Electronics help

[abunaitoo]

People here are so helpful. I know someone can guide me.
Trying to do this as cheap as possible. All old stuff just around the house.
I'm trying to make a countdown timer for our shooting matches.
Whistle and stopwatch is just to hard to juggle.
Needs to be hand held, with a repeatable start/stop function.
I've adapted a small, battery powered, kitchen timer to plug into the microphone plug.
The amp is an old home stereo amp. 20W output.
Wire is one half of the shielded single wire cable from a RCA stereo speaker wire.
It seems to be working, except I'm getting some buzzing when the timer is plugged in.
I'm thinking it maybe some kind of feedback from the timer.
Would installing a diode, or two, help???
It the wire the wrong type to use????
Any suggestion on what else might work????

[waynem34]

Maybe put more distance between amp and buzzer.Could be feedback.

[aspangler]

Your buzz can be corrected by using the inside conductor of the cable and grounding the sheild to the amp. Ask me how I know.

[abunaitoo]

Your buzz can be corrected by using the inside conductor of the cable and grounding the sheild to the amp. Ask me how I know.

The wire I'm using has a single inner core wire and a outer shielding wire.
I hooked up the inner to the red on the timer, and the shield to the black.
The black in the timer is also connected to the neg of the battery.
The mic plug is two wire. The black to the shield, the red to the core.

[MaryB]

What port are you plugging into on the amp? Speaker wire is not good for low level signals either. Get a shielded jumper cable like you would use between the amp and a tape or cd player

[aspangler]

The wire I'm using has a single inner core wire and a outer shielding wire.
I hooked up the inner to the red on the timer, and the shield to the black.
The black in the timer is also connected to the neg of the battery.
The mic plug is two wire. The black to the shield, the red to the core.
Try a .01 MFD capacitor across the mic input. ( inner conductor and shield.) What you are getting is AC picked up by the input to the amp. You can go as high as .1 MFD for what you are doing. You need to get the AC out of the input.

[abunaitoo]

What port are you plugging into on the amp? Speaker wire is not good for low level signals either. Get a shielded jumper cable like you would use between the amp and a tape or cd player
The timer is plugged into the mic jack.
I thought I could use a RCA wire as it is a shielded wire.
I have a mic that is used.
I unscrewed the sleeve on the plug, and the wire looked almost the same as the RCA wire.
I call it a speaker RCA wire because it's from the old stereo I have in the car.
I think it's the same thing as a RCA jumper wire.

[abunaitoo]

Try a .01 MFD capacitor across the mic input. ( inner conductor and shield.) What you are getting is AC picked up by the input to the amp. You can go as high as .1 MFD for what you are doing. You need to get the AC out of the input.
I may not be understanding.
The timer is 1.5v DC.
Is the AC coming from the amp????
Would the cap be wired to connect the inner and shield????
A little confused.
Maybe I'm going about this all wrong.
The timer had a beeper in it.
I was thinking I could just replace the mic with the timer by wiring it through the beeper.
Am I mistaken????

[6bg6ga]

Your buzz can be corrected by using the inside conductor of the cable and grounding the sheild to the amp. Ask me how I know.


I'll bite....how do you know?

[2wheelDuke]

Maybe I'm not understanding correctly, but wouldn't the headphone connection and the timer on a cell phone do the job?

[2wheelDuke]

Could you use a cell phone and a patch cable to the headphone jack? Most have timers built in.

[MaryB]

So it was an inner wire with insulation then braid over the top? Try moving from the mic jack to one of the other inputs like a tape in. I am guessing you are way over driving the mic port for starters. Mic jacks are very very sensitive and take very little drive to produce output.


The timer is plugged into the mic jack.
I thought I could use a RCA wire as it is a shielded wire.
I have a mic that is used.
I unscrewed the sleeve on the plug, and the wire looked almost the same as the RCA wire.
I call it a speaker RCA wire because it's from the old stereo I have in the car.
I think it's the same thing as a RCA jumper wire.

[Cmm_3940]

I may not be understanding.
The timer is 1.5v DC.
Is the AC coming from the amp????
Would the cap be wired to connect the inner and shield????
A little confused.



The AC is entering via induction from an external source. Your kludged input cable probably doesn't have a consistent ground on both ends and is acting like an antenna. By adding a decoupling capacitor between the positive input and chassis ground, you will shunt any unwanted high freq. buzz away from the amp input. If you are getting a low freq buzz, like from 60Hz fluorescent lighting or transformers nearby, you may need a cap in series with the input to get rid of it.

More on filter design here:

http://www.electronics-tutorials.ws/filter/filter_4.html


Maybe I'm going about this all wrong.
The timer had a beeper in it.
I was thinking I could just replace the mic with the timer by wiring it through the beeper.
Am I mistaken????

The problem here is that your timer and the amplifier have two different grounds. Ground for the timer is the negative pole on the battery. Ground for the amp is it's chassis, and the internal power supply. Since they don't share a common ground, you have a sort if 'open loop', which lets in external signals, i.e., noise, via induction.

[abunaitoo]

Sometimes I just want to kick myself.
Ever over think a solution to a problem????
The AMP has a AUX RCA jack on the back.
It's designed to do things like what I'm doing.
I changed the plug to an RCA and all is good.
I gotta remember to think of other solutions before just jumping in.
Thank you all for your suggestions.

[6bg6ga]

It all boils down to knowledge and experience and knowing what product to use. First of all you have the wrong equipment. Home junk should be left at home and not used in a commercial application. Your little stereo is rated to drive a 8 ohm speaker per channel. Consideration to cable length run should come into play here. The longer the run the larger the wire needs to be in order to keep from loosing power. In your instance you should be purchasing something along the lines of a TOA BG30 or the likes. A commercial amplifier will run a 70 volt line. By using a 70volt line you do not have to worry about long cable runs because you could run your speakers off 18 ga or even 22 ga wire. Speakers could be simple 70 volt horns tapped at 7.5 watts each. The efficiency would be a lot greater and thus more output level.

Sorry, I had to chuckle when you were trying to input signal into a mic jack. Mic level is typically 60 db down from line level so as pointed out you were over driving the input. Now, I could get into how to cure this problem by the useage of a transformer and a pad that would have gotten rid of all the noise and would have worked. One thing to remember..... mic signal goes into a mic input. Phone signal goes into a phono input. Do not try to input a line level input into either the phono or the mic input.

Getting back to the amplifier...... my suggestion here is to retire the home amplifier and pick up something like a TOA or Peavey mixer amplifier. This will ease your problems in setup ease of operation and possible additions in the future. You can usually find something on ebay for $10-20 that will last far longer than something that isn't designed to do the job.

Can't resist this one....ask me how I know. I do very large format sound systems like football stadium systems so I deal with junk like this every day. I'm one of the people that gets shipped around the country when things don't work right because some self appointed tech thinks he or she can change things, rewire things, or try to add to a system.

[abunaitoo]

Thanks for the suggestion.
We're doing this on the cheap.
Flee market AMP, looks like home made speakers, kitchen timer.
Just a mix of cheap to free stuff.
It's only used two times a year, so we don't want to spend anything if possible.
At least a learned a little something.

[abunaitoo]

Back again.
The old AMP kind of died. The volume control is making a big racket when turned.
I got a Radio Shack PA AMP. MPA-25. 20w
It has two mic jacks on the front, and a AUX/PHONO RCA plug on the back, with a switch between them.
The mic works fine.
The timer is plugged into the AUX jack.
It seems to be working, but like ccm 3940 posted, it might not be how it's suppose to be done.
I'd like to try and make it right.
I'd like to use a kitchen timer. It seems to be the easiest to operate, is cheap, and is perfect for how we are using it.
Is there another kind of timer that would work better????

[Driver man]

Back again.
The old AMP kind of died. The volume control is making a big racket when turned.
I got a Radio Shack PA AMP. MPA-25. 20w
It has two mic jacks on the front, and a AUX/PHONO RCA plug on the back, with a switch between them.
The mic works fine.
The timer is plugged into the AUX jack.
It seems to be working, but like ccm 3940 posted, it might not be how it's suppose to be done.
I'd like to try and make it right.
I'd like to use a kitchen timer. It seems to be the easiest to operate, is cheap, and is perfect for how we are using it.
Is there another kind of timer that would work better????

Your volume control might just need a spray of crc.

[abunaitoo]

The old AMP had been giving trouble for a while.
It looked like it was not in the best of condition.
That's why I got the new one.
It's used, but looks almost new.
The speaker wires are about 6 feet long. Looks like regular two wire speaker wire. Two speakers.
I think the beeper in the kitchen timer is a high-impedance piezoelectric transducer (what ever that is).
It just might be that it's not meant to do what I'm trying to make it do.
It does work, but I don't want to damage the AMP.
Maybe a kitchen timer is not the best one to try and do this.
Any suggestions on what else I might use????143313143314143315

[edctexas]

You are trying to get the beep from the timer to go through the amp? The Piezo transducer is NOT a speaker. It produces a beep when a DC signal is applied to it. Your amp only amplifies AC signals (tones) not a DC signal. You will need something to make an AC signal (tone) from the DC signal that the timer puts out. Right now I can not offer a device to do that but I could hunt around if you are determined to proceed.

Ed C

[Cmm_3940]

Transducer just means a device that converts one kind of energy into another. In this case, your beeper is producing an electrical signal, most likely a square wave, via an oscillator and the piezo is converting the electrical signal into an audible signal. Probably way more than you wanted to know about transducers.

You are correct to use the AUX input to the amp. The phono input is much more sensitive and you may risk damaging the amp if your beeper feeds it too big of a signal. Hook your speakers up between common and 8Ω for a single 8 ohm speaker, or common and 4Ω if you are using two 8 ohm speakers in parallel or a single 4 ohm speaker. As far as the input between the beeper and the amp, if it's working, I wouldn't mess with it and wouldn't worry about it either. If this is a better amp than your old one, it could already have some caps/shunts/filters/decouplers/whatevers inside it to avoid the problem you were having before. A PA amp shouldn't be too picky about the quality of what you feed it.

ETA: Oh, and yeah. Loud bursts of noise when you turn a volume control is caused by dirt or oxidation inside the control. Sometimes it takes as little as rapidly turning the knob back and forth for a while to clear it up. There are also specialized things you can squirt in there like Driver Man pointed out. If the oxidation is too bad though, it means replacing the part.

Have fun,

Chris

[Driver man]

The simplist way of all to do what you want is to plug a microphone into the amp and position it near the timer. That will work just fine.

[MaryB]

DeOxit is the best thing for control cleaning, available as a spray online... I would use a small mic as suggested instead of maybe setting up a ground loop or over driven input that can damage the amp.

[CGT80]

OP, what is wrong with using a cell phone? Who doesn't have a cell phone these days? Even an old phone would work fine as long as it has a countdown timer loaded on it. Some people end up trashing their old phones.

I use a timer app that I downloaded for free. You can choose the sound it makes when it goes off. Mine is a siren sound, which would probably be fine for the range.

I have also thought about how I would run a timer and direct shooters, if I was to take over a silhouette match for the current directors. My voice doesn't do well with a bunch of yelling. A simple amp, cell phone, and microphone that could run from a 12v battery would be great. Our shooting line is 50-75' wide and I don't think the system would have to be obnoxiously loud, but just enough to simulate a person yelling out commands.

[abunaitoo]

The simplist way of all to do what you want is to plug a microphone into the amp and position it near the timer. That will work just fine.

I have some parts from old telephone around.
What if I take the speaker from one and wire it close to the original of the timer????
I'd wire it to a plug that would fit into the AUX outlet.
Can I even do something like this?????
Could it be this simple????

[Driver man]

I have some parts from old telephone around.
What if I take the speaker from one and wire it close to the original of the timer????
I'd wire it to a plug that would fit into the AUX outlet.
Can I even do something like this?????
Could it be this simple????
No. A microphone has to plugged into a microphone socket because a microphone is generally a low output source and needs the microphone signal to be amplified by a preamp which is built into the microphone input circuit inside the amp. The aux input is generally driven by signal which has already been amplified up to a specific level and needs to be plugged into a skt,usually RCA that is designed to handle these already amped signals.(this is why they use different connecters)
Buy a cheap $5.00 stereo microphone and maybe an adapter to convert the plug size from small to large (3.5 to 6.3) if needed and simply plug in. If you plug a microphone into a aux input you may get a little bit of sound and a whole lot of buzz. If you plug an aux (RCA) signal into a microphone input you can massively overload the amp causing all sorts of serious problems.

[MaryB]

Aux is typically 1 volt peak to peak input

[abunaitoo]

So the telephone mic will not work.
I knew it couldn't be that simple.
I'll see if I can find a small mic and merge the timer and mic together.
Thanks

[Driver man]

So the telephone mic will not work.
I knew it couldn't be that simple.
I'll see if I can find a small mic and merge the timer and mic together.
Thanks

Telephone mic might work if you plug it into the mic skt. I dont know what the impedance of telephone mics are but worth a try. Use the mic input only and not the aux.