ECM8000 Mods

Doink,

The hardest part of the microphone is an output driver. It should have low output impedance and enough current capabilities to drive long cables. Yes, the circuit you reference to is very simple, but has serious compromises. First, the output impedance is very high at about 3 Kohm, so you won't be able to drive long cables, and connected to regular mic pre will result in serious degradation in bass response becase of impedance mismatch. Second, if you decide to do it anyway, I would suggest to make at least a "Linkwitz mod" so the capsule will have much better overload capabilities and better sound. If you go this way, here I would suggest to try Bob's idea you can find above about 'flipping' the capsule.
 
Finally I made some guitar and drum clips. Have a listen. Please note, we did not have any time to find the best position for the drums, neither the person who played them is a professional drummer. So, if it is possible, or if you can, please disregard 'artistic value', just listen to these tracks from the point of view of difference in the sound and SPL handling (esp. on kick), only.







 
I was informed that the stock drums clip doesn't work. I uploaded it agian, so here are the drum files:



 
Wow, night and day!

I think my plan will be to build the mic in the link I posted, then if that doesn't work out, get the B and do these mods. I don't think I could build an ECM8000 from scratch, even with it all drawn out.

I'm still waiting for the parts to get here.
 
It's been awhile since this project was over, but I still get emails and PMs about it. So here some more updates.

First, I cut off the resonator from the capsule--if you take black fabric jobbie off the capsule you will see that input hole is only about 2mm. Very carefully, with Xacto knife I cut it so, that the whole diaphragm is exposed to sound wave. Take great care not to damage diaphragm here.
Also, I changed a capsule tip--grill for tappered one. The original ribbed one was great for measurement purposes, but just did not sound musical to me.
That's how the last tracks I posted were recorded.

In a future I am planning to change the ciruit for a tube one, and also DIY my own capsule, so it will be much less noisy and would handle much more SPL (I am talking about 150-160 db).
But wait a second, is it a Behringer ECM8000 mod anymore?
 
Marik said:
Doink,

The hardest part of the microphone is an output driver. It should have low output impedance and enough current capabilities to drive long cables. Yes, the circuit you reference to is very simple, but has serious compromises. First, the output impedance is very high at about 3 Kohm, so you won't be able to drive long cables, and connected to regular mic pre will result in serious degradation in bass response becase of impedance mismatch. Second, if you decide to do it anyway, I would suggest to make at least a "Linkwitz mod" so the capsule will have much better overload capabilities and better sound. If you go this way, here I would suggest to try Bob's idea you can find above about 'flipping' the capsule.
Click to expand...

If you 'flip' the capsule, should you have to solder the standard "Linkwitz" mod?

Gune
 
Interesting to see this thread back up. I was reading it just the other day. Recently picked up an ECM8000 myself.

Reckon I might as well go ahead and do some mods on it, I already scratched up the "nose cap", pulled it off, and ripped the wires off the capsule =D
 
Gune said:
If you 'flip' the capsule, should you have to solder the standard "Linkwitz" mod?

Gune
Click to expand...

Not if the internal FET is symmetric. Flipping it in that case is identical to the mod. The way it could be assymetric is if there is a lower impedence path, like a diode or something, between the source and the gate. Some mic FET's have them and some don't. If they don't, they operate in "self biased" mode which relies on the junction leakage which should be pretty much the same between gate/source and gate/drain.

Best way to find out is to try it. If the quiescent current (voltage across the load resistor) changes signifigantly when flipped using the same supply voltage and load resistor, then it is assymetric and you will have to mod it instead. The experiment won't damage it using the usual voltages.

Oh, in case it's not obvious, when you flip it, keep the load resistor connected to the same pin. I.e. flip both the FET and the resistor between supply and ground.


Bob
 
I'm just now catching onto this tread. The link to the Linkwitz mod is down now. Does anyone have a consolidated build instructions, part list, pcb, anything that I could go on? Thanks!

Ben
 
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Hello All,

How is the nose cap secured on the ECM8000?
I try to dismantle it, but I failed.
I do not want to use brute force now, as I want to use it in the future...
 
seekup1982 said:
I'm just now catching onto this tread. The link to the Linkwitz mod is down now. Does anyone have a consolidated build instructions, part list, pcb, anything that I could go on? Thanks!

Ben
Click to expand...


still in the works?
 
JFET Pair

Marik and fellow DIYers, I've read through this thread three of four times and a thread over at Prodigy Professional (http://www.homerecording.com/bbs/showthread.php?t=111051&page=9&pp=25) to try to understand your (Marik's) mic pre. I have a few questions about the pre amp, if this is the wrong place to bring this up or there is information elsewhere that would help me, please point me in the right direction (I'm pretty new to this forum (this is my first post)).

1. Is the bottom JFET (of the pair) a constant current source? If so how is of use the the top JFET?

2. Since pin number 3 is tied to ground from an A.C. stand point, how is a ballanced output possible?

I understand everything to the left of the JFET pair and most of the things to the right, however help in understanding how the JFET pair work would be very much appreciated.
 
I thought after 2 years the interest to this thread was long gone...

I see almost 16700 hits. That's a surprise :eek: :eek: :eek:

Depth Charge said:
1. Is the bottom JFET (of the pair) a constant current source? If so how is of use the the top JFET?
Click to expand...

The top JFET is a source follower and the bottom, as you rightly noticed is its constant current source. It has a unity gain (as any SF) and it's output impedance is about 32 Ohm.


2. Since pin number 3 is tied to ground from an A.C. stand point, how is a ballanced output possible?
Click to expand...

It's called impedance balancing. Many modern microphones have this kind of topology. You can find an explanation here (scroll to the bottom):


http://www.uneeda-audio.com/zbal.htm
 
Substitute JFETs

Ah, so a signal isn't actually sent down line 3 like it is on line 2, line 3 just has the same impeadance to ground so that it picks up as much interference as line 2 so that the difference between them is just the desired signal? That's really quite elegant!

Would I be right in thinking that the 82 Ohm output resistor should actually be 79 Ohms (if the JFET output impedance is 32 Ohms) but 82 Ohms is the closest standard value?

Marik said:
Oops, I just payed attention I missed 47uf/50V electrotolytic before 15K resistor....
Click to expand...

By before the 15KOhm resistor do you mean to the left of it, or does it not matter whether it is to the left or right of the 15KOhm resistor?

I can't seem to find anywhare in the UK that sells the 2SK170 or 2SK389 GR, any suggestions for a substitute?

Thank you very much for your quick replies to my questions guys!
 
Wait, a capacitor in series with the 15K resistor would stop the front end of the circuit from receiving power, I'm a little confused now. Did you mean a cap from one end of the 15K resistor to ground?
 
Depth Charge said:
Would I be right in thinking that the 82 Ohm output resistor should actually be 79 Ohms (if the JFET output impedance is 32 Ohms) but 82 Ohms is the closest standard value?
Click to expand...

Yes.

By before the 15KOhm resistor do you mean to the left of it, or does it not matter whether it is to the left or right of the 15KOhm resistor?!
Click to expand...

I don't remember what I meant, but schematics looks right. I think later I replaced that cap with 220Mf value.

I can't seem to find anywhare in the UK that sells the 2SK170 or 2SK389 GR, any suggestions for a substitute?
Click to expand...

Quick googling gave me next sources:

www.borbelyaudio.com
http://www.grandata.co.uk/

Also some of the below might have it:

http://www.e44.com
http://www.radioson.com
http://www.gotronic.fr
http://www.cibot.com
http://www.radiospares.fr
http://www.farnell.com
http://www.selectronic.fr
http://www.electronique-diffusion.fr
 
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