Multiple detent pots

[Goodrat]

Looking for a source for pots on the headphones I'm building. Mouser or Digikey do not seem to have much selection. I'd like to find a multi detent.
I've got a few ideas for speakers, but suggestions would be welcomed too.

[bbsailor]

Re: Multiple detent pots

Headphone volume controls may not be that critical because most of the time I max out the headphone volume to hear the deep signals. If I want to lower the volume I use the volume control on the detector or readjust the threshhold.

Since you are building headphones, here are some thoughts to ponder.

The biggest challenge for optimizing headphone use is to maximize the signal to noise ratio (SNR). This is done by either increasing the signal or reducing the noise or doing both. Using good sound isolation headphones does a good job of eliminating 24 to 29 db of outside noise (depending on the model of ear protectors being used to make the headphones). Also, trying to maximize the output from the metal detector output circuit helps.

Most detectors use a 200 to 300 ohm series resistor to limit the sound to the headphones compared to the full sound level going to the internal speaker. This means that low impedance headphones form a simple voltage divider with low impedance headphones producing the most losses. That is why higher impedance headphones like Grey Ghosts or Timberwolfs at 150 ohms sound louder than many lower impedance hi fi stereo models.

One way around this headphone mismatch is to use an active circuit with a 1K to 2K ohm input impedance that will provide a better match to the lower headphones impedance. This better match results in hearing the very faint signals as well as some of the noise in the detector audio output circuit as well as the search coil's radiated signal.

Try to use the ideas that were patented by Depthmaster to put a transistor in series with the headphones. In fact, you could use two transistors cascaded with a gain of about 10 x with a bypass switch to have either 100x, 10x or total bypass 0x gain. Put this in a metal box to shield against outside signal pickup. Use shielded cable to the headphones to further improve the system, then you should be able to listen to the noise level in the metal detector circuit itself and know that you are squeezing as much gain out of the system as you possibly can. Do all this with a 1.5 volt battery and it will be self limiting to preserve your ears from loud blasts.

You can even experiment by putting some back-to-back diodes before the output, between the two cascaded amplifier stages or at the input stage using an optional switchs. This will allow you to see just where the limiting provides the best audio results without too much complex circuitry. You can experiment with silicon or germanium, or LEDs to find the ones that work and sound best.

Remember that all these techniques to better hear faint signals do limit the dynamics of the sound. These sound dynamics typically help tell the operator how deep a targest is located. This would suggest that any outboard device should have some way to bypass it once a target is located so you can return to using normal signal dynamics to better estimate the target depth.

Most detectors have not pushed the limit on creative audio post processing. Just boosting the volume will not do it alone(protect your ears)!

I was playing with the Korg PX4, a guitar outboard audio processor, to see what I could do to enhance the audio out of my Sovereign.
By playing with the various gain settings and compression settings, I could definately begin to listen to those faint signals, hear the coil radiating as well as the floor level noise in the Sovereign audio circuit itself. Since we are not talking about high fidelity with metal detectors, the complexity should be much less than the PX4 and be similiar to what I outlined above.

I hope this will stimulate some discussion.

bbsailor

[bbsailor]

Reference: Good background information

Check out this link.

See the relationship of power to headphone performance and also see a list of headphone specifications. Look at impedance and sensitivity.

http://headwize2.powerpill.org/tech/dbohn1_tech.htm

[Goodrat]

Re: Multiple detent pots

What is critical about the volume control for me is, how it feels. I need a multi detent because that will sell.
As far as volume, the 5volt square wave should be plenty of signal. Simply use speakers above 150 ohms. I have everything I need except a good pot.

[Ray]

Re: Multiple detent pots

check www.jameco.com I noticed a pot with multiple detents when I was purchasing some parts for the Hammerhead.
Ray

[Goodrat]

Ten detent?

Thanx Ray. I noticed one reads 10 detents.
The pot on the phones I have now seems to have about 40 clicks. Do you think that would mean I want more than ten? Or am I confused?

[Ray]

Re: Ten detent?

I think I would give them a call and talk to someone about it. They may have some thing that is not listed or they can maybe special order for you if you have a part number.
Ray

[Carl]

Re: Multiple detent pots

Many moons ago, Radio Shack of all places, had a "stereo pot" with detents. It was one-size-fits-all, namely 100k.

- Carl