Hi,
I need a portable microphone preamplifier for occasional use. I found Analog Devices SSM2019 preamplifier chip. It needs only one resistor for gain adjustment.
Can I really make a single chip preamp with it? Can I just add a resistor, and connect mic to IN+ and IN-, add batteries to V+ and V-, and tie OUT and REF to RCA CD input jacks of cheap home stereo? No singing. Just speaking to <100 audience. Volume is what I need, not quality. Thanks.
I need a portable microphone preamplifier for occasional use. I found Analog Devices SSM2019 preamplifier chip. It needs only one resistor for gain adjustment.
Can I really make a single chip preamp with it? Can I just add a resistor, and connect mic to IN+ and IN-, add batteries to V+ and V-, and tie OUT and REF to RCA CD input jacks of cheap home stereo? No singing. Just speaking to <100 audience. Volume is what I need, not quality. Thanks.
Well, what kind of microphone is this? In case of an electret you would have to provide a low-noise bias supply as well. Not a big deal when you're using 9V blocks anyway, run 6.8k to +9V. Then an input coupling cap (47µ electrolytic), bias resistor, two 100-220 µF electrolytics for power buffering, a few ground connections, and you should be set. A gain of 100 should be OK.
Are you aware of how you'd have to wire up the whole shebang?
Are you aware of how you'd have to wire up the whole shebang?
Cheap But Effective....
$70.00 or so.
Behringer: TUBE ULTRAGAIN MIC100
Behringer MIC100
A wireless mic system is another solution.
Dan.
$70.00 or so.
Behringer: TUBE ULTRAGAIN MIC100
Behringer MIC100
A wireless mic system is another solution.
Dan.
Attached schematic is my understanding of your reply.
1) Dynamic microphone with 1/4" plug, not detachable cable type. 15' chord.
2) Can I use bipolar type for input coupling cap? Since I don't care about quality, I can go with a lower value and lose some low frequency. Correct?
3) I don't understand "bias resistor". Did you mean the gain setting resistor?
4) Can I just use caps without resistors in battery power? (since I don't care about quality as far as sound is not unbearably noisy?)
5) I am going to put this in a metal case. Should I float ground from metal case?
Thanks.
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Your schematic is almost there but wouldn't work since the noninverting input does not have a DC current path. The input transistors may only need a few hundred nanoamps of base current but those need to come from somewhere.
A mic like 1) usually is wired up balanced (you may want to check). I.e. no coax, just two wires twisted. You could go for a balanced input then. It wouldn't even need to have input coupling caps at all. Just run one 2k2 resistor per input pin to ground for appropriate input impedance and a DC current path. (Helps draining ESD and stuff, too.)
(Do make sure you stick the schematic of the finished circuit underneath, you never know what you may want to do with the thing in the future.)
4) If you already have two 9V batteries, you can use the midpoint between them as a perfectly fine ground - the resistors are only needed if you want to split a single supply.
5) Ground should connect to case in exactly one spot. The output would seem to be a suitable place, for example.
BTW, I would not rely on DC offset being so small that you can do away with an output coupling cap. 10µ bipolar electrolytic should be fine.
The gain setting resistor should be a metal film type, but I guess you knew that. Doesn't need to be anything overly fancy other than that (not non-magnetic or anything). The 2k2 input resistors should also be metal film, primarily for tolerance reasons.
Like in the Fig. 4 application circuit, I would also include a few hundred pF worth of ceramic cap in between the two inputs. You will have to try whether this keeps out RFI well enough, otherwise some more filtering effort will be required.
A mic like 1) usually is wired up balanced (you may want to check). I.e. no coax, just two wires twisted. You could go for a balanced input then. It wouldn't even need to have input coupling caps at all. Just run one 2k2 resistor per input pin to ground for appropriate input impedance and a DC current path. (Helps draining ESD and stuff, too.)
(Do make sure you stick the schematic of the finished circuit underneath, you never know what you may want to do with the thing in the future.)
4) If you already have two 9V batteries, you can use the midpoint between them as a perfectly fine ground - the resistors are only needed if you want to split a single supply.
5) Ground should connect to case in exactly one spot. The output would seem to be a suitable place, for example.
BTW, I would not rely on DC offset being so small that you can do away with an output coupling cap. 10µ bipolar electrolytic should be fine.
The gain setting resistor should be a metal film type, but I guess you knew that. Doesn't need to be anything overly fancy other than that (not non-magnetic or anything). The 2k2 input resistors should also be metal film, primarily for tolerance reasons.
Like in the Fig. 4 application circuit, I would also include a few hundred pF worth of ceramic cap in between the two inputs. You will have to try whether this keeps out RFI well enough, otherwise some more filtering effort will be required.
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