Can it be done? Yes.
Can it be done by swapping components? No.
Image below shows a Modulus-86 Rev. 1.0 board fitted with the Rev. 2.0 servo. It's definitely possible to do, but I will definitely not recommend it as a production solution or support it.
If you would like a Parallel-86 type amp with the new DC servo, I suggest looking at the Modulus-286 MONO. I have two assembled boards left. Gain matched to within ±0.0075 dB. The pair is on sale for $599 (normal price is $400/each, so $800/pair).
Tom
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If someone wanted to pursue this (knowing its not a supported modification), would the general approach be a sister board with the relay circuit mounted as close as possible to the resistor its replacing using header pins & sockets (or something like this)? Similar to the DC servo mod picture you posted in post #123. Or would that still be creating to large of a loop area?
Thanks!The promised measurements attached. The output voltage is in blue and indicated on the left vertical axis. The supply voltage is in red and plotted against the right vertical axis. The horizontal axis is time in seconds (10-second span). The supply was turned on/off at the 2-second mark. I did this by hand, so my reaction time is included here as well.
The startup and shutdown transients are a few mV for the Modulus-686 prototype. I think it's fair to say that the Modulus-686 starts up and powers down without any audible clicks or pops.
You get a little more of a turn-off transient with the lab supply as it discharges faster when it's turned off. The softer response of the Power-86 and Antek transformer is a bit gentler on the output transient.
Note that we're pretty far down in voltage here. We're talking a few millivolt of pop, max. The 800 uV output offset voltage provides a nice sense of scale.
I did measure the Modulus-86 Rev. 2.01 for comparison. The turn-on transient of the Modulus-686 is ~30x better than that of the Modulus-86 Rev. 2.0, which is ~2.5x better than Modulus-86 Rev. 1.0.
Told ya I was learnin' an' improvin'...
Tom
So 3mV max, that is lower than the DC offset I typically get from my nc400 (specified at 50mV max, but typically around 10 to 20mV on the ones I measured IIRC).
So if I follow your graphs I better use a SMPS for power on and a linear power supply for power off
POS: don't hesitate. I used Ncore 400 monoblocks to drive the CDs on my M2s but then I made a pair of Parallel 86 monoblocks in bridged mode to drive the CDs. The P86s are even more transparent and neutral than the Ncores. The Ncores were relegated to the woofers. I've ordered the 686 PCBs and they will replace the Ncores on the woofers
I have a pair of mudushop mini dissipante (3U, 300mm, 250mm internal width) that I planned to use to install my 4 nc400 + SMPS1200, but now I wonder if that would not be an almost perfect fit for the 686...
Hey, if I use the 686 for the HF then maybe I should use a bridged pair of nc400 per side for good measure
Oh, I just connected the dots, iansr!
It is coming along slowly, but the results are encouraging!
A daughter board would be the least sucky way short of implementing the change on the circuit board.
A better way would be to put the additional gain in the preamp.
Tom
I have a pair of mudushop mini dissipante (3U, 300mm, 250mm internal width) that I planned to use to install my 4 nc400 + SMPS1200, but now I wonder if that would not be an almost perfect fit for the 686...
Hey, if I use the 686 for the HF then maybe I should use a bridged pair of nc400 per side for good measure
You can find the heat sink requirements for the MOD686 in Post #66. Contrast that with the information you get from Modushop. I think you'll find the Mini Dissipante to be a bit skimpy in the heat sink department. The regular 3U Dissipante would be a better choice.
That said, as I point out in Post #66, you could use the Mini Dissipante with a thermal switch to turn the amp off if it should ever get too hot.
I'm not quite sure what you're referring to here. The THD+N of the MOD686 is a bit lower than that of the MOD86. Make sure you are comparing the THD+N for the same load impedance as the THD does go up a bit with 4 Ω load (higher output current -> higher THD).
The THD at 1 W, 8 Ω for the MOD686 is currently spec'ed at ~2x the THD of the MOD86 at 1 W, 8 Ω. I was having some issues with my precision oscillator, so odds are the number for the MOD686 will improve once I get those issues resolved.
I don't know where you see 4-5x.
No, but if you like cranking the tunes and have somewhat inefficient speakers, it doesn't take much to exceed the power envelope of the MOD86 on the peaks. The MOD686 sounds better under those conditions.
Tom
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Hi Tom,
I did notice the Mod286 unpopulated and stereo versions are gone from the website. So does that mean that you are sunsetting the Mod286?
I know the Mod86 will go away when the LME49710s run out.
I've thought long and hard about what to do with the Modulus-286. Most build it as a mono amp, but at a build cost of about $250 the Modulus-286 is honestly too expensive, especially with the Modulus-686 in town. It is also not set up well for automated assembly and as I've pointed out earlier, I can deliver a much better product if I leave the assembly to the pros.
I plan to offer the following Modulus amps long-term:
- Modulus-86: Thru-hole only for those who want to build from scratch.
- Modulus-286 (MONO): SMD pre-populated and finished module.
- Modulus-686: SMD pre-populated and finished module.
So basically the sun has set on the stereo version of the Modulus-286. The mono version will be on sabbatical once the two remaining modules sell. I'll see if I can bring to market a Modulus-286 Rev. 2.0 (mono only) at a competitive price point. If I can't make the costs work, the sun will set on the Modulus-286 and I'll offer just the MOD86 and MOD686.
The current price on the remaining pair of Modulus-286 amps is where I hope to land with the fully assembled version of the Modulus-286 Rev. 2.0. I'm willing to trade off a little bit of performance in exchange for the lower cost. Just saying...
For the Modulus-86, I will either provide the LME49710NA or redesign the amp to use the LME49720NA, which is still in production.
Tom
Sorry I just looked at the bottom line figures of
Ultra-low 0.00026 % THD+N (140 W, 8 ohm, 1 kHz) for the 686 and 0.000061% for the 68, but these are obviously under different conditions.
If I look at the THD+N at 1W into 8R:
Mod 86 ~ 0.0015
686 ~ 0.0008 (both at 20dB gain)
So the 686 seems to be 2X lower.
Thanks for the comments on the sound.
I don't have a regular dissipante to compare but it looks like the heatsinks are the same for identical dimensions, and their dissipation figures also look identical.
They're different measurements. For the Modulus-686, it's THD+N. For the Modulus-86 it's THD (no +N). I haven't measured the THD (no +N) of the Modulus-686 yet as I'm having issues with my precision oscillator (Victor's oscillator that you can find floating around on the 'net).
Tom
35 um. The output pour is as wide as practically possible (about half the board width in many spots) and pretty short. On top of that, the layout is made in such a way that the output pour is inside the feedback loop, hence the loop gain of the amp (which is astronomical) will compensate for any voltage drop across the output pour. The only items outside the feedback loop are the output inductor and the output connector.
Often it pays to work smarter rather than harder.
Tom
Often it pays to work smarter rather than harder.
Tom