Modulus-86 build thread

Mrshazbot,

Good to hear that you've got both channels running, and congratulations on your successful build.

Too soon to say much about the amp other than it's dead quite and sounds super clean. I'll report back after giving it some good listening time.

The first impressions sound familiar. :) Tell us more once you have more hours of listening to the amplifier in your system.
 
I finished my build yesterday and spent the day running music through it. Very impressive Tom! Like others have said, its dead quiet with no music playing and sounds fantastic. I'm the worst at describing how things sound but I'll try. Everything sounds so clean and effortless. I think this is as close as I've been to achieving the "wire with gain". My speakers are Klipsch RP-600M's (96dB sensitivity) so the amp has an easy job driving them.

I know that building it dual mono is totally overkill but it let's me sleep better at night. Pretty sure the SMPS is happier and will probably last longer with such an easy load. Thanks again Tom for your fantastic design. If anyone reading this is on the fence about building the Mod86, just do it! It's the best amplifier I've ever had.
 

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Okay, I got it up and running.

I followed Tom's instructions to pull out the op-amps and after doing that, the problem was gone. I then put them back in and removed them one by one to isolate which one it was. After figuring that out, I figured it had to something around the opamp. From the very beginning of the build, I told myself if I made any mistake, it would be that I put one of the blue capacitors in the wrong place. They are so tiny and hard to read and therefore would be the hardest to troubleshoot. I pulled out the magnifying glass and headlamp and started inspecting each one . C6 ended up being some random capacitor that didn't match anything else in the entire build. So I would like to think that Mouser just put the wrong one in the bag but the truth is that I probably made the mistake.

After replacing it, the amp fired up perfectly.

Too soon to say much about the amp other than it's dead quite and sounds super clean. I'll report back after giving it some good listening time.

I used the 2U Dissapante and had them cut the holes on the rear panel. I created the CAD design which was a first for me and I didn't screw it up so was happy about that. I went with the larger chassis in case I ever wanted to add more channels in the future.

How was drilling the mounting holes in the riser plate/heatsinks? Building mine into a pair of 3u dissipantes, I know it's super overkill but I'm eventually going for a full LX521 build.
 
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It was really easy for me. I bought some cheap tool off amazon to drill the hole then tap the thread. So far its worked every time using M3 thread size however i question how durable this tool will be over the long run. Based on how often I need to use the tool, it works for me just fine.

Here is a picture of the exact tool I bought and the lube.
 

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Hey Tom,

I know you're against external power supplies and umbilicals, among other things because of the added impedance of the cord and subsequent decreased performance within the audio band.

I was wondering if connecting a laptop PSU (ie. 48 DCV) and once inside the enclosure creating ±24 DCV from it (floating ground?), and adding regulation would be a valid approach.

Thank you
 
The "floating" ground would be tied to the GND of the input jack(s), and hence to the GND of the signal source, which might be connected to protective earth ("mains ground"). Hence the "minus" output of the external brick would be pushed to -24V relative to mains ground. Many bricks prefer their "minus" output close to mains ground. I learned this the hard way when I thought I could used two 24 V bricks to make a power supply providing -24/0/+24 rail voltages. The brick for the negative rail was not happy.
 
Many bricks prefer their "minus" output close to mains ground. I learned this the hard way when I thought I could used two 24 V bricks to make a power supply providing -24/0/+24 rail voltages. The brick for the negative rail was not happy.

I think in some bricks the negative rail is connected to mains ground, actually. So when you connect two bricks in series you end up shorting out the negative supply. I've come across that before.

I was wondering if connecting a laptop PSU (ie. 48 DCV) and once inside the enclosure creating ±24 DCV from it (floating ground?), and adding regulation would be a valid approach.

Valid? Sure. But also very hard to do without ruining the performance, even if you do find a laptop brick or SMPS that can tolerate having its negative output floated from the mains ground. You would need to develop a ground reference that will allow significant current (say the load current) to be sourced and sunk without adding any ground bounce. That's a rather tall order.

If you want a single-supply Modulus-86, you're likely better off redesigning the circuit.

Tom
 
I think in some bricks the negative rail is connected to mains ground, actually. So when you connect two bricks in series you end up shorting out the negative supply. I've come across that before.



Valid? Sure. But also very hard to do without ruining the performance, even if you do find a laptop brick or SMPS that can tolerate having its negative output floated from the mains ground. You would need to develop a ground reference that will allow significant current (say the load current) to be sourced and sunk without adding any ground bounce. That's a rather tall order.

If you want a single-supply Modulus-86, you're likely better off redesigning the circuit.

Tom
I was thinking in a DC to Dual DC like CUI PDQE10-Q24-D24-T but obviously for higher power output. Not sure if that even exists. Is this still floating negative? I mean, given that it exists with more power (big if), and it's not floating, and we add regulation after that DC to ±DC, would that be viable without affecting the amp circuit?
Thank you!
 
I think in some bricks the negative rail is connected to mains ground, actually. So when you connect two bricks in series you end up shorting out the negative supply. I've come across that before.

The negative rail isn't directly connected to the mains ground in my bricks, but the brick was still unhappy (flashing LED, no output). I guess there is some glue logic testing (protecting) the output for (from) unwanted conditions. I did what must not be done, and the brick wasn't unhappy anymore.
 
Not sure if that even exists.

The Mean Mell IRM-60 series I use in the SMPS-86 perform very well. Their main drawback is that their 2.5 A current limit, which limits the output power to 28 W (4 Ω). The voltage limits the output power to 28 W into 8 Ω, but that's usually not surprising. It provides plenty of power for a desktop system, and I've used it in a living room setting as well. But some find it too easy to drive the supply past its limits, which causes the supply to turn off.

Is this still floating negative?

That would depend on the design of the particular power brick. Class II devices should be able to tolerate being connected in series. They may not all perform well that way, though. That's a question for the applications engineers at the manufacturer you choose.

The negative rail isn't directly connected to the mains ground in my bricks, but the brick was still unhappy (flashing LED, no output).

Whacky!

Tom
 
The Mean Mell IRM-60 series I use in the SMPS-86 perform very well. Their main drawback is that their 2.5 A current limit, which limits the output power to 28 W (4 Ω). The voltage limits the output power to 28 W into 8 Ω, but that's usually not surprising.

Yes, and I'm 99% sure I'll end up using the SMPS86, but the question was if plugging DC to the chassis was feasible somehow, to avoid main at all costs. I think that's why I posted a DC to dual DC converter in my latest post link. Obviously not sure if we're comparing apples to apples (power ratings aside) with the floating neg/ground.
 
Yes, and I'm 99% sure I'll end up using the SMPS86, but the question was if plugging DC to the chassis was feasible somehow, to avoid main at all costs.

DC to the chassis is not a good idea. You never know exactly how the rest of your system will deal with that - unless you build everything yourself and go through the schematics and design process.

I think that's why I posted a DC to dual DC converter in my latest post link. Obviously not sure if we're comparing apples to apples (power ratings aside) with the floating neg/ground.

I did click the link, but missed the fact that it was a dual supply. My bad. Yes, something like that is exactly what you want. You'll want higher power, of course.

I have yet to find a dual SMPS that's suitable for the Modulus-series. Many dual supplies have a strong positive supply, and a trickle current negative supply. So you'll see, say +24 V @ 5 A, -24 V @ 250mA and that kind of stuff. Those are not useful. You need preferably 5-6 A capability on both the positive and the negative output.

If you do find something that you think is a good fit, please post a link. I'd be very interested.

Tom
 
I did click the link, but missed the fact that it was a dual supply. My bad. Yes, something like that is exactly what you want. You'll want higher power, of course.
no problemo man, my fault not being able to express as well.

I have yet to find a dual SMPS that's suitable for the Modulus-series. Many dual supplies have a strong positive supply, and a trickle current negative supply. So you'll see, say +24 V @ 5 A, -24 V @ 250mA and that kind of stuff. Those are not useful. You need preferably 5-6 A capability on both the positive and the negative output.
ah, good point there

If you do find something that you think is a good fit, please post a link. I'd be very interested.

Tom
awesome! I think i found smth in mouser around $700/800, but looking for more consumer not pro
 
Yeah. The best I've found so far is the Mean Well RPS-series. I've used the RPS-400-27-C with the Modulus-686 with good results. Results with the RPS-400-36-C (36 V version) have been mixed. Some have reported that the SMPS made audible noise (mechanical vibration/noise). So your milage may vary.

I keep drooling over a pair of RPS-200-27-C for powering a stereo MOD86 amp. I should try those at some point.

Tom