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Modulus-686: 380W (4Ω); 220W (8Ω) Balanced Composite Power Amp with extremely low THD
Modulus-686: 380W (4Ω); 220W (8Ω) Balanced Composite Power Amp with extremely low THD
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Old 4th February 2018, 06:18 AM   #1
tomchr is offline tomchr  Canada
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Arrow Modulus-686: 380W (4Ω); 220W (8Ω) Balanced Composite Power Amp with extremely low THD

The Modulus-686 is a balanced composite bridge/parallel amplifier. It uses six LM3886 amplifier ICs to provide nearly 400 W into 4 ohm loads at vanishingly low distortion. With a typical output current capability of 33 A, the Modulus-686 easily drives even the most challenging loads, including loads with impedance dips into the 2 ohm range.

You can find the build pictures from a couple of representative builds by following these links. This is not an exhaustive list.
  • Sledwards12375's build: Post #931
  • Daansan's build: Post #864. Note that this post includes a comparison to a $14k commercial amp and also a detailed description of the level of customer service received before and during the build process.
  • HarmonicTHD's build: Post #776 (progress) -- Post #844 (finished)
  • My build for the Vancouver Island DIY Fest: Post #601 (progress) -- Post #608 (finished)
  • Mattattnet's build: Post #818
Key Features:
  • Mono construction.
  • 4-layer, gold plated, ROHS compatible circuit board. Professionally assembled in Calgary, Canada.
  • Output power: 380 W (4 ohm) -- 220 W (8 ohm).
  • Ultra-low 0.00026 % THD+N (140 W, 8 ohm, 1 kHz).
  • Ultra-low 0.00029 % THD+N (260 W, 4 ohm, 1 kHz).
  • 16 uV RMS (A-weighted, 20 dB gain, 20 Hz - 20 kHz) output noise.
  • 1 kHz + 5.5 kHz IMD <-110 dBc @ 1 W.
  • Gain: +26 dB. Changeable by resistor option. Minimum gain: +20 dB.
  • On-board EMI/RFI input filter and ESD protection.
  • Power supply agnostic circuit architecture. The Modulus-686 performs identically on an unregulated supply as it does on a well-regulated supply.
  • Board dimensions: 8.25 x 2.30 inches (approx. 210 x 60 mm)
Full set of measurements found in Post #252 and Post #254. The transient response is shown in Post #331.

Also note that the Modulus-686 can be built for lower output power by lowering the supply voltage. For example, by running the Modulus-686 on 27 V, it will provide 125 W into 8 Ω and 200 W into 4 Ω. Lower output power allows for a smaller heat sink. For a more comprehensive list of output power vs supply voltage, see Post #486.

It is always my goal to offer a positive build experience. Many businesses can deliver a good experience when all goes according to plan. In my view, examining the level of customer service when something doesn't go quite as planned is much more indicative of the quality of a business. Such an example is shown in Post #864. Note that all turned out well in the end. Also note the comparison of the Modulus-686 to a 12000 Euro (~$13600) commercially available amp towards the end of Post #864.

The Modulus-686 combines the learnings from the Modulus-86, -286, and some of the compensation tricks employed in the HP-1 to form a state of the art power amp. It is intended to operate from a +/-36 V supply and will provide the same stellar performance when powered by a switching supply as it does from a regular linear unregulated supply. A Power-86 with a 2x25 VAC, 500 VA transformer or a pair of Mean Well RPS-400-36 would work well for a mono MOD686 build. As seen in the third THD+N plot, the max output power is a little lower with the Power-86 as the rail voltage droops a little under load.

The Modulus-686 is currently available in two board options:
  • All surface mounted devices (SMD) pre-populated.
  • Fully assembled and tested amplifier module.
Update 2018/10/25: Do note that once the current board stock has sold, the SMD pre-populated option will be eliminated and I will only offer the fully assembled module option.
Unlike my past projects, I will not offer bare boards for sale. There are a couple of reasons for this:
  • Focusing on assembled and partially assembled modules allows me to lower the cost to everybody's benefit.
  • Supplying assembled and partially assembled boards allows me to serve my customers better and broaden my customer base.
  • Machine-soldered SMD boards perform much more consistently and reliably than hand soldered boards -- even for competent builders.
So basically, I can deliver a higher quality product by leaving the SMD assembly to the pros. This benefits everybody.

The full description of the Modulus-686 is available on its product description page: Neurochrome :: Modulus-686 :: 220W (8Ω); 380W (4Ω) @ 0.00026% THD+N.. A picture of the prototype is attached here.

The Modulus-686 circuit boards have arrived from the manufacturer. You can order yours here: https://www.neurochrome.com/product/modulus-686/

Thanks,

Tom
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Modulus-86, 186, 286, 286 Kit, & 686: 40-240W (8Ω) at <-120dB THD. HP-1: 3W/20Ω, -130dB THD, 128dB DNR.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right

Last edited by tomchr; 6th November 2018 at 05:31 PM.
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Old 4th February 2018, 07:36 AM   #2
soongsc is offline soongsc  Taiwan
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Great to see this higher powered model available. I look forward to getting two channels to go with the Mod86 Hope they have a similar sound impression for best compatibility.
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Old 4th February 2018, 10:54 AM   #3
Studley is offline Studley  United Kingdom
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Tom, to confirm, its $249 for 1 channel, so need to order 2, yes?

PS. Tried to order but it says no shipping options available so I can't complete the order.

Last edited by Studley; 4th February 2018 at 11:11 AM.
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Old 4th February 2018, 11:25 AM   #4
soongsc is offline soongsc  Taiwan
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Tom, what components are surface mounted? Cap? Resistors?
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Old 4th February 2018, 02:19 PM   #5
HarmonicTHD is offline HarmonicTHD  Switzerland
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Hi Tom

When reusing my Pwr86 supply, do I need bigger caps?

Will the PSSR and th CMRR similarly high as for the 286?

Given that the 686 can provide up to 33A, does the board-side output connector have to be increased in its amp spec?

Thx
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Old 4th February 2018, 02:28 PM   #6
soongsc is offline soongsc  Taiwan
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Default Modulus-686: 380W (4Ω); 220W (8Ω) Balanced Composite Power Amp with extremely low THD

Quote:
Originally Posted by soongsc View Post
Tom, what components are surface mounted? Cap? Resistors?
closer look seems to show only two caps, 6 chips, 2 inductors and 3 connectors are through hole. So it makes sense to just get the boards fully assembled. Just wondering though, lead free solder I suppose?
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Old 4th February 2018, 03:11 PM   #7
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by Studley View Post
Tom, to confirm, its $249 for 1 channel, so need to order 2, yes?
Yep. You'll need two for a stereo amp.

Quote:
Originally Posted by Studley View Post
Tried to order but it says no shipping options available so I can't complete the order.
Argh!! What a horrible time for my website to act up. I'm sorry about that. Would you try to hit Reload in your browser when you view the cart and shipping calculator? If that does not fix it, please toss me an email (tomchr@neuro...)

The "No Shipping Available" happens sometimes after I install the latest bug fixes in the various code pieces on my website, which I did just the other day. Hitting Reload will usually fix it.

Unfortunately I am not able to reproduce the issue on my end at this time. If the issue persists after you hit Reload, please let me know. It's a lot more fun to run a business when your customers can buy stuff from you.

Quote:
Originally Posted by HarmonicTHD View Post
When reusing my Pwr86 supply, do I need bigger caps?
Nope. My measurement was done with the stock Power-86 and an Antek AN-5225 transformer.

You'll need a large heat sink for the MOD686. My test heat sink is 0.4 K/W and got quite toasty (60-65 C) during the torture test of the MOD686. You might be able to squeeze by with a 3U ModuShop/DIY Audio Store Dissipante series chassis. I'd feel more comfortable with a 4U. You can see their heat sink specs here: http://www.modu.it/CARATTERISICHE_TERMICHE_DISS.pdf

Quote:
Originally Posted by HarmonicTHD View Post
Will the PSSR and th CMRR similarly high as for the 286?
It should be about the same. Maybe slightly lower, but not meaningfully so.

Quote:
Originally Posted by HarmonicTHD View Post
Given that the 686 can provide up to 33A, does the board-side output connector have to be increased in its amp spec?
33 A peak is 23 A RMS, so the output connectors should be fine even if you decide to run the full current continuously. For music reproduction you'll have plenty of margin, even if you hit the 33 A peaks...

Quote:
Originally Posted by soongsc View Post
closer look seems to show only two caps, 6 chips, 2 inductors and 3 connectors are through hole. So it makes sense to just get the boards fully assembled. Just wondering though, lead free solder I suppose?
You are correct. Two inductors, two caps, three connectors, and six LM3886es are the thru-hole components. The board is ROHS compatible, so gold plated with lead-free solder.

You can wind the output inductor yourself. I'll give instructions for how to do that in the design doc. Or you can buy the inductor from me. I had a bunch custom wound. They were definitely not cheap, but man it sure is nice with a plug-n-play solution.

Tom
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Modulus-86, 186, 286, 286 Kit, & 686: 40-240W (8Ω) at <-120dB THD. HP-1: 3W/20Ω, -130dB THD, 128dB DNR.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 4th February 2018, 04:05 PM   #8
Studley is offline Studley  United Kingdom
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Checkout now working Tom
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Old 4th February 2018, 04:21 PM   #9
tomchr is offline tomchr  Canada
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Yep. I see your order. Thank you.

Tom
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Modulus-86, 186, 286, 286 Kit, & 686: 40-240W (8Ω) at <-120dB THD. HP-1: 3W/20Ω, -130dB THD, 128dB DNR.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 5th February 2018, 02:23 AM   #10
soongsc is offline soongsc  Taiwan
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So what would be the gain for the boards? Is 26db the default? Users can change to 20db if they wish?
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Last edited by soongsc; 5th February 2018 at 02:38 AM.
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