Hi guys. I've got a Rane MS1 microphone preamp, and it's got 1k input impedance. I'm interested in upping the input impedance, and I'm sure someone here could provide me with guidance.
The MS-1a has 10k input impedance, and I read in another forum that R7 and R8 in the MS-1a schem set the impedance. Is this true? Here is the schematic:
http://www.rane.com/pdf/old/ms1asch.pdf
Does this mean that to up the impedance of the MS-1 I would change corresponding resistors R6 and R7? If so, would I change them to the same value? The input stage is similar but not identical.
http://www.rane.com/pdf/old/ms1sch.pdf
Any guidance would be appreciated.
Of less importance, people also talk about changing out the opamps, but I'm not sure that given the circuit, there would be much of a noticeable or necessarily positive effect. It seems like the strongest thing I could do is add bypass caps to the signal path electrolytics. Any opinions on this?
Thanks!
The MS-1a has 10k input impedance, and I read in another forum that R7 and R8 in the MS-1a schem set the impedance. Is this true? Here is the schematic:
http://www.rane.com/pdf/old/ms1asch.pdf
Does this mean that to up the impedance of the MS-1 I would change corresponding resistors R6 and R7? If so, would I change them to the same value? The input stage is similar but not identical.
http://www.rane.com/pdf/old/ms1sch.pdf
Any guidance would be appreciated.
Of less importance, people also talk about changing out the opamps, but I'm not sure that given the circuit, there would be much of a noticeable or necessarily positive effect. It seems like the strongest thing I could do is add bypass caps to the signal path electrolytics. Any opinions on this?
Thanks!
Yes, R6 and R7 defines the input impedance, and changing them to 20KOhm would give you the 10KOhm input impedance. Those 20K resistors seem to be precision resistors. You could use standard 22K resistors, just get a handful of them and match them. Also, use metal film resistors, not carbon film resistors.
Depending on availability, it just might be cheaper to get two 1% metal film resistors.
I would not change anything else if you are happy with the preamp otherwise, but I have not looked closely.
Good luck, Peter
Depending on availability, it just might be cheaper to get two 1% metal film resistors.
I would not change anything else if you are happy with the preamp otherwise, but I have not looked closely.
Good luck, Peter
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looks like the second schematic shows a pair of 1.24k (1k24) resistors loading the balanced input.
That is equivalent to 620ohms
I see the first schematic shows inductors on the input for extra interference attenuation.
You could add this yourself.
A bead just big enough to pass both wires from pins 2 & 3 through, would raise the impedance before the two caps. Those two caps should be connected to shell/chassis at the input socket, not to audio ground.
That is equivalent to 620ohms
I see the first schematic shows inductors on the input for extra interference attenuation.
You could add this yourself.
A bead just big enough to pass both wires from pins 2 & 3 through, would raise the impedance before the two caps. Those two caps should be connected to shell/chassis at the input socket, not to audio ground.
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