Understanding Headphone Specifications, & Home Made Blast Limiters

[Critterhunter]

Forgot to post this picture of the Treasure Ears...

 

[Critterhunter]

Otlew, those Treasure Ears do seem to be a perfect match and the price is right. With a home made limiter they look like the ideal setup. Independent left/right volume control is important. Due to slight differences in tolerances for speaker construction or somebody with bad hearing in one ear that can be a big help. With my Sonys I've got the left ear stuffed with some extra foam because it always seems a little louder than my right ear with these headphones. I'm not sure if that's due to my hearing or if the right speaker is just not as loud. Makes sense that lower impedence (resistance) would allow certain audio signals to break through and sound off easier. That could be important I guess for deep/ultra soft targets or ones at specific frequencies I would figure. If anything that might play a role in power consumption like Jim said. The really high impedence of the Grey Ghosts (can't remember but I think it was well over 100 ohms) is why I feel they had such flat audio which also sounded fairly muffled. Like listening to music through a tin can.

I am one of those people who has a deficit between ears, I discovered that at 17 years old. So I guess I have been defective for most of my 63 years

With that said I need to be able to boost volume to my "bad ear" and need the separate volume controls, so that is one of my must haves. The Sovereign GT certainly has a learning curve and I don't want another impediment.

I hope your able to arrive at a good homemade limiter as I just can't seem to move off of the recommended optimum of 32 Ohms and would like to give the Treasure Ears a go.

I fixed the difference in left/right volume on mine by stuffing the left ear with some extra phone. Not sure if it's my hearing or the headphones. The Sonys don't have left/right or even an inline volume control, but those can be bought at Radio Shack. I don't use one though. No point. Individual left/right volume control could easily be hacked into the Sonys with a variable resistor at each speaker. I may look into doing that. Those Treasure Ears of course already have left/right volume control.

What I'm probably going to start off doing is make a few limiter circuits to try my Sonys on. Even if that works well later I'll pick up those Treasure Ears. They sure do look perfect for the GT. 32 ohms matches what I always read for GT specs. Might be different on older Sovereigns. With a limiter on those Treasure Ears I bet they'd be killer, not to mention much cheaper than others with limiters. Only thing I'd like to hear is if anybody has used these headphones on a Sovereign. One never knows just how well certain headphones will sound until they are tried. Of course like Crazyman said a lot of that falls down to individual hearing traits, but something as small as speaker brand inside the headphones can make all the difference, even if the numbers line up.

 

[Tony in FL]

I hope your able to arrive at a good homemade limiter as I just can't seem to move off of the recommended optimum of 32 Ohms and would like to give the Treasure Ears a go.

I don't think you need worry about only using only a headphone rated for 32 Ohms. The manual for the GT suggests a range:

Headphones are recommended for serious treasure hunting for several reasons: they are
more sensitive to slight target signals than the loudspeaker and their use will increase
battery life. The socket will accept most stereo headphones with a 1/4" jack. If your
headphones have a "Stereo/Mono" switch, set it to "Stereo". Minelab recommends
headphones to be between 32 and 100 Ohms.

 

[synthnut]

Crazyman,
That was my next question was about the cord ...My AT's have a straight cord and it DRIVES ME UP THE WALL !!....It hangs on EVERYTHING !!.....I"m gonna cut the cord and put a spiral cord on it !!..... I'll also look into the new Sony phones you posted ...Thanks , Jim

The MDR V-150's from what I have been reading have a very hyped low and midrange and a flat high end ....So your lower and mid tones are hyped ....The frequency range that the detectors are putting out are clearly in the "MID" reagion .....When you have phones that are close to being overdriven to begin with , get a sudden surge of more mids or more bass, it's just enough to bring them over the edge ..... Also , bringing up the volume of ANY amplifier whether it be a headphone amp, or a musical amp, or a home entertainment amp, to it's peak volume is going to introduce more distortion also ... There is a sweet spot where an amplifier lives that has the right amount of S/N ratio ....( Signal to Noise ratio ) ...... Bringing up the volume of said amplifier also brings up the gain ..... I'm STILL not convinced that by bringing the volume all the way on the Sovereign is going to be giving you that much more gain that will be beneficial to the additional distortion that you will be getting from lower impeadence headphones .....Again , as Crazyman points out , he really loves the tones he get's from these phones ......I'm assuming that he is using some sort of volume control , or he's litenning to a bit of distortion in some cases ......Again too , everyone's hearing is different ..... I'm going to try some lower ohm headphones just to see if I can get the same change in tone that Crazyman speaks of .....THIS is KEY to figuring out what targets are there !!....... THIS is what a lot of other detectorists should be paying attention to .....ESPECIALLY the Tesoro crew where tone is EVERYTHING !!.... Remember the chain of what takes president when detecting ...TONE IS KING !!.....Jim

 

[Critterhunter]

That's a good question- Crazyman, where are you setting the volume using the Sonys on your GT, and do you hear any distortion if you are going full blast with GT volume? Like I said, I hunt with it all the way down on them and the audio is great, good scale from shallow to deep stuff to tell depth, and I have no problem hearing the deepest targets with low volume set that way either.

 

[crazyman]

There is probably a few other things that come into play. It also could depend on the coil. The tones I get from my S-8 are very different from what I get with the stock 10 inch. With the Sony's the tones are bit sharper and closer together with the 10 inch than with the S-8. I can hear the difference between a zinc and a silver dime with the S-8 and the Sony's but I can't with the 10 inch and I suppose there might be a difference also with 10X12 SEF. The S-8 tones are a little wider and smoother than the stock 10 to my ears and seem to fall somewhere between the old white Coinsearch coil and the newer slimline.

 

[synthnut]

Crtter.
This is my point ...Is it possible to have ENOUGH gain without having to raise the volume of the Sovereign all the way up ? ..... Again , I'm not convinced ....Maybe it's another case of "We're all diffrerent " ......Jim

 

[crazyman]

Critter, I probably don't have the best hearing but I do hear the distortion at full volume. I run my volume at about 3:00 as I like the tones better there but large shallow targets are a bit to loud but not enough to hurt my ears.

 

[synthnut]

I'm sure that the different coils will have something to do with the tone also ....You make mention of this ......Critter made mention of the different tone of the 10 x 12 being SO MUCH different than the other coils , but one thing will remain constant is the headphones .....If they are doing a better job on one coil, they should also be doing a better job on ALL the coils ...I would tend to believe that ALL of us have some sort of hearing disability .... I use to play in bands all the time .... I can remember being up on stage and having my vision blurred from certain notes that were played !!..... It's a good thing we hunt with headphones , or I'd be walking around with my detector going HUH,? WHAT? all day !!..... Jim

 

[synthnut]

I just ordered these ....I'll let you know how they work out .....Inline volume control and 1/4 inch adapter included ....Free shipping and only had to pay tax ...Under 20 bucks !!......Last of the BIG TIME SPENDERS !!......Jim

http://www.radioshack.com/product/index.jsp?productId=2272473

 

[Critterhunter]

Jim, I understand that depending on the headphones low volume may produce better deep target volume than other headphones. What I'm wondering about is if there is something internal in the GT that causes deep targets to be reported with full volume where as they wouldn't with it low. The Minelab techs seem to hint to that so that's why I'm wondering. I haven't noticed it myself but you never know. Always hedge your bets is the way I look at it. If I can rig up a limiter then I can go full blast audio to bring up the deep stuff in volume yet not have the surface or large stuff blast my ears.

 

[synthnut]

Here are my thoughts ......Since the Sovereign is a much more simple machine than the E Trac , the volume, and the gain are tied together in one control .....The volume control ......So yes , there is more gain as you turn up the volume ......You really need to either have headphones that have a lower impeadence so as not to blow your earls out, or you have to have more closely matched impeadence phones, and have a volume control to contol the volume ....Your limitter is going to come in handy as you said on targets closer to the surface ....I'll never forget hearing targets that almost took my head off with the Sovereign when I first got it ......I also remember digging down 3 inches or so and not being able to feel/hear it with my Garrett Pro Pointer ......and digging ANOTHER 3 inches down and FINALLY start to hear it with my pointer .......THAT my friend freaked me out because the target was so loud and clear that I thought it was on the surface ..... The Evolution that you hear me talk\ about with the E Trac, is just another example of what most call "bells and whistles " is the fact that the E Trac has seperate gain and volume controls ...... When you bring up the gain on the E Trac it makes deep targets sound like shallow targets ........This way , you can turn your volume down and not have your head blown off when you hit targets .......The depth meter on the E Trac is yet another one of those bells and whistels that help you when you have your gain all the way up so you know where your target is because as I said , deep and shallow targets sound the same ....... I am giving this theory the benefit of the doubt by purchasing the headphones that I listed ....They are 60 ohm phones , so they SHOULD BE too loud with the volume turned all the way up , but they can be contolled becase they come with a volume control ....I will THEN be able to better assess whether or not having the volume all the way up will be of any benefit to me .....Again , I will only be able to speak for myself , because everyones ears are different .....Hopefully it will make for better detecting .....??????......We'll see !!.....Jim

PS ...Let us know when you have your limitter built ....I saw that one limttter that you had the link too ....Looks interesting and simple to build .....Simple for you anyway .....I'm no electronic wiz ...as a matter of fact , I'm no wiz at all !!,.... Jim

 

[Birdseed]

Just a couple of points on phones & impedance. In simple terms!!!
Minelab, I believe specify 32 Ohm phones.
To use lower impedance phones than this will increase the load on the audio amplifier as these phones require more current or "Amps", potentially shortening battery operating time between charges, also the output amplifier will be subject to more thermal stress with the lower the impedance. The lowest impedance phones (4 Ohms or less) are almost the same as a short circuit across the output.
Using higher Impedance phones requires the output amplifier to deliver higher voltage to drive them efficiently, this puts less stress on the detector but will result in the phones becoming less efficient as the mismatch gets higher.
Using phones in the range 32 to about 150 Ohms would probably be indistinguishable to the user and will not hurt the detector.
On the subject of limiters, two back to back silicon diodes simply installed across the phones input will effectively limit noise peaks to 0.6Volts and then, simply adjusting the volume control on the headphones will ensure comfortable listening.

Peter downunder

 

[otlew]

On the subject of limiters, two back to back silicon diodes simply installed across the phones input will effectively limit noise peaks to 0.6Volts and then, simply adjusting the volume control on the headphones will ensure comfortable listening.

Peter downunder

Super simple diodes, I am going to dig through my old electronics parts bin when I return home. I use to have a pretty wide assortment of discreet components from my hobby days. What we may need to do, is apply the KISS Principle to this issue.

 

[JASONSPAZ1]

Went to Target today to look for the lightweight Sony headphones that work best with the Sov GT. They did not have any. However I found these Nady Audio HP-03 headphones that have 32ohms and have an inline volume control. They work so much better than my killer B's I had as I can now hear a better seperation in tones of targets. And the best part is that they where marked down on clearance from 29.95 to 7.00

I lucked out.

Take Care
Jason

 

[kered]

Here are my thoughts ......Since the Sovereign is a much more simple machine than the E Trac , the volume, and the gain are tied together in one control .....The volume control ......So yes , there is more gain as you turn up the volume ......You really need to either have headphones that have a lower impeadence so as not to blow your earls out, or you have to have more closely matched impeadence phones, and have a volume control to contol the volume ....Your limitter is going to come in handy as you said on targets closer to the surface ....I'll never forget hearing targets that almost took my head off with the Sovereign when I first got it ......I also remember digging down 3 inches or so and not being able to feel/hear it with my Garrett Pro Pointer ......and digging ANOTHER 3 inches down and FINALLY start to hear it with my pointer .......THAT my friend freaked me out because the target was so loud and clear that I thought it was on the surface ..... The Evolution that you hear me talk\ about with the E Trac, is just another example of what most call "bells and whistles " is the fact that the E Trac has seperate gain and volume controls ...... When you bring up the gain on the E Trac it makes deep targets sound like shallow targets ........This way , you can turn your volume down and not have your head blown off when you hit targets .......The depth meter on the E Trac is yet another one of those bells and whistels that help you when you have your gain all the way up so you know where your target is because as I said , deep and shallow targets sound the same ....... I am giving this theory the benefit of the doubt by purchasing the headphones that I listed ....They are 60 ohm phones , so they SHOULD BE too loud with the volume turned all the way up , but they can be contolled becase they come with a volume control ....I will THEN be able to better assess whether or not having the volume all the way up will be of any benefit to me .....Again , I will only be able to speak for myself , because everyones ears are different .....Hopefully it will make for better detecting .....??????......We'll see !!.....Jim

PS ...Let us know when you have your limitter built ....I saw that one limttter that you had the link too ....Looks interesting and simple to build .....Simple for you anyway .....I'm no electronic wiz ...as a matter of fact , I'm no wiz at all !!,.... Jim

Jim, I'm understanding things the other way round, lower impedence higher possible volume, high impedence lower overall volume, I may be wrong.

Another thing i have noticed is the Koss UR30 i think are 100ohms, if 32 ohms was better why do they supply them, or is the best ohm rating on the other minelab detectors different? I have some still in the packet, i think i'll try them(if i can keep them on my head)

 

[synthnut]

Kered,
You're right in your theory that Lower impeadence is louder and higher is lower in volume and not as efficient ...Maybe I have to proof read what I say, or say it differently next time .... I couldn't find a listing on what the E Trac is rated for ohm wise ......The phones that are supplied are nice phones , and are no longer listed on the Koss site , so they are probably dicontinued and Minelab proabably got a good deal on nice phones .....They sound OK on my stereo !!...... I guess it may seem kinda shady to supply your top of the line detector with cheap phones , even if they do a better job !!.... Cloth is more comfortable than Leather, but people would rather have leather for the intereior of their cars ...?????? .....



Jason,
Nice score on the NADY's !!..... I'll be they'll sound GREAT on the Sovereign .....Dont forget to give us the details ....Thanks and good luck with them .....Jim

 

[Critterhunter]

Well, I don't believe it works like that. When we are talking pre-amps or amplifiers there are three so far as I know in the GT. There is a RX coil pre-amp inside the coil designed to do an initial boost of the signal being received. Inside the GT the sensitivity control is another amplifier. As you increase sensitivity it increased the gain of the signal being received. With higher gain more noise is introduced and there comes a point when target signal is overwhelmed by introduced signal noise. Hence why sensitivity can't ride high all the time. Stray RF noise, ground mineral "glare", onboard component noise, etc. The third would be the audio amplifier.

After reading about the Minelab techs saying something to the effect of full volume providing best depth, more than likely I think this has little to do with actual depth of the machine. That would be odd to wire a machine in such a way that volume control is some how tied to sensitivity (gain) on the RX signal. More than likely what they are referring to is the bottom end of the audio amplifier. If you have volume all the way down a ultra deep/soft target might not be strong enough to be picked up by the audio amplifier and reported. With full volume it's going to grab even the lowest of lowest in terms of soft signals and amplify it. That's my theory, anyway, The volume control being tied to some kind of target amplification on the RX side is highly doubtful in my mind. It's more to do with insuring the audio amplifier reports even the slightest sound off. Opinions?

On the Ohm specifications...Where did you read that the GT specs recommend 32 to 100 ohms? I could be wrong but I'm pretty sure the manual says 32 ohms only from memory. If the info you posted is a general Minelab recommendation for all their machines then that would explain a lot. I know for me those Grey Ghosts which I think are 100 ohm or more were so flat that I couldn't understand why they would have a good reputation. I figure they probably match up and work well with other machines, but they sure didn't for me on the GT.

 

[Tony in FL]

After reading about the Minelab techs saying something to the effect of full volume providing best depth, more than likely I think this has little to do with actual depth of the machine. That would be odd to wire a machine in such a way that volume control is some how tied to sensitivity (gain) on the RX signal. More than likely what they are referring to is the bottom end of the audio amplifier. If you have volume all the way down a ultra deep/soft target might not be strong enough to be picked up by the audio amplifier and reported. With full volume it's going to grab even the lowest of lowest in terms of soft signals and amplify it. That's my theory, anyway, The volume control being tied to some kind of target amplification on the RX side is highly doubtful in my mind. It's more to do with insuring the audio amplifier reports even the slightest sound off. Opinions?

I was also also wondering why max volume was recommended as this would not seem directly related to the actual depth of the machine. I agree that by amplifying weak signals to the point that they picked up by the audio amplifier and thus discernible to the user seems to make sense and in effect might allow for the possible detection of an otherwise missed target. On my Excalibur I typically run at half volume. I have tried full volume but it changes the tonal quality of the signals. It would be interesting to run some tests with both the GT and Excalibur to see if max volume really provides more depth.

On the Ohm specifications...Where did you read that the GT specs recommend 32 to 100 ohms? I could be wrong but I'm pretty sure the manual says 32 ohms only from memory. If the info you posted is a general Minelab recommendation for all their machines then that would explain a lot. I know for me those Grey Ghosts which I think are 100 ohm or more were so flat that I couldn't understand why they would have a good reputation. I figure they probably match up and work well with other machines, but they sure didn't for me on the GT.

I pulled the range of 32 to 100 Ohms directly from the GT manual. You are referring to the back of the manual where it lists the specs of the machine, which does only specify 32 Ohms. However in the section talking about the benefit of using headphones with the GT it recommends a range of 32 - 100 Ohms. To me this suggests that the specifications page simply omitted the upper end of the recommended range. Lending further support for this range are the UR-30's which seem to be produced by Koss specifically for Minelab detectors which are rated at 100 Ohms.

 

[synthnut]

I did not say 32 to 100 ohms ...That was someone else ...I mentioned 50-100 ohms ......100 ohms which I now see that Tony posted is from what I gather for the Sovereign GT .... I gave 50 to 100 as a figure that I used in my theory not Minelabs .....I didn't even know that Minelab metioned 32 -100 .....I knew that the Soveriegn was a 32 ohm machine only ...The E Trac mentions nothing about it's specs and the E Trac is the detector that they supply the 100 ohm Koss phones with .... ????........ Anytime a device has an ohm rating , such s the Sovereign does, it normally will not hurt the amplifier or the unit to run a higher ohm load ....Going the other way and short change the ohm rating WILL hurt the electronics ..... The higher you go past the ohm rating , the less sensitive , and the less efficient the phones will be ..... The tone actually smooths out and takes more current to drive the phones ...This is why they don't seem as loud and can probably get to the point of being dull sounding .....Materiel that the phones are made of also has to do with what they sound like ....

I got 2 " gains " mixed up .....Sorry bout that .......What I was reffering to with the gain going higher with the volume , is the gain of the AUDIO AMP ......I see that the gain setting on the E Trac is not for the audio amp but for the coil itself ..... I got those mixed up .....My mistate ...... Actually , I like the way they set it up on the E Trac to have the gain of the coil sending a STRONGER signal to the audio amplifier so you don''t have to turn the volume up like you do on the Sovereign which I'm STILL NOT CONVINCED you have to do ..... You have a signal coming from your coil .....You then take that signal , and send it to the audio amplifier .....The audio amplifier sends that informaton to your headphones for you to listen to .......This being said , the signal is the same if the gain of the actual signal is not boosted by turning up your Sensitivity .....It remailns the same ....The only thing that changes is the volume from the audio amplifier if you don't touch the Sensitivity .......Who is to say that I can't hear the deeper targets that are in the ground with the volume up 1/2 way ? ...... Maybe my hearing is better than yours ..... What I am saying is , if the signal is already a constant , and all you are doing is audibly making that signal louder , who is to say that I can't hear it at a lower volume ? ......If the CONSTANT coil signal is only being audibly boosted by the volume control , and I can hear it at a lower volume , what am I missing ? .....and ear ache ? ........ As I said earlier ....I'M NOT CONVINCED that the volume being up so high is better unless you are hard of hearing !!..... Unless someone can prove to me that more of the orignal coil signal is getting thru by turning up the volume of the audio amplifier , than I will keep it where I find it the most comfortable for me ..... I'll know more when I get my new phones with the volume control ...I'll be able to investigate targets both ways ......Jim