This is an unbalanced mic buffer for measurement mic use. It will be built into the mic wand and allow easy swapping of ECM capsules for loudspeaker testing and capsule testing and provide for longer cables than the ECM capsule alone.
The output will go to an unbalanced mic pre with switchable gain and from there to unbalanced sound card line in. All inputs and outputs in the chain are unbalanced.
I posted my first try in another forum. See post #37 here: http://www.diyaudio.com/forums/solid...quested-4.html
After a lot of reading and outlining the discussion of jan.didden and Amblifier in the thread above, I think I have come up with an improved circuit below.
Here are my calculations. Pardon the non-conventional presentation.
Ic = .0045 A = 4.5 mA (Should swing a bit less than 4.5V P-P into 1k. Input will probably never see more than 1V P-P [but you never know!] and load should be well above 1K)
Re = 9V/.0045 A = 2000 Ohm = 2k
2N5210 hfe = 250
Ib = .0045/250 = .000018 A = .018 mA
Bias string I = (10)(.000018 A) = .00018 A = .18 mA
Bias string Rb = 9V/.00018 A = 50000 Ohm = 50k
Rb2 = (4.5V+.65V)/.000018 A = 28611 Ohm = 28.7k
Rb1 = 50000 Ohm - 28611 Ohm = 21389 Ohm or 21.5k or Rb1a = 5k and Rb1b = 16.5k
MIC bias resistance 9k or Rm1a = 3.01k and Rm1b = 6.04k
RL and CL are loads for the sim. PS is either 9V battery or 9V regulated supply located at the mic pre about 40 feet from the buffer circuit.
Can C4 and or C5 be left out since C3 is very close to the rest of the circuit?
Any help or advice on improving this unbalanced buffer will be appreciated. The idea is to be able to get it to work well and to get it into a mic wand or connector.
Here is the circuit and its sim from LTS.
Thanks
The output will go to an unbalanced mic pre with switchable gain and from there to unbalanced sound card line in. All inputs and outputs in the chain are unbalanced.
I posted my first try in another forum. See post #37 here: http://www.diyaudio.com/forums/solid...quested-4.html
After a lot of reading and outlining the discussion of jan.didden and Amblifier in the thread above, I think I have come up with an improved circuit below.
Here are my calculations. Pardon the non-conventional presentation.
Ic = .0045 A = 4.5 mA (Should swing a bit less than 4.5V P-P into 1k. Input will probably never see more than 1V P-P [but you never know!] and load should be well above 1K)
Re = 9V/.0045 A = 2000 Ohm = 2k
2N5210 hfe = 250
Ib = .0045/250 = .000018 A = .018 mA
Bias string I = (10)(.000018 A) = .00018 A = .18 mA
Bias string Rb = 9V/.00018 A = 50000 Ohm = 50k
Rb2 = (4.5V+.65V)/.000018 A = 28611 Ohm = 28.7k
Rb1 = 50000 Ohm - 28611 Ohm = 21389 Ohm or 21.5k or Rb1a = 5k and Rb1b = 16.5k
MIC bias resistance 9k or Rm1a = 3.01k and Rm1b = 6.04k
RL and CL are loads for the sim. PS is either 9V battery or 9V regulated supply located at the mic pre about 40 feet from the buffer circuit.
Can C4 and or C5 be left out since C3 is very close to the rest of the circuit?
Any help or advice on improving this unbalanced buffer will be appreciated. The idea is to be able to get it to work well and to get it into a mic wand or connector.
Here is the circuit and its sim from LTS.
Thanks