digital controlled mic amp

M

martin griffith

Guest
This is a Studer mic amp
http://home.datacomm.ch/gronerfamily/DIY/D19_MicAD/D19_MicAD_Op_Serv47.jpg

I just dont know if I like it. It looks messy. Or am I missing out on
a great innovative design


martin
 
martin griffith wrote:

This is a Studer mic amp
http://home.datacomm.ch/gronerfamily/DIY/D19_MicAD/D19_MicAD_Op_Serv47.jpg

I just dont know if I like it. It looks messy. Or am I missing out on
a great innovative design
Click to expand...
Just use TI's PGA2500.

Graham
 
"martin griffith" wrote ...
This is a Studer mic amp
http://home.datacomm.ch/gronerfamily/DIY/D19_MicAD/D19_MicAD_Op_Serv47.jpg

I just dont know if I like it. It looks messy. Or am I missing out on
a great innovative design
Click to expand...
Why does it look "messy" to you? Looks pretty much de
rigueur if you want digital control of a rather sensitive
analog circuit (like a mic preamp).

Using the extra mic transfomer winding in the feedback
circuit (presumably to adjust gain) is a new one on me.

OTOH, as Mr. Bear suggested, TI makes a replacement
which is monolithic and perhaps better performing also.
 
martin griffith wrote:
This is a Studer mic amp
http://home.datacomm.ch/gronerfamily/DIY/D19_MicAD/D19_MicAD_Op_Serv47.jpg

I just dont know if I like it. It looks messy. Or am I missing out on
a great innovative design


martin
Click to expand...
It only looks messy if you do not understand the circuit.
--
ciao Ban
Bordighera, Italy
 
On Mon, 29 Aug 2005 04:49:13 GMT, in sci.electronics.design "Ban"
<bansuri@web.de> wrote:

martin griffith wrote:
This is a Studer mic amp
http://home.datacomm.ch/gronerfamily/DIY/D19_MicAD/D19_MicAD_Op_Serv47.jpg

I just dont know if I like it. It looks messy. Or am I missing out on
a great innovative design


martin

It only looks messy if you do not understand the circuit.
I was trying to work out the disadvantages/advantages of running a mic
Click to expand...
transformer into a virtual earth.with the i/p z deterimed by r134 or
R142. That doesnt look like a quiet solution. I havent seen this done
on a mic amp before.
It might mean that you can get away with having a small(cheaper)
transformer.

I'd normally go with Mr Bears sugg. of a pga2500, but that doesnt
quite have the headroom of a 5534


martin
 
"martin griffith"
"Ban"
It only looks messy if you do not understand the circuit.

I was trying to work out the disadvantages/advantages of running a mic
transformer into a virtual earth.
Click to expand...

** You do not understand the circuit - it ain't no virtual earth to the
tranny.

The secondary is being used in "feedback input " mode - ie the signal is
introduced between the negative input of the op-amp and the reference point
of the feedback network. This allows the positive input to be grounded and
eliminates common mode input signal.

Can only be used with a floating signal source, ie from a tranny or a phono
cartridge with modified leads.



........... Phil
 
martin griffith wrote:

On Mon, 29 Aug 2005 04:49:13 GMT, in sci.electronics.design "Ban"
bansuri@web.de> wrote:

martin griffith wrote:
This is a Studer mic amp
http://home.datacomm.ch/gronerfamily/DIY/D19_MicAD/D19_MicAD_Op_Serv47.jpg

I just dont know if I like it. It looks messy. Or am I missing out on
a great innovative design


martin

It only looks messy if you do not understand the circuit.
I was trying to work out the disadvantages/advantages of running a mic
transformer into a virtual earth.with the i/p z deterimed by r134 or
R142. That doesnt look like a quiet solution. I havent seen this done
on a mic amp before.
Click to expand...
That puzzled me too. Maybe it's a whacky configuration I didn't fathom straight
away.

Inverting configurations are indeed invariably noisy and I wonder what kind of
load it presents tothe mic.


It might mean that you can get away with having a small(cheaper)
transformer.

I'd normally go with Mr Bears sugg. of a pga2500, but that doesnt
quite have the headroom of a 5534
Click to expand...
Stick a 10dB gain stage after the PGA2500. That'll resore the headroom. Shame
though. Best they could do with 5V supplies.

Graham
 
On Mon, 29 Aug 2005 16:47:39 +1000, in sci.electronics.design "Phil
Allison" <philallison@tpg.com.au> wrote:

"martin griffith"
"Ban"

It only looks messy if you do not understand the circuit.

I was trying to work out the disadvantages/advantages of running a mic
transformer into a virtual earth.


** You do not understand the circuit - it ain't no virtual earth to the
tranny.

The secondary is being used in "feedback input " mode - ie the signal is
introduced between the negative input of the op-amp and the reference point
of the feedback network. This allows the positive input to be grounded and
eliminates common mode input signal.

Can only be used with a floating signal source, ie from a tranny or a phono
cartridge with modified leads.



.......... Phil


Thanks, thats a bit clearer, I'll do a bit more head scratching
Click to expand...



martin
 
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