Modulus-86: Composite amplifier achieving <0.0004 % THD+N.

[soongsc]

Hi Tom, what temperature coefficients are the resistors?

 

[tomchr]

The ones that matter for performance are down around 25 ppm.

Tom

 

[soongsc]

I think this is quite an interesting update. How does it sound compared with the earlier versions?

 

[sq225917]

Exactly the same, sounds like nothing, obs.

 

[sq225917]

Jesus Tom, that imd is spectacular. We'll done.

 

[yoaudio]

Hi Tom,
Are you going to do a major design update to the rest of the Modulus family, namely the Modulus-286?

 

[billshurv]

Jesus Tom, that imd is spectacular. We'll done.

I was thinking that too. Looks like the AP hit the end stops at lower frequencies.

 

[tomchr]

Jesus Tom, that imd is spectacular. We'll done.

Thank you. Yeah. The IMD is basically the noise floor of the system as far as I can tell.

Hi Tom,
Are you going to do a major design update to the rest of the Modulus family, namely the Modulus-286?

The only planned changes to the Modulus family is that the Modulus-186 will likely retire once I've sold out. I have 45 of them left.

I have no planned changes to the Modulus-286 or Modulus-686 other than remeasuring their performance with the new AP.

Tom

 

[timgrindell]

Nice one Tom
But where to buy the LM3886.............
There doesn't seem to be alotta stock available out there.
t

 

[Baobei]

I've found some at Reichelt, not sure if they deliver to NZ...

 

[timgrindell]

Thank you about Reichelt.
It seems that export in not provided.
t

 

[tomchr]

B+D Enterprises had some last I checked: B+D Enterprises - Home page

Tom

 

[wcwc]

B+D Enterprises had some last I checked: B+D Enterprises - Home page

Tom

They have a few less now. Now have enough for the Mod686.

 

[permanens]

Hi Tom. Do you have any explanation of the negative rail oscillation when clip the signal at composite amp?

Can you fix this problem with any procedure or just reduce the issue to an acceptable level?

 

[tomchr]

The LM3886 itself and any composite amplifier with the LM3886 will have some amount of rail sticking and occasionally a short-lived parasitic oscillation where it exits clipping. The clipping behaviour of the Modulus-86 is actually very clean for a composite amp. That's not just my opinion. Others have verified this and commented in this thread and/or the Modulus-86 Build Thread.

I've made the Modulus-86 as well-behaved as I can. It's stable even with 2.2 uF in parallel with 8 Ω and marginally stable with 4.7 uF || 8 Ω load.

Tom

 

[tomchr]

This is a typical example of the large-signal transient response of the Modulus-86 Rev. 3.0. 10 kHz, square wave input. 8 Ω load. No signs of oscillation or instability here.

Tom

 

[permanens]

This is a typical example of the large-signal transient response of the Modulus-86 Rev. 3.0. 10 kHz, square wave input. 8 Ω load. No signs of oscillation or instability here.

View attachment 1025259

Tom

Thank you the answer.
Ok, but the square wave not equal the clipping behaviour. Can you show me the modulus clipping level on a scope?

 

[tomchr]

I don't have the plot handy for Rev. 3.0, but here's Rev. 2.1:


Note that the rail buzz is very low in amplitude, short-lived, and only show up with hard clipping. I'm hoping my builders have the savvy to turn the music down once it sounds distorted.

I would obviously rather be without the rail buzz and I spent considerable design effort reducing it. I'm trading off performance below clipping for performance during clipping. I hope we can agree that it's desirable to have an amp that has good performance below clipping.

Unfortunately I don't have access to the internal nodes in the LM3886 so I can't turn its protection circuits off. I suspect the SPiKe protection is what's causing the rail buzz. Either that or saturation in the VAS. I don't have access to that node either.

Tom

 

[tomchr]

And now the Modulus-86 build video:

In this video I show you how to build a full stereo amp using the Neurochrome Modulus-86, Power-86, Guardian-86, and Intelligent Soft Start along with a 2x22 VAC, 200 VA power transformer and a Neurochrome Modulus Chassis.

You can find the build videos for the Modulus-86 and Power-86 here:

• Modulus-86:
• Power-86:

Tom

 

[BrianL]

Tom, kinda quiet lately and I noticed that your chassis offering is out of stock. Is this a victim of supply chain issues? Are you going to restock?