• The Vendor's Bazaar forum is for commercial offers and transactions. Only unmoderated members can post here.

    diyAudio provides this forum for the convenience of our members, but makes no warranty nor assumes any responsibility. We do not vet any members. Use of this facility is at your own risk. Customers can post any issues in those threads as long as it is done in a civil manner. All diyAudio rules about conduct apply and will be enforced.

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

Jump to Latest
#2,488
sq225917 said:
Jesus Tom, that imd is spectacular. We'll done.
Click to expand...
Thank you. Yeah. The IMD is basically the noise floor of the system as far as I can tell.

yoaudio said:
Hi Tom,
Are you going to do a major design update to the rest of the Modulus family, namely the Modulus-286?
Click to expand...

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
 
#2,495
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
 
#2,496
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.

Modulus-86 Rev. 3.0_ Transient Response (8 ohm).png


Tom
 
#2,498
I don't have the plot handy for Rev. 3.0, but here's Rev. 2.1:
MOD86_R2p1_Clipping.jpg

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
 
  • Like
Reactions: permanens
#2,499
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
 
  • Like
Reactions: xschop, ricyuyc and YashN
You must log in or register to reply here.
Top Bottom