Modulus-86 build thread

I would put the safety ground as close to the IEC inlet as practical.

I also suggest rotating the transformer to keep the wiring on the secondary as short as possible (and away from the amp inputs). This may mean that you need a second ground point for the transformer shield. That'l fine.

Drill baby. Drill. :)

Tom
 
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man a bolt and a few more nuts(2nd ground) then i think i can start putting the power/modulus boards together

ran into real problems when mounting the XLR jacks. i attempted to make a template for the large hole and the 2 mounting holes, but when it came time to screw it on, everything was off. had to shift both plugs a 1m to get the mounting screws to seat, its totally ugly and im sad it didnt work out well.

making the power 86 mounts has a small clearance issue with the 4 posts, its way too tight. i used the power 86 board as the template, but when i drilled the holes, something went went out of spec.

hopefully just monitor issues going forward

thanks @tomchr for the suggestion of 2 ground posts, appreciate your help through this process
 

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its totally ugly and im sad it didnt work out well.
That will completely fade after you’ve completed the amp and are listening to it. :yes: Who cares what the back and underside look like when you almost never see it? I’ve had some shameful chassis mishaps recently and forgave myself once the device was sending music out from within its electrical voodoo innards. :clown:
 
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Acceptance is part of mindfulness too. It seems to be part of some North American indigenous approaches as well. At least I've come across it in the Blackfoot traditions. We westerners could learn something... :)

And note that acceptance does not mean surrendering or having to like something. You can accept without judgement. I've always hated the saying, "it is what it is", because it - to me - indicates surrender. I prefer "it is what it is, but I don't have to like it".

Tom
 
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Hello all - I'm building a 4 channel Modulus 86 amp and have learned a lot going through this thread and @tomchr has been great at answering questions by email. I'm an experienced DIY'er but not in the area of electronics or audio in general so I have what may be some basic questions I'm hoping to get some insight on.

First... power buttons. I prefer a front mounted push button and I dont have space in my chassis for Tom's ISS that allows for a low voltage power switch. I may have just enough height to orient one on its side but prefer to avoid that if possible. I have a SPST 120V 15A latching push button on hand (https://www.amazon.com/dp/B0CL37KQYT?ref=ppx_yo2ov_dt_b_product_details&th=1) which I may try first. Tom's documentation recommends a DPST switch to separate both live and neutral and the same vendor has one but its larger and needs a larger hole in the front panel which I don't want to do until I know I've got a solution. What are my odds of success with this? Will the inrush current of my Antek AS-3222 (300VA) destroy this SPST button? Would a DPST be better? Will an RC snubber help (I don't pretend to know anything about this, just repeating what I have read)?
 
That should work. Should... I would prototype it before drilling holes in the front panel. I've had mains switches that failed after 1-2 weeks of use due to the in-rush current. An RC snubber across the switch might help with the arcing. Might...

If the switch lives up to its 15 A rating I'm not overly concerned.

An SPST switch will work. Just make sure you break the live connection (marked L on the IEC inlet) and not the neutral (marked N). Also make sure to use an appropriately sized fuse.

Tom
 
Great, thanks Tom. I'm going to start with a 5A fuse and only increase if needed. Happy to hear that I'm not completely off base here. A quick look at IEC's with integrated rocker switches looked like DPST (2 in, 2 out) so I was concerned about the SPST. If the switch does fail quickly, does a DPST and/or RC snubber theoretically increase the robustness to the inrush?
 
The RC snubber might. It's intended to prevent arcing of the switch. I'd survey existing schematics to find good values. I'd guess that something like 10 Ω + 10 nF is pretty good. Do keep in mind that if the snubber capacitor fails, you could end up with a scenario where someone pokes around inside the amp thinking that it is off only to be electrocuted and die. So I'd use a safety class Y capacitor for this as it is designed to fail open circuit. Or ... scrap the snubber and just select a beefier switch.

I originally had a 2 A switch very similar to yours in the Modulus-286 Kit LE where it controlled the power to an SMPS300RE from Connex. The SMPS has a built-in inrush limiter, but the switch still died after a few days of daily use. I had no issues with the 10 (or 16) A switch I replaced it with.

Fusing is pretty complicated to get right. Oversize the fuse and you don't get protection. Undersize it and you get nuisance blows. I generally recommend 2-3 x VA/Vrms, where VA is the VA rating of the power transformer and Vrms is the nominal mains voltage. If this math gets to past 10 A you definitely want to add a soft start. Also: Use a slow-blow (time delay) fuse.

Don't just order one fuse. Order a couple of each value near the low end and the high end of the range. Fuses are not super expensive, so you'll regret saving $2.50 now only to have to spend $20 in shipping later.

Tom
 
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