Discrete Opamp Open Design

[bcarso]

Originally Posted by fas42

My personal feeling is that it will be the one that has the best rejection of noise and interference by the very nature of the topology. Obviously PSRR is a prime culprit to be investigated, but what about throughout the rest of the circuit: if the circuit is poorly executed by a DIY'er and can easily pick up stray signals, couple with extraneous influences, then how many weak spots in this, theoretical design, sense, occur through the circuit at the various junctions of the parts?

Frank

Got to keep loop areas small, and use FETs where possible due to their appreciably lower propensity to rectify RF. Run lots of current to make the signals liable to contamination proportionally larger. Go balanced wherever possible, even internally. These are all things available to us that are constrained by comparison in ICs.

Many years ago Walt Jung was giving a talk about opamps and their ability to self-rectify RF. As a question/comment from the floor, I suggested that, due to their purportedly good matching in a dual, that one opamp might be used as the RF detector and its output deployed to subtract the detected envelope from the actual signal-processing one. Walt thought it a good idea. I'm not sure if anyone ever tried it.

Nowadays the interfering frequencies are so high, such as from cellphones, that the scheme would likely be impractical. And there are other ways.

[RNMarsh]

Originally Posted by gpapag

Harmonics will not be seen. The idea is that noise will increase. But how this
noise will be measured in the presense of such a big population of main tones?

But new relevant methods are already proposed :

http://www.listeninc.com/PDFs/paper_...Listen_Inc.pdf

George

This is good.... I had suggested broadband random noise generator in place of music. [ Since I have one in stock.]
I'll download that paper and reread it. Thx

[Joachim Gerhard]

George, the measurements are explained in post 1099. From left to right, top to bottom :
Noise test, Belcher Test, Sine-square superposition.
No, i do not know any dynamic speaker that has such low distortion at such high volume.
Yes, the Quads have very low distortion but mecahnics are a crook and they do not play much louder then 100dB. When you strip them and make a really rigid frame they are cool up to a certain volume. You will be also be surprised about the compromised parts they use. For example there is an input cap before the transformer that has to substituted, and then the terible clamp overload supression. Nevertheless a stroke of genius.
Horn speakers can have low third but they still have high second.

[Joachim Gerhard]

Here is an astounding claim from National Semi. I would call that settling time. What happens after an aprupt transient ? How long does the opamp need to pull the output to zero ?

[RNMarsh]

Originally Posted by RNMarsh

This is good.... I had suggested broadband random noise generator in place of music. [ Since I have one in stock.]
I'll download that paper and reread it. Thx

A good appl for DADiSP software.

[RNMarsh]

Originally Posted by Joachim Gerhard

Here is an astounding claim from National Semi. I would call that settling time. What happens after an aprupt transient ? How long does the opamp need to pull the output to zero ?

And you thought that kind of advertizing was only done in high end audio :-)

[RNMarsh]

[QUOTE=Joachim Gerhard;3172806]Yes, the Quads have very low distortion but mecahnics are a crook and they do not play much louder then 100dB. When you strip them and make a really rigid frame they are cool up to a certain volume. You will be also be surprised about the compromised parts they use. For example there is an input cap before the transformer that has to substituted, and then the terible clamp overload supression. Nevertheless a stroke of genius.
QUOTE]

I use a pair of TC Sounds LMS Ultra 5400 18 inch and 4 each Cerwin Vega 15 inch to take care of the bottom... then the Quads (modified). Super low distortion and high spl where it is needed. You can really hear what equipment sounds like - the good, bad and the ugly. -RNM

[fas42]

Originally Posted by RNMarsh

very nice results --- Do you have data on other speakers/drivers that are as good? Such as, one of my favorites I drag out every so often -- The New Quad electrostatic speakers? I understand they re very low distortion full range speakers. My reference speakers for very low distortion and very flat response.

One that shapes up nicely, optimised dynamic design is: NRC Measurements: Vivid Audio Giya G2 Loudspeakers

This has also received excellent subjective reviews ...

Now, if only one can get to like the look of it ...

Frank

[bcarso]

Originally Posted by Joachim Gerhard

Here is an astounding claim from National Semi. I would call that settling time. What happens after an aprupt transient ? How long does the opamp need to pull the output to zero ?

Sigh. It seems each generation must learn anew.

[RNMarsh]

Originally Posted by john curl

Why not try a variation of this circuit as well, Richard? A few resistor changes, and it should be OK.

Ok. Do you have any measured data on it?