The MONGREL (supersym II)

[ostripper]

Ahhh - At it again , to refine what I know already works. The original supersym(s) are now a year old , they have not gone to the fiery pit ... they even are very pleasing to listen to .

I just had to try for more stability , lower THD and the "MONGREL" is what I came up with. It is STILL the same core circuit-a single ended LPT with the Otala/Hitachi VAS but with a few improvements.

1. - 2 current sources and a cascode on the differential - much better linearity and PSRR in the "front end" , also.. ABSOLUTE signal symmetry at the input pair.

2. - lower differential current,slightly higher VAS current - better for running standard type 2 or 3 EF's with difficult loads and better linearity .

3. - Standard double EF but with type 3 current sources - carrier "suckout" ,less Xover distortion.

4. - better Vbe (complimentary)


Picture 1 is the circuit.

Picture 2 is the BEST FFT I have ever produced from a class B. The distortion is damn low , too. (pix 3)

On this set of simulations , I nearly was able to go to sub 10pF for Cdom and the simulation did not "choke". Soon I will tweak the open loop gain and global compensation but I suspect it is already close by the impressive stability I have already observed.
It seems Mr. Carlos (DX) saw the first one (supersym) , because now his amps are "locked and loaded" full of CCS's , this is how you really use them .... each of the 4 (CCS's) has a very valuable electrical as well as a noticeable sonic improvement. We don't waste valuable part around here !!

OS

Any comments or suggestions would be highly appreciated.

[ostripper]

TOO MUCH OLG ... arggg.

see plot below... I guess I will be busy.
OS

[Nrik]

Ostripper: eventhough you still want to fiddle with the OLG and feedback, then the project is still very impressive.
I hope many people will buildt it just like Symasym.
One question: What are the ethomylogical content of the names of your amps? How did you come up with these names "Symasym", "Mongrel" ?
They sound very cool and unique.

[AKSA]

Good circuit, Pete.

Dominant pole around 1500Hz, HF pole around 5MHz? Man, that's fast!

Do you feel the EFII with CCS is better sounding and lower distortion?

Shows very high OLG despite loading down the VAS with 110K, too.

Hugh

[ostripper]

Thank you , Hugh.

I did place the DC feedback components on the wrong side of the main feedback resistor. This is corrected in (attachment 1) . This brought max OLG to 65db and unity to a respectable 1.2mhz (attachment 2)... This amp would make a VERY good high output video amplifier. I am happy. I suspect even with the changes 80v/uS slew would be a walk in the park for this circuit.

Do you feel the EFII with CCS is better sounding and lower distortion?

It is better sounding as well as more stable. The CCS's lower the high order harmonics of the Xover distortion by 6-10DB ! As a added bonus the OPS is more stable. This amp can almost work without Cdom .. WOW at 12pf it breaks out at 1.2mhz (unity gain point ?-attachment 3) and will run happy at 22p. Even while oscillating , it still stays electrically stable (it still amplifies) , this is unlike all my other simulations.

(Attachment 4-5) is the best symmetry I have seen from a single ended input stage.

By Nrik -One question: What are the ethomylogical content of the names of your amps? How did you come up with these names "Symasym", "Mongrel" ?

The symasym was mike brittner's creation , I upped the power and used newer parts to make the "supersym" . The "MONGREL" is ... part symasym ,part doug self type 3 OPS , inproved pioneer input stage (CCS's , not a stupid resistor), and economical output devices... A REAL MUTT.

So the "boys" can play I have attached "mongrel.ZIP" , LT simulation. Unzip "mongrel.asc" and "mongrel.txt" into same folder or desktop. NO models to hunt down , all you need is in the text. The simulation reads from the text.
OS

[ostripper]

Square wave was good , except a tad bit of overshoot. (attachment 1) 50v/us at 47pF is acceptable. At 22pF I had 87V/uS ... but too much overshoot.

This is worthy of a few pieces of FR-4 (I'm gonna build it. )

[Dr.EM]

This looks promising as a high power version of Symasym, which is a great sounding amplifier (I'm using 2 stereo ones!)

I look forward to seeing a PCB and mabye European equivalent parts. Will this amplifier be compatible with Symasym in terms of phase response, to be used in a bi/tri amplified active setup with the original?

[ostripper]

I look forward to seeing a PCB and mabye European equivalent parts.

I already have most of this amp and some of the improvements up and running. (attachment 1) I added the current sources with 1 trimmer each to adjust the standing current between 25-60ma. at 40+ma this amp sounds nearly identical to the 200 watt class A $7000 genesis amp which I a/b 'ed it to.

phase wise this amp is nearly identical to the original "symasym" the cascode has 0 effect on phase and the CCS's at the OPS have no effect either.

As far as parts...
Input - ksa992/ksc1845 or 2n5551/5401 or any Vceo 160-< / Hfe 60 - 200

Vas - mje340/350 mediocre - 2sa1381 / 2sc3503 superior (video amp - Hfe 100 +)

drivers - mje15033/32 or 2sa1837 / 2sc4793

Any outputs MJ or MJW or NJW (on semi) Hfe 25 - 50 (250v+ Vceo)

PS voltage +-55 to +- 85VDC . on shutdown amp below still works down to +- 10v !! No turn on "thump" as well.

In both the real amp and the sim I have used all these with only minor adjustments. Very wide parts margin for this circuit.
OS

[ostripper]

I got it . No cutoff like the krill or super class A. A Little positive feedback into my type 3 CCS's and good to go.. !

Look at the plots (1,2) . One issue , at high power , OPS become more typical Class B. At 10-20w neither output cuts off and the FFT shows .0008 or less and almost no 3rd or 5th harmonic.

Circuit is the last attachment.
OS

[ostripper]

I did a .step command with input as the variable and this shows that it is normal for the type 3 to "resist" cutoff. Hence the low distortion components. I only augmented this effect with a little positive feedback.

This is shown in attachment 1 at various output levels.

OS