Surf Pro Kit

[dime196604]

Maybe a dumb question here. Does the polarity of the headphones or speaker matter when you wire it up to this board? If so what would be the best way to figure out what pin is positive and negative on the board?

[Qiaozhi]

Maybe a dumb question here. Does the polarity of the headphones or speaker matter when you wire it up to this board? If so what would be the best way to figure out what pin is positive and negative on the board?

Neither headphones nor speakers are polarity sensitive.

Speaker polarity only matters in hi-fi systems, where you want the speaker cones to all push or pull the air in the same direction. Otherwise, if you send the same signal to both speakers and one pushes while the other pulls, you can hear some strange phasing effects. The same applies to systems with more than two speakers of course.

[dime196604]

Now i have a question on sting the onboard delay trimmer. What is the best way to go about this. I have tried doing it by ear but i don't really hear a difference in signal strength. Is there another way to set the delay? Also after finding the perfect delay setting, should i go back and recheck the offset? Or will it stay the same once i have set the offset to 0v? I am close to being done with this project but not there yet.

[dime196604]

This is the only wave I can get while trying to set the damping. the only part that changes is the little negative peak on the bottom. so I do believe I am doing something wrong here

[FatBob]

You should be looking at the output of the first opamp and see something like this;

[dime196604]

You should be looking at the output of the first opamp and see something like this;
[ATTACH]36791[/ATTACH]

Bob, my scope pic was at pin six of ic NE5534. I'm not 100%, but i thought this was the output of the first opamp. Am i looking at the wrong place with my scope?

[FatBob]

Well if you miscounted and were at 2 instead of 6 you might get that picture.

Pin 6 being the output cannot go beyond the power supply rails. As you see in my
pic I have ~9V. I cannot tell the voltage range on your scope...

[dime196604]

I do not think I can tell the voltage range on my scope. So I could just have it on the wrong setting. The only thing I have used my scope for is setting modulation on AM transceivers. other then that I really don't have a clue how to use it. My scope it a old two channel 200Mhz tecktronics. only channel one works. Would you have any suggestions on what rang I should have my scope set it for adjusting the damping on my MD?

[FatBob]

Well if you look at my scope picture I have 2V vertical and 4us horizontal.

You could start with those settings and see if you can get something like my picture...

[dime196604]

ok thanks. I will have a look and keep u posted. Thanks for the help.

[Koala]

Now i have a question on sting the onboard delay trimmer. What is the best way to go about this. I have tried doing it by ear but i don't really hear a difference in signal strength. Is there another way to set the delay? Also after finding the perfect delay setting, should i go back and recheck the offset? Or will it stay the same once i have set the offset to 0v? I am close to being done with this project but not there yet.

Delay is a tricky one as at one setting it is good for one type of target but useless on others. Make it best for the other types and those that were excellent are now useless.


As an example if I set the delay best for a gold ring its useless on a fibula. Get a selection of different targets you hope to find and adjust for best comprises.

Offset stays put on the Barracuda no need to re adjust.


Delay does alter with different coils.

[dime196604]

Delay is a tricky one as at one setting it is good for one type of target but useless on others. Make it best for the other types and those that were excellent are now useless.


As an example if I set the delay best for a gold ring its useless on a fibula. Get a selection of different targets you hope to find and adjust for best comprises.

Offset stays put on the Barracuda no need to re adjust.


Delay does alter with different coils.

That's helpful advice. is there a extreme where I don't want to go with the delay? I have read here on the forum that u can make the MD not work by adjusting the delay wrong

[6666]

Here is an example of the type of targets you eliminate as you increase the delay.

[Koala]

That's helpful advice. is there a extreme where I don't want to go with the delay? I have read here on the forum that u can make the MD not work by adjusting the delay wrong

If it's the same as the barracuda then yes there is enough adjustment in the delay to make the detector not work at all.

i wave a gold ring over the coil turn the delay one way until it starts to loose a lot o depth then the other way until it starts to chirp an not work too good your compromise setting will be somewhere between the two

[Tibuck19]

Use an adjustable damping resistor tool:
10k pot in series with a 200R resistor, and a 2k resistor in parallel with both the pot and resistor. This will give you an adjustment range from 181R to 1672R.
Attach the one good channel of your oscilloscope to the output of the preamp, and adjust the pot until you achieve critical damping. Disconnect the adjustment tool and measure the final resistance. Replace with a fixed resistor that has the closest value.

THANK YOU loll