Nope. I was looking at it the wrong way. Your drawing cleared that up. That's a very neat trick. As you said, you'll need to cut and bend the long leads on the LM3886 so they go through the holes properly, but that aside, I don't think further modifications are needed.
Yep. A neat trick. Good to know. Thanks.
Tom
For the Modulus-686, that's certainly the case. Even with the 5U (210 mm tall) ModuShop Dissipante heat sink, you'll need to run the MOD686 on ±27-28 V for it to survive with music at clipping levels in to a 4 Ω load without overheating (which I define as a heat sink temperature above 60 ºC).
Other LM3886-based circuits may be better candidates for the parallel mounting of the LM3886.
Tom
Just had a look at my unpopulated Mod86 and looks like it would or wouldn't fit by a hair. Very tight. Short legs are actually softly bended like 1/1.5mm, that depth that is OK when perpendicular to the board would convert into "height" (distance to the board) when parallel. Also, it cannot work if you don't bend the short legs "upward". Maybe other designs, but I don't think this is possible with the Modulus
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I'm going to have to retract my recommendation of the 36 V Mean Well RPS-400 for use with the Modulus-686. So far six mono blocks of Modulus-686 + Mean Well RPS-400-36(-C) have been built. In four of them, the Mean Well switchers whine audibly. The low idle current of the Modulus-686 (350-360 mA) causes the switchers to operate in burst mode, which creates a bit of mechanical vibration in supply transformer, thus resulting in a subtle but audible whine. That's not up to my quality standards, thus, I can no longer recommend using the RPS-400-36.
If you are aiming to get the full 240/360 W (8/4 Ω) output power from the Modulus-686, I recommend using a transformer-based supply, such as my Power-686 with a 2x25 VAC or 2x26 VAC transformer 650-800 VA.
I have built eight channels of Modulus-686 (four stereo amps) and powered them from the Mean Well RPS-400-27-C. I had a pair of RPS-400-27 (cage free version) powering my prototype stereo Modulus-686 as well. I have not observed this supply whine, thus, I will still recommend the RPS-400-27 for a stereo Modulus-686 for those wanting a "safe-n-sane" build delivering 130 W (8 Ω) and 200 W (4 Ω). In fact, I used three such amps to demo the LXmini+sub at Burning Amp last weekend, so my confidence in that combination is high.
Tom
If you are aiming to get the full 240/360 W (8/4 Ω) output power from the Modulus-686, I recommend using a transformer-based supply, such as my Power-686 with a 2x25 VAC or 2x26 VAC transformer 650-800 VA.
I have built eight channels of Modulus-686 (four stereo amps) and powered them from the Mean Well RPS-400-27-C. I had a pair of RPS-400-27 (cage free version) powering my prototype stereo Modulus-686 as well. I have not observed this supply whine, thus, I will still recommend the RPS-400-27 for a stereo Modulus-686 for those wanting a "safe-n-sane" build delivering 130 W (8 Ω) and 200 W (4 Ω). In fact, I used three such amps to demo the LXmini+sub at Burning Amp last weekend, so my confidence in that combination is high.
Tom
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Nothing wrong with either, really. The transformer-based supply is certainly more forgiving of momentary overload than the SMPS. The SMPS wins on size, weight (hence, shipping cost), output impedance, and often also cost, though.
Tom
Emphasis mine. I had a similar problem when using the EPP series Meanwell to power a highly-efficient class D amp.
You had the whine when you used the fan output to power an LED. No whine when the LED was not connected. Correct? Or is there more to the story?
I'm not using the fan output for anything.
With the RPS-400-27, I get zero whine. That supply works great when powering a pair of MOD686 modules. I've used ten of those supplies so far and none of them have shown any issue. Thus, I'm rather puzzled why the 36 V version does.
Tom
The RPS-400-27 and RPS-400-27-C I've used have been dead quiet. I've built four stereo amps using those supplies and they've all been quiet.
Unfortunately, the 36 V version, the RPS-400-36 (and -C) does whine, at least for some builders. So far I know of three such builds and two of them whine.
So the bottom line is that if you're building a Safe-n-Sane Modulus-686, you have the option of using the RPS-400-27 (-C). That'll require a 3U ModuShop Dissipante (or Mini Dissipante) or equivalent heat sink. You can also build a regular ±28 V supply using a transformer (2x22 VAC @ 400-500 VA) and my Power-686.
For those who aim to push the MOD686 to the limit, I recommend ±36 V from a 2x25-26 VAC @ 800 VA transformer along with a Power-686. The ModuShop Dissipante 4U would be a good chassis choice here.
Tom
Unfortunately, the 36 V version, the RPS-400-36 (and -C) does whine, at least for some builders. So far I know of three such builds and two of them whine.
So the bottom line is that if you're building a Safe-n-Sane Modulus-686, you have the option of using the RPS-400-27 (-C). That'll require a 3U ModuShop Dissipante (or Mini Dissipante) or equivalent heat sink. You can also build a regular ±28 V supply using a transformer (2x22 VAC @ 400-500 VA) and my Power-686.
For those who aim to push the MOD686 to the limit, I recommend ±36 V from a 2x25-26 VAC @ 800 VA transformer along with a Power-686. The ModuShop Dissipante 4U would be a good chassis choice here.
Tom
There seem to be two issues -- acoustic noise emitted by the supply and electrical noise that gets through the Mod-xxx amp and to the drivers (which then causes noise). It would not be surprising to me that the acoustic noise is caused by looseness of the transformer windings and so could vary from unit to unit. It would not seem that the electrical noise (either radiated or conducted) would be something that varies from unit to unit.
Of the two guys who had issues with the Mean Well RPS-400-36, one decided to go with a Power-686 and transformer instead. To the best of my knowledge, that conversion went well.
I've been working with the other guy. I shipped a couple of constant current sources that could be used as loads to him and he experimented with those. He concluded that drawing an additional 150-200 mA over the idle current of a stereo pair of Modulus-686 (= 2 x 350 mA) would completely eliminate the supply whine. The final solution will be a pair of 180-240 Ω, 25 W, heat sink mounted resistors, one connected to each supply. I don't enjoy wasting power like that, but adding those resistors will very likely eliminate the problem once and for all and will provide reliable operation. This particular builder uses very large heat sinks, so the added dissipation is not an issue.
As far as I understand it, the mechanical whine was subtle and tolerable - especially with the amp in an enclosure. Unfortunately, the supply sends out some rather nasty spikes on the supply lines in burst mode. These ended up coupling through to the amplifier output, resulting in noise in the tweeters. Again, low amplitude, but annoying nonetheless and certainly not up to my quality standards.
Meanwhile, I'm having no issues with the ten Mean Well RPS-400-27 that I've used to power stereo amps, even though they should be running deeper into burst/discontinuous mode in my setup. That's something I need to ask Mean Well about. If I had an issue, I would have picked it up during the THD vs output power sweeps (and in listening tests). The tweeters in the LXmini are quite efficient.
So, in conclusion, for those who build the Modulus-686 for ±36 V operation I recommend running a Power-686 with a suitable mains transformer (2x25-26 VAC @ 800 VA for a stereo amp; 400-500 VA for a mono block).
Those opting for a safe-n-sane build (±27 V) can consider using the RPS-400-27-C ... or the Power-686 with a 2x22 VAC @ 300-400 VA (stereo); 150-200 VA (mono).
Tom
I've been working with the other guy. I shipped a couple of constant current sources that could be used as loads to him and he experimented with those. He concluded that drawing an additional 150-200 mA over the idle current of a stereo pair of Modulus-686 (= 2 x 350 mA) would completely eliminate the supply whine. The final solution will be a pair of 180-240 Ω, 25 W, heat sink mounted resistors, one connected to each supply. I don't enjoy wasting power like that, but adding those resistors will very likely eliminate the problem once and for all and will provide reliable operation. This particular builder uses very large heat sinks, so the added dissipation is not an issue.
As far as I understand it, the mechanical whine was subtle and tolerable - especially with the amp in an enclosure. Unfortunately, the supply sends out some rather nasty spikes on the supply lines in burst mode. These ended up coupling through to the amplifier output, resulting in noise in the tweeters. Again, low amplitude, but annoying nonetheless and certainly not up to my quality standards.
Meanwhile, I'm having no issues with the ten Mean Well RPS-400-27 that I've used to power stereo amps, even though they should be running deeper into burst/discontinuous mode in my setup. That's something I need to ask Mean Well about. If I had an issue, I would have picked it up during the THD vs output power sweeps (and in listening tests). The tweeters in the LXmini are quite efficient.
So, in conclusion, for those who build the Modulus-686 for ±36 V operation I recommend running a Power-686 with a suitable mains transformer (2x25-26 VAC @ 800 VA for a stereo amp; 400-500 VA for a mono block).
Those opting for a safe-n-sane build (±27 V) can consider using the RPS-400-27-C ... or the Power-686 with a 2x22 VAC @ 300-400 VA (stereo); 150-200 VA (mono).
Tom
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Pictures of my new build
Just wanted to post a few pictures of my new Modulus-686 build.
Thanks to Tom for the great amplifier!
Dissipante 5U x 400 chassis
ISS into Power 686 with Antek 25v 600VA transformer (had it already, no need in my system for the full 800VA)
Original style mounting brackets with metal backed LM3886s.
Standard 16ga wiring, Guardian 686 boards.
All boards tested perfectly and the amp fired up first time without a hiccup.
Compared to my Modulus 86 it is just a quiet, but seems to have just that little bit more authority I was looking for.
It seems it was a good idea to go with the standard power supply in the 686, rather than the Meanwells I used in the 86 build.
Matt
Just wanted to post a few pictures of my new Modulus-686 build.
Thanks to Tom for the great amplifier!
Dissipante 5U x 400 chassis
ISS into Power 686 with Antek 25v 600VA transformer (had it already, no need in my system for the full 800VA)
Original style mounting brackets with metal backed LM3886s.
Standard 16ga wiring, Guardian 686 boards.
All boards tested perfectly and the amp fired up first time without a hiccup.
Compared to my Modulus 86 it is just a quiet, but seems to have just that little bit more authority I was looking for.
It seems it was a good idea to go with the standard power supply in the 686, rather than the Meanwells I used in the 86 build.
Matt
Attachments
Very cool. Thank you for sharing. I'm glad you like it.
Good choice. Pretty packed too. It's nice to see the full ISS+PWR686+MOD686+Guardian-686 in action. Nice touch with the mezzanine plate atop the transformer too.
If you haven't already, you might want to add a little heat shrink on the mains connections of the IEC inlet. That's a rather small detail, though. Nice build!
That's awesome. Just the way I like it.
Tom