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dac I/V convertion with very low distortion
dac I/V convertion with very low distortion
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Old 17th August 2012, 02:51 PM   #211
Joachim Gerhard is offline Joachim Gerhard  Germany
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C9 i made quite high, 8200uF.
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Old 17th August 2012, 04:01 PM   #212
MiiB is offline MiiB  Denmark
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should you not gnd the transistors for the base currents to get a GND lock on it somewhere...??
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Old 17th August 2012, 04:03 PM   #213
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by MiiB View Post
should you not gnd the transistors for the base currents to get a GND lock on it somewhere...??
it was an error i already delete the posts.
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Old 17th August 2012, 04:04 PM   #214
Shinja is offline Shinja  Japan
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I think the distortion is caused by Cob and Zout of Q1/Q4/Q13/Q14 ,not base current.
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Old 17th August 2012, 04:10 PM   #215
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by Shinja View Post
I think the distortion is caused by Cob and Zout of Q1/Q4/Q13/Q14 ,not base current.
You have to make the voltage stable in the up and down nodes if you want to achieve very low distortion, i think i know how to do that, but today i have no time. Next week.
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Old 17th August 2012, 10:07 PM   #216
EUVL is offline EUVL  Europe
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Joachim,

Re post #208, you are basically back to the original Leach design :

Moving Coil Cartridge Head Amps

With all its pro's and con's.


Cheer,
Patrick
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Old 17th August 2012, 11:01 PM   #217
Joachim Gerhard is offline Joachim Gerhard  Germany
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Yes, Patrick, on the surface it looks like the Leach but the bias transistors do something different.
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Old 17th August 2012, 11:06 PM   #218
EUVL is offline EUVL  Europe
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The bias transistor is like that of Hawksford, right ?

Hawksford Discrete IV with a Twist


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Old 17th August 2012, 11:22 PM   #219
Joachim Gerhard is offline Joachim Gerhard  Germany
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The Hawsford is more complex i think. Q2 is tied to the supply and Q3 feeds back ( forward ? ) to the input transistor.
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Old 17th August 2012, 11:28 PM   #220
Joachim Gerhard is offline Joachim Gerhard  Germany
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As i see circuit pots 208 the bias transistors sense the base current of the input transistors and add them to the other polarity of the output.
In the Leach the bases of the input transistors are simply held on a constant potential.
I use an optimized Leach input stage in my Nobrainer Phono. That does not have a floating supply though and filters and clamps the base current of the input transistors to ground for a 3dB noise advantage. Here the big electrolytic does that job.
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