dac I/V convertion with very low distortion

[Joachim Gerhard]

C9 i made quite high, 8200uF.

[MiiB]

should you not gnd the transistors for the base currents to get a GND lock on it somewhere...??

[smms73]

Originally Posted by MiiB

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.

[Shinja]

I think the distortion is caused by Cob and Zout of Q1/Q4/Q13/Q14 ,not base current.

[smms73]

Originally Posted by Shinja

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.

[EUVL]

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

[Joachim Gerhard]

Yes, Patrick, on the surface it looks like the Leach but the bias transistors do something different.

[EUVL]

The bias transistor is like that of Hawksford, right ?

Hawksford Discrete IV with a Twist


Patrick

[Joachim Gerhard]

The Hawsford is more complex i think. Q2 is tied to the supply and Q3 feeds back ( forward ? ) to the input transistor.

[Joachim Gerhard]

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.