Modulus-86 build thread

[tomchr]

I would drape the drain wire with some heat shrink and add it to the crimp connection on the spade connector that connects to the mains ground. You can connect it where you currently have the wire nut but that just makes the 'antenna' (i.e., the drain wire connection) longer, thus, more likely to radiate EMI.

I'm thinking/hoping that you just used the wire nut as a place holder. They're really not appropriate for use inside equipment.

For everyone else's benefit: Note that shielded mains wire is NOT required. Regular wire works just fine.

Tom

 

[henrylrjr]

The wire nut was just to convey my thought. It would be soldered or crimp connected. And I was wondering about the exposed drain wire becoming an antenna.

 

[tomchr]

Fair worry. And some might further argue that the shield itself could become an antenna, in particular if left disconnected at one end, which begs the question about how to best terminate it. I don't know the answer to that. The answer likely depends on which problem one is trying to solve with the shielded wire in the first place. I don't have a clear sense of that either.

DIY being DIY anyone is obviously free to geek out about whatever they want to geek out about. I just hope it doesn't result in a bunch of support requests as I'm stretched pretty thin as it is.

Tom

 

[CanPeng]

Hey all!

Not sure if anyone else will find this as helpful as I did, but I threw together some quick STL files for the Modulus-86 and the Power-686 so I can 3D map out my build to ensure everything fits (+ 3D print templates I can rough up during the chassis build to make sure everything fits IRL without wrecking a real board!)

If you might find that helpful for similar reasons, I've attached the STL files for your use 🙂

They just have the holes for mounting, nothing else, so you'll need to measure your caps if you want to use them for vertical planning! Not entirely sure how accurate the Mod-86 file with the 90 degree brackets is, so take that one with a grain of salt until I can print it and compare it to my built board.

Let me know if you end up using em!

Cheers

 

[tomchr]

FWIW: The brackets (and the LM3886) overhang the edge of the board by 0.019". Thanks for creating the models.

Tom

 

[ajvar]

Hi, I am long time lurker but never post on this thread.
I built pair of PD parallel LM4780 monoblocks that play beautifully even today. Going through my stocks, I found another 4 LM4780 chips that I've got long time ago, when they were available for free as evaluation samples 😁. I also found 4 x LM3875 that I got the same way...
I would like to build another pair of monoblocks, this time bridge/paralleled LM4780 and I understand that can be done with Parallel-86 boards that are not available any more. Is there any chance to get these boards today, or maybe the files that will help me to make them? I really enjoy the sound of the LM chips and Tom has extensive offerings and support for LM3886, so I thought I'll give it a go.
Main reason for this is that my speakers are bit on the ineffective SPL side, and the current monoblocks are pushing at best 60W into 8Ohm. My thinking is that bit of extra power (reported 100W into 8Ohm) will make some difference when coupled with beefy PS.
Thanks to all and apologies up front for any dumb questions or requests.
George

Edit: The info would relate to Parallel 486 I presume...

 

[tomchr]

You may have some luck if you put a 'wanted' ad in the Swap Meet. As you point out, I no longer offer the Parallel-86 boards.

Tom

 

[ajvar]

You may have some luck if you put a 'wanted' ad in the Swap Meet. As you point out, I no longer offer the Parallel-86 boards.

Tom

Thanks Tom, will do
George

 

[BrianL]

George, maybe the Modulus 686 would do what you want? That would seem a lot easier to implement.

 

[ajvar]

George, maybe the Modulus 686 would do what you want? That would seem a lot easier to implement.

Hi Brian,
My intention was to use the LM4780 that I already have, is this board suitable?
Thanks,
George

 

[BrianL]

Oh, I thought you were just wanting more power. I forgot that back when Tom had a kit using the LM4780, it was not pre-assembled.

 

[henrylrjr]

I bought two populated Parallel 86 boards from Tom some years ago. And last month I took them out of storage and built an amp with them and it sounds great.

 

[tomchr]

My intention was to use the LM4780 that I already have, is this board suitable?

The only board of mine that the LM4780 will fit is the Parallel-86. I discontinued it about a year after the LM4780 went out of production.

Tom

 

[ajvar]

Thanks to all for the answers, looks like I’ve hit the wall on this one.
George

 

[tomchr]

I often recommend the ModuShop chassis for the Modulus amps. While the thermal data for the heat sinks are available through ModuShop's parent site, HiFi2000, they can be a bit tricky to find. Nelson Pass just posted his measurements of the heat sinks available through the DIY Audio Store, hence, ModuShop: https://www.diyaudio.com/community/threads/store-heat-sinks-thermal-numbers.392902/#post-7191509

Unlike most heat sink measurements, which are done at a temperature rise of 70 ºC, Pass measured at a temperature rise of 30 ºC. This is much more representable of the safe use of an external heat sink. It also means you can use the data directly without any temperature correction.

You can see Pass' thread for more detail, but the important numbers are below:

• Dissipante 2U x 300 mm: 0.56 ºC/W (= K/W)
• Dissipante 3U x 300 mm: 0.44 ºC/W (= K/W)
• Dissipante 4U x 300 mm: 0.36 ºC/W (= K/W)
• Dissipante 5U x 400 mm (actually two 5U x 200 mm together): 0.19 ºC/W (= K/W)

Thanks @Nelson Pass

Tom

 

[stretchneck]

I often recommend the ModuShop chassis for the Modulus amps. While the thermal data for the heat sinks are available through ModuShop's parent site, HiFi2000, they can be a bit tricky to find. Nelson Pass just posted his measurements of the heat sinks available through the DIY Audio Store, hence, ModuShop: https://www.diyaudio.com/community/threads/store-heat-sinks-thermal-numbers.392902/#post-7191509

Unlike most heat sink measurements, which are done at a temperature rise of 70 ºC, Pass measured at a temperature rise of 30 ºC. This is much more representable of the safe use of an external heat sink. It also means you can use the data directly without any temperature correction.

You can see Pass' thread for more detail, but the important numbers are below:

• Dissipante 2U x 300 mm: 0.56 ºC/W (= K/W)
• Dissipante 3U x 300 mm: 0.44 ºC/W (= K/W)
• Dissipante 4U x 300 mm: 0.36 ºC/W (= K/W)
• Dissipante 5U x 400 mm (actually two 5U x 200 mm together): 0.19 ºC/W (= K/W)

Thanks @Nelson Pass

Tom

Direct from Modushop too…

 

[tomchr]

Oh, nice. ModuShop doesn't specify which temperature rise was used. I know they contracted with a local university for the measurements, so I'm assuming the standard 70-75 ºC T_rise was used.

In fact, let's do the math. Table below of temperature correction factors is from Aavid. Pass measured 0.56 K/W for the 2U/300, which would correspond to 0.56/1.257 = 0.45 K/W at 75 ºC T_rise. ModuShop says 0.45 K/W. Yay.

Either way. More data. More better.

Tom

 

[MG IIIA]

Not to diminish the discussion about the commercial chassis, which are nice, I include a photo of my Modulus-86 project with a home-made chassis. I bought the boards (version 2.40) over a year ago but was slow in finishing them. The LM3886 ICs were sold to me for cost by a very kind member of the DIY audio community. The components are certainly a tight fit on the board. I used a flashlight to inspect the undersides of the boards to make sure I had no solder bridges. I put sockets in the gain resistor location, currently set for about 26 db gain to accommodate using my Openamp 1 phono preamp’s output which is controlled by a pair of 1000 ohm Bournes conductive plastic pots. I use an Ortofon 2M Black cartridge with this preamp.

I bent and welded the chassis from 18 gauge sheet metal with the front panel being a leftover piece of 16 gauge stainless (with a scratch in it) for a commercial kitchen counter. The handles were on sale for $1.49 at Menards. The panel supporting the amplifier boards is removable with the power transformers and rectifier boards mounted in the bottom part

of the chassis. The project is in the “recently operational” stage and obviously needs bodywork and paint.

This amplifier sounds absolutely wonderful. Great resolving power. Acoustic instruments have weight and impact and tonal correctness. Great ambient information (which I assume some people call “soundstage”). The speakers I am using are Magnepan MG 0.7s. I am very pleased overall with this project.

 

[tomchr]

Love the DIY chassis. I've built quite a few like that, though I used scrap aluminum from a metal recycling place.

I'm glad you like the Modulus-86. Thank you for sharing.

Tom

 

[spippy71]

Hi, I finally finished and tested Modulus-86 and Power-86 amplifier. Also included the Intelligent Soft Start and Chassis.