Modulus-86 build thread

Hello Tom ;

I am using Toroidal transformer + Power - 86 for my mod-86 amplifier atm. I am planing to replaced Power - 86 with APEX regulated psu. (Pls see attached file)

I guess psu noise will be lower. Can i expect to get better THD+N?

I quote, from one of Tom’s original Modulus 86 design manuals:

The power supply rejection ratio of the Modulus-86 amplifier is truly excellent. Hence, the Modulus-86 performs as well on an unregulated supply as it does on a regulated supply. This is one of the benefits of the composite amplifier topology. The only advantage of using a regulated supply with the Modulus-86 is that the peak output power will be a few watt higher, as the regulated supply will experience less voltage droop as the load current is increased.

This is DIY, and of course you are allowed to experiment. But given the design topology of the Modulus series of amplifiers, I would spend time streaming more music and understanding that music has a crest factor and we as humans don’t typically listen to sine waves ;-)

Thanks Anand for fast response;

I read that part before. As you know power-86 is only bulk C capacitors but also in the power 686 section of the manual mentioned as here below;

"Option for C-only and CRC snubbers included for the advanced builders." I want to be advanced :) I can use CRC or CRC+ CAP MULT or regulator etc.. If it make sense for sure in the means of distortion performance.

I am asking this to Tom because i do not have the measurement equipments to evaluate. Real world performances of these variations.

Things can change by the time;

In the same section;
He mentioned about RC snubber in power 686
"RC snubber to eliminate coupling of diode switching noise into sensitive circuits."

But in contrast;
"As expected, the snubbers made no difference in the output ripple and noise of the power supply. Thus, it is rather irrational to expect it to change the output of the amplifier through the power supply"

It seems snubbers are not effects amplifier as more sensitive DAC circuits.
So i wish we can have a chance to see the different power supply performance as we saw for the sunubbers.
The Modulus amps are power supply agnostic. They really don't care if the supply is regulated or not. What you will get from the APEX supply when used with the Modulus amps is:
  • Increased heat dissipation
  • Increased cost
  • Increased circuit complexity -> lower reliability
  • Lower max output power (due to the drop-out voltage of the regulator)
The THD+N or output noise of the amp won't budge.

If you're fine with these drawbacks there's no harm in trying.

Note, though, that LM3886 amps without the Modulus error correction would likely benefit from a regulated supply. This includes the LM3886DR.

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Hello Tom;

Mostly on discrate design i used to connect speaker ground to end of psu pcb zero volt point. Thats why i use my modulus in this way and its works like a charm at the end all goes to chasis star point but at the same time i wonder if "gnd spk out" on modulus pcb has less noisier than my current setup. Or you just put it for easy installation?

Thanks in advance....
This would likely help quite a few people:

It's just a "short" (11 minutes) video on basic amplifier testing using a newly built Modulus-86 as an example.

That's great. Such a helpful and informative video - explained to me why my multimeter AC measurement are so off the wall and also shows how to use the multimeter without the need for the bench AC voltmeter for just some quick and cheerful measurements. Just out of interest @tomchr - that DC offset is really low. Does that amp have DC servo or some such?