Modulus-86 build thread

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Well, a month from the 3rd anniversary of starting this I've got ready to make swarf. Progress report (well rejig report as initial fit test failed). But I have a question. Using a 200*160*40 heatsink for each pair of channels would 6 M3 bolts be enough to hold that in place? Into metal no issue, but using hurricane nuts into MDF which is first for me...
 
Bill,

If I understand your design you have an MDF case and will use M3 screws or bolts through the heatsink and into hurricane nuts countersunk into the inside of the case? I suspect you chose M3 so that the bolt/screw head will fit between the pitch of the heatsink fins without having to machine the fins themselves.

M3 is a rather small thread falling close to a #4-40 UNC. I have not been able to find hurricane nuts in that size on the web. The area of concern would likely be whether the flange of the nut provided enough bearing area on the MDF to avoid "blowing through" the MDF when tightened. What is the OD of the M3 hurricane nut flange?

I would be inclined to go with at least a #8-32 UNC hurricane nut here going seat of the pants rather than based on a technical analysis.
 
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Kevin: Partly for ease of maching, but partly because in some parts I only have 20mm width to play with.

Of course doesn't help that various tapped inserts are called 'hurricane nuts' :). I'm planning on using these Zinc Alloy Threaded Inserts - Headed Hex-Drive Inserts/Type D .

It's not ideal but I promised SWMBO that the amplifiers would fit into the speaker bases.
 

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I'm a bit concerned that those nuts will rip out if one grabs the amp by the heat sink. M4 would offer more grip due to the larger circumference.

Alternatively, long machine screws could go through the heat sink and chassis wall and be fastened with lock nuts on the inside.

One could also entertain the thought of adding some adhesive between the chassis and the heat sink. Then the smaller threaded inserts could probably be used. Of course, if you even have to take the amp apart in that case, you'd be hating life. Tradeoffs, tradeoffs. :)
Even something like double-stick tape can be surprisingly strong. I don't know how well it handles the heat, though. With that size heat sink, the heat sink won't get terribly hot, though. Maybe 40 ºC when you really crank the tunes. Probably 50-60 ºC during continuous sine wave testing at the worst case dissipation.

Tom
 
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Well it's easier to pick up via the front support which is not only glued on, but glued to the vinyl wrap! Lasted 25 years. No more nails is an option. It will be on spikes as well so I will be able to get fingers under it to pick up. All options. More later...
 

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Bill,

It looked like the smallest size in the link was an M4. I haven't used those particular style fasteners with MDF but in my experience MDF tends to delaminate into a fuzzy blowout when a coarse thread with a fairly deep profile like the outside of those is threaded into a pilot hole in MDF. I think a hurricane style nut with a flat flange behind the MDF has better chances of success and I'd go at least M4.
 
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D'oh. It was the knock ins that go smaller. Ah well, that's that one sort of sorted :). A re-inspection shows I can only drill though on the flat panel so might as well go all the way through and use M4 knock ins from the back Zinc Alloy Inserts - Headed Knock-in Inserts/Type B. If that fails then glorp.

As for other challenges in the first fit test I discovered that the capacitor board is too big so I need drop back to Tom's recommended 22000uF. I was seriously considering mounting the transformer outside the box (nice flat section there) for a few minutes. Getting at the power connections to the boards will be impossible once installed which is another minor pain to fix.

This is what happens when you try and do something no one else has ever considered (and for good reason :) ). Next time it's standard boxes. But this will be nicely stealth and I think one more check and I can drill the first hole :).
 
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Indeed. If you look at attached you can see the stand/plinth from the front. All you actually need is the front section and something at the back for the speaker to rest on. If plan 'A' fails then there is a modushop box that will fit and give me some more and studlier room to play with.
 

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Chris: Thanks, they are a 'long term' project. Eventually will dipole the bass, but for now they do the job, even if in a 'difficult' room.

Tom: Have the transformers (12 months now :eek:) but will be using SMPS on my next project for the kitchen. There I have the box already (Denon POA-F100 I bought for a surround experiment that never happened). I have more space in there esp as will be lower power.

Will all be worth the wait...
 

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206 W into 8 Ω @ 0.0006 % THD+N verified. 350 W (4 Ω) when my lab supply hits its current limit. I expect the actual limit to be closer to 400 W.

6 x LM3886 + LME49724 + OPA1642 in a Bridge/Parallel Differential Composite Amp architecture.

Availability: Preorders by end of January 2018. Full production towards mid/late February.

Just saying... ;)

Tom
 

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