TOPIC: Re: Low quality design or faulty mic ?

Hi everybody!
I started to mod my mic. This is the first result with a generic 220uf electrolytic installed where George suggested:

noise floor without cap:


noise floor with cap:


So a great first result. No spikes at all!!

I'll now try with an LT1763 3.3V regulator to see if the noise floor can even go down. Indeed George has a noise floor of about -90dBFS while I achived about 53-133= -80dbFS.

Unfortunately I don't have a good selection of smd parts so I can't test the mod suggested from minidsp team

off topic: how can you switch from db to dbfs scale in REW? so we can compare better our results!

thanks!!

Michele

willshui wrote:
I think... It's affected. Mine is #0514 and has got the spikes from 1kHz as you can see from the graph. Open rew and do a measure with no sound in your room (measure the silence )

hi, your pictures are too small to see. Can you tell me how to measure the "silence"? Thanks.

georgio wrote: Hey George, thanks for the work you've done on finding a fix... Question: any suggestion on where to find one of these capacitors? I looked on eBay and Amazon and I'm confused, not so easy to find.
devteam wrote: What size are these resistors? I can only do down to 805 as that's the limit of my equipment and my eyesight (not to mention shaky hands... I'm 62). How do we know which Rev we have? do they correspond to batch? like first batch is Rev A, second batch is Rev B and third batch is Rev C? Are you saying a reworked board will be available to all owners of a Rev B UMIK who wish to swap out their current board? Any details on the specifics of how this updated board mod is going to be 'rolled out' to the owners who want/need it?

miki_ada wrote: In the upper left of the RTA window there is a little drop down box... click on it and select.
willshui wrote: Use the RTA window and wrap your mic in a towel if need be to achieve a lower silence.

sorry, here are the images.

without any additional cap:


with 220uF:


As suggested by monomer, you have only to do a measurement with rew as usual but in a silent room.

There are many suppliers of electronic parts. Farnell, Mouser, RS components, Digikey are some of the biggest in the world. On ebay you will find (search 220uf 10V) it and you will pay less of shipment if you buy it in your country.
Anyway, if you are looking for something like this (the caps that gives the results in the previous image, it's a 220uf 16V electrolytic capacitor, but better is a 220uF 6.3V that should be smaller)



you can find it maybe in electronic shops near your home.0603... but if you are used to 0805 you should be good even in 0603

My UMIK serial is 700-0635. Is this a revB or revC? Is there an offer for exchanging older versions for revC?

Thank you,

--Stefanos

Dear All,

FYI, please have a look at this thread here if you have any questions with regards to this noise floor modification. www.minidsp.com/forum/18-umik-questions/8868-umik-1-update

Great work from Georgio and Michelle on the modifications! A simple test that can be performed once the microphone opened.

DevTeam

Ok guys, here I am.
I did various test on the Umik-1 to improve the noise floor.

First of all, I used a netbook (asus 1215B e-350) to do the test and my mic serial is 0514.

Second thing, after some while, I noticed that the mic is noisy itself but the supply provided from the USB port can really do some mess and increase the performance of the mic. WIth my netbook, I found that with or without the external power adaptor the things changed a lot.
So, I repeated some test, but not all because the cable that connects the mic to the circuit were damaged after many tests and I even break a part of the PCB for my fault.

Third, I think the best thing to do is to put a capacitor where George suggested. It's very easy to do and with an electrolytic 470uF 6,3V almost all the noise is suppressed. It's a simple and powerful mod. On my netbook, the noise is very low even with the power adaptor. I putted an extra capacitor (100uF 10V) after the ferrite bead used to filter the usb supply but it's not so useful I think. Anyway it should not make the things worse.

Fourth thing: I build up a low noise reg with a LT1763 3,3V to feed biasing circuit of the capsule (look on the web for miniVreg) but the results are worse than the simple capacitor. Really. For sure it's not a circuit designed for this particular chase but if you want to use a low noise reg it's up to you. It could be very useful with high internal gain (24/30/36dB) but only if projected ad hoc.

Last thing: I sat the internal gain at 12dB. For sure the noise floor increase but for me this is a good set-up so I can use the mic not only for loudspeaker measurements. You have to modify the value in the calibration files. For me I changed from "Sens Factor =-22.68dB, SERNO: 7000514" to "Sens Factor =-10.68dB, SERNO: 7000514" (12db gain).

Now the results and some photos. Let me know.

Original mic without any mod, no power supply:


Original mic without any mod, with power supply:


Mic with 220uF cap, no supply::


Mic with 220uF cap, with supply:


Mic with LT1763 3,3V, no power supply:


Mic with LT1763 3,3V, with power supply:


Mic with 470uF on mic power line + 100uF on 5V supply, no supply:


Mic with 470uF on mic power line + 100uF on 5V supply, with supply:


Mic enclosed (470uF on mic power line + 100uF on 5V supply), no supply:


Mic enclosed (470uF on mic power line + 100uF on 5V supply), with supply:


Photos of the mod:

LT1763 regulator (the two resistor inparallel are used to obtain 1950Ohm)




Two capactor mod (470uF 6,3V and 100uF 10V suggested)


the smaller capactor is soldered on the pins of the input 3,3V regulator


the bigger capacitor is applied on 3,3V supply of the mic capsule:



Hope it helps.....


Michele

@ Michele,

Thanks for the very good update! Unfortunately, it seems like the picture are not showing for some reason. We have a little bug on this forum under firefox it seems to post pics. We're doing a website upgrade these days so it will be fixed in new website. In the mean time, you can post the pics using Internet Explorer.

As for your comments, we agree that indeed adding a capacitor is indeed the easiest way to go at it.

DevTeam

I did various test on the Umik-1 to improve the noise floor.

First of all, I used a netbook (asus 1215B e-350) to do the test and my mic serial is 0514.

Second thing, after some while, I noticed that the mic is noisy itself but the supply provided from the USB port can really do some mess and increase the performance of the mic. WIth my netbook, I found that with or without the external power adaptor the things changed a lot.
So, I repeated some test, but not all because the cable that connects the mic to the circuit were damaged after many tests and I even break a part of the PCB for my fault.

Third, I think the best thing to do is to put a capacitor where George suggested. It's very easy to do and with an electrolytic 470uF 6,3V almost all the noise is suppressed. It's a simple and powerful mod. On my netbook, the noise is very low even with the power adaptor. I putted an extra capacitor (100uF 10V) after the ferrite bead used to filter the usb supply but it's not so useful I think. Anyway it should not make the things worse.

Fourth thing: I build up a low noise reg with a LT1763 3,3V to feed biasing circuit of the capsule (look on the web for miniVreg) but the results are worse than the simple capacitor. Really. For sure it's not a circuit designed for this particular chase but if you want to use a low noise reg it's up to you. It could be very useful with high internal gain (24/30/36dB) but only if projected ad hoc.

Last thing: I sat the internal gain at 12dB. For sure the noise floor increase but for me this is a good set-up so I can use the mic not only for loudspeaker measurements. You have to modify the value in the calibration files. For me I changed from "Sens Factor =-22.68dB, SERNO: 7000514" to "Sens Factor =-10.68dB, SERNO: 7000514" (12db gain).

Now the results and some photos. Let me know.

Original mic without any mod, no power supply:


Original mic without any mod, with power supply:


Mic with 220uF cap, no supply::


Mic with 220uF cap, with supply:


Mic with LT1763 3,3V, no power supply:


Mic with LT1763 3,3V, with power supply:


Mic with 470uF on mic power line + 100uF on 5V supply, no supply:


Mic with 470uF on mic power line + 100uF on 5V supply, with supply:


Mic enclosed (470uF on mic power line + 100uF on 5V supply), no supply:


Mic enclosed (470uF on mic power line + 100uF on 5V supply), with supply:


Photos of the mod:

LT1763 regulator (the two resistor inparallel are used to obtain 1950Ohm)




Two capactor mod (470uF 6,3V and 100uF 10V suggested)


the smaller capactor is soldered on the pins of the input 3,3V regulator


the bigger capacitor is applied on 3,3V supply of the mic capsule:



Hope it helps.....


Michele

Sorry Devteam, I'm working to made the pics visible... can you cancel this and the previous one post? Keep the first with the pictures not visible, I need the url of the pics....

miki_ada wrote: