Off-hand, the theoretical noise floor of a microphone is at -139dBu. But what really is it you want to measure?
http://rupertneve.com/company/notes/impedance-and-noise/
http://rupertneve.com/company/notes/impedance-and-noise/
I want to measure microphone (dynamic & condenser type) output level, audio signal and DC bias of a mic preamp.
I'm choosing between Agilent U3402A 5 1/2 digit Dual Display at $600 and Agilent 34401A 6 1/2 digit at $1,072.
Agilent Technologies Test Equipment - U3402A - Multimeters - Bench - Allied Electronics
Agilent Technologies Test Equipment - 34401A - Multimeters - Bench - Allied Electronics
I'm choosing between Agilent U3402A 5 1/2 digit Dual Display at $600 and Agilent 34401A 6 1/2 digit at $1,072.
Agilent Technologies Test Equipment - U3402A - Multimeters - Bench - Allied Electronics
Agilent Technologies Test Equipment - 34401A - Multimeters - Bench - Allied Electronics
I heard that many of the U-series equipment are rebranded products from asia. So you may want to take that into consideration.
The HP 34401a is blue blood Agilent and has been the standard for a long time. You can't go wrong with it if you can afford it.
A used HP 3457 is far cheaper and its performance is in the same class of HP 34401a.
The HP 34401a is blue blood Agilent and has been the standard for a long time. You can't go wrong with it if you can afford it.
A used HP 3457 is far cheaper and its performance is in the same class of HP 34401a.
I think an oscilloscope will be far more useful in (pre)amp design than a multimeter...
Greetings,
Andreas
Agreed!
Get a used Tek 7000 series with a differential plug-in. you can then measure uV on top of a lot of common mode offset and noise.
DMM will read nonsence here and you'll have no choice but believe it!
I already have a Tek TDS2012B scope. Right now I'm using a Fluke 179 (6,000 count) multimeter, will this suffice?
That is not much use for low level measurements! 2mV/cm max sensitivity and very high bandwidth.
As previously asked - what do you want to measure?
Re: "Right now I'm using a Fluke 179"
this is OK for AC voltages in power circuits but only has a specified AC Voltage bandwidth up to 500Hz - so not much good for Audio....
Fluke spec sheet: http://assets.fluke.com/datasheets/2155a.pdf
Let us know what you want to measure and further assistance can be given, as said before!
Mik
this is OK for AC voltages in power circuits but only has a specified AC Voltage bandwidth up to 500Hz - so not much good for Audio....
Fluke spec sheet: http://assets.fluke.com/datasheets/2155a.pdf
Let us know what you want to measure and further assistance can be given, as said before!
Mik
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For a bench DMM with the full Audio bandwidth for AC measurements and maths functions for dB and dBm measurements - perhaps the Fluke 8846A
However for Noise and low level AC measurements a good Analog true rms AC millivolt meter is probably best - if you find a good one with an AC output, you can then use this to act as a 'pre-amp' for your 'scope. Look as a starting point also for an instrument with bandwidth and weighting filters for Noise Measurements built in. The Radford ANM2 would be my first choice.
Personally I have instruments very similar to both, amongst many others, together with Tek 7000 series 'scopes and various plugins as suggested earlier in this thread for measuring Audio Circuitry and there really isn't a 'one stop solution' to do all of what you are asking!
Mik
However for Noise and low level AC measurements a good Analog true rms AC millivolt meter is probably best - if you find a good one with an AC output, you can then use this to act as a 'pre-amp' for your 'scope. Look as a starting point also for an instrument with bandwidth and weighting filters for Noise Measurements built in. The Radford ANM2 would be my first choice.
Personally I have instruments very similar to both, amongst many others, together with Tek 7000 series 'scopes and various plugins as suggested earlier in this thread for measuring Audio Circuitry and there really isn't a 'one stop solution' to do all of what you are asking!
Mik
IMO, a meter is rarely the right choice for these measurements. I'd consider building a nice preamp for your scope, maybe differential and maybe with some built in filters, to duplicate the scope plug-in functions, so you can get down to the noise floor and so you can make accurate small signal response measurements.
Conrad
Conrad
IMO, a meter is rarely the right choice for these measurements. I'd consider building a nice preamp for your scope, maybe differential and maybe with some built in filters, to duplicate the scope plug-in functions, so you can get down to the noise floor and so you can make accurate small signal response measurements.
Conrad
well Conrad, how do you think the OP, Ronnie4416, will be able to adequately build, test and calibrate such a 'preamp' which fundamentally is very similar to the reasons for this thread being posted?
I'm sure He and others following this thread will be very interested in your response
Mik
Not terribly difficult really. Start with a low noise opamp setup for some fixed gain and flat response. There's a plethora of them out there these days. Check the noise with the input shorted and with various values of input shunts. Check the response with a divider. Speaking of dividers, making up some decent dividers would probably be extremely useful for the mic preamp too. Now, I am assuming the OP has a scope to use the preamp with, as a meter alone isn't sufficient to design signal amplifiers with a great deal of confidence. Since we're talking response, hopefully I'm not assuming too much by assuming a signal generator is also available. Once a flat amplifier is available, some simple RC filtration should be added, since specifying noise without specifying bandwidth tends to be a meaningless exercise. IMO, the main purpose of the preamp isn't so much looking at the output signal of the mic amp, which should be of reasonable amplitude on its own, but for looking at output noise, supply noise and signals on what is supposedly "ground".
CH
CH
For a bench DMM with the full Audio bandwidth for AC measurements and maths functions for dB and dBm measurements - perhaps the Fluke 8846A
8846A price is $1,395 almost same price as Agilent 34410A ($1,298 @ Test Equipment Depot) these meters have 6.5 digits resolution. If this is overkill for mic preamp design what about considering the Agilent U3402A 5.5 digit resolution for $600 (Agilent Technologies Test Equipment - U3402A - Multimeters - Test & Measurement - Allied Electronics) which is less than half the price of 8846A or 34410A.
If 5.5 digit is still too much maybe I'll just settle with my basic Fluke 179 (6,000) handheld meter or find a better handheld meter like the Fluke 287/289.
The 34410A is a really nice meter; we have a couple at work. I'd love to have one on my bench, but there's simply nothing in audio that requires 6.5 digits of resolution or justifies the cost of the thing. The useful features are things like programmable filtration, zeroing and offset. I think it also measures capacitance and maybe inductance. The other place it shines is resistor matching/measurement. If you want to make precision dividers (you do, whether you know it yet or not), the 4-terminal resistance measurement is excellent. OTOH, for far less money you can get one of the old HP 345x meters with similar accuracy. They are, however, way bigger than the new meters. You just need to be sure it works and is calibrated. I use a 3455 and am just as happy as if I was in my right mind.
Conrad
Conrad
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