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Old 27th October 2012, 08:17 AM   #501
smms73 is offline smms73  Portugal
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Thanks for your input Zinsula and shinjA . I will comment later.
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Old 27th October 2012, 09:08 AM   #502
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Quote:
Originally Posted by smms73 View Post
DR , I'm not very good with English. Can you elaborate that?

To know the noise that each component are adding, I use ltspice, is very fast and gives me good results .
But please post your method.
DR = dynamic range.

Using Ltspice is an easy way but a) I don't know how accurate it is, can you
point to where the noise specs in the BJT models are so I can check this out
b) Does Ltspice give an RMS S/N ratio? I haven't played with this feature.
Looking at FFT baseline 'grass' is not very meaningful. For example, if the
FFT graph shows noise at -140dB then the RMS noise floor (20kHz BW) is
not -140dB. It depends on the FFT sweep bandwidth. c) You may not
develop a good intuitive knowledge to understand the mechanisms.
I'll post some simple current source noise calcs a bit later. Many will already
know this but hopefully it will benefit some.
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Old 27th October 2012, 09:31 AM   #503
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Quote:
Originally Posted by smms73 View Post
Terry, Prof Malcolm Hawksford call it feedforward. I think that he is the inventor of this type of X connection.
to stabilize it, is very simple, only need to connect a capacitor in the base of transistor driver to ground.
I never saw the Hawksford circuit, was just doing my own thing, but this
doesn't surprise me, he seems to have come up with just about everything


Quote:

I use them because is the one that gives me the best results, but there are others ways, one very simple way is using jfet in the place of the drivers transistors. The problem is that it needs a p channel jfet , and this are getting rare (2sj74), I will talk about this later.
Yes from memory I got the lowest distortion with x coupled arrangement,
as stated I think the voltage headroom really helps here.

Quote:

Subjective results, are subjective . One man remedy can be other man poison . But I can include a way to deactivate the Hawksford X connection in the Pcb.
WRT subjective, yes some people like 'detail' some like 'music'
WRT deactivation option, might be a worthwhile addition.
Once you get rid of the x coupled connection, the choice of devices
becomes very critical.

Quote:

One way or another, I would like very much to see the schematics of your implementation of the circuit, ( you have my email).
I just dug through my archives - there are a few, You have mail.
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Old 27th October 2012, 09:44 AM   #504
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I would not worry about Pch JFETs. They are still around. Especially the BL grade (Idss from 6.5 to 12mA) and in low quantaties.


BTW,
your English is fine!


/S

Quote:
Originally Posted by smms73 View Post
Terry, Prof Malcolm Hawksford call it feedforward. I think that he is the inventor of this type of X connection.
to stabilize it, is very simple, only need to connect a capacitor in the base of transistor driver to ground.
I use them because is the one that gives me the best results, but there are others ways, one very simple way is using jfet in the place of the drivers transistors. The problem is that it needs a p channel jfet , and this are getting rare (2sj74), I will talk about this later.

Subjective results, are subjective . One man remedy can be other man poison . But I can include a way to deactivate the Hawksford X connection in the Pcb.

One way or another, I would like very much to see the schematics of your implementation of the circuit, ( you have my email).
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Old 27th October 2012, 10:15 AM   #505
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SPICE is actually very good at calculating noise as long as the semi models are relatively OK. They do not have to be exact. Just in the ballpark so to speak.

JFETs, for ex have the parameters AF and KF but SPICE also uses all the resistances in the JFET model to get the total noise.


BTW, SPICE does RMS noise calculations.

/S

Quote:
Originally Posted by zenelectro View Post
DR = dynamic range.

Using Ltspice is an easy way but a) I don't know how accurate it is, can you
point to where the noise specs in the BJT models are so I can check this out
b) Does Ltspice give an RMS S/N ratio? I haven't played with this feature.
Looking at FFT baseline 'grass' is not very meaningful. For example, if the
FFT graph shows noise at -140dB then the RMS noise floor (20kHz BW) is
not -140dB. It depends on the FFT sweep bandwidth. c) You may not
develop a good intuitive knowledge to understand the mechanisms.
I'll post some simple current source noise calcs a bit later. Many will already
know this but hopefully it will benefit some.

Last edited by staccatiss; 27th October 2012 at 10:37 AM. Reason: Added RMS noise info
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Old 27th October 2012, 10:17 AM   #506
MiiB is offline MiiB  Denmark
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I wonder would it not be possible to cascode the output of the ESS dac with a jfet, then you don't have to worry so much about distortion due to higher impedance
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Old 27th October 2012, 11:49 PM   #507
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Quote:
Originally Posted by staccatiss View Post
SPICE is actually very good at calculating noise as long as the semi models are relatively OK. They do not have to be exact. Just in the ballpark so to speak.

JFETs, for ex have the parameters AF and KF but SPICE also uses all the resistances in the JFET model to get the total noise.


BTW, SPICE does RMS noise calculations.

/S
Thanks, I'll check it out and see how accurate it is.

I'm much more comfortable calculating based on device specs and resistor
values. The disadvantage of using spice is it does not encourage a good
understanding of the actual noise generating mechanisms and noise gain of
the circuit.
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Old 28th October 2012, 08:45 AM   #508
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You are right that it does not help to understand all the nosie mechanisms. I do not but I have gotten to understand what affects noise. Like source resistors, FB resistor, semi noise of course, series resistors.

To do a manual, correct noise calculation takes some heavy duty math integral work, and that can be done in a math program like the noise "guru" Mr Vogel does in his book where he uses MatCad.

Semi noise consists of many (3?) factors, and they are not linear with freq, ie low frew noise is higher than at medium freq. I do not think that even Vogel takes this into account...but SPICE dows

BTW, could you also email me or PM me the schematics I think you sent to smms73? Thx!


/S

Quote:
Originally Posted by zenelectro View Post
Thanks, I'll check it out and see how accurate it is.

I'm much more comfortable calculating based on device specs and resistor
values. The disadvantage of using spice is it does not encourage a good
understanding of the actual noise generating mechanisms and noise gain of
the circuit.
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Old 28th October 2012, 02:07 PM   #509
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are there performed listening tests against other versions like D1 and I/U outputs with modern OPAs?
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Old 29th October 2012, 02:47 PM   #510
smms73 is offline smms73  Portugal
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I have read the walter jung´s text about current sources that Ken Newton post, and i have chose the basic current source of post #486 , it gives 80 db of psrr at 100Hz.

first image EMU1212M noise, second image output noise in 470 ohms.
Attached Images
File Type: png emu_noise.PNG (59.0 KB, 260 views)
File Type: png noise_out.PNG (69.7 KB, 258 views)
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