ultra low dist pre Sandman distortion null

[padamiecki]

Hi
Reading Tube Cad Journal by Mr. Broskie I found this circuitry.
You can try any opamp in this configuration.
At 10Vpp at the output @10kOhm thd is<0,001%.
Reading the schematic watch label net “In” connection.
cheers

 

[chip2000]

anyone tested this shematic?

 

[dchisholm]

What is the purpose of this circuit?

The atch LTSpice circuit file modifies some of the directives in the Original Poster's file and runs faster. Read the comments in the circuit file to understand my changes.

Dale

 

[padamiecki]

What is the purpose of this circuit?

analog line level pre?

 

[padamiecki]

do you want to get power amp with similar low distortion?
better get read: "More Thoughts on the Sandman Distortion Null Topology" from OTL Design & Sandman Error-take-off Amplifier

 

[Elvee]

analog line level pre?

It makes (a little) sense for a power amplifier where the load is floating, but for a preamp or anything line-level, it is unusable unless one adds a transformer which would kill any benefit gained with this scheme

 

[padamiecki]

It makes (a little) sense for a power amplifier

why only a little?

it is unusable unless one adds a transformer which would kill any benefit gained with this scheme

how about his solution when output is isolated with the capacitors?

 

[wintermute]

Dale, options ptrantau and changing to gear are useful when there are problems with convergence with a particular circuit. If the circuit converges without problems then yes, probably best to leave them off.

I've only ever used ptrantau with very small numbers (there seems to be a sweet spot with problem circuits), I've never tried turning it off completely...

Tony.

 

[Elvee]

why only a little?

Because building a complete second amplifier just for the purpose of improving the first one is probably a waste of resources: with twice the original investment, you'd be able to build a much better amp to begin with, perhaps better by itself than a tandem of lesser quality amplifiers.

how about his solution when output is isolated with the capacitors?

This doesn't change the fact that this cannot work in a purely unbalanced configuration

 

[padamiecki]

Because building a complete second amplifier just for the purpose of improving the first one is probably a waste of resources: with twice the original investment, you'd be able to build a much better amp to begin with, perhaps better by itself than a tandem of lesser quality amplifiers.

Dear Elvee
I did not check
but I have got a "feeling" that from two superior dirt cheap LM3886 plus a few extra parts you can squize >>ten times better performance than one single LM.
Is it worth? I cannot check now.
but this is about poweramp... not fit to this thread

 

[Elvee]

Dear Elvee
I did not check
but I have got a "feeling"

Beware of your feelings: they seem to play tricks with you.

I have tested the idea on the LT1970 power amp: the result is less than convincing.....

 

[padamiecki]

poor1970?

you are great Elvee,
but it seems like LT1970 has poor quality by itself, attached the sim of single device 20kHz, 10Vpp output into 15 Ohm.
Do you have the model for LM3886 or other high quality power chip amp?

 

[Elvee]

I don' have a model for a dedicated chip amp. Another member of the community perhaps?

 

[bear]

Is this different than a basic bridged amplifier?

Seems like one would want to try one of the variants of the feedforward techniques with the relatively low cost chip amps? What held these ideas back the most was (as noted before) the cost associated with duplicating the second amplifier...

_-_-