The MONGREL (supersym II)

[ostripper]

I used KT's tricks to get my -180DB noise floor and I'm glad I did.

Below plots are so far beyond the blameless or it's UDL clone that Wahib MUST simulate this one. .000032% and -150 H5/7/9 (or better at 1K) ...what the heck!! The only bad thing is that H3 is dominant as compared to H2.

Gonna build this one.. HAVE to!!
OS

[keantoken]

OS, many popular amps have the dominant H3 characteristic. In LTP amps anyways, the dominant H2 criteria can be difficult because H2 will dodge around depending sheerly on the Hfe variance of the outputs, matching of dual VAS (singleton VAS eliminates this mechanism, albeit at some expense), etc. For consistently dominant H2 there needs to be a non-symmetrical stage somewhere.

I am very impressed with this amp's performance. I will simulate the cascaded differential.

Will you try my method for adjusting the compensation? In my headphone amp I used a trimmer for R115, and will set with a resistor when finished.

- keantoken

[ostripper]

Originally Posted by keantoken

Will you try my method for adjusting the compensation? In my headphone amp I used a trimmer for R115, and will set with a resistor when finished.

- keantoken

Could I just .step{rcomp}R115 (r17 on the PX) , sit back and watch the action ??

I did this to the Diff resistors on both pairs and the CCS. I just hit .000008%/1k THD .
OS

[keantoken]

That's fine, I'm used to the babylonian method.

- keantoken

[ostripper]

Originally Posted by keantoken

That's fine, I'm used to the babylonian method.

- keantoken

WHAT is that you said... steps are nice ..see cause and effect. Did what you said... used a grossly big 1uF for the cap and stepped from 22 to 500R .The "effect" diminished after 330R. "the effect" is a increase of the UGP along with increasing phase margin as the resistor value is increased with diminishing returns after 300R , at least with a 1uF cap. (Below)
OS

[keantoken]

Something else is compensating the amp so that the RC comp network plays minimal role.

If it were not, I believe you would see the best specs at 5-10R.

Try removing C9 in your previous schematic (attached for convenience). This may seem counter-intuitive, but I believe you will get higher OLUG point this way, along with increased OL BW. Plus, you will be using compensation updated to your actual design.

I should probably use the step command, I just forget to. I just memorize the important parts of the previous plots.

- keantoken

[ostripper]

It will do a bode plot without C9 , but will oscillate or give "timestep too small" errors without it in a standard signal test.
Pioneer uses 2 39pF caps in series in a obscene lead comp arrangement. i might also try to lower the amount of GNFB by using the 22k/470 ratio to set the overall gain.
OS

[keantoken]

Try hanging 100pF off Q8's collector to ground, see if that makes the simulator work.

"timestep too small" error happens, I believe, when the simulation contains risetimes so fast that the timestep is too large to accommodate the specified simulation accuracy/tolerance. Not sure though. I will simulate this amp and check things out myself.

- keantoken

[ostripper]

Originally Posted by keantoken

Try hanging 100pF off Q8's collector to ground, see if that makes the simulator work.

"timestep too small" error happens, I believe, when the simulation contains risetimes so fast that the timestep is too large to accommodate the specified simulation accuracy/tolerance. Not sure though. I will simulate this amp and check things out myself.

- keantoken

I tried the shunt compensation , both symmetrical and one sided - to ground (like roenders folded cascode amp) no go.. I DID get your 1 or 10 uf + 10-100R R/C combo to take over the com.p to make the amp stable. what that did was increase the distortion to .01% versus .000008% for the values in the PX schema , even after adjusting for optimal Vbias and voltage amp current.

It still "befuddles" me what is really happening here.
pioneer must of had a "guru" on hand for this one.
OS

[keantoken]

Also, C6 will complicate the operating point solution severely. You may record it's voltage in a normal sim and parallel a voltage source across it, this will make the simulation more consistent.

- keantoken