GC SuperSymmetry

[Nelson Pass]

I am always pleased when this thread lurches back to life.

[Vix]

Originally Posted by Nelson Pass

I am always pleased when this thread lurches back to life.

Hehehe...I remember the day when this thread was started. I was at the seaside, having a break (from amps, forum, studying...), but couldn't resist sneaking into the forum for just a couple of minutes...and saw THIS thread!

Splash! I remember like it was just yesterday!

[codex]

hi,
i want to change my previous bridge gainclone base lm3886 with this SuSy gainclone.
can i use my schematic below? ztx450 replaced with bc550.
need advice..

[njepitt]

Juma,

I've been thinking about what amp to build for the LP section of the bi-amping project I'm working on, and browsing this thread I just saw your schematic on post #682 here. I agree with Carl_Huff when he says it deserves it's own thread; although I understand why you don't want to write it all twice, for those of us who can't read Serbian it would be a big help...
It certainly looks a lot more interesting than a datasheet-based LM3886 solution that I was considering...

In any event, since I (at least) can't read Serbian, may I ask a couple of questions ? (Probably stupid ones, but you're probably used to that from me by now... )

1. You say above you use this without the input section, after your BF862 preamp without output cap, but with another buffer... If you *had* an output cap on the preamp you would just connect to the 3k3 resistor on pin 8 of the OPA1632, correct? Your schematic for the BF862 preamp *has* cap on the output, so I presume you're using an altered version? (Or did I miss something? - quite possible...)

2. Since your circuit uses the inverting outputs of the OPA549s, am I right in thinking this would have to be inverted again to bi-amp with a non-inverting amp on the HP section? (Such as F5, which is my plan...) Can your schematic be altered in any simple way to give a non-inverting output?

3. How much power should this give into a 4 ohm speaker? (I may be stuck using a car audio (sub)woofer for bass...)

Cheers

Nigel

[okapi]

Originally Posted by juma

Hi zei,
here is the schematic with fully-differential (balanced) input.
I left out the PS coupling parts and pinout of chips, you have them in schematic in post #672.
Some part values are different in this new sch. - don't worry about that, the amp sounds better this way.

Cheers !

Hi Juma,

that schematic makes me think you have been modeling the circuit.

1. would you mind posting your model file?

2. do you get different % distortion on the outputs?

Thanks,

Tim

the problems i was having earlier with peaking were related to using the OPA1632 model that is preloaded into TINA-TI. When i switched to the latest version downloaded from the OPA1632 page the problem disappeared.

[juma]

Originally Posted by okapi

Hi Juma,
that schematic makes me think you have been modeling the circuit.
1. would you mind posting your model file?
2. do you get different % distortion on the outputs?

Hi Okapi,
I used Tina just for quick schematic drawing (free version won't let me simulate the circuit with more than two ICs).

Originally Posted by okapi

...When i switched to the latest version downloaded from the OPA1632 page the problem disappeared.

There you have it - all that simulations are not really reliable (except for really simple circuits - but you don't need complex sim software for them). Nothing beats the old school - built it and tune it
BTW, you can use the THS4131 chip, it's practically the same thing as OPA1632.

[juma]

Originally Posted by njepitt

...
1. You say above you use this without the input section, after your BF862 preamp without output cap, but with another buffer... If you *had* an output cap on the preamp you would just connect to the 3k3 resistor on pin 8 of the OPA1632, correct?

Correct. Preamp has the buffer on its output so we don't need another one on amp's input (I suppose that master volume pot is before the active x-over ?), but we do need a coupling cap since preamp's buffer output sits on +12V DC

Originally Posted by njepitt

...
Your schematic for the BF862 preamp *has* cap on the output, so I presume you're using an altered version? (Or did I miss something? - quite possible...)

You got to have it somewhere, take your pick, the only thing you shouldn't do is to let the DC voltage enter the amp through the input connection...

Originally Posted by njepitt

...
2. Since your circuit uses the inverting outputs of the OPA549s, am I right in thinking this would have to be inverted again to bi-amp with a non-inverting amp on the HP section? (Such as F5, which is my plan...)
Can your schematic be altered in any simple way to give a non-inverting output?

It's irrelevant - you can easily trace the phase polarity through the whole circuit and turn the speakers right way around since neither end of the speaker touches the ground connection.
Yes, OPA549 can be easily used here in non-inverting mode but I find that it makes it sound inferior.

Originally Posted by njepitt

...
3. How much power should this give into a 4 ohm speaker? (I may be stuck using a car audio (sub)woofer for bass...)

With +/-20V PS the SuSy configuration (fundamentally, it's a bridge) will give you about 100W RMS max. on the 4 ohms speaker.

[wensan]

The Close Loop Common Gain still remain 1.




The Close Loop Common Mode Gain is not suppressed.


Separate it symmetrically become a Fully Differential Amplifier with Common Mode Feedback.

[wensan]

I had built such "Ultra Symmetry" circuit as a pre-amplifier and a power amplifier in Taiwan 5 years ago!

[Nelson Pass]

It has occurred to me previously that you are a dangerous
guy to have loose, Wen-san.