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Old 8th August 2012, 10:15 PM   #61
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Well, as they say, there are many ways to skin a cat. So, sure, there are a number of ways to deal with this DC current offset. I have a method that I like, as I'm sure others have their own method.

One thing that I think is important to note is that the DAC manufacturers specify their performance ratings based on the specific I/V converter circuit that they show in their data sheet. The entire reason that DAC manufacturers went to the balanced outputs is because they realized they could reduce distortion by using an attached circuit that had a really high CMRR. So, their THD figures are based on attaching a circuit to the DAC that has a corresponding high CMRR. This means, that for these kinds of I/V circuits (like the Zen/Cen/Sen also), you need two of them plus a following circuit that has a high CMRR, since none of these circuits has any CMRR capability. For stereo, you need four of them. If someone just uses the Iout+ pin only, for example, the distortion will be much higher than that quoted by the manufacturer. So, this is a tough problem.
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Old 8th August 2012, 10:33 PM   #62
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Sure, one of the reasons i often listen to vinyl, another can of worms. When i am really exhausted i play my guitar and shut up my mouth.
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Old 8th August 2012, 10:50 PM   #63
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by Joachim Gerhard View Post
In post 54 smms73 already suggested a method to trim the offset.
i have change my mind.
the best way to trim the offset is in the upper ccs, we only need to increase 6.2ma to the upper ccs. no problem.

Last edited by smms73; 8th August 2012 at 11:10 PM.
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Old 8th August 2012, 11:09 PM   #64
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Cool, good solution.
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Old 8th August 2012, 11:42 PM   #65
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by dirkwright View Post

One thing that I think is important to note is that the DAC manufacturers specify their performance ratings based on the specific I/V converter circuit that they show in their data sheet. The entire reason that DAC manufacturers went to the balanced outputs is because they realized they could reduce distortion by using an attached circuit that had a really high CMRR. So, their THD figures are based on attaching a circuit to the DAC that has a corresponding high CMRR. This means, that for these kinds of I/V circuits (like the Zen/Cen/Sen also), you need two of them plus a following circuit that has a high CMRR, since none of these circuits has any CMRR capability. For stereo, you need four of them. If someone just uses the Iout+ pin only, for example, the distortion will be much higher than that quoted by the manufacturer. So, this is a tough problem.
I don't see any problem in using 4 of this circuits ,as they can be constructed for a fraction of a premium OP amp, we can use transistors like bc546 and the performance will be great. IM going to use smd ,so the price will be very low.

the classic current to voltage converter build with the opamp don't have cmrr capability either, it also need a differential to single end converter. Or you can use balanced connections to the power amplifier.

Relax


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Old 8th August 2012, 11:44 PM   #66
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BC327 and BC337 is much better and more symmetrical. There is also an SMD version.
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Old 8th August 2012, 11:52 PM   #67
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This is the SMD type:http://jumi.lut.fi/elko/datat/BC807.pdf
They have lower Rbbe`, 30 Ohm compared to 140 Ohm of the BC550,560, so less paralleling is necesary for low noise.
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Old 9th August 2012, 12:03 AM   #68
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There are also some very ineresting SMD Zetex with high and linear Hfe and low Rbee`.
More tomorrow.
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Old 9th August 2012, 08:45 AM   #69
MiiB is offline MiiB  Denmark
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This circuit has potential.... very nice concept. with good housekeeping, it has potential to be a great performer.

Joachim could it be mirrored into something like the sampler output..??

Last edited by MiiB; 9th August 2012 at 08:51 AM.
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Old 9th August 2012, 10:18 AM   #70
Shinja is offline Shinja  Japan
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how about this mod to merge differential current from dac.
I made current source Q9 and Q10 works as current mirror.
I3 is for Icq of Q3 and Q6.

this configuration looks similar to
http://home.tiscali.nl/data.odyssey/Super_TIS.html
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File Type: jpg dsc.jpg (82.8 KB, 413 views)

Last edited by Shinja; 9th August 2012 at 10:34 AM.
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