Do you know any other way besides transformers or caps to block DC?

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user 37518 said:
Im doing achoustic instrumentation in which the phase between mics is critical, so yes theres something wrong with LF phase shift in some applications.
There is nothing wrong with phase-shift due to the High-Pass response. This phase-shift never exceeds 90°, which ensures that signals are always in the same quadrant, so combine without negative interference.
You are confusing this with distance-related phase-shift, which creates a non minimum-phase system.
 
What's the cutuff frequency in a typical servo circuit? One Hz? A tenth of a Hz? It's well below the claimed audible 20Hz, regardless, and any phase shift in the audio band is insignificant. There are much more serious phase shift problems in any multi-driver speaker crossover.
 
Loving this thread.  Might someone direct me to any reading material on the relationship of DC offset and tx performance or what makes a 'bad' servo bad? For example I'm confused by some mic pre kits that allow the user to jumper-bypass caps, as if to suggest it might be a 'tone' one is looking for in an output tx.

Thank you!

Edit: Hope you don't mind the interjected question, DF.
 
boji said:
Might someone direct me to any reading material on the relationship of DC offset and tx performance
Not specifically. You have to understand ferromagnetism and how permanent bias shifts the magnetizing curve. Then you understand what DC offset results and that it may not be such a big issue, within limits.

or what makes a 'bad' servo bad?
Like any piece of electronics, bad design. The two main issues with servos are the lack of control range and inadequate frequency response.

For example I'm confused by some mic pre kits that allow the user to jumper-bypass caps, as if to suggest it might be a 'tone' one is looking for in an output tx.
Coupling a xfmr via caps creates a resonant circuit, that ususally results in a hump at subsonic frequencies. It may actually overload the output stage if VLF noise is present. There are ways to damp this resonance, but actually it's not very often implemented.
 
What about using a gyrator on the output as a shunt to to ground with fc set to 0.1hz?

Nothing in series with the audio path or the feedback loop.
 
5v333 said:
What about using a gyrator on the output as a shunt to to ground with fc set to 0.1hz?

Nothing in series with the audio path or the feedback loop.
It would be in parallels though; same possible adverse effects. More so, considering it would have to shunt a possibly hefty output stage.
 
Winston O'Boogie said:
Not seen that, do you have an example?

I've seen (though not experimented much with) taking the output of the DC servo into a transistor as a voltage to current converter to tweak the quiescent of the top or bottom in an output stage.  It could be argued that this is not in the signal path. 
And that would be utterly wrong... Signal is voltage AND current. Both should be as little distorted as can be.
 
Winston O'Boogie said:
I am genuinely interested in your opinion as to whether you think shunting quiescent current would have less of an impact over say the last DC scheme I posted. 
With regard to the 2nd implementation, I would be concerned as the compensation loop is modulated by the output signal; then I'm afraid shunting quiescent would also be subject to same issue. Practical current sources are not perfect.
It is just a first impression, though...
 
I guess by putting synthetic inductance in parallell with an OT would also lower the ability of the amp to drive the lowend of the OT...

 

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