sorry Eva,
It's a little more complicated than that. Let's look at those excellent for MC transistors produced by Rohm - the 2SB737 and 2SD786 - we loved them , made heaps of MC front ends out of them , always biassed at 2+mA! for low noise with low source impedances! Then there's the electret condenser microphone preamp having to deal with sources of Mohms not tens of Ohms. Very different.
Horses for courses.
Greg
It's a little more complicated than that. Let's look at those excellent for MC transistors produced by Rohm - the 2SB737 and 2SD786 - we loved them , made heaps of MC front ends out of them , always biassed at 2+mA! for low noise with low source impedances! Then there's the electret condenser microphone preamp having to deal with sources of Mohms not tens of Ohms. Very different.
Horses for courses.
Greg
you will find low noise phono and mc pre design with noise analysis here:
http://www.national.com/an/AN/AN-222.pdf#page=1
more info from national on noise calculation:
http://www.national.com/an/AN/AN-104.pdf#page=1
http://www.national.com/an/AN/AN-222.pdf#page=1
more info from national on noise calculation:
http://www.national.com/an/AN/AN-104.pdf#page=1
amplifierguru said:
It's a little more complicated than that. Let's look at those excellent for MC transistors produced by Rohm - the 2SB737 and 2SD786 - we loved them , made heaps of MC front ends out of them , always biassed at 2+mA! for low noise with low source impedances! Then there's the electret condenser microphone preamp having to deal with sources of Mohms not tens of Ohms. Very different.
Greg
hienrich said:before anything else
it is also customary to know which topology are you refering
for.....
because talking about noises it varies with amplifier topologies used...
for better noise rejections used the MIRROR IMAGE topology.
rgrds,
macweb
can you give some sample schematics of your preferred circuit topology for an mc stage?
thanks for helping guys.
Suggest you also look at the ZETEX Semiconductor design notes at http://www.zetex.com/3.0/3-8-2a.asp . Look at DN11 for a MC amp. They don't give specific information biasing, just a design idea.
Regards,
Ray
Regards,
Ray
There is a schematic for a MC amp at http://www.st-and.demon.co.uk/Audio/700/700page5.html . In this case the transistors are biased at abut 1.3 mA. Years ago I saw a design for a MC amp where the input transistor was biased at 10 mA. If I recall correctly they used a TIP30 as the first stage because of the low base spreading resistance of around 10 ohms.
Regards,
Ray
Regards,
Ray
the circuit from zetex is usually called discrete opamp. I've made that and currently used as mc frontend with addition of current sources. but i'm still not contented with the performance, it still has noise, about -50db i think with a 30db gain. it might be because my mc fontend has still no case.
the mc frontend circuit from armstrong looks quite like an mc headamp. i haven't tried that.
the mc frontend circuit from armstrong looks quite like an mc headamp. i haven't tried that.
jondavis said:the circuit from zetex is usually called discrete opamp. I've made that and currently used as mc frontend with addition of current sources. but i'm still not contented with the performance, it still has noise, about -50db i think with a 30db gain. it might be because my mc fontend has still no case.
the mc frontend circuit from armstrong looks quite like an mc headamp. i haven't tried that.
Any schematics for your circuit?
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