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Old 20th November 2010, 03:13 PM   #1912
masag1 is offline masag1  Germany
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Hi VT67,

although your post is not signed with your name, and there is no "please" or another polite phrase in it, I have sent you pm with the link where you can order them.

Regards

Sam
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Old 20th November 2010, 03:20 PM   #1913
VT67 is offline VT67  Belgium
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Vielen Dank Sam.

Regards
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Old 20th November 2010, 03:27 PM   #1914
masag1 is offline masag1  Germany
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Gerne.
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Old 21st November 2010, 12:30 PM   #1915
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I persuaded Jürgen Hensler to make me two of his wounderfull coils. They will be 1mH, 1.5 Ohm so the noise contribution will be even less then the 0.75mH, 4 Ohm i am using now. The coils will be wound on double e-core audio material. That way the coils are much smaller and less prone to hum pickup. I will also try Mu-Metal shielding. This is scheduled to be ready on wednesday evening, one day before ETF, so this is tight.
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Old 21st November 2010, 07:21 PM   #1916
masag1 is offline masag1  Germany
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Stay cool and easy.

Go for the ETF.

VG

Sam
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Old 21st November 2010, 07:53 PM   #1917
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Watch out for distortion in Mu-metal shields. It can be measured.
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Old 21st November 2010, 10:55 PM   #1918
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Thanks John, for that advice. Sofar i have some experience with Lundahl and Sowter products in MU-metal cans but honestly i am not measuring distortion much at the moment.
My transistor circuits get simulated so i see if i land in the ballpark. Usually i design for better then -80dB distortion at 20kHz into 600 Ohm at 1V, mainly second harmonic. Better is fine and i was able to design open loop circuits that are better then -100dB but i did not find a direct correlation if that sounds any better. I focussed more on listening recently. When i want very low distortion i am using modern Opamps or a combination of Opamps with discrete Output or Input stages or both. Together with my Josi team i also designed a discrete Opamp with very low distortion. The PCB´s are ready but we did not find the time to stuff them. But listeners tell me that they like my discrete designs better. Again something i can hardly prove by measurements. Are we still measuring the wrong things ?
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Old 22nd November 2010, 01:18 PM   #1919
masag1 is offline masag1  Germany
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Die MU_Folie geht heute noch mit der Post raus.

VG

Sam
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Old 22nd November 2010, 01:56 PM   #1920
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Thanks Sam, when i have luck it will all come together. I talked to Jürgen Hensler today and typical for him he said :" I whould not like to waiste time so i make you some coils that are tapped at 0.56, 0.75 and 1mH". Fine, then i have some fexibility. Playing around with the big air coils to reduce the humm i put a small piece of Mu-Metal over them and could hear the sound of metal over the speakers !!!!!! Cristal clear ! First i thought this is really bad but then it occured to me that i should try the oposite and make the hum stronger. After fumbling around a bit i got the sound of the motor in the speakers. I use a silicon belt that is glued and not cast so at the joint there is a small discontinuety. I could clearly hear the sound it makes when it passes the pulley at each revolution. Tack, Tack, Tack... Whow, this is not only a musical intrument and an electromagnetic microphone but also a superb analysing tool. Strange enough that i also was on the other hand able to reduce the hum to a point where decent music reproduction could be heard. Let´s see what Jürgens coils will bring to the table " ...... will pot them in wax... very small airgap located at the inner...... " It whould not be the first time he surprises me.
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