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Old 20th March 2013, 01:30 PM   #8691
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Quote:
Originally Posted by Joachim Gerhard View Post
That is strange, my build is qiet.
question: was your build just the front end and then you used it as a head amp or you build the daughter board on the paradise?
Because Simulation of the entire circuit shows acceptable noise performance, but by any means not in pair with what you like and that is why I was wondering about that.
I will post the noise performance a little later...
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Old 20th March 2013, 01:38 PM   #8692
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I used it as a head amp only and fed that into an external MM stage.
I have not implemented any of the new balanced version into the Paradise but i will.
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Old 20th March 2013, 02:11 PM   #8693
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here is noise simulation
Attached Images
File Type: jpg TransY Noise.JPG (76.8 KB, 220 views)
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Old 20th March 2013, 02:12 PM   #8694
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and here is the schematic
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File Type: jpg TransY SCH.JPG (78.5 KB, 217 views)
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Old 20th March 2013, 02:32 PM   #8695
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It depends of cause on the transistor models but the rise in the bass is not good.
Anyway, i do not want to make a balanced transimpedance input any more.
Lets go back to the older circuit.
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Old 20th March 2013, 02:55 PM   #8696
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ok.

Leet me plug the new circuit in and see how it looks like noise wise.

BTW with the same models I can get the paradise to be at least 3dB quiter thus I am not so sure that in this instance the noisefloor of the models is playing a big role but I might be wrong and in that case please point me out to the right model to use to have a more realistic result.
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Old 20th March 2013, 05:08 PM   #8697
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Quote:
Originally Posted by Joachim Gerhard View Post
It depends of cause on the transistor models but the rise in the bass is not good.
Anyway, i do not want to make a balanced transimpedance input any more.
Lets go back to the older circuit.
Your master intuition was right.
The older circuit simulates just perfectly noise wise.
It looks extremely interesting and it could be made completely balanced from in to out.
I am wondering if enough gain can be reached with Jfets as well.
I will have to simulate this as well.
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Old 20th March 2013, 05:12 PM   #8698
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Just put a correction of your schematic on the Masterpiece thread.
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Old 25th March 2013, 11:26 AM   #8699
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Today i istalled the new software for the DCA75 pro curve tracer. It adds some more functions. Here you see measuremets taken on a pair of Zetex medium power tranistors that are known to be low Rbb. What i find interesting is the curve Hfe over collector current. The PNP has full Hfe, even at very low idle.
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File Type: jpg Zetex hfe ic.JPG (108.3 KB, 131 views)
File Type: jpg Zetex hfe vce.JPG (95.3 KB, 116 views)
File Type: jpg Zetex PN junction.JPG (87.5 KB, 113 views)
File Type: jpg Zezec Ic Vce.JPG (104.4 KB, 53 views)
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Old 25th March 2013, 05:34 PM   #8700
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There is a lot of discussion about what amp is CFB or VFB on DIYAUDIO. Some theoreticians even went so far that a CFB amp does not exist and that it is a flawed VFB amp at best.
I watch this but do not comment much. The biggest discussion is if the correction signal is current or voltage. I think this is nearly impossible to answer. Pure current has zero voltage and pure voltage has zero current so it is always something in between. Also there is confusion about a current drive amp that has a high output impedance and CFB ( current feed back ) what is not the same. I learned that the topologies are differentiated by the open loop gain and the open loop bandwidth. VFB usually has very high gain at low frequencies and CFB usually has less gain but a wider open loop bandwidth. That has consequences how the different topologies have to be compensated. For example a CFB amp usually does not allow a cap to be placed in parallel with the feedback resistor or it gets unstable. What can be done in case of overshot is to place a passive low pass filter BEFORE the map.
Why do i mention this here ? Well, because Frans is coming up with a really innovative power amp and he had some issues to make it stable. So we had a rather long meeting on Frickelfest Light about if his amp is VFB or CFB. Stay tuned.
http://www.analog.com/static/importe...64003sect1.pdf
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