clintrubber
Well-known member
Here's more on the BeyerDynamic circuit from this thread:
http://www.groupdiy.com/index.php?topic=7375
I guess I better move this here to the Drawing Board.
I traced the relevant part of one micpre-channel, it goes like this:
The pdf file contains both the circuit & an AC-sim.
The graph in the pdf shows two nodes: the total output (OUT) and
the interm. signal after the ComplFeedbackPair (CFP_OUT).
Input-signal was 1 mV.
The total of six traces is explained by the sweeping of the C1-value,
that's the cap between TX & Q1.
Note this card seems to be intended for a speach/conference-system,
so the bandwidth was poor (with the orig C1-value of 0.47uF).
#1.
Gain is very high, some 70 & 90 dB for CFP_OUT respect. OUT.
But I didn't see any provision on this card for connection to an external gain-control.
I want to add such a thing, likely along the lines of
http://sound.westhost.com/project13.htm
This will also give a more usable situation at the higher frequencies.
#2.
Realizing the general setup of the Beyer-circuit is a bit
like that ESP-circuit (apart from the actual amp),
the absence of the input-resistor pops up
(there's 1k2 in the ESP-circuit, but 'nothing' in the Beyer).
So if I'm understanding this correctly could it be that
the Beyer-circuit is doing the zero-Z-tranny trick then ?
(more on that here:
http://headfonz.rutgers.edu/zero-Z-tranny.pdf
http://www.groupdiy.com/index.php?topic=4864 )
And then there should be pre-TX stuff outside the card,
probably in the form of a stepped pad, realizing the
sought after gain-control.
Any ideas about all this ?
Thanks / Regards,
Peter
http://www.groupdiy.com/index.php?topic=7375
I guess I better move this here to the Drawing Board.
I traced the relevant part of one micpre-channel, it goes like this:
The pdf file contains both the circuit & an AC-sim.
The graph in the pdf shows two nodes: the total output (OUT) and
the interm. signal after the ComplFeedbackPair (CFP_OUT).
Input-signal was 1 mV.
The total of six traces is explained by the sweeping of the C1-value,
that's the cap between TX & Q1.
Note this card seems to be intended for a speach/conference-system,
so the bandwidth was poor (with the orig C1-value of 0.47uF).
#1.
Gain is very high, some 70 & 90 dB for CFP_OUT respect. OUT.
But I didn't see any provision on this card for connection to an external gain-control.
I want to add such a thing, likely along the lines of
http://sound.westhost.com/project13.htm
This will also give a more usable situation at the higher frequencies.
#2.
Realizing the general setup of the Beyer-circuit is a bit
like that ESP-circuit (apart from the actual amp),
the absence of the input-resistor pops up
(there's 1k2 in the ESP-circuit, but 'nothing' in the Beyer).
So if I'm understanding this correctly could it be that
the Beyer-circuit is doing the zero-Z-tranny trick then ?
(more on that here:
http://headfonz.rutgers.edu/zero-Z-tranny.pdf
http://www.groupdiy.com/index.php?topic=4864 )
And then there should be pre-TX stuff outside the card,
probably in the form of a stepped pad, realizing the
sought after gain-control.
Any ideas about all this ?
Thanks / Regards,
Peter