Harvey Gerst
New member
I promised Marik I would take some pictures of the circuit inside my original ECM8000. Here they are:
ECM8000 Mods
- Thread starter Marik
- Start date
Flatpicker
...
So, now that the capsule is floating, did you have to put a screen around it like the schematic shows?
Marik
Pro Microphone Design
Harvey,
Thank you for the pics. It seems that you have the same version as Ausrock. It has the same circuit, as mine stock, but different PCB layout and instead of suface mount coupling caps they use electrolytics.
Flatpicker,
<So, now that the capsule is floating, did you have to put a screen around it like the schematic shows?>
No, the body of the mic works as a screen. You have to insulate the capsule from the body= from the ground. I did it applying coat of polyurethane to the capsule. Be carefull not to apply it to the black material covering the diaphragm, as it will change the sound.
Drummer4Life05,
<How much would someone charge to perform that MOD that Marik just posted? Would you be willing to do it Marik?>
Yes, I can do it for anybody--just PM me. If there is enough interest, I think it would be a good idea to make a dedicated PCB. Alternatevly, I will be more than happy to help and give tips to those, who can perform the mod themselves.
I will be out of town until mid March. After that I will send it to Harvey. We will see what is his verdict.
<I'd love to hear how they now compare to something like MXL 603s (what I was originally going to buy, but maybe I can save some $$$$), or even Rode NT5's.>
ECM8000 is very different from these mics. First, it is omni; second, it is a very small diaphragm mic, so it has completely different direction pattern. Keep in mind that if your room acoustically is not good, or noisy, the mic will pick these flaws very 'nicely' unless you use it for close micing. These mics will be awsome to record with Jecklin disk.
One more thing. The output of the modded mic is about 4-5db less than stock one. Originally, I made additional gain make up JFET stage. However, to get a nice sound out of it I had to bias it pretty high, so the supply voltage dropped considerably. The fact that Audix is actually about 9db lower than ECM8000, made me feel that for sake of sound quality, it is better to leave it as it is, as any modern pre crancked up 4 extra db's won't add noticable noise.
Thank you for the pics. It seems that you have the same version as Ausrock. It has the same circuit, as mine stock, but different PCB layout and instead of suface mount coupling caps they use electrolytics.
Flatpicker,
<So, now that the capsule is floating, did you have to put a screen around it like the schematic shows?>
No, the body of the mic works as a screen. You have to insulate the capsule from the body= from the ground. I did it applying coat of polyurethane to the capsule. Be carefull not to apply it to the black material covering the diaphragm, as it will change the sound.
Drummer4Life05,
<How much would someone charge to perform that MOD that Marik just posted? Would you be willing to do it Marik?>
Yes, I can do it for anybody--just PM me. If there is enough interest, I think it would be a good idea to make a dedicated PCB. Alternatevly, I will be more than happy to help and give tips to those, who can perform the mod themselves.
I will be out of town until mid March. After that I will send it to Harvey. We will see what is his verdict.
<I'd love to hear how they now compare to something like MXL 603s (what I was originally going to buy, but maybe I can save some $$$$), or even Rode NT5's.>
ECM8000 is very different from these mics. First, it is omni; second, it is a very small diaphragm mic, so it has completely different direction pattern. Keep in mind that if your room acoustically is not good, or noisy, the mic will pick these flaws very 'nicely' unless you use it for close micing. These mics will be awsome to record with Jecklin disk.
One more thing. The output of the modded mic is about 4-5db less than stock one. Originally, I made additional gain make up JFET stage. However, to get a nice sound out of it I had to bias it pretty high, so the supply voltage dropped considerably. The fact that Audix is actually about 9db lower than ECM8000, made me feel that for sake of sound quality, it is better to leave it as it is, as any modern pre crancked up 4 extra db's won't add noticable noise.
Last edited:
Swapmaster
New member
Does this mod change the response graph of the mic? If not, would using a WM61 capsule be possible?
Flatpicker
...
I think he did use a WM61. The schematic reads WH61, but he probably meant WM61Swapmaster said:
Hey Marik..
I see you using a 10V Zener diode for regulating the mic capsule supply voltage, and I had an idea pop into my head...
I was wondering (since I haven't gotten one yet to play with) if the noise from that is signficant or not.. I don't know offhand how sensitive to supply noise the capsules are, but it might be an improvement to put a voltage regulator in there instead.
Might be a bit of a struggle to squeeze one in, but you probably could get a TO-39 version of a LM317 (would need a few extra parts) or maybe a 7808. (wouldn't) Too bad there isn't a common 10v version. 12V might be too high for a WM-61. You could put a smaller cap in than that big 220uF, for a little more room.
What do you think? I'd add a load resistor to provide maybe 5-10 mA of current thru the regulator, they quiet down a bit with some load, the capsule and resistor divider would probably only load it a mA or so.
I thought of this due to recently building a RF white noise generator for testing my Ham radio, and it uses a zener (with a HUGE of ampification, though) as the wideband noise source!
A regulator should be a much quiteter supply than the zener, as well as better supply rejection, whether that would actually be a noticable reduction in noise or not, it would be interesting to find out..
I see you using a 10V Zener diode for regulating the mic capsule supply voltage, and I had an idea pop into my head...
I was wondering (since I haven't gotten one yet to play with) if the noise from that is signficant or not.. I don't know offhand how sensitive to supply noise the capsules are, but it might be an improvement to put a voltage regulator in there instead.
Might be a bit of a struggle to squeeze one in, but you probably could get a TO-39 version of a LM317 (would need a few extra parts) or maybe a 7808. (wouldn't) Too bad there isn't a common 10v version. 12V might be too high for a WM-61. You could put a smaller cap in than that big 220uF, for a little more room.
What do you think? I'd add a load resistor to provide maybe 5-10 mA of current thru the regulator, they quiet down a bit with some load, the capsule and resistor divider would probably only load it a mA or so.
I thought of this due to recently building a RF white noise generator for testing my Ham radio, and it uses a zener (with a HUGE of ampification, though) as the wideband noise source!
A regulator should be a much quiteter supply than the zener, as well as better supply rejection, whether that would actually be a noticable reduction in noise or not, it would be interesting to find out..
Marik
Pro Microphone Design
Jon,
Thank you! Excellent suggesion.
You know, honestly--I thought about it at first and then....forgot.
< don't know offhand how sensitive to supply noise the capsules are, but it might be an improvement to put a voltage regulator in there instead.>
Yes, the capsule is quite sensititve to the noise. In fact, I spent a great deal of time to quiet it down. The 15K and 220um cap are sufficient to suppress it to minimum, however the voltage regulator should be definitely better. Higher voltages ( I tried up to 14V) on the capsule make situation worse.
<7808. (wouldn't) Too bad there isn't a common 10v version.>
Do you know the trick with diode in the middle leg? Two diodes should do.
<What do you think? I'd add a load resistor to provide maybe 5-10 mA of current thru the regulator, they quiet down a bit with some load, the capsule and resistor divider would probably only load it a mA or so.>
We cannot do it. Don't forget, here we have barbarian practice to put two 6.81K resistors at the phantom rails for 14ma total current. The circuit current is already about 5 ma, which is a lot for the mic. The further increase will drop the voltage significantly.
Anyway, I gotta try it and see...
Thank you! Excellent suggesion.
You know, honestly--I thought about it at first and then....forgot.
< don't know offhand how sensitive to supply noise the capsules are, but it might be an improvement to put a voltage regulator in there instead.>
Yes, the capsule is quite sensititve to the noise. In fact, I spent a great deal of time to quiet it down. The 15K and 220um cap are sufficient to suppress it to minimum, however the voltage regulator should be definitely better. Higher voltages ( I tried up to 14V) on the capsule make situation worse.
<7808. (wouldn't) Too bad there isn't a common 10v version.>
Do you know the trick with diode in the middle leg? Two diodes should do.
<What do you think? I'd add a load resistor to provide maybe 5-10 mA of current thru the regulator, they quiet down a bit with some load, the capsule and resistor divider would probably only load it a mA or so.>
We cannot do it. Don't forget, here we have barbarian practice to put two 6.81K resistors at the phantom rails for 14ma total current. The circuit current is already about 5 ma, which is a lot for the mic. The further increase will drop the voltage significantly.
Anyway, I gotta try it and see...
Last edited:
Cool. It sounds good. If you ever have anything, I'd love to hear the results. Sounds very nice. I don't know if you recorded anything previously that you could rerecord as a before-after test, but even just something on its own would be cool. How much $ do you think this cost you overall?
Marik said:
Oh, yeah.. raising the ground lead above ground, temporarily forgot that one.. I'd put a bit of bypassing across them, not as noisy as zeners but putting a couple more junctions in there probably would keep the regulator from being as quiet as it could be.
Great.. love to hear how it works.. I'm not sure how much current is neccicary for noise reduction, might be just a mA or two.. I know that minus regulators need a bit of current to regulate properly, and are probably worse than the positives. Try up to as much as you can get away with.. maybe a little dab will do ya.. maybe it's not needed.
I need to do some reading on the phantom powering system.. sounds like there's special requirements to work with.
arcanemethods
New member
Rossi said:
I use this:
http://www.web-tronics.com/2200-mtp.html
It's a silver ink pen. More than enough conductance. That path is a _very_ low current path. I coat the trace with silicone or E6000 after the ink dries. Beware of closing off the vent hole.
Bob
arcanemethods
New member
Marik said:
I have reason to believe that it is mostly Johnson noise from the acoustic damping resistance of air and from that of the pressure equalization vent. I'll be really curious to see if your effort results in a reduction.
Bob
Marik
Pro Microphone Design
<It's a silver ink pen. More than enough conductance. That path is a _very_ low current path. I coat the trace with silicone or E6000 after the ink dries. Beware of closing off the vent hole.>
Bob,
I was thinking of using it, however prices on this stuff are high.
<I have reason to believe that it is mostly Johnson noise from the acoustic damping resistance of air and from that of the pressure equalization vent. I'll be really curious to see if your effort results in a reduction.>
As I mentioned before, after a few attemps I gave up playing with capsule itself. I use WM61A capsule instead of stock WM60. It has 4 db lower noise. Better filtering reduces the noise compare to the stock mic even further.
I believed that besides of acoustic dumping resistance noise, the FET contributes into overall noise in significant way. If you have other thoughts please share.
Canopus,
<I don't know if you recorded anything previously that you could rerecord as a before-after test, but even just something on its own would be cool.>
I have a stock unmodified one, and yes, I will record something and post it.
<How much $ do you think this cost you overall?>
So far to me it cost at least 50 hours of trying different things, soldering, listening, recording, comparing etc. Plus some scandals and accusations like 'your mics are more important than me' etc. And.... parts cost.
Bob,
I was thinking of using it, however prices on this stuff are high.
<I have reason to believe that it is mostly Johnson noise from the acoustic damping resistance of air and from that of the pressure equalization vent. I'll be really curious to see if your effort results in a reduction.>
As I mentioned before, after a few attemps I gave up playing with capsule itself. I use WM61A capsule instead of stock WM60. It has 4 db lower noise. Better filtering reduces the noise compare to the stock mic even further.
I believed that besides of acoustic dumping resistance noise, the FET contributes into overall noise in significant way. If you have other thoughts please share.
Canopus,
<I don't know if you recorded anything previously that you could rerecord as a before-after test, but even just something on its own would be cool.>
I have a stock unmodified one, and yes, I will record something and post it.
<How much $ do you think this cost you overall?>
So far to me it cost at least 50 hours of trying different things, soldering, listening, recording, comparing etc. Plus some scandals and accusations like 'your mics are more important than me' etc. And.... parts cost.
Swapmaster
New member
Dont' worry too much about accusations like 'your mics are more important than me'. No matter what your hobby is, a woman will always think it is more important than her. But remember that their hobbies ARE more important than you and they will tell you so without hesitation.
clintrubber
New member
Hi - sorry if this appears twice after all - but it seems like
the first time posting something went wrong.
<<And I like the twist with the ground of the capsule at a mid-tap.>>
<Normally, to make the capsule's FET to swing a lot of voltage,
you would need to use +/- voltage (+ to drain, and - to source through bias resistor) and to connect the capsule's body (internally connected to diaphragm) to ground. Since we have only + polarity of the phantom supply, we fake it. This way diaphragm in reference to the FET is still at
the same relationship.>
So if I understand it correctly the capsule's body is lifted because the source has been lifted as well, OK ?
<Yes it is a dual matched FET. It got to the place of 2A1349 (same package).
You could use matched 2SK170 here, as well.>
Nice, that could be convenient.
<<#1 could it be that the 1M biasing resistor should also be halfway the supply i.s.o. ground?>>
<No, I use this resistor as a gate leak one, so the buffer is self-biased.
If you connect it as a bias resistor the stage will draw too much current and the supply voltage will drop considerably.>
I'm not sure how to understand the self biasing in combination with a current source.
Doesn't the lower JFET (which is configured as a current source) determine the current draw of the 2-JFET buffer ?
Assuming the lower JFET is set for say some 3 mA (just a rough guess from an average -GR-JFET), this sounds like the upper JFET prevents the lower JFET from fully reaching that estimated 3 mA ? As a consequence the output impedance of the current source can suffer since the lower JFET isn't in saturation.
To prevent too big of a current: another approach could be to change the dimensioning of the current source so that it does develop its full current (in combination with a higher bias-voltage for the upper JFET.
<(know that, done that)>
Right ! Better than theory !
I must add that I don't know how sonics will change (for better or worse) and if all this probably neater biasing really matters, but the benefit from using a current source i.s.o. a resistor might improve things further.
So again, in the end the sound matters, however it is achieved.
Bye,
Peter
the first time posting something went wrong.
<<And I like the twist with the ground of the capsule at a mid-tap.>>
<Normally, to make the capsule's FET to swing a lot of voltage,
you would need to use +/- voltage (+ to drain, and - to source through bias resistor) and to connect the capsule's body (internally connected to diaphragm) to ground. Since we have only + polarity of the phantom supply, we fake it. This way diaphragm in reference to the FET is still at
the same relationship.>
So if I understand it correctly the capsule's body is lifted because the source has been lifted as well, OK ?
<Yes it is a dual matched FET. It got to the place of 2A1349 (same package).
You could use matched 2SK170 here, as well.>
Nice, that could be convenient.
<<#1 could it be that the 1M biasing resistor should also be halfway the supply i.s.o. ground?>>
<No, I use this resistor as a gate leak one, so the buffer is self-biased.
If you connect it as a bias resistor the stage will draw too much current and the supply voltage will drop considerably.>
I'm not sure how to understand the self biasing in combination with a current source.
Doesn't the lower JFET (which is configured as a current source) determine the current draw of the 2-JFET buffer ?
Assuming the lower JFET is set for say some 3 mA (just a rough guess from an average -GR-JFET), this sounds like the upper JFET prevents the lower JFET from fully reaching that estimated 3 mA ? As a consequence the output impedance of the current source can suffer since the lower JFET isn't in saturation.
To prevent too big of a current: another approach could be to change the dimensioning of the current source so that it does develop its full current (in combination with a higher bias-voltage for the upper JFET.
<(know that, done that)>
Right ! Better than theory !
I must add that I don't know how sonics will change (for better or worse) and if all this probably neater biasing really matters, but the benefit from using a current source i.s.o. a resistor might improve things further.
So again, in the end the sound matters, however it is achieved.
Bye,
Peter
arcanemethods
New member
Marik said:
I think it can be found at a lower cost but I never considered $13 or $14 worth worrying about. It's very useful stuff and if stored upright in a fridge will last a long time.
RE the noise, a friend of mine took one apart and just hung an equivalent capacitor across the FET in place of the diaphragm to measure the pure FET contribution to a WM61A and it was considerably less tha half of what it was before the modification. The difference can only be atributable to acoustic Johnson noise.
Another way of viewing acoustic Johnson noise is thermally agitated air molecules impinging on the diaphragm. The level of this is related to temperature and the acoustic resistances involved in the device.
The following paper was the first quantitative treatment of it I found:
http://scitation.aip.org/getabs/ser...=cvips&gifs=Yes&jsessionid=513271077874424341
and Dick Campbell sent me a response to that paper that appeared in a subsequent issue of the journal that specifically called it Johnson noise and did a further analysis of it, strongly implicating the pressure equalization port. I don't have a link to that response, unfortunately.
Bob
arcanemethods
New member
I believe the bias in microphone FET's such as are used in the WM60 or WM61 is done via the leakage current through an integrated diode connected from source to gate and that the bias voltage is essentially zero regardless of the voltage on the can.
Any voltage between the can and the gate/backplate is effectively ignored so that the can could be left at circuit ground for induced noise shielding.
Bob
Any voltage between the can and the gate/backplate is effectively ignored so that the can could be left at circuit ground for induced noise shielding.
Bob
Flatpicker
...
Ha! You think it's bad now, wait until you have kids!Marik said:
Not that they're not worth it, but they greatly limit your time, which is why you're doing all this and I'm not helping. 
Anyway, wives/girlfriends never seem to see the other side of things. You've made a great pioneering contribution here, one that will probably stand for years to come. And I, for one, am very grateful!
Marik
Pro Microphone Design
arcanemethods said:
Bob,
Are you talking about conventional connection? Then yes, it is self biased, and is done through gate to source forward current, which is very small. However, I am using it as 'cathode follower', and believe that source resistor (which is BTW another source of the noise--I am using here Vishay 0.1%) sets the current--
tell me if I am wrong here--I was trying and couldn't find information about these FETs used in Panasonics. I read somewhere that these are "in house" ones. I was under impression that most of the noise comes from leaky gate junction, and attributed it to lack of gate-leak resistor. These guys usually high Mohms--U-47-100M, U67-400M, M49-150M, etc. Smaller capsule mics use up to 2Gohm.
Another question is about difference between WM60 and WM61. Once again, because of lack of information, I was under impression that the difference in their output and noise specs are because of different FETs, and mostly their different stray capacitance, which
loads the input. The 'conventional' connection makes it worse. The 'source follower' connection, where the gain is essentially unity, but the output is still different, also suggesteded that. However, now I start thinking that it might be a result of different back chamber construction...
I would appreciate your input or any info on that.
arcanemethods
New member
I had always thought that Vgs was held at zero by integrated diode leakage (many microphone FET's explicitly show them in the data sheets) but yesterday the following appeared in the micbuilders Yahoo group (formerly MicDIYers). I'd like to know what you make of it:
http://groups.yahoo.com/group/micbuilders/message/469
Frankly, this topic is starting to drift over my head and I would appreciate whatever you think the truth is.
Bob
http://groups.yahoo.com/group/micbuilders/message/469
Frankly, this topic is starting to drift over my head and I would appreciate whatever you think the truth is.
Bob