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Thread: ECM8000 Mods

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    ECM8000 Mods

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    OK folks,

    Today I went to local GC and got ECM8000--just to play with it and to see what it's capable of. Of course, before the listening, the very first thing I opened it up. I swear, I remember seeing somewhere on forums a picture of its PCB with tiny transformer. The picture on the box also shows a transformer. I got quite a shock--you know, when you expect something for sure and it's not there. It was not in mine! Anyway I don't care much for that, as you can imagine which quality it should be considering $39 for the whole thing. I opened the capsule (I had to put some strength). I heard rumors, and it indeed suspiciously looks like Panasonic WM60:

    http://www.panasonic.com/industrial/...wm60_a_dne.pdf

    I 'reversed' schematics. The input stage is on BC118 (silicon transistor), and output on A1349--I could not find any documentation, but it looks like two transistors in one body. The crutial signal path capasitors are surfice mounts , and the board is full of other 'goodies'.
    As for the mods.
    The very first thing is capsule itself. The Panasonic (as many other electrets) has a built in FET. This FET is responsible for the noise and low SPL. The easiest way to go is to make a 'Linkwitz mod'. Originally, the FET is hooked up without source resistor. The mod is to hook it as a source follower, which reduces noise and increases SPL to 140Db.
    There is another capsule--WM61 which has about 4Db lower noise, but also lower SPL. However with Linkwitz mod the SPL is still at very respectable 134Db. The ultimate solution would be disassemble the capsule, cut off the internal FET and instead, use 2SK170, selected for high transconductance. I will probably have to order some Panasonics and play with them.
    Tomorrow I will start serious listenings, measurements, tweakings, recordings, etc. I will also try to use Oktava 012 pre (I will have to modify it a little to make it work) to see if and how much difference it makes.
    So, Gentlemen,
    If you are interested and don't get bored, please let me know and I will keep you posted on the progress.

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    Thumbs up Re: ECM8000 Mods

    Originally posted by Marik
    The very first thing is capsule itself. The Panasonic (as many other electrets) has a built in FET. This FET is responsible for the noise and low SPL. The easiest way to go is to make a 'Linkwitz mod'. Originally, the FET is hooked up without source resistor. The mod is to hook it as a source follower, which reduces noise and increases SPL to 140Db.
    Right on.

    It's about time someone came up with a mod for that thing. It just seems like such an obvious candidate for it.

    Keep us posted, and thanks.

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    Re: ECM8000 Mods

    Originally posted by Marik
    ...I swear, I remember seeing somewhere on forums a picture of its PCB with tiny transformer. The picture on the box also shows a transformer. I got quite a shock--you know, when you expect something for sure and it's not there. It was not in mine! ...However with Linkwitz mod the SPL is still at very respectable 134Db. The ultimate solution would be disassemble the capsule, cut off the internal FET and instead, use 2SK170, selected for high transconductance. I will probably have to order some Panasonics and play with them...
    I didn't think there'd be a transformer, but you never know. That's really good 'cause had there been one, it'd be pretty cheap and would have just caused another "work-around".

    As far as the capsule's FET causing the noise, I guess that kills the FET replacement idea. Anyway, the Linkwitz mod is pretty simple. It's like: Doh! Why doesn't Panasonic sell them like that in the first place??!! And do we know for sure the sensitivity isn't going to drop after changing the polarity of the FET? I wonder if we can find out what Earthworks is doing that makes theirs so much quieter.

    Concerning the surface mount caps, the hard partís not replacing them, itís finding out whatís in there in the first place.

    (edited to add more info)
    Last edited by Flatpicker; 01-28-2004 at 07:13.

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    This is a post from Arny Kruger on rec.audio.pro this morning:

    "A well-known local choral group - the Detroit Concert Choir use a QTC1 matched pair mounted on a high stand. That plus spot mics for the soloists.

    If you want to listen to some real-world evidence of how noisy QTC1s really are, here's where you can get their recordings for a nominal charge: http://www.detroitconcertchoir.org/ . You can probably email them and find out which mics were used for which recordings.

    I'm using what I thought are the far noisier ECM8000s, and the noise that shows up on my recordings is basically the room, not the mics. (see additional comments below).

    Here's a recent technical discussion of the self-noise of the ECM8000's from one of our sister NGs:


    From: Norbert Hahn <hahn@hrz.tu-darmstadt.de>
    Message-ID: <lvquuvcvafp6gv381hn4cul6hjd5tig5rk@4ax.com>

    "Today I did some measurements with some of my mics, AKG Body C 480 B with CK61 ULS capsule (Equivalent noise level (IEC 651 A weighted) 13 dB, Sennheiser MKH50 (Equivalent noise level 12 dB) and the Behringer ECM-8000. Microphone preamp was a Behringer UB802."

    "Hm, well the ECM-8000 has about 10 dB more noise than the Senn and the AKG, which measure the same when reduced to a single number."


    As I read this, these measurements put ECM8000 self-noise in the 22-23 dB range. But there are some other relevant issues that are discussed in more detail about 2/3 through this post.

    Note that the mic preamp used was hardly SOTA, but the mics in question are pretty sensitive so the mic pre wasn't seeing terribly low-level signals.

    Ironically 22-23 dB noise puts ECB-8000s in the same range of self-noise as the spec on the QTC1 per http://www.earthwks.com/ns/qtc1.html . Yes, this is pretty stinky by the standards of some large-diaphragm mics.

    Note that the ECM8000 is flat up to about 25 KHz, while the QTC1 is flat up to about 40 KHz. It's probable that the QTC1 has a far smaller diaphragm, which makes the modest self-noise spec more impressive.

    Returning to the comments of the person (Norbert Hahn) who tested various mics for self-noise:


    "However, the frequency curve of the unfiltered self noise is quite different: The ECM 8000 has almost white noise between 300 Hz and 15 kHz, dropping then with 6 dB per octave. Between 300 Hz and 30 Hz the self noise rises by 18 dB at lower frequencies. Thus, the self noise of the ECM 8000 sounds like a mixture of pink and white noise."

    "The frequency curve of the self noise of the AKG looks like pink noise between 30 Hz and 3 kHz and like white noise between 3 kHz and 45 kHz."

    "The frequency curve of the self noise of the Sennheiser MKH 50 is quite different. Between 30 Hz and 4 kHz is looks pretty much like pink noise (a little more rise at lower frequencies though), but above 6 kHz the noise rises by 8 dB within one octave, peaking at 18 kHz. Above that the noise drops by 18 dB/octave. So that mic has the least amount of noise in the same octaves where the ear is most sensitive."


    This is one of those things that doesn't seem to show up on many spec sheets - the spectral content of noise very much affects how we perceive it. Spectral content is much of the difference between the sound of wind blowing, the sound of sea crashing on rocks, and a 150 psi air hose hissing its heart out given that the 20-20 KHz or A-weighted SPLs were the same.

    My own take on this issue is that small-diaphragm omnis can get a bad rap for noise because they are so truly omni. If there's a noise in the room they'll probably pick it up. For example, many of my recordings include trivial but personal comments made by the musicians and people in the audience, made in low voices and whispers while they are waiting for things to start. Not so with cardioids in the same general vicinity.

    I still lust after a pair of QTC1s, but its probable that I am getting a fair simulation of them with my ECM8000s. Probably good enough of a simulation to judge a number of relevant issues, like "Are small omnis for me and my application?"

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    Thanks, Harvey - very interesting points here indeed! I checked rap this morning, but missed that post.

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    I'm actually not bothered as much by the self-noise thing as I am with the SPL handling. It's one of those things where it would be nice to be able to take advantage of an omni for the sake of close-mic'ing without as much proximity effect. There might also be accoustic considerations, which can only be exaggerated by the characteristics an omni mic brings to the table (let's face it -- a lot of our basements aren't Abbey Road), furthering the utility of being able to close mic.

    Problem is on most loud sources, it just plain clips, so really close-micing isn't an option in a lot of situations. And it is an issue with this particular mic.

    Marik, I'm not sure if this helps at all, but I have a couple of Audix TR-40's here. I might be willing to lend one of them to you for a few days (for scientific purposes) if I have your word that it will be returned quickly and in one piece.

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    I only use my 8000s for drum overheads and they do a great job. No noise issue at all and no clipping trouble. They are a bit noisy if you try to use them for quiet acoustic recording though, so I just don't do it. For 40 bucks they're hard to beat.
    Last edited by StevenLindsey; 01-28-2004 at 15:35.

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    Harvey, Thank you for very interesting and as always, very informative post. I will go to RAP later to check it.

    <Note that the ECM8000 is flat up to about 25 KHz, while the QTC1 is flat up to about 40 KHz. It's probable that the QTC1 has a far smaller diaphragm, which makes the modest self-noise spec more impressive.>

    The diaphragm in ECM8000 is actually very small--6mm diameter, the rest is just a housing. If you look at the mic from the capsule, the black thing is the actual size of the diaphragm.

    Flatpicker,

    <As far as the capsule's FET causing the noise, I guess that kills the FET replacement idea. >

    I don't know what kind of FET is used in the capsule and its specs. It might be a very good one, but it might be not so. Only experiments can show it. The 2SK170 is a very nice sounding and very low noise device, so IMO it would be worth at least to give it a try. If it doesn't work I just loose $5 and my time, but what I learn is worth more than that. Oh yeah, and if I don't try I just won't sleep at nights .

    <Why doesn't Panasonic sell them like that in the first place??!! And do we know for sure the sensitivity isn't going to drop after changing the polarity of the FET? >

    I wish they were selling them without FET at all. The sensitivity is not the biggest issue--it can be easily taken care of later, in the preamp circuit. The simple changing of bias of the first stage will do the job.

    <I wonder if we can find out what Earthworks is doing that makes theirs so much quieter.>

    I heard many times that Earthworks use Panasonics which are selected for low noise and frequency response, but again, it's just rumors.

    Chessrock,

    <I'm actually not bothered as much by the self-noise thing as I am with the SPL handling.>

    Same here, my main intention is to see what this small diaphragm is capable of sonically and how far it can go. If along the way I will be able to drop the noise by some dbs it would be nice...
    Of course, I will completely rebuilt the preamp section as well.

    <Marik, I'm not sure if this helps at all, but I have a couple of Audix TR-40's here. I might be willing to lend one of them to you for a few days (for scientific purposes) if I have your word that it will be returned quickly and in one piece.>

    You've got my word! It would be very nice of you, and of course, I'd be very interested to compare to mine, when I have something done with it.

    Finally, I found data for A1349, so later tonight I will redraw the schematics nicely and neatly (as much as I can), and post it along with some pics, if you are interested.

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    Im soo glad that this forum has gotten back to Mics.

    Ill keep lurking and listening.

    Malcolm
    Strap it Cross Dat Stereo Buss !!

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    Originally posted by Marik
    You've got my word! It would be very nice of you, and of course, I'd be very interested to compare to mine, when I have something done with it.
    Feel free to PM me with your contact info if you'd like, and I'll try to get a hold of you in the next week or so. It seems to me like the Audix does slightly better with the noise floor, and has a lot better SPL handling, so it would be interesting to know what they do to achieve that. Who knows -- you might be on to something. I'd hate to see you put Stapes out of business, though.

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