Topic: SP-CMC-4U mics from Sound Professionals

[Church-Audio]

So everyone jumped on the battery box bandwagon, There was a decrease in distortion but it was primarily from connecting the mic to the LINE INPUT, and secondarily because of the use of a voltage over 5 volts. There has been talk about increasing the voltage to 12 or 15 volts that does not do shit for distortion percentages in most electret capsules.

Chris

So I originally had a pair of CMC-8s that loved to distort at high SPL.  I decided to get the three wire done (by hyper-plane) and using the 9v battery box, I still get a little distortion, but it isnt nearly as bad.  I wonder if there might be something up with my mics (maybe i need to clean them or something?).  I am running CMC-8s (3-wire mod) > 9v battery box (3-wire) > MT 24/96 (mic in).

Now, one thing I thought of was using a 12v battery instead.   I wonder if those little mini 9volts are too weak for the mics (at least for the amount of time I need to use them for).  Any thoughts Chris?

I am always amazed at how some people say their CMC-8s never distort, yet mine will.

Three wire reduces the distortion of these mics to about 4% at 114db.. My mod reduces the output of the capsule by a further 4db from three wire, but it decreases the distortion down to 0.5% at 114db! so when you combine my mod with a good preamp you get very good signal to noise ratio and very good spl handling. So you lose some gain but you gain some headroom. This mod should not be done for people that want to do nature recording but I suspect most people that want to do nature recording would want to go to a DPA 4060. And not use a cardioid at all.

Chris

[poorlyconditioned]

So everyone jumped on the battery box bandwagon, There was a decrease in distortion but it was primarily from connecting the mic to the LINE INPUT, and secondarily because of the use of a voltage over 5 volts. There has been talk about increasing the voltage to 12 or 15 volts that does not do shit for distortion percentages in most electret capsules.

Chris

So I originally had a pair of CMC-8s that loved to distort at high SPL.  I decided to get the three wire done (by hyper-plane) and using the 9v battery box, I still get a little distortion, but it isnt nearly as bad.  I wonder if there might be something up with my mics (maybe i need to clean them or something?).  I am running CMC-8s (3-wire mod) > 9v battery box (3-wire) > MT 24/96 (mic in).

Now, one thing I thought of was using a 12v battery instead.   I wonder if those little mini 9volts are too weak for the mics (at least for the amount of time I need to use them for).  Any thoughts Chris?

I am always amazed at how some people say their CMC-8s never distort, yet mine will.

Three wire reduces the distortion of these mics to about 4% at 114db.. My mod reduces the output of the capsule by a further 4db from three wire, but it decreases the distortion down to 0.5% at 114db! so when you combine my mod with a good preamp you get very good signal to noise ratio and very good spl handling. So you lose some gain but you gain some headroom. This mod should not be done for people that want to do nature recording but I suspect most people that want to do nature recording would want to go to a DPA 4060. And not use a cardioid at all.

Chris

I don't know about your measurement methodology, Chris, but three-wire and your "4.7k" mod should be similar in terms of distortion.  Also, you will notice that most wiring diagrams, like AT8533 power modules, AKG CK1000, CK9x, etc. all use three-wire powering of the FET, so I am not the only one who thinks this is the correct circuit!  I agree with you that the 4.7k mod "throws away" some possible gain (the 4dB you report), but it is useful for at least two reasons: 1) it allows the mic to be powered with two wires only (saves wiring complexity), 2) it allows you to use "standard" two wire battery boxes (eg., 1/8" miniplug).  I have pretty much converted all of my mics to two-wire/4.7k mod for this reason.

OK, to all you doubters out there.  You may think your mics are not distorting.  But even at moderate levels, there is something there.  Change to three wire or 4.7k mod and you *will* see an improvement in sound quality, even at moderate volumes.  You might not hear it, but it is there...

Oh yeah, as far as the DPA406x, there is a lot going on inside that capsule.  I *think* there is some kind of active circuit (one or more buffer transistors).  In addition to handling overload with only two wires, this mic has some kind of impedance converter so it can drive long cables and/or low impedance inputs, like transformer input preamps.  I have not taken one apart though, so I don't know exactly what is inside.  Any volunteers, lol??

  Richard

[Church-Audio]

So everyone jumped on the battery box bandwagon, There was a decrease in distortion but it was primarily from connecting the mic to the LINE INPUT, and secondarily because of the use of a voltage over 5 volts. There has been talk about increasing the voltage to 12 or 15 volts that does not do shit for distortion percentages in most electret capsules.

Chris

So I originally had a pair of CMC-8s that loved to distort at high SPL.  I decided to get the three wire done (by hyper-plane) and using the 9v battery box, I still get a little distortion, but it isnt nearly as bad.  I wonder if there might be something up with my mics (maybe i need to clean them or something?).  I am running CMC-8s (3-wire mod) > 9v battery box (3-wire) > MT 24/96 (mic in).

Now, one thing I thought of was using a 12v battery instead.   I wonder if those little mini 9volts are too weak for the mics (at least for the amount of time I need to use them for).  Any thoughts Chris?

I am always amazed at how some people say their CMC-8s never distort, yet mine will.

Three wire reduces the distortion of these mics to about 4% at 114db.. My mod reduces the output of the capsule by a further 4db from three wire, but it decreases the distortion down to 0.5% at 114db! so when you combine my mod with a good preamp you get very good signal to noise ratio and very good spl handling. So you lose some gain but you gain some headroom. This mod should not be done for people that want to do nature recording but I suspect most people that want to do nature recording would want to go to a DPA 4060. And not use a cardioid at all.

Chris

I don't know about your measurement methodology, Chris, but three-wire and your "4.7k" mod should be similar in terms of distortion.  Also, you will notice that most wiring diagrams, like AT8533 power modules, AKG CK1000, CK9x, etc. all use three-wire powering of the FET, so I am not the only one who thinks this is the correct circuit!  I agree with you that the 4.7k mod "throws away" some possible gain (the 4dB you report), but it is useful for at least two reasons: 1) it allows the mic to be powered with two wires only (saves wiring complexity), 2) it allows you to use "standard" two wire battery boxes (eg., 1/8" miniplug).  I have pretty much converted all of my mics to two-wire/4.7k mod for this reason.

OK, to all you doubters out there.  You may think your mics are not distorting.  But even at moderate levels, there is something there.  Change to three wire or 4.7k mod and you *will* see an improvement in sound quality, even at moderate volumes.  You might not hear it, but it is there...

Oh yeah, as far as the DPA406x, there is a lot going on inside that capsule.  I *think* there is some kind of active circuit (one or more buffer transistors).  In addition to handling overload with only two wires, this mic has some kind of impedance converter so it can drive long cables and/or low impedance inputs, like transformer input preamps.  I have not taken one apart though, so I don't know exactly what is inside.  Any volunteers, lol??

  Richard

Hey Richard they are very similar but there is a least with the circuit I was using to test a difference with the AT 853 I did not test the three wire vs my mod with any other mic. So I should quantify my statement that I found with the AT-853 vs my 4.7k mod that there was still more distortion in the 4.7k mod then in the three wire using the circuit I built. Based on your schematic.

[Arni99]

So everyone jumped on the battery box bandwagon, There was a decrease in distortion but it was primarily from connecting the mic to the LINE INPUT, and secondarily because of the use of a voltage over 5 volts. There has been talk about increasing the voltage to 12 or 15 volts that does not do shit for distortion percentages in most electret capsules.

Chris

I am always amazed at how some people say their CMC-8s never distort, yet mine will.

I am sure MY sp-cmc-8 cards would DISTORT if i taped the same show at the same venue at the same spot WITH you .
For really loud indoor rock shows(pearl jam, chili peppers) I always use my sennheiser MM-HLSC-1 cardioids. Am sure they would also distort if I stood in front of the PA...or the soundguy has severe ear-damage yet and fires 120 or 130dB into the audience;).

[Javier Cinakowski]

Am sure they would also distort if I stood in front of the PA

I doubt it.  I threw some serious SPL's at the HLSC's, no distortion. Jet engine approved...

[Alchemy]

I have a Knopfler tape that was done near the stacks with the HLSC's and when listening closely, you can definitely hear some slight bits of bass distortion in parts. He was running with two wire with a battery box. It's all about location...location...location...I think.

[Arni99]

I have a Knopfler tape that was done near the stacks with the HLSC's and when listening closely, you can definitely hear some slight bits of bass distortion in parts. He was running with two wire with a battery box. It's all about location...location...location...I think.

I feel most on the safe side with my sennheisers at loud amplified indoor arena rock shows.
the sp-cmc-8 cards sound crystal clear BUT too thin IMHO.
The Sennheiser HLSC(MKE40´s) sound coloured but good, with more punch behind the sound.

Right now my Sennheiser MM-HLSO omnis(MKE-2s) are my favourite Mics both regarding sound and size .

[roggae]

I want a pair of the HLSO or the DPA4060. 

I wonder if the DPA's are worth the price compared to the HLSO?

[Arni99]

I had the chance to test "old" 4.7k modded AT853s(SP-CMC-4) for some days.
The strange thing I realized was almost no separation between left and right mic.
When I spoke into the left mic(right mic was far away) both indicators on the levelmeter bounced up to almost the same level?!
Is this a result of the 4.7k mod?
The 4.7k mod on these mics was done within the 3.5mm plug and not within the capsules.
I could see 1 small resistor when i opened the plug.

[Javier Cinakowski]

I had that same problem arni.  My mod was originally done using 1 resistor in the mini plug sharing the yellow wire.  In theory the signals should not combine, but they do.  I had the mod redone with 2 resistors, one on each yellow and the results are fantastic...  You must match the resistors.

[Arni99]

Am sure some "masters of soldering" can explain why signals are combined and not separated when using 1 resistor only .