Monolithic SuperSymmetry with Current Feedback

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#442
You could read from this picture how hard I was struggling with the grounding--soldering, resoldering, resoldering... 🙂

JH
 

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#445
Re: I easily could be wrong

Sawzall said:
but I thought in this amp was supposed to "float" with respect to ground? And with this assumption, DC offset was not material.

(This is as much a question as it is a statement....)
Click to expand...

Well, the power supply is symmetrical about gnd. So, to get a nice max dynamic range signal with both polarities clipping at (almost) the same time, you want your output in rest to be zero volts. I mean, in the extreme, if you have a rest output of +5VDC with +/- 10VDC supplies, the max output voltage undistorted would be less then some 2VRMS. With the output at zero, you would get some 5VRMS which means more then 4 times the output power (just rough guesses, don't shoot me if I am 20% off).

But other than that, it will work, as was shown by several posts above.

Jan Didden
 
#446
As I have damaged one of my AD811s, (soldering iron to brain fault), to build Rookie's totally IC circuit, I have to order some more, but as they are expensive I thought I might have a go at one of the other designs that you geniuses have come up with.

Searching around in my bits box, I have found some OPA 2604 dual FET opamps, and for output devices I have either MJL3281/1302s or MJ21193/4.

I am tempted by Bernhard's circuit at the moment because he seems to have the most stable version, any reason why it would not work with these devices?

(edit) or for a lower powered version some MJE340/50)
 
#447
pinkmouse said:
As I have damaged one of my AD811s
Click to expand...

Too bad for the AD's...and for you, of course. We could have had a fourth version.:devilr: :bawling:

I wouldn't use the MJE340/50, you will toast them. Only 0.5A Max collector current.
As for the MJL3281/1302 vs. MJ21193, the MJL3281 has a higher Hfe; 60 vs. 25.
You might have a problem with the OPA2604. Doesn't look like it's a current feedback OP.

/Hugo - thinks Bernhard is a genius.
Really don't know how you made your circuit work. Nevertheless, nice job!! 🙂
 
#449
pinkmouse said:

Searching around in my bits box, I have found some OPA 2604 dual FET opamps, and for output devices I have either MJL3281/1302s or MJ21193/4.

I am tempted by Bernhard's circuit at the moment because he seems to have the most stable version, any reason why it would not work with these devices?
Click to expand...

You could try non-current-feedback-OPs also, may be its no supersymmetry, I don't know, but I guess, something will come out of the speaker 😉

Just the OPs need to be single units - no double.

May be it is possible to use double, if paralleled.

I would like to use NE5532, have ceramic packages.


My approach to a N-fet-only-circuit failed miseralbly, lots of trouble :bawling:

Just tried on a piece of paper.
 
#451
jh6you said:


I recommend to try to get the transistors having high dc current gain, hFE. Being as good output current boosters of full capacity, they could cover wide range of power of the amp, IMHO.

JH
Click to expand...

Looks like it's the 3281s then. Now all I have to find are some easily available and cheap CF opamps😉

Just as another thought, would there be any advantage/disadvantage in running the outputs at a higher voltage? I know the output of the opamps is limited to 15-0-15, (or whatever the rail to rail % is), voltage swing, but would higher Ve on 3281s give any benefits?
 
#452
Re: Re: Msscf

Bernhard said:

So I am also little bit afraid that your circuit is on the razors edge.
Click to expand...

Bernhard

You are very talented in appraising your things just by saying others are bad without knowing them. 😉

Could you show me the scope measurement results about your amp? 🙄
Could you tell me how your amp sounds? 🙄

JH
 
#453
pinkmouse said:

but would higher Ve on 3281s give any benefits?
Click to expand...

Yes, we could get an advantage later.

As Nelson Pass has said earlier in this thread, we could manage output swing greater than op amp output swing. This will be possible if we separete supply-powers with different values to OP amps and the current boosting transistors.

JH
 
#455
Re: Re: Re: Msscf

JH,


jh6you said:


Bernhard

You are very talented in appraising your things just by saying others are bad without knowing them. 😉

Could you show me the scope measurement results about your amp? 🙄
Could you tell me how your amp sounds? 🙄

JH
Click to expand...


You know...

I know a lot about your circuit 🙄

- The schematic.

- It gets DC offset if you decrease some resistor values.

- Still more DC offset compared to other similar circuits 🙄

I do not stand alone with my opinion.


My amp sounds good with headphones, I have no speakers with passive crossovers to make another listening test.

I build a 20V PSU soon and try the amp on my plasma tweeters.


Ringing - singing - overshooting may look better in my circuit because of the 100 ohm resistors.

Otherwise I have to do compensate the OPs too, or look for other ones which are not so fast.


By the way, in your circuit the ground connection we were talking about, is made also: the 100ohm that go from output to ground, IMHO useless and on the wrong place.
Should be on the -inputs.


But honestly, I'm just a bloody beginner in amp design... :clown:
 
#458
Bernhard said:



May be the supersymmetry operation (who understands that :scratch: ) depends on the use of cfb OP.
Click to expand...

Bernhard,

Super Symmetry is a concept. Concepts can be implemented with a large variety of components. I am not aware of the NEED for CF in these circuits, although as shown by you and JH it is POSSIBLE to use them.

Don't make it more complex than it is. Opamps don't "know" in which circuit they are. They are a one-trick pony: they only try to adjust their output voltage so that their input voltages are (pretty well) equal. If you look at it that way, your (and JH's amp) is really not that difficult to understand. Start to assume that the opamp's + input is higher than the - input, and work from there.
You will also appreciate that CF or VF may make a difference on how easy or difficult it is to implement what you want, but the CONCEPT is the same.

Jan Didden
 
#459
Re: Re: Re: Re: Msscf

Bernhard said:


JH,

You know...
I know a lot about your circuit 🙄

- The schematic.
- It gets DC offset if you decrease some resistor values.
- Still more DC offset compared to other similar circuits 🙄

I do not stand alone with my opinion.
My amp sounds good with headphones, I have no speakers with passive crossovers to make another listening test.
I build a 20V PSU soon and try the amp on my plasma tweeters.
Ringing - singing - overshooting may look better in my circuit because of the 100 ohm resistors.
Otherwise I have to do compensate the OPs too, or look for other ones which are not so fast.
By the way, in your circuit the ground connection we were talking about, is made also: the 100ohm that go from output to ground, IMHO useless and on the wrong place.
Should be on the -inputs.

But honestly, I'm just a bloody beginner in amp design... :clown:
Click to expand...


Bernhard

You know my circuit without understanding it.

JH
 
#460
janneman said:

You will also appreciate that CF or VF may make a difference on how easy or difficult it is to implement what you want, but the CONCEPT is the same.
Click to expand...

Sure that VF works with the error voltage between the +/- inputs while CF does with the error current. I understand that the basic idea of Supper-Symmetry in this thread has been started based on the condition that the left and right op amps should communicate each other with current. In this respect, CF is now deemed to be better for us to achieve the goal. As you might know very well, I tried with VF, so far with no success. Sometimes the practice unlikely follows the theory.

JH
 
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