Hi
I'm a happy buyer of 2x Modulus-86 from tomchr (Neurochrome). I need advice choosing a SMPS (want to avoid touching mains) and speaker protection board (will build 8 Ohm speakers of ~87/92 db).
I was about to buy Tom's SMPS-86 as well despite not getting all the amps power (not critical I guess). But it just has a primary output and maybe the speaker protection board needs an auxiliary 12/15V. Didn't have time to investigate/ask for help so I got the boards anyway.
Now investigated just a bit on supplies and found Connex SMPS300RE which has main (to choose from +/- 24-30-36) and secondary (+/- 12-15), if I understood properly. What I can see from the pics is hazardous areas are not protected, looks weird to me. Also, which outputs should I choose for the amps?
On speaker protection I just found a board on ESP site (Rod Elliott) but I'm not sure it would be good for my amp/supply combination.
Any advice/alternative solutions on any of the two, (SMPS / speaker board) or the combination, would be welcome.
Thank you
I'm a happy buyer of 2x Modulus-86 from tomchr (Neurochrome). I need advice choosing a SMPS (want to avoid touching mains) and speaker protection board (will build 8 Ohm speakers of ~87/92 db).
I was about to buy Tom's SMPS-86 as well despite not getting all the amps power (not critical I guess). But it just has a primary output and maybe the speaker protection board needs an auxiliary 12/15V. Didn't have time to investigate/ask for help so I got the boards anyway.
Now investigated just a bit on supplies and found Connex SMPS300RE which has main (to choose from +/- 24-30-36) and secondary (+/- 12-15), if I understood properly. What I can see from the pics is hazardous areas are not protected, looks weird to me. Also, which outputs should I choose for the amps?
On speaker protection I just found a board on ESP site (Rod Elliott) but I'm not sure it would be good for my amp/supply combination.
Any advice/alternative solutions on any of the two, (SMPS / speaker board) or the combination, would be welcome.
Thank you
The Modulus-86 will perform as well on an SMPS as it does on a linear supply. For the SMPS, I recommend either my SMPS-86 or the Connex Electronic SMPS300RE. As you've noted, the MOD86 will "only" provide 28 W (8 Ω) with the SMPS-86 as the SMPS-86 is a ±24 V, 2.5 A supply. Using the SMPS300RE (get the ±30 V version) will allow you to unleash all the power of the MOD86. One SMPS300RE provides enough power for a stereo MOD86 amp intended for music reproduction.
As you've also noted, the SMPS300RE features an auxiliary supply. Whether you get the ±12 V or ±15 V version is irrelevant for the MOD86 as it doesn't use the aux supply. It could be relevant for your protection circuit, however.
I don't personally offer a protection circuit (yet), as I don't use one in my amps, but I've heard good things about Rod Elliott's (ESP) products. That's probably a good place to start.
If your goal is to not mess with the mains voltage ever, your best bet is to buy a fully assembled amplifier in a chassis. Second best would be to go with my SMPS-86 where you can solder everything to the board, put the board in a chassis, and just plug in the mains power cord. That said, the SMPS-86 does not have any shielding or other barrier to prevent your from touching the mains voltage if you get your fingers in the wrong place. That's part of the risk you accept once you take on a DIY project that plugs into the mains. The SMPS300RE is the same way. The main difference between it and my SMPS-86 (as far as the mains connections go) is that with the SMPS300RE you will need to connect a fused IEC inlet to a power switch and from there to the SMPS300RE. On my SMPS-86 I handle all those connections for you.
Tom
As you've also noted, the SMPS300RE features an auxiliary supply. Whether you get the ±12 V or ±15 V version is irrelevant for the MOD86 as it doesn't use the aux supply. It could be relevant for your protection circuit, however.
I don't personally offer a protection circuit (yet), as I don't use one in my amps, but I've heard good things about Rod Elliott's (ESP) products. That's probably a good place to start.
If your goal is to not mess with the mains voltage ever, your best bet is to buy a fully assembled amplifier in a chassis. Second best would be to go with my SMPS-86 where you can solder everything to the board, put the board in a chassis, and just plug in the mains power cord. That said, the SMPS-86 does not have any shielding or other barrier to prevent your from touching the mains voltage if you get your fingers in the wrong place. That's part of the risk you accept once you take on a DIY project that plugs into the mains. The SMPS300RE is the same way. The main difference between it and my SMPS-86 (as far as the mains connections go) is that with the SMPS300RE you will need to connect a fused IEC inlet to a power switch and from there to the SMPS300RE. On my SMPS-86 I handle all those connections for you.
Tom
That's awesome
Good. Question now is, if using underpowered supply, let's say yours or connex at ±26V, I assume less W are generated, less heat dissipated, smaller heatsink needed, right? How much would a pair of efficient speakers compensate the decrease of amp power?
Yes, I was thinking in the aux supply in case I need to power other secondary boards. Eventually. My doubt on ESP project 33 (link) is, if I understood correctly, it needs to be powered from same supply as the amp.
The power supplies (+ve and -ve) shown in these diagrams will normally be the power amp supply rails. Do not try to substitute different supplies unless you know exactly what you are doing, or the circuit may not work properly. This is especially true of the muting circuit, but incorrect supplies will (may) also affect the DC detection circuit. Like most of my projects, this is intended for experienced constructors.
That would surely affect SQ, and make the aux supply not needed. I don't know anything about speaker protection so many doubts here. Anyone knows of other options?
Well, not ever, but I'd want to avoid as much messing with mains as possible.
Yeah, actually I still haven't discarded your SMPS. The fact that it includes the fused IEC and it seems much more "closed box" than the connex, even at the expense of power. Only doubt is if I ever need an extra supply for other things.
Thank you again for all the help
Sergi
With my SMPS-86 (±24 V @ 2.5 A) you'll get 28 W into 8 Ω (voltage limited) and 28 W into 4 Ω (current limited) for a mono build.
With the Connex SMPS300RE (±24 V version) you'll get 28 W (8 Ω) and 56 W (4 Ω), both voltage limited.
With ±24 V you can use a slightly smaller heat sink on the LM3886 than you would at ±30 V regardless of the type of supply used.
If you drop 3 dB of power and increase your speaker efficiency by 3 dB, you'll end up with the same max SPL. The difference between 40 W and 28 W is: 10*log(40/28) = 1.55 dB.
There's always the risk that a protection circuit will affect the sound quality. Those types of circuits are not without issues. One issue is that relays will cause audible distortion as their contacts degrade. In the protection circuit I'm planning, I'm currently looking at using MOSFETs for the switching. Only challenge there is that I need to be able to perform the switching without degrading the performance of the MOD86, which is a tall order.
Fair enough.
That's exactly why I made it that way.
Nothing prevents you from adding a second supply in the chassis or from tapping off the ±24 V to feed a separate regulator.
Tom
That sounds good...
I want to avoid having 2 mains input, plan is to have a smallish enclosure. But I'm now realizing about feeding more stuff from same supply, I'm just stupid I didn't think about it earlier.
thank you!
You mean stereo, isn't it? In any case, one related question. If amp should output 50% more power than the speakers (is that a right value?), using your SMPS86 I should aim for speakers with around 20W RMS. Is that assumption ok?
Thank you
Just received the boards and mouser parts! Really fast! Now I just have to decide on the power and speakers.
Be very careful with power ratings for loudspeakers; there is no established method to derive the figure and speaker manufacturers vary widely in the measurement methodology, that is assuming there is any measurement methodology at all, which is a dicey assumption. Some are just figures pencilled in by the marketing department, not the engineering staff.
Generally speaking you are better off ignoring the wattage rating of loudspeakers, and seek other specifications to fulfil your needs instead. In particular the efficiency rating (expressed as xxdB 1w/1m or ~2.83v/1m) is the best reasonable indicator of how loud you can expect it to play.
Choose speakers based on their efficiency versus your power amp's capabilities and your desired listening level (maximum anticipated level). If you never clip your amp, you can use almost any speaker (within reason, some have SPL limits so don't buy a speaker that won't play as loud as you desire).
Some manufacturers give a range (eg 20~100 wpc) but this is just the efficiency and SPL or excursion limits offered in a very, very general way.
Anyone with experience with warranty work or speaker repair will tell you there are more speaker failures with 20 watt amps than 200 watt amps, and we are talking users with the same speaker.
28wRMS is a pretty reasonable power output for an amp provided the room isn't too large, to play even incrementally louder you would need to be in the 80~200 watt class. Personally, I wouldn't worry about it; just don't clip the amp and you should be fine.
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Good info, thank you. I don't think I need to clip the amp and I'm looking for "relatively" high SPL full range drivers. I don't have a big room anyway.
A stereo Modulus86 would work with ±24-30V. For the auxiliary output, still don't know, most uses would need boards working at 12-15V if I'm not mistaken, but haven't found a clear winner.
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