Powering 4.5V Ringford CZ034 mics

[ivop]

[Edit 2007-06-12  The final, working circuit to power 4.5V mic capsules is here ]

Hi,

First a short introduction:

I have made several live recordings over the past ~ten years using a Sharp MD MT-15 recorder and a simple Trust computer microphone (mono). With the recorder on mono, I can record almost two and a half hours so I can turn it on (at the toilets of the venue ) well before the concert starts. The quality, although mono, surprised me, so I never bothered changing my setup. I had some distortion a few times, but that was mostly my own fault, i.e. recording level above 10/30. Only once I could not even record at 1/30 because of the sound level at where I was standing.

Yesterday I found this forum and today I decided to take apart that old "trusty" mic. Turns out there is a small electret condenser mic inside, which is the Ringford CZ034. I found the specs online here .

Currently I use the mic-in of my recorder which delivers about 0.5-1V (I assume, I cannot find the manual anymore, but it cannot be much more as the MT-15 is powered by two AA batteries). According to the specifications, the EZ034 operates best at 4.5V. So, my questions are:

1. Would it be worth the trouble to build a battery pack? My assumption is that I could record through line-in and increase the recording level significantly (>20/30) and have a wider dynamic. Is that correct?

2. If so, could I use the schematic posted on this forum and rewire the 9V battery to skip 50% of the cells? (4.5V lantern batteries are quite big)

3. Is the EZ034 any good at all? I have considered buying another Trust mic (they cost less than $10) and rewire both as a stereo mic.

Thanks for your time!

[small update: I found an old Trust headset in the closet. I took it apart and it contains the same CZ034 condenser mic. So, I already have two of them ]

Edited June 12, 2007 by ivop

[ivop]

Hi again,

After reading a lot more on this forum and doing some googling, I drew the attached schematic with xfig. I think it should suffice to power my two 4.5V mics by a standard 9V battery cell. Can anybody more knowledgeable on the subject verify that?

I am planning on buying the parts this tuesday and build it, unless somebody tells me I am way off track here Any comments?

Thanks in advance,

[edit 2007-06-07 removed faulty diagram]

Edited June 7, 2007 by ivop

[ivop]

Hi again,

I have built the above schematic and it works!

[update: but not how it should. the mics are overpowered... read next posts]

[edit 2007-06-07 removed remarks that do not apply to the latest design; pictures might still be useful to somebody]

A few remarks:

- The Ringford 4.5V condenser mics seem to be a little bigger than the Panasonic WM-61's, so I used shrink tubes of two different sizes.

- I have put the whole circuit inside an old battery casing. When I filled up the space between the voltage divider and the rest of the circuit, I used a little bit too much glue. That's why the cable and 3.5mm socket part stick out a bit. It should be possible to make a perfect fit.

- To make sure you can fit it inside the empty casing again, go easy on the glue. If you used too much by mistake, you can use a piece of sandpaper to reshape the blob.

- It is important that all components are completely covered by glue. They should not touch the inside of the casing.

- I used a small piece of shrink tube to avoid the cable from splitting any further.

- I butchered two old Trust microphones for the two capsules. If you have any unused mics lying around, you might try the same. I do not advice on buying full mics, just to take them apart. Buying a pair of electret condenser mics only is a lot cheaper.

Here are the pics of the mic (similar to greenmachine's but with 4.5V mics) and of the battery pack. They are a little fuzzy, but I didn't notice I had forgotten to put my camera in macro mode well after I had finished glueing it all together, so I couldn't retake them (and yeah, I bought quite some spare parts perhaps I build a 9V version later)

Edited June 7, 2007 by ivop

[Strungup]

Hi again,

After reading a lot more on this forum and doing some googling, I drew the attached schematic with xfig. I think it should suffice to power my two 4.5V mics by a standard 9V battery cell. Can anybody more knowledgeable on the subject verify that?

I am planning on buying the parts this tuesday and build it, unless somebody tells me I am way off track here Any comments?

Thanks in advance,

from the look of that circuit are you sure that your getting 9 volts to the Mics?, just because you split the voltage and shunted it to ground , doesnt garauntee stable power ,Also that design means a constant drain on the batteries whether your plugged in or not . the impedance of the mics would have to be calculated , and factored in ,a couple of Zenier diodes and proper resistor bridging would give you 4.5 stable and isolate the power supply to each mic . ( but of course the box starts getting bigger ) if the mics are capable of 9 volts then no problem .

Just two cents that all.

Edited May 30, 2007 by Guitarfxr

[ivop]

from the look of that circuit are you sure that your getting 9 volts to the Mics?, just because you split the voltage and shunted it to ground , doesnt garauntee stable power ,Also that design means a constant drain on the batteries whether your plugged in or not . the impedance of the mics would have to be calculated , and factored in ,a couple of Zenier diodes and proper resistor bridging would give you 4.5 stable and isolate the power supply to each mic . ( but of course the box starts getting bigger ) if the mics are capable of 9 volts then no problem .

Just two cents that all.

I see. My "design" is flawed in various ways. I mistook the voltage divider as a new "black box" providing 4.5V but the two capsules (~2k ohm each) + resistor are connected in parallel to one of the divider's resistors so the total resistance is lowered (a lot). So the mics actually get a lot more than 4.5V, which is not good according to the CZ034 specs. It is something like: 4.75 / (1/(1/4.75+1/6.75+1/6.75) + 4.75) * 9 = 6.36 V

My old physics lessons are all coming back to me now I will have to come up with something better.

Thanks for your reply!

[ivop]

This is what I have come up with.

D1 is a 4.5V +/- 1% zener diode

R1 is chosen to provide the proper I(z) for D1 (depends on the type/brand of D1)

R2 = R3 = 4k75 +/- 1%

C1 = C2 = 2.2uF

T1 is chosen to have a proper current limit

Any comments? Should I just stop this endeavour and buy a pair of 9V mic capsules?

Thanks in advance.

[edit 2007-06-07 removed wrong design]

Edited June 7, 2007 by ivop

[Strungup]

This is what I have come up with.

D1 is a 4.5V +/- 1% zener diode

R1 is chosen to provide the proper I(z) for D1 (depends on the type/brand of D1)

R2 = R3 = 4k75 +/- 1%

C1 = C2 = 2.2uF

T1 is chosen to have a proper current limit

Any comments? Should I just stop this endeavour and buy a pair of 9V mic capsules?

Thanks in advance.

That looks good , make sure the zenier is of the proper current rating for dissapation purposes, And you may wish to add a microswitch to the power , for on and off

Nice drawing by the way

Edited May 31, 2007 by Guitarfxr

[ivop]

That looks good , make sure the zenier is of the proper current rating for dissapation purposes, And you may wish to add a microswitch to the power , for on and off

I did some further reading on the subject and I came to the conclusion my 2nd design was still flawed. I misread sample diagrams and have the zener the wrong way around. It is more common to invert the zener and hence invert almost the whole circuit. Attached was my third attempt. I think I have covered pretty much everything now.

Nice drawing by the way

Thanks  I did it in good old Xfig. For this one, I switched to Inkscape and started to create my own small library of components.

When I have some more spare time next week, I will build this and let you all know how it works out (values for Rx et cetera).

Although I am going to buy a pair of 9V capsules anyway, this has become something I have to get working right 

[edit 2007-06-07: removed rev. 4 design]

Edited June 7, 2007 by ivop

[ivop]

Here's the latest revision of the 4.5 V battery pack. It includes all components I used and it works perfectly.

It uses a 5.1 V zener diode because of the voltage drop of the transistor. It fits perfectly inside an old 9V battery casing. If you leave out the switch

(so it cannot turn off in your pocket by accident) you have to keep in mind that the circuit will constantly drain power, so you have to disconnect the battery

if it's not in use.

I did not take any pictures during the build process but it looked fairly similar to the pictures I posted before

Edited June 7, 2007 by ivop