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PostPosted: Thu Mar 15, 2007 8:21 pm 
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Hi Greg,
Impressive graphs. I really appreciate if you can measurement also imd and thd vs. frequency. From SKA also, of cource.

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-Pasi


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PostPosted: Thu Mar 15, 2007 10:35 pm 
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Hi Pasi,

Yes I'll get to those.

I have to focus first on cleaning up the frame buzz of this computer or it will dominate all the readings, see the attached SKpre THD which seems to limit to 0.001% (but shows 0.0007% live), and shows the A wtd effect of reducing the frame buzz component. Maybe I'll have to regulate the supply to the soundcard.

Also I need to attenuate the outputs so I can raise the levels to 2Vrms so noise doesn't so much dictate the floor.

Greg


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PostPosted: Thu Mar 15, 2007 10:51 pm 
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Here's the standard 60Hz and 7KHz IMD + noise test. There's every likelihood that the figures are dominated by the frame buzz of the computer.


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PostPosted: Sun Apr 08, 2007 9:13 pm 
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Thought that since I have some 2SK170's and 2SJ74's on hand that I would build a FET version of the SKpre to evaluate.

The bias currents are some 5 times higher for the complementary FET diff'l input stage but the BJT second stage shouldn't change nor should the loading on the 80dB onboard regs.

Thanks to Fred for talking 2SK170's.

So far -


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PostPosted: Mon Apr 09, 2007 6:11 am 
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It's up and running.

I will fine tune the FB compensation and post some tests in coming days.

Greg


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PostPosted: Tue Apr 10, 2007 3:45 am 
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Hi Greg,

...................I hope you understand that if the circuit is bootstrapped in any way, you will be spanked. :lash: ........ :mrgreen:

Jam


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PostPosted: Tue Apr 10, 2007 7:28 am 
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Heheh Jam,

Who me bootstrap... seriously!
All those little green clone electro's are not telling.

Truth be known there are no less than 4 in there. The PSU's are as well.

Ahh, they've all been 'outed' - relief.

Greg


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