Modulus-86 build thread

Probably about 175 W into 8 Ω. With the linear supply, the rail voltage does droop a bit at the higher output power, so you won't quite make it to 200 W.

Math says 330 VA is enough for 4 Ω for music reproduction. I'd need to measure the output power in that case to give a number.

Boy... I really need to get off the pot and start that MOD686 vendor thread. Stay tuned.

Tom
 
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Having the power needs discussion here is good. Means I can wind up Tom for all his posts about NOT needing huge power :D.

Did look again at ROM figures for how much power the next evolution of my speakers will need. I was going to have a stack of 4 faital pro 6FE100 open baffle on each side. A solid 90dB/w over the range I am using them, so 4 gives equivalent of 96dB/w. Rickie lee jones 'ghetto of my mind' at an average of 85dB* would need a massive 25w to handle the peaks with this setup. Roll in the EQ I would need between 120 and 80Hz to deal with the baffle and we would be knocking on the door of 100W. A 286 per side on bass duty driving a paralleled pair of drivers would be just about perfect for that. And much louder that I am normally allowed to listen at.

*The dimensions of the room mean that, for a first approximation, 85dBa out of each speaker equates to 85dBa at listening position.
 
Probably about 175 W into 8 Ω. With the linear supply, the rail voltage does droop a bit at the higher output power, so you won't quite make it to 200 W.

Math says 330 VA is enough for 4 Ω for music reproduction. I'd need to measure the output power in that case to give a number.

Boy... I really need to get off the pot and start that MOD686 vendor thread. Stay tuned.

Tom

Do you have any power supply recommendations for the 686?
 
±36 V SMPS if you want to break 200 W. Two Mean Well RPS-400-36 may be the ticket. I think that's what I'll try for a mono build. I'm currently using two RS-600-36 for the testing. Those are great in the lab but their fans are super loud. The RPS-400-series does not have a fan.

2x25 VAC @ 350-500 VA feeding a Power-86 will max out around 175 W as I recall.

Tom
 
Having the power needs discussion here is good. Means I can wind up Tom for all his posts about NOT needing huge power :D.

Well. Don't forget that for quite a while I was arguing that the BPA topology was morally inferior. That's another of my chains that you can yank... :)

I'd still argue that the applications engineers at National missed the mark with the BPA200. It's not bad, but could be improved. It will drive an 8 Ω load just fine but will run out of steam with a 4 Ω load. If you want to drive a 4 Ω load, you really need to use six LM3886es. You can see my rationale here: Taming the LM3886 - Output Power.
There's also an interesting little quirk in the BPA200 design. If the negative supply starts up before the positive, the amp will latch up. It will draw a lot of current for a few seconds until it recovers and starts up. With a current limited supply, that's no big deal, but with two SMPSes with different startup times capable of delivering 16+ A, that could mean trouble. In most implementations you'd never notice. I found it by coincidence in the lab. That's why the final version of the Modulus-686 board contains a few extra components to make sure that the amp is shut down if the imbalance between the positive and negative supply is greater than 4-5 V.

Of course, I then went ahead and took the BPA topology to a whole new performance level with the differential composite topology. I've attached the block diagram of the '686 so you can see what the topology looks like.

Tom
 

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Probably about 175 W into 8 Ω. With the linear supply, the rail voltage does droop a bit at the higher output power, so you won't quite make it to 200 W.

Math says 330 VA is enough for 4 Ω for music reproduction. I'd need to measure the output power in that case to give a number.

Boy... I really need to get off the pot and start that MOD686 vendor thread. Stay tuned.

Tom

Thanks that will do with my current speakers.

What if I would upgrade my speakers let’s say to these ones
KEF Reference 5 loudspeaker Measurements | Stereophile.com
with a impendance of 4 over a wide range and dropping down to 3ohms. Would a 686 be able to handle this with the right powersupply?
How many amps can the 686 supply? I remember a single LM3886 is around 7 to 11A?
 
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±36 V SMPS if you want to break 200 W. Two Mean Well RPS-400-36 may be the ticket. I think that's what I'll try for a mono build. I'm currently using two RS-600-36 for the testing. Those are great in the lab but their fans are super loud. The RPS-400-series does not have a fan.

2x25 VAC @ 350-500 VA feeding a Power-86 will max out around 175 W as I recall.

Tom

Tom
The received wisdom is that SMPS' are bad news for audio applications because they spray lots of noise inducing radiation around. By implication it seems like you have a different view?
 
The received wisdom is that SMPS' are bad news for audio applications because they spray lots of noise inducing radiation around.

That was probably true back in the 1970ies or 1980ies when the switching supplies were these fancy new things made with leaded components and their associated large loop areas (think large radiating antennae). Modern supplies use SMD components for a number of reasons, including smaller size and, thus, lower loop areas and lower emissions. Circuit designers understand the EMI problem a lot better now and are designing the circuits to be as gentle on the surrounding environment as possible. Modern supplies are also subject to a range of regulations regarding emissions, both those conducted back onto the mains and those emitted to surrounding circuitry.

The Mean Well RPS-400-36 that I am thinking to recommend for the MOD686 is a medical switcher which meets a wide range of EMI standards and safety standards. If it's good enough for life-saving equipment, I'm thinking it's good enough for your audio amplifier... :)
Note that the signals measured for EKG and EEG, for example, are in the uV range. Those systems would be much more sensitive to any supply-related EMI and the medical switchers work fine there.

Also note that the performance plots I've shown so far have all been measured with an SMPS. I am seeing the same performance with a Power-86 and an Antek AN-5225 power transformer, except the max output power is about 175 W rather than the 220 W you get with the SMPS. That's due to the rail voltage droop of the linear supply.
My measurements are done on the lab bench. I don't do anything special to keep the setup shielded, so what you see is about worst case for EMI.

Now, I'm not saying that all SMPSes are created equal. I definitely encourage you to read the data sheets before buying.

Not in my experience. We could compare data though. I went through the process of necessary for certification using switching supply. The efficiency actually is a plus.

I agree. The cost tends to be lower too. The exception to this is in the US, where the low-cost Antek transformers tend to make the linear supplies slightly less expensive than a comparable SMPS. International builders will likely find the SMPSes to be lower cost. Many SMPSes have auto-sensing inputs and are compatible with the mains voltages world wide. That greatly simplifies the mains wiring.
The RPS-400-series from Mean Well takes this a step further by offering a +5 V standby voltage and low-voltage power-on. It would be trivial to design a small board that would allow for low-voltage switching of the supply. This would mean that the builder would connect the mains voltage from the IEC inlet to the SMPS and that's it. All other wiring is handled on the low-voltage side.

Note that the RPS-400 comes in a 27 V flavour as well. You can dial it up to 28 V. That's perfect for a Modulus-86.

Tom
 
OK sorry, my mistake, fans are optional, only TF/-SF series come with fans installed.

Correct. Also note that the "400 W" RPS-400-series will only deliver 400 W when fan cooled. At natural convection, it becomes a 250 W supply. I'm thinking that for audio use, that's just fine, though. Due to the crest factor of music, a fan will not be needed.

Thanks for that Tom. Think I'll give the SMPS a go. You once advised me that it was a bad idea to put a power amps linear PS in a separate enclosure. Does that also apply to a SMPS?

Yep. The problem with umbilical cords is the added impedance of the cord and the pulse currents flowing in the cord. The cord is the problem. Not the supply feeding the cord.

Tom
 
Modulus-686 Vendor Thread: http://www.diyaudio.com/forums/vend...-power-amp-extremely-low-thd.html#post5330257
Let's continue the MOD686-related discussions there.

I've updated my website to include the MOD686 as well: Neurochrome :: Modulus-686 :: 220W (8Ω); 380W (4Ω) @ 0.00026% THD+N.
I will flesh out the page some more once the first samples of the professionally assembled boards arrive.

...and am now accepting pre-orders: Modulus-686 Order Page

I'm trying a new measurement: 1 kHz + 5.5 kHz IMD. Siegfried Linkwitz seems to advocate for this measurement as in his experience it correlates especially well with the perceived listening experience. It is worth noting that the MOD686 performs 20-30 dB better than the best amps listed on his website: Amplifier Distortion
Note: I used 917 Hz + 5.5 kHz due to a limitation in the APx525 signal source.

Thanks,

Tom
 

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I'm trying a new measurement: 1 kHz + 5.5 kHz IMD. Siegfried Linkwitz seems to advocate for this measurement as in his experience it correlates especially well with the perceived listening experience. It is worth noting that the MOD686 performs 20-30 dB better than the best amps listed on his website: Amplifier Distortion
FYI, Linkwitz added a couple more to the LXMini's Amp page, but the 686 still beats them all. VERY impressive results, Tom!

People who are skeptical about SMPS perfomance, please note that the ATI Ncore's performance there seems to be limited by its linear power supply.
 
I had listened to the LXmini’s in Sea Ranch. Sounded a bit harsh and fatiguing, Siegfried attributes it to the cheap electronics. The larger system sounded more closer to my normally listening but with better bass performance. I am planning to get the MiniDSP 2x4HD this year, but using FIR filters to linearize the phase.
 
My modulus86

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Dear diyaudio friends
Finally i finish my modulus86. Firstly i would like to thanks toTom.
I buy pcb andi start. You know all process. I use all inner cables OCC. Signal lines and speaker lines are furutech alpha series occ.. dc voltage and 220vac line cables are elecaudio 2.5mm wire... my input connectors are neutrik xlr, my binding posts are WBT cu/gold. Transformers hammond 120VA 2x22vac. I made soft start with emi filter and speaker delay. My amp is dual mono L and R channel gnd not connect each other. I like dual mono desing ;)... my dac is es9028pro and it has on iv ad797 (diyinhk board and dimitris software) my player cubox i 4x4 and volumio. My speaker are sonus faber venere 2.5 and all cables are furutech alpha series occ (xlr,speakerand power chords and usb). My dac and modulus86 are so much good couple. They are amazing...my friends and i are schock, so much clear and transparent sound detail and vision perfect.. we dont want stop music. Thanks everyone:)