New Modulus-86 Build ?s

When you're powering 2 separate channel PCBs, is it okay to just parallel the power wires from the SMPS output lugs to each board? That's what I've done. Is there any ill effect?
You can wire the boards as shown in Post #19 or you can daisy-chain them. I.e., wire from the SMPS to one board and then continue to the other. In theory, what's shown in Post #19 should give you a smidge better channel separation, but the difference will be subtle if there is a difference.

Either way, keep the supply connections tightly bundled, especially for V+ and V-. And keep them away from the input wiring to the extent possible.

If I daisy-chain them, I may be able to save a little wiring length. I'll wait and see during final assembly what's the best approach.
Further operational and sound check after partial assembly. Still waiting for a custom low-voltage remote control and soft-start board. Once that's installed, I can finish up the wiring, and closeup the enclosure. Since there is no room left in the chassis :) I'm forgoing speaker-protection. The built-in chip protections provide me enough safeguards (and peace of mind) for my use case.

Here are a few pics.

Here is my finished project of the Mod-86. It's been finished for a while now, but I was working on a 'mate' for it as well. I'll have a thread over on DIYAudio on that soon. As you know, I chose a rather unconventional enclosure for this build. Mostly due to challenging myself with the mechanics of the formfactor, materials and size I was going for. To me, there's more work involved, to layout the design, making sure I have all the materials, trial and error of the layout and gathering everything before I start. It's just my approach. I was a project planner in my former life. :) To be honest, my dad introduced me to Heath kits in the early 60's, so I have a love of building electronics things now. Unfortunately, I have to make up the assembly manual as I go with my unique pieces. So, for my last 6 project builds, I've turned to a variety of low-profile mini-ITX computer cases. Many of these computer cases are classified as HTPC (home theater PC) enclosures, are readily available on Amazon, and usually relatively inexpensive. You will also need a 3D printer as I heavily use 'panels' for a variety of project's individual needs.

Another thing I like about almost all PC cases - whether small or large - is they all bring a momentary soft switch, and at least two LEDs (power and HDD) already integrated into the front panel. A couple years ago, when building one of my streamer projects into an ITX case, I had a remote, low-voltage soft-start switch designed by another DIY friend (JanHofland) that would take advantage of a single switch, that would double as Standby/On operation. I have a couple versions of the soft-switch if interested. PM for more info.

Remote Soft-start Module.

For my Modulus 86 build, I chose the mini-ITX case that can be found on Amazon here. They go by a couple of names; Goodisory, or Xqbox. They also come in a variety of colors, and even a smoked glass top. This model of the case - the A01 - is one of the smallest cases I have used, so it's not always suitable - depending upon the project scope and size. However, for preamps, small chip amps, and even small..ish DACs it may be suitable. One of my challenges using these cases, is to see how well my intended usage will play out. Most work out, but I have had to use a bigger case with some projects. My building blocks for this project were; 2 x Modulus 86 amp modules, 1 x SMPS, custom remote softstart, and the elephant in the room - the heat sink!

The finished Modulus-86 modules.

As mentioned in some of my earlier posts, I had two big challenges to get everything to fit properly and safely. (1) the size and shape of the heatsinks, and whether they could fit inside, or outside, and (2) where would all the necessary I/O go.

(1) Heatsink (HS)- How was I going to keep the chipamps happy with their heat? First of all, my target use case for this amp was for near-field listening. I didn't need to squeeze every ounce of power out of the amp. So, for starters I used a lower voltage SMPS PSU (+-30VDC). They are generally smaller, lighter and work perfectly fine in this application. The other issue was, could I get a single HS inside the case - with everything else? No chance! That left me only two other mounting options; (1) the outside side panels, or (2) a single larger HS on the back panel. My only conclusion had to be the back panel. So that's what I ended up with. I did end up using an aluminum spreader plate to make it all work. Under normal listening, the HS barely gets warm to the touch. It does make the overall unit deeper, but I could live with that.

Final heatsink installed on back.

The nex challenge was the I/O. With the heat sink on the back, this only left a narrow strip of space on the bottom for the; IEC jack, speakers jacks, and the inputs. I went through several iterations with various size jacks, but I needed to ensure there was no potential of anything shorting on the HS. So, the space was severely limited after I saw that some of nicer jacks I normally would just be too tight of a fit. Btw, I was using a printed 3D panel for the I/O and to fit the space. Here's a couple different suite of jacks I tried.

Two different suites of jacks that I did not end up using.


Ruled these two approaches out, because I wanted to get away from using a lot of exposed metal fittings, I found the perfect solution in an unlikely place. What if I use very low profile banana jacks used on test gear? Using this approach would make everything safer (no accidental failure point), AND I could finally use some nice silicone wires for the speaker connections. This solution solved both issues, and a much more flexible (no pun intended) approach. Here's my final I/O layout. I even found some RCA interconnects with PVC casing plugs. Once hooked up, nothing exposed. Perfect.

Final version.

New feet installed. :)

Finished product.


So how does it sound? I have this amp currently hooked up in the living room - having recently moved my vintage HP-100 to that room. I can only say it did not disappoint. I'm a guy who likes dynamics and a lot of it. When it comes to specs, I look at two numbers - the SNR and dynamic range. Ok, may more numbers. :) ) I want to hear the quietest quiet, to the loudest loud music - without any hum, or noise. This is usually a good measure of the dynamics of the music. This amp paired very well with the HP-100s, and really did show off the dynamics of the music. In fact, I had the HP-100s in the basement with the thought of selling them, since they are a highly sought after vintage speaker. But I could not believe my ears with what I was hearing using the HP-100s. Every note was clearly articulated, full and clear. Good sound stage and open..ness with plenty of controlled bass. I like it when I can hear the vocalist take a breath, and the clarity of an unwavering pitch of a sustained note. The music was jumping out of the speakers! And, my ultimate test, the music was not fatiguing. If I can listen for hours without wanting to give my ears a rest, then everything is good. Of course it helps if the original recording is done well, and your playback source is a comparable and worthy DAC. For this simple first audition, my source was from my library of FLAC files and the little Tone Board 1. Sure, it's dated by today's DAC standards, but it still performs very well.

Thanks Tom for bringing a great sounding amp with a unique design to the DIY community. Well worth the $$$ I spent on this project.

Off to listen to more music...

Here's a teaser. My build of the preamp below will be profiled over on the DIYaudio forum soon.


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Thanks Tom for bringing a great sounding amp with a unique design to the DIY community. Well worth the $$$ I spent on this project.
You're quite welcome. Thank you for your detailed write-up.

I'm glad to hear that your amp came together nicely for you. The Mini-ITX chassis is an interesting idea. I like that kind of chassis reuse as it allows you to get something that looks good without spending a fortune.

Working in confined spaces has its challenges. But that's why I like to do it. Planning, designing and execution in a different, non-traditional, unique (to audio) form factor is where I find the joy of the journey. Albeit a longer journey. :) But, when the end result produces amazing music it makes it all worthwhile. Plus, I always learn about materials, methods and some basic engineering know-how on how to solve a problem or two.

It's a great passion, and now that I'm in retirement I have the time to devote to such projects.