Modulus-686: 380W (4Ω); 220W (8Ω) Balanced Composite Power Amp with extremely low THD

[tomchr]

Alright! Throwing down the gauntlet! It's a race. Who finishes first? THD or I? Stay tuned...

If I've appeared a bit stressed lately, it's because I've pushed very hard on getting a Modulus-686 build together before I head out on vacation (and Vancouver Island DIY Fest). Today, I received the last bits from Digikey, hardware from McMaster-Carr, and - more importantly - two chassis from ModuShop.

Let the building begin!

You know you're a small business owner when you geek out over packaging. I love how ModuShop packages things. Each panel is covered in shrink wrap plastic so it doesn't get scratched. Then all the panels and heat sinks are packaged together in more shrink wrap so they don't bang around inside the box. Some may argue that it's a lot of plastic, but it sure is nice to have everything arrive in pristine condition.

The chassis comes with a basic set of self-adhesive feet. They'll do the job, but I wanted something fancier, so I ordered the vibration dampening feet from ModuShop. They stand pretty tall, so we'll see how they work out. I would have preferred a basic pair of larger round feet (like the vibration dampening feet but without the height added by the rubber used for the dampening action), but it looks like I'll have to get those elsewhere if I end up not liking the vibration dampening feet.

My starting point is a ModuShop Mini Dissipante 3U x 330 x 300 mm. I went with an anonymous front panel and a fairly basic digital print on the rear panel. The print is pure white and stands out very sharp on the panel. I like it.
The rear and bottom panels are the most modified. I had ModuShop cut all the holes and thread the 3 mm holes for the mounting screws on the rear panel. I also had them add some ventilation slots on the bottom panel along with a few holes. The last hole in the bottom panel where I've sanded the anodized coating off is for the grounding lug.

The two supplies are Mean Well RPS-400-27-C and the li'l board in front is the Mean Well Control.

Tom

 

[brian92fs]

I like the speakON conneçtors. But what's the L+R connector for?

 

[drpro]

For folks with only one ear or hearing aid

 

[wcwc]

If you standardize on 4 connector Speak-ons, you could use a single speakon connector to a biamped speaker. So Tom could build 2 stereo 686’s and have a single speakon connector go to each of his Lx-minis. I was planning to wire up all my amps that way.

 

[tomchr]

If you standardize on 4 connector Speak-ons, you could use a single speakon connector to a biamped speaker. So Tom could build 2 stereo 686’s and have a single speakon connector go to each of his Lx-minis. I was planning to wire up all my amps that way.

That is precisely my plan.

Tom

 

[chris719]

" ... The Mean Well switching bricks feature the seals of approval from a plethora of international organizations, including CE, so there really shouldn't be any issue there. ..."

CE is self-certifying; ie there is no testing body or outside certification procedure. If the manufacturer says it meets CE, it does, basically, so it's not a robust certification, like, say TUV, CSA, UL, etc where the device must be tested to comply and a number is issued that can be verified by the body.

There is, of course, the so-called "China Export" CE mark, where even items that do not require CE standard compliance are marked with the CE symbol out of China. Not suggesting Meanwell is a suspect, but broadly speaking the mark alone doesn't necessarily mean anything on Asian manufactured products.

With other standards bodies requiring compliance and testing of samples of the product, counterfeit compliance marks are a problem also with some China-manufactured goods, but at least the certificate compliance number can be referenced to reveal the fake label.

I subscribe to Canada's safety and health authority eMail notifications. It's a bit of a nuisance as there are near daily recalls of one to sometimes five different products, and by far the majority of items are children's clothing (fire and choking hazards, mostly), toys, jewelry with lead or cadmium coatings, etc.

Of the remainder there are some recalls by responsible manufacturers, some label compliance recalls of imported products etc but the remainder include counterfeit CSA / ULc / cULus compliance markings on products sold by major retailers, such as electric lamps, lithium batteries improperly manufactured without the safety electronics (there's a flex PCB in every one) that create a fire hazard, etc.

Consumer Product Safety - Canada.ca

The UK, EU, USA, etc have similar programs.

What you said is true, but a quick look at PDFs shows you that Mean Well has a broad offering of supplies which are not just self certified. I am using a MW brick for another purpose but it is IEC/EN60601-1-2 certified for medical, which is not just some CE mark that is stamped on. It has to be tested to that standard. No one in medical would buy those supplies if they were unable to supply their test report or if they though it was faked.

 

[BrianL]

I believe you can pull the certification test reports off their site.

 

[tomchr]

Done! I'll post test results tomorrow.

The box is pretty densely packed, but there is enough room for everything. The completed amp weighs in at just shy of 8 kg.

As expected the feet are rather tall, so the amp sits a little proud. I think I rather like it actually. It goes well with the compact form factor of the chassis I think.

Tom

 

[supernet]

Great job Tom

Do you think 2U height of this case would be enough for pair of MOD686 boards?

 

[zman01]

Tom,

Compact and "pro" looking build - well done!

 

[ukhopeful]

The chassis comes with a basic set of self-adhesive feet. They'll do the job, but I wanted something fancier, so I ordered the vibration dampening feet from ModuShop. They stand pretty tall, so we'll see how they work out. I would have preferred a basic pair of larger round feet (like the vibration dampening feet but without the height added by the rubber used for the dampening action), but it looks like I'll have to get those elsewhere if I end up not liking the vibration dampening feet.
Tom

I used these in my 286 build:
Aluminium damping feet Black 44x17mm M4 (Unit) - Audiophonics

 

[ukhopeful]

The box is pretty densely packed, but there is enough room for everything.
Tom

Not quite Tom, you forgot the Guardian-686s

 

[HarmonicTHD]

Done! I'll post test results tomorrow.

The box is pretty densely packed, but there is enough room for everything. The completed amp weighs in at just shy of 8 kg.

As expected the feet are rather tall, so the amp sits a little proud. I think I rather like it actually. It goes well with the compact form factor of the chassis I think.

Tom

Cool. You win, I had work today to pay for all this ;-)

By the way I noticed you changed the Molex connectors from 90deg to upright. I considered the same for my built precisely due to space reasons. Could PM my the Mouser part numbers please?
Thx and good luck at the audio meeting.

 

[misterdog]

The chassis comes with a basic set of self-adhesive feet. They'll do the job, but I wanted something fancier

Hockey pucks ?

Cool build there Tom.

 

[tomchr]

Great job Tom

Thank you.

Do you think 2U height of this case would be enough for pair of MOD686 boards?

I highly doubt the heat sinks of the 2U will provide enough cooling. I'll know for sure in a few hours. I fully expect the heat sinks on the 3U chassis to reach 60 ºC with music (32-tone AP multi-tone, ~10 dB CF) at clipping with 4 Ω load.

Compact and "pro" looking build - well done!

Thank you. Yeah. I really like how it turned out. I was vacillating between the 3U Dissipante and the 3U Mini Dissipante. I'm glad I went with the Mini. I like the "power cube" look.

Tom

 

[tomchr]

Not quite Tom, you forgot the Guardian-686s

True. I did consider adding them to the rear panel (or the heat sinks), but ran out of time.

Cool. You win, I had work today to pay for all this ;-)

Meh. Work is highly overrated. Just don't go anymore.

I had to pay for all this so that I can maybe sell more boards in the future and get paid. Oh, well. I like what I do.

By the way I noticed you changed the Molex connectors from 90deg to upright.

The Molex P/Ns are: 172065-0202 and 172065-0206. There's a slightly less expensive tin plated version, but it's out of stock at Mouser. The tin plated ones are: 76829-0102 and 76829-0106. They're easy to find at the various distributors if you type in Mega-Fit and use their parametric search to narrow down the results.

The compact vertical connectors are new from Molex. They have a little locating peg that it supposed to go into a hole on the board. Well... These didn't exist when I made the footprint for the connectors on the MOD686, so the PCB does not have these holes. You'll have to cut the peg off (which is super easy) and maybe file down the stub a bit if your end cutters leave a bump.

Without the locating peg, you really have to really pay attention when you mount the connectors as if you get the orientation wrong on the power connector you will fry the board. Guaranteed! The locking tabs on the connectors face the heat sink. It's pretty obvious once you have the parts in hand, but you do have to pay attention.

Hockey pucks ?

I like using hockey pucks as a scale indicator.
I wouldn't be the first ever to use pucks as feet on equipment, though. I've seen them used as door stops as well.

I went with the ModuShop vibration dampening feet. They do the job. They even come with felt pads that you can stick to the bottom, which is nice. They just seemed a bit overwhelming when I looked at them in the bag they came in.

Tom

 

[HarmonicTHD]

Thanks for the Molex part no. I prefer the gold contacts you listed.

Once I finished the soldering I will finalize the layout before ordering the 4U Dissipantes. That will tell me where I need the upright Molex connectors.

Today after the real work ;-) I got the resistors and diodes soldered on the two ISS. Probably done before the weekend.

 

[Johnny2Bad]

What you said is true, but a quick look at PDFs shows you that Mean Well has a broad offering of supplies which are not just self certified. I am using a MW brick for another purpose but it is IEC/EN60601-1-2 certified for medical, which is not just some CE mark that is stamped on. It has to be tested to that standard. No one in medical would buy those supplies if they were unable to supply their test report or if they though it was faked.

I specifically stated that I don't have any suspicions about Meanwell. And the post I replied to mentioned CE and only CE. Other certifications are more robust, although a well respected manufacturer will also have units tested to CE compliance when they send units out for CSA, TUV, and a dozen other national standards, rather than rely on their own self-certification. But that is optional, versus other electrical standards which are mandatory, and if they so choose, it's a small additional cost when it's already five figures per model to send out for test to one of the handful of labs who can certify to (for example) TUV (Germany) compliance.

Medical Grade power supplies must meet both IEC 60601 (Global) and national standards (eg: European EN 60601-1, the U.S. ANSI/AAMI ES 60601-1, the Canadian CAN/CSA C22.2 No. 601.1, Japanese JIS T 0601-1, etc).

I felt it was relevant to address the issue, as DIY'ers are more likely than others to purchase Asian manufactured goods from the usual suspects, and CE compliance is a rather weak mark that should not be over-relied upon, especially when alone.

 

[tomchr]

Do you think 2U height of this case would be enough for pair of MOD686 boards?

At ±27 V with 4 Ω load and "music" (AP 32-tone) signal played at clipping levels, the heat sinks on the ModuShop Mini Dissipante 3U x 300 chassis reach 62 ºC with 23 ºC ambient. This is hot enough that you can't hold on for more than a second or two - so if you need to move the amp, you'll need gloves!

Thus, I stand by my recommendation of using the 3U ModuShop Mini Dissipante or Dissipante chassis.

If you're using 8 Ω loads only, you'll likely find that the 2U chassis is enough. However, I cannot with good conscience recommend that people build an amp that I know will not operate for hours with music at clipping levels with a 4 Ω load.

All that said, the MOD686 passes with flying colours.

Tom

 

[tomchr]

Anyone going to Burning Amp? You'll find me in Siegfried Linkwitz & Nelson Pass' "LX Room". My Modulus-686 amp will be used to power a pair of LXmini+sub.

https://www.magiclx521.com/epages/17940394.sf/en_GB/?ViewObjectPath=/Shops/17940394/Categories/news

Tom