Mod-286 build thread

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.... almost done just the inductors and the connectors. Mouser has this female connector for the power connection to the board on backorder and didn't deliver the two parts to me. Anyone having an idea for an alternative?

The male connector (see pic) I have.
 

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Looks workmanlike Harmonic...I must say that once we cross the SMD threshold my days of diyAudio as hobby are over. I've done one simple repair on an SMD board - while my LED lit magnifying goggles did a good job of compensating for presbyopia they were of little help in holding my middle-60's hands nearly steady enough to reliably stay on the target joint. Enjoy it while you are young!
 
:). I am hitting fifty next year so I need to hurry :)

Took about 15 hours total and a hurting back to complete. Now I am ready to mount some hearsinks for testing and get the LM3886s in. If all tests ok I need to order some housings.

As for the inductors, I didn't hit quite the specified value (ca. 8-9% below). despite following the instructions closely. At least, they were all within 3% of one another. Of course, it could also be that my cheap tester isn't too accurate. What do you guys think - close enough or should I redo them?
 

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.... almost done just the inductors and the connectors. Mouser has this female connector for the power connection to the board on backorder and didn't deliver the two parts to me. Anyone having an idea for an alternative?

Mouser is out of stock with an expected delivery date of August 21st. Digikey has it in stock. I'm about to place an order with Digikey. Let me know via email if you'd like me to get a pair for you and mail them.

As for the inductors, I didn't hit quite the specified value (ca. 8-9% below). despite following the instructions closely.

You're fine. The value isn't super critical.

Looks workmanlike Harmonic...I must say that once we cross the SMD threshold my days of diyAudio as hobby are over.

I do agree that the days of leaded parts are probably numbered. Many of the more exciting parts are now SMD only - and small SMD at that.
That said, I can see the DIY audio field drift in the direction of various vendors providing preassembled modules or partially assembled modules that you then buy and put in a box customized to your liking.

Tom
 
Phew. I am on a roll today. :)

:). First hot test of the first board. Magic smoke still inside. Output offset measured with the shortened input pins. 0.00mV. :).

Now some barbecue... and possibly the 400Hz test later. Wish me luck and certainly a healthy appetite.
 

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Thanks bud.

Ah. No more 400Hz test today.... I am tired. Besides I am not 100% certain how to hook up the function generator to the input and before I mess something up I better think twice about it.

Do I hook up the minus from the function generator to pin 1 & 3 and the plus to pin 2? Or do I leave pin 1 (gnd) floating?
 
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Tom you got mail. I appreciate it. Thx.

So I see. I'll get with Digikey shortly and keep you posted via email.

... again some progress.... now mounted some heatsinks for testing only. There probably too small and I haven't applied any thermal paste yet either.

Nice progress. Yeah. The heat sink is too small for actual use but fine for testing. Scrap the nylon screws, though. Nylon will stretch and result in a poor thermal connection between the IC and the heat sink over time. This will cause an increase in THD. Just use regular metal machine screws. The IC package is isolated so you don't have to worry about short circuits there.

Do I hook up the minus from the function generator to pin 1 & 3 and the plus to pin 2?

Yep. Exactly like that. Unless your function generator has balanced out (which few of them do). If your function generator has a 50 Ω output, I recommend terminating the cable into 50 Ω (so connect 50 Ω - or 49.9 Ω - from pin 1+3 to pin 2 on the MOD286 input). The termination isn't so critical with sine wave testing, but should you decide to try a square wave, you'll need the termination.

Tom
 
Actually, Andrew, the terms "biamping", "triamping", etc., have been in common use in the USA for at least 40 years (especially in pro audio circles where it began) to refer to what you are calling an "active loudspeaker" -- a system with a line-level crossover that separates the incoming signal into band-limited signals to drive separate amplifiers that drive each particular driver (woofer, mid, tweeter, etc.)

Though not common, 'high end' speakers were 'biamplified' and 'triamplified" even in the early '70s. Bozak sold at least one crossover for biamping their Concert Grand and Symphony systems, one amp to the woofer and the other amp to the mid/tweeter (passive LC between them). The Magnepan Tympany IIIa was biamped with a separate amp driving the low frequency panels and another amp doing the mid/tweet panels; those really in the know had a 3-way line-level crossover and separate amps for each. Audio Research sold a number of crossovers for the various early Magneplanar systems. Google will lead you to documentation for a number of these crossovers and you can see that the terms 'biamping' (or 'bi-amping') and triamping were used in the way I described.

From what I have observed, the term "active loudspeaker" generally refers to a system where all the electronics are integrated into the speaker 'box' (mains voltage and line-level (or digital) in --- sound out). The earliest example I know of was a Philips speaker that these days would be classified as a 'mini-monitor' similar in size to a BBC LS3/5. Where you draw the terminology line of demarcation between a fully integrated box and the same stuff with electronics in a separate box(es).

The confusion began when people in high end audio started using the term "biamping" to refer to the odd practice of using two full-range amplifiers to drive one speaker whose passive speaker-level crossover could be separated into low-pass and high-pass sections, each with their own terminals. Unfortunately the audiophile world knew little of the original, correct, use of the term which had been in common use in the audio workd for decades at that point; hence the confusion. Those trying to be less confusing tend to refer to this as "passive biamping".
 
Guys, thanks for the hints.

So.... yes yes yes... it plays music.... hurray.

The 400Hz test went as expected. I put in a 0.1Vpp signal and as expected, out came 1V. Remember I built the Mod286 in its 20dB (10x) gain version, not in the standard 26dB (20x) version. The best part, the DC output offset remained always at 0.00mV - great.

After that I connected an old JBL desktop speaker and switched it on again. No plop. Absolute silence. Then I hooked up an old MP3 player and voila --- it works. The music comes out great as far one can judge from the MP3 and the old and small speaker. I cranked it up all the way ... all good and clean and no distortions - just as expected :)))))

After a long day yesterday, I might check the second board tonight, will see. Cross the fingers, that it also works as great as the first board.
 
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did you examine the output on an oscilloscope? Did you look at variations in overshoot when you change loadings?
Did the overshoot get any worse when a variety of low value capacitors were added across the loads?
Did the ringing if any get damped quickly?

After all that is done, try repeatedly doing a cold start and recheck the output noise and output offset.

Then add on a disposable speaker to listen to the output.
 
"A variety of low value capacitors"? What do you consider low value? And how quick is "quickly"?

The plots are eluding me at the moment but here's the synopsis: The MOD286 shows a clean square wave up to about 8 Ω || 100 nF. At 220 nF you'll start seeing some degradation of the edge. At 470 nF you'll get a slight and well-damped overshoot. At 1.0 uF the overshoot gets a little worse but damps out within a half cycle as I recall. 2.2 uF results in pretty serious overshoot that takes more than a cycle to die down. Don't go there. 4.7 uF will make the amplifier oscillate. Definitely don't go there.

For capacitive load testing, I test at a minimum of three points per decade (1.0, 2.2, 4.7) from 1.0 nF to 1.0 uF to make sure I don't have any holes in the stability test coverage. For my headphone amp I extended the test down to 47 pF.

Tom
 
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Hey guys. I didn't do these tests, as I am not even sure how to conduct those. I just followed the final checklists in the Mid286 manual and after passing, hooked up the old (dispensable) speaker. And tata it worked. Meanwhile I did the same with the second board and it worked too right of the bat. :))) I am very happy that everything went without a glitch.

As for the tests described by you I am not sure either if the "oscilloscope" which I have is even capable. It's a cheap digital thing for some 150 bucks. I was just able to do the 400Hz sine test and see that the output is roughly the 1V and therefore about 10 times the input amplitude.

What do you think should I give it a try and do these tests or do you think if the music sounds well, that everything else is a ok?
 
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I've done the tests for you during my prototyping. That's one of the many things you get when you buy my products. You get stuff that actually works out of the box and has been thoroughly tested. This allows you to build with confidence. Confidence. That's what I sell.

If you have assembled the board according to the BOM, measure < 1 mV of output offset, the amp has the expected gain, and it sounds great in your test speaker, I'd say you have a successful build. Enjoy the music.

If you want to admire the technical performance of the amp, press on with the tests that Andrew suggested. They are by no means required, though.

Tom
 
Sounds great. For now I will focus on the next step and choose some cabinets. I might come back to those tests once I've got everything else done, just out of interest if I can learn something from it.

Regarding cabinets. I am going for the Modushop Dissipante 3u. I am thinking that might give me enough room if I ever wanted to upgrade to the announced stronger Neurochrome amp. Tom can you tell already if the heatsinks on the big Dissipante will also handle your new project - just in case?
 
Yes for the 3U with 400mm depth two!! heatsinks per side measuring 200 x 120 x 40mm are included whereas for the 300mm depth version one heatsink per side of 300 x 120 x 40mm is built in. Tom, did you mean one can get 200w across one or two heatsinks of 200mm length?

Also does anyone have experience with the optional inner baseplate for these cabinets? Seems to me they would provide some 5-10mm standoff from the outer baseplate, which could make mounting of the internal components more convenient.

Thx.
 
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