ruffrecords

iiiMyMic
« on: May 22, 2017, 04:50:00 PM »
I recently purchased this mic from China after it was discussed here. When it arrived I noticed it had a rattle if shaken so I took it apart. As you can see from the attached pic, one of the screws holding the diaphragm has fallen out. Can I just put this back or do I need to do something special to ensure correct tension?

https://drive.google.com/open?id=0B_n67A1hN3qtcDJSNkNpdW1xT0k

Cheers

Ian


Re: iiiMyMic
« Reply #1 on: May 22, 2017, 05:36:18 PM »
Just put back till snug. Done.

ruffrecords

Re: iiiMyMic
« Reply #2 on: May 22, 2017, 06:17:37 PM »
Just put back till snug. Done.

OK, done that. Seems to work fine. Thanks.

Cheers

Ian

RuudNL

Re: iiiMyMic
« Reply #3 on: June 15, 2017, 05:03:50 AM »
The diaphragm shows a very interesting pattern, or is it just the picture?
Also it seems there are little spots all over the diaphragm, at regular distances. (Or is it the backplate?)
Where did you get this one?
There is a solution for every problem!

http://www.vansteenisaudio.nl

ruffrecords

Re: iiiMyMic
« Reply #4 on: June 15, 2017, 06:11:17 AM »
The pattern is real. It is not an artefact of the photo.

This mic was mentioned on a thread here (I cannot find it any more) as an interesting cheap mic that might be worth investigating so I decided to buy one. I got it from Aliexpress:

https://www.aliexpress.com/item/ESound-34mm-Brand-Professional-Gold-Large-Diaphragm-Best-Quality-Condenser-Microphone-Studio-Recording-Microfone-Broadcasting/32784545874.html?spm=2114.13010608.0.0.a6gerW

Cheers

Ian

RuudNL

Re: iiiMyMic
« Reply #5 on: June 15, 2017, 12:24:14 PM »
Thanks!
There is a solution for every problem!

http://www.vansteenisaudio.nl

Re: iiiMyMic
« Reply #6 on: June 16, 2017, 01:21:30 PM »
you should return the mic...
removing even one screw affects diaphragm's tension...
and the screw has probably touched the diaphragm , and made some permanent damages...

Re: iiiMyMic
« Reply #7 on: June 19, 2017, 08:45:21 AM »
Hi Ian,
Are you planning on converting the imic to valve ?
Quite a small body on it ,space will be at a premium .
One excellent topology Im experimenting with at the moment is the Bruel and Kjaer cathode follower principle ,the output transformer resides in the power supply and the cathode follower feedback is terminated at the power supply end of the cable .
As the B&K mics are for measurement there almost all omnis ,but the same circuit works well with traditional side address condenser capsules too ,with a lowered capsule bias voltage of course.
the other nice thing about the B&K is that the cathode follower output is available at the psu allowing it to drive a high impedence valve preamp and therefore eliminating the usual transformer coupling from the mic circuit itself .
Ive converted a behringer B-1 ,just using a strip of vero board for now ,what I intend to do is actually solder the sub min tube directly to the 7 pin output socket at the base of the mic ,the only other components that reside in the mic itself are the grid resistor and the potential divider /blocking cap for the capsule bias voltage , this arrangement would make it really easy to convert almost any condenser mic into a valve mic very quickly and easily .
Anyway hopefully some food for thaught.....

ln76d

Re: iiiMyMic
« Reply #8 on: June 19, 2017, 09:48:29 AM »
You would be surprised how small tube mic can be ;)
I've built tube mikes even in smaller bodies :D

Re: iiiMyMic
« Reply #9 on: June 19, 2017, 09:56:10 AM »
Another great benefit of the cathode follower is it provides huge input resistance to the capsule ,many time the grid resistors value, thus maximising capsule output voltage, the bandwidth is also huge due to the NFB loop encompassing the output cable.


ruffrecords

Re: iiiMyMic
« Reply #10 on: June 19, 2017, 12:13:53 PM »
I have no plans to convert it to a tube mic but it might make an interesting project for the future.

Cheers

Ian

RuudNL

Re: iiiMyMic
« Reply #11 on: July 01, 2017, 09:11:03 AM »
What a joke... I ordered one of these, mainly for the body.
The microphone arrived with a broken capsule mount and the capsule itself was secured with only one screw...
Fortunately the capsule doesn't look damaged.
On the PCB, one (47 ohm) resistor to pin 2 of the XLR connector was missing!...
There were holes in the PCB for teflon feedthroughs, but the wires of the resistors were simply dangling free, just not making contact with the grounded copper of the PCB.
FET is a 2SK30A, polarisation voltage from the DC/DC converter is a little over 40 volts.
One thing is clear: the manufacturer doesn't spend too much money on quality control!  ;D
There is a solution for every problem!

http://www.vansteenisaudio.nl

Khron

Re: iiiMyMic
« Reply #12 on: July 01, 2017, 10:28:24 AM »
One could argue "you get what you pay for" ;D

That being said, the BM800's i got WERE still in one piece (although granted, they're plain electrets for half the price :P )
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

RuudNL

Re: iiiMyMic
« Reply #13 on: July 01, 2017, 11:12:14 AM »
Well, anyway it has a 'real' condenser capsule.
After a bit of changes (FET bias was way off...), it even doesn't sound too bad. (Although I am only going to use the body and the (metal) shockmount.
There is a solution for every problem!

http://www.vansteenisaudio.nl

ruffrecords

Re: iiiMyMic
« Reply #14 on: July 01, 2017, 04:39:23 PM »
Well, anyway it has a 'real' condenser capsule.
After a bit of changes (FET bias was way off...), it even doesn't sound too bad. (Although I am only going to use the body and the (metal) shockmount.

Are you talking about the same mic I bought (iiiMyMic) or something else?

Cheers

Ian

RuudNL

Re: iiiMyMic
« Reply #15 on: July 01, 2017, 05:02:10 PM »
Are you talking about the same mic I bought (iiiMyMic) or something else?

Cheers

Ian

Yes, it's the same one! You inspired me more or less...  ;D
The one I have was rather noisy. I increased the value of the capacitor in parallel with the 6.8 v. zener from 47 to 470 uF.
Also I added a resistor of 470 ohm in series with the 6.8 v. zener. This brought down the zener noise (and the overall noise at the output) significantly, without changing the voltage on the audio board very much.
The capsule itself isn't really bad, although I have a feeling that some low end is missing.
I have to test this further. As far as I can see the electronic circuit is 'flat', so I suspect the capsule.
There is a solution for every problem!

http://www.vansteenisaudio.nl

ruffrecords

Re: iiiMyMic
« Reply #16 on: July 02, 2017, 03:15:00 AM »
Yes, it's the same one! You inspired me more or less...  ;D
The one I have was rather noisy. I increased the value of the capacitor in parallel with the 6.8 v. zener from 47 to 470 uF.
Also I added a resistor of 470 ohm in series with the 6.8 v. zener. This brought down the zener noise (and the overall noise at the output) significantly, without changing the voltage on the audio board very much.
The capsule itself isn't really bad, although I have a feeling that some low end is missing.
I have to test this further. As far as I can see the electronic circuit is 'flat', so I suspect the capsule.

This mic was mentioned in a thread here that I can no longer find. That is what inspired me to try one. Yours looks to be in very poor condition compared to mine. But I have no experience with correct microphone construction. I will now take mine apart and look at it with more critical eyes. The capsule is rather intriguing though isn't it?

Cheers

Ian

RuudNL

Re: iiiMyMic
« Reply #17 on: July 02, 2017, 04:07:11 AM »
I think you saw the microphone here: https://groupdiy.com/index.php?topic=65738.0
Yesterday I measured the frequency response of the amplifier/impedance converter circuit, and it is ruler flat from 20 Hz-20 KHz.
The capsule looks very 'special', but it is only the rear diaphragm that has the strange pattern, the front looks normal.
Also I noticed that the capsule is thin (in size), compared to other cardioid capsules.
There is a solution for every problem!

http://www.vansteenisaudio.nl

ruffrecords

Re: iiiMyMic
« Reply #18 on: July 02, 2017, 05:21:49 AM »
I think you saw the microphone here: https://groupdiy.com/index.php?topic=65738.0
Yesterday I measured the frequency response of the amplifier/impedance converter circuit, and it is ruler flat from 20 Hz-20 KHz.
The capsule looks very 'special', but it is only the rear diaphragm that has the strange pattern, the front looks normal.
Also I noticed that the capsule is thin (in size), compared to other cardioid capsules.

Thanks for finding the link. I was beginning to think  had imagined it.

Cheers

Ian