Carl - you should tell people more about
your "Smart AA Charger" if you haven't
done so already.
Brooce, Hartford
Hi Brooce... I have posted about the Smart Charger and talked about it on the show, but no longer remember where or what.
I will talk about it again soon... it's very interesting stuff.
It has made charging batteries fun and I keep it running so my portables always have fully charged power.
It's a unique charger and it's
much better for the batteries.
Brooce
Neil, in you Reply # 15 you give the formula for determining the capacitor value to bypass the source resistor.
The numbers I used in the equation include:
R = 6.8k
lowest frequency = 80 Hz
The result I get is .0000002
What value do you come up with running the same numbers?
I figured 0.29 uF but be aware that the equation was for bypassing a source resistor in a common source amplifier where the signal is taken from the drain. From what you said dirung the ALPB TeamSpeak meeting this is not the case for your circuit.
To calculate the needed C the resistance "seen" by the capacitor needs to be used. For a source follower used as I think you have this would include the source resistor, the transformer resistance, the a.c. resistance seen looking into the source of the FET, and the transformed a.c. resistance ol the load. This involves drawing the a.c. equivalent circuit of your circuit and calculating the R to use.
It is not as complicated as it appears and if you will provide your circuit diagram I can explain this.
Neil
Oh, I follow that.
Amazing that so much is going on in such an otherwise small circuit.
Your recollection from the meeting description of the diagram is correct.
Today, after I make my rounds and tend to a few things I'll scan and post the circuit for Alpmic 16.3c.
Hey Hi Everybody!
PREFACE - The last hour was spent poking at the wierd software supplied with my scanner.
It is documented in a way that causes me to prefer a coma to being conscious.
It tells me I'm building a PDF file when all I want is a JPEG.
If I am persistent I end up with a JPEG but I can't grasp the logic so it never gets easier.
By this time you should admire me for the effort.
ON TO BUSINESS - We are building a microphone based around no-longer-available Radio Shack discontinued electret mic capsules. It's called the Alpmic and an earlier version of it is documented at the ALPB Website.
Neil Radio8Z has been educating me on aspects of circuit design and this is a higher learning experience.
THE LATEST CONCOCTION
FRUSTRATION ALERT: Repeated attempts to link the Circuit Diagram have belligerently failed. I won't put up with it and am driving away at a high rate of speed to show my contempt for the internet's failure to show even a hint of artificial intelligence. So long suckers!!
Posting JPEG Not Be Easy
The Circuit Diagram May Be Seeable
The following is circuit data:
B! = standard 9 Volt battery
C1 = 2 uF based on the 2-mic capsules pulling 1 mA apiece
C2 = As yet undecided
M1, M2 = Discontinued Radio Shack off-the-rack electret capsules
R1, R2 = 909 Ohms
R3 = the resistor that sets the voltage seen by the mic capsules... the data sheet tells us it will accept 1 to 10 VDC and the Optimum is 4.5 VDC. Our circuit provides 3.69 VDC;
___ discussion: The output destination, the "load", is 2K (RDL RU-MX4 Mixer); According to Neumann Microphone Corporation White Paper source impedance should be 1/5 of load impedance in condenser mic circuits. This circuit does not achieve that ideal but uses available parts;
T1 = is a transformer bought for a few cents at a surplus store and is otherwise unknown. It has worked in previous tests as a viable mic transformer;
Present subjective impression of how it sounds... not too bad, acceptable, maybe pretty good.
Any questions should be addressed to me.
In the 1990s my wife and I knew everything about print and video, including the fact that JPEG was a color format and some other thing was better for black and white, possibly BMP.
Now I only know that I don't know.
Without the value of R3 and the d.c. resistances of the transformer windings and the turns or impedance ratio the calculation for C2 given the cutoff frequency cannot be done.
Probably the best way to proceed is to try different values for C2 until you get the sound you want. Bear in mind that a change in the load impedance will affect the cutoff frequency for this circuit.
Neil
Many thanks Neil for contributing to the microhone project.
Given the unknown status of the transformer we move to the other option you recommend... comparing the result of various capacitors for C2 until we hear the "best" result.
If curiosity arises we have a program utilizing this version (v16.3c) of the Alpmic so give it a listen unless you don't.
Blare OnAir July 4th in the TeamSpeak Open Room
Changed R3 to 6.6k to bring up the voltage seen by the mic capsules to 4.169 V.
Changed C2 (by the way, it was initially 1 uF as a starting point in the previous version) to 10 uF, the next closest value available on hand.
Made a recording
Alpmic V 16.3d Blare OnAir Lite
Neil said: "Probably the best way to proceed is to try different values for C2 until you get the sound you want. Bear in mind that a change in the load impedance will affect the cutoff frequency for this circuit."
To make sure we are talking about the same thing...
The "cutoff frequency" is the low end of the frequency spectrum, right?
Since in any case the cutoff frequency will be below voice range I am wondering how to "listen" for a difference without the presence of very low frequency audio.
I do not have any musical instruments or other low frequency devices.
In fact I'm thinking that whether the frequency rolls off at 80 Hz or 40 Hz doesn't make any difference for a voice mic.
Taking a break from ongoing computer complications we reviewed the state of our AA Ni-MH batteries as used in the TECSUN PL-310 and Grundig FR-200, the radios used for outdoor activity and range testing.
Lately the TECSUN, which has a 3-Bar Battery Indicator and serves as our battery checker, was continuously showing 3-Full Bars that never changed.
The batteries all looked low on the Radio Shack MICRONTA 22-032A Battery Tester, so we launched a review of everything involved.
First of all, rechargable AA's themselves...
Months back when we installed the OPUS BT-C3100 V2.2 Smart Charger we also ordered a large pack of new AA Re-chargeables rated at 2400 mHh, but in practice they presented an unexpected problem: the type we got from Amazon are slightly thicker than standard batteries, and will not fit in one of the battery-wells inside the TECSUN.
This forced us into the position of mixing old and new batteries and different power ratings, i.e., 2400, 2100, 2050, and 1500 mAh.
The TECSUN contains a distinct warning: DO NOT MIX OLD AND NEW BATTERIES. But it seems to me they are talking in that case about Alkaline (un-rechargeable) batteries and not re-chargeables.
And another caution from the TECSUN Manual, "Do not mix different power ratings". But this advisory is printed in the section on using the TECSUN with a USB power cable to re-charge batteries in the radio... they certainly wouldn't re-charge evenly if they were of differing power ratings... but we never re-charge them in the radio, so that caution may not apply to simply using the batteries to power the radio.
Also learned was that the radio needs to be told whether the installed batteries are Alkaline or Ni-MH, and there is a button for entering the correct information manually. Previously we thought this happened automatically.
The manual told us how to get a fresh start and get rid of those "full bars" on the battery indicator: simply allow the radio to sit around with no batteries, and as the internal charge decays the readings all default to a reset status.
All the batteries are being re-charged in the Smart Charger and everything is swell.