simple free body diagram shows what I'm talking about here. Rest assured one could easily design a a stand out of this to hold desktop speakers.
The real issue I see with this approach is the "tip-over factor" if you bump the speaker that's sitting up high on top of this stack. This is why my first thought went to a separate stand that sits over-top of the amps that has a wider base for stability.
I continue to enjoy these amps every single day as my go-to listening. I'm so impressed that it's hard to swap them out with another option.
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To add to the value of these F5m Redux amps, I tallyed up the cost for me of the F5m kit in a Modushop chassis. Below is what I came up with as a cost comparison to what Nelson will be asking for these bad mamajamas!
The value of the F5m Redux is tremendous and that's not taking into account the versatility of the smaller form factor. This design is a real champion!
If Nelson Brock had a company I could invest in, I most certainly would.
| Item | Source | Cost |
| F5M Full Kit | diyaudiosore.com | $ 110.00 |
| Back Parts Kit | diyaudiosore.com | $ 80.00 |
| Modushop 4U Deluxe | diyaudiosore.com | $ 370.00 |
| Wiring | Bezo's Bookstore | $ 30.00 |
| Transformer (AS-3218) | Antekinc.com | $ 42.00 |
| Rhthatcher Boards | diyaudio/Etsy | $ 5.00 |
| Additional Hardware | Bezo's Bookstore | $ 20.00 |
| Subtotal | $ 657.00 | |
| Tax | $ 67.67 | |
| Shipping | $ 100.00 | |
| Grand Total | $ 824.67 |
The value of the F5m Redux is tremendous and that's not taking into account the versatility of the smaller form factor. This design is a real champion!
If Nelson Brock had a company I could invest in, I most certainly would.
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In case anyone was tempted, please do not stand on your amplifiers 😂