Transformerless SM58

[Folkcafe]

If I do the mic comparisons, do you have a suggestion as to which of these available to me I should use - I've also got a behringer 1820 and somewhere an old Lexicon Omega, if either of those jump out (good or bad) plus a pair of Behringers = x32 and x32 rack sitting in the store. I know they claim to be the same design as the midas preamps?

What, not even some bare bone Millennia HV preamps? This test sucks already.

On a serious note, not sure what a comparison of stage vocal mics will tell us on unknown voices. Crowd seems into it so why not.

 

[drtechno]

this leading into preamp impedance test is interesting in a confusing way..... reading a couple articles the highest impedance is recommended it seems but then the most infamous sought and copied is 1073 which is 1.2k and 300ohm....and the ISA110 1.3~1.5k the other most famous preamp, neither being 10k ohm or even 3k ohm.

JZ mics in short says

• High Load Impedances (the impedance on your preamp) will give you more overall level
• Higher impedances also tend to make the low-end and low-midrange content of the mic much flatter, as well as have no dampening effect on the higher frequencies
• Low Load Impedances (again, relating to the input of the preamp) will result in a lower output signal
• Low Load Impedances also add more emphasis on the low end and lower midrange frequencies, as well as picking up the resonances lower down the spectrum much more.
• You'll sometimes find that the upper frequencies are slightly more diminished and the mic will lack that upper detail

The ISA One has 4 settings:

• Low - 600 Ohm
• ISA 110 (we referred to this as Mid for the video) - 1400 Ohm
• High - 2400 Ohm
• Very High - 6800 Ohm.

So which preamp will it be? Tascam mentioned seems to be in the center impedance, but the Midas might be better for a test?

ISA 110 is an op amp mic preamp and the loss interaction is centered around its input transformer that terminates with a 2.2K resistor. But the termination impedance is not constant, so its higher input impedance at lower gain levels.

 

[drtechno]

If I do the mic comparisons, do you have a suggestion as to which of these available to me I should use - I've also got a behringer 1820 and somewhere an old Lexicon Omega, if either of those jump out (good or bad) plus a pair of Behringers = x32 and x32 rack sitting in the store. I know they claim to be the same design as the midas preamps?

I would have to dig and find info on the 1820 but the omega is an instrumentation amp type like is in a lot of interfaces (INA217)

 

[rob aylestone]

I think it's that we've all got a fixed perception if common mics, which might be wrong. We are looking at 'labels' - as in X is dull, Y is bright, Z is thin and W is bassy - DrTechno's comments made me wonder a bit if people can hear the things we give the labels to? So a pretty simple task - record 8 mics on the same subject, and it probably has to be in the same place, with the rest of the chain the same, on a 'normal' preamp, so it's more generic than specific. Then, the mic swaps make some sort of sense, if we listen carefully. If I number the mics, and make the recordings shortish and control distance, we can note the ones we hate, like or are just sort of OK on. If everyone hates one, likes another - then it's worked. If everyone has different likes and dislikes, then that too actually says something.

 

[drtechno]

I think it's that we've all got a fixed perception if common mics, which might be wrong. We are looking at 'labels' - as in X is dull, Y is bright, Z is thin and W is bassy - DrTechno's comments made me wonder a bit if people can hear the things we give the labels to? So a pretty simple task - record 8 mics on the same subject, and it probably has to be in the same place, with the rest of the chain the same, on a 'normal' preamp, so it's more generic than specific. Then, the mic swaps make some sort of sense, if we listen carefully. If I number the mics, and make the recordings shortish and control distance, we can note the ones we hate, like or are just sort of OK on. If everyone hates one, likes another - then it's worked. If everyone has different likes and dislikes, then that too actually says something.

I imagine the character is the same, but slightly different from different mic pres due to the way they make the input circuit so they can provision a condenser mic. The Phantom power circuits as well as the coupling are losses the passive dynamic mic must pass through. In reality, the input impedance comes from the source impedance of dynamic mics and the input impedance for condenser mics is the ac load of the input termination. These combination condensor/dynamic mic preamp designs they settled on to support both types has always been a design compromise in one way or another. Which really questions why they continue into recording world with them in the first place. A PA console, I see the benefit of generically supporting both types, But one would think they would do something more audiospecific in the recording sector.

You've mentioned that your Midas M32 has an input impedance of 10K (schematic attached). Which is derived from 13.6K from the phantom power injecting resistors, 10 ohm plus the resistance of the capacitor at test fequency plus the 47K Rin resistor in series that is in parallel to the 13.6K (~96020) for the actual impedance of approx. 11,912.72 ohms. The dynamic mic signal has to pass through the 10 ohm resistors and the 47uf cap and the resistance at that frequency to the ideal infinite impedance of the gain device.

One thing I wondered is why recording people haven't looked at broadcasting equipment and how they make mic preamp circuits that are specific to dynamic mics. They don't have any of the phantom power, and the blocking capacitors. I do notice they limit the impedance to 200 ohms in the lowest design and their datasheet distortion rating is derived from shorting the input and measuring noise floor at 50, 80, and 100% gain. Its way different than how they measure but don't guarantee specifications in recording sector equipment.