source: ECM Mic Preamplifier
Heys guys so I am building an electret microphone acoustic guitar pick up.
I have successfully built a mic pre amp with electret microphone according to the above diagram.
When I hook the output directly to the guitar amp it will produce a decent sound level but there is no comparison to that produced by a electric guitar. I know this is all about a output impedance ( hi-Z, low-Z, etc...) Here is the discription on the web site about this preamp "the overall voltage gain of the preamplifier is about 100x or 20dB"
One thing I have to mention about is I am using BC556 instead of BC549 since I don't have them around. Will it affect the amplification rate?
I guess I need a secound stage amplification in order to make the signal as larger as a guitar (hi-Z) output. Can anyone please tell me what I need in my secound stage? Another mic preamp? or audio preamp?
Thanks in advance.
I would expect this circuit to produce a voltage gain about 100x, which corresponds to 40dB. This is a lot of amplification and I wonder that you experience a lower level than the one delivered by an electric guitar.
Btw, powered by a 9V Block, power consumption is about 4~5mA, imho too much for a good battery lifetime.
To improve this, you should alter the emitter resistors of 2nd stage to 10kOhm.
Btw, powered by a 9V Block, power consumption is about 4~5mA, imho too much for a good battery lifetime.
To improve this, you should alter the emitter resistors of 2nd stage to 10kOhm.
I cannot guarantee my bulid is 100% correct and maybe for some reason the mic capsule is bypassed the amp circuit. Just guessing...
That is the point where tele-diagnostics get difficult.
Anyway, the drawn circuit diagram should be ok.
To trace the error, at first you could check the dc-values of all "nets" of the circuit and add these values to the circuit diagram and post the new circuit diagram here.
The circuit should be powered by its DC source with no signal at the input.
Anyway, the drawn circuit diagram should be ok.
To trace the error, at first you could check the dc-values of all "nets" of the circuit and add these values to the circuit diagram and post the new circuit diagram here.
The circuit should be powered by its DC source with no signal at the input.
Consider this is not a complicated circuit. I am going to bulid this one again once I got the bc549 from taydaelectronics. This may even take fewer work than debugging the circuit.
btw. I have just buit a even simpler one using a single 2N3904. schematic as following:
This one even generated a larger single than the previous one I built. So based on the schematic, can someone please tell me which one is better in sound quality, theoretically?
Many thanks.
btw. I have just buit a even simpler one using a single 2N3904. schematic as following:
An externally hosted image should be here but it was not working when we last tested it.
This one even generated a larger single than the previous one I built. So based on the schematic, can someone please tell me which one is better in sound quality, theoretically?
Many thanks.
You used PNP transistors instead of NPN in the other one, so it wouldn't work at all - you probably made a loss rather than a gain.
The first circuit will give more gain (as it has no negative feedback), and will have a lower output impedance. Presumably though the second circuit will have lower distortion, as it has negative feedback.
But why not just use a simple opamp?, far higher quality and dead simple to set the gain to exactly what you want, and adjustable if you need. Here's a suitable circuit:
Attachments
I try to open you circuit but it is too small for me to read.
Are you talking about this one?
An externally hosted image should be here but it was not working when we last tested it.
Actually I am a bit afraid of building a op-amp preamp. Since I fail couple time, with different op-amp...Despite it is a simple circuit...
Yes that one, I don't know why it went small?.
Opamps are VERY easy to use, easier than the transistor circuit you posted, build one and have a go - if it doesn't work post pictures and we'll try and help.
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