Reducing iron tone on a CZ? again...

I've posted here a few times about modding a CZ to reduce the volumn of the iron tone while leaving the other tones/volumns as is. Someone mentioned about using an inline EQ to do this and I was hesitant to use this method as I didn't want external gadgets hanging onto my detector. So...

What I would like to try is designing a very small EQ volumn level to be connected internally to the output jack for the 200Htz frequency which I believe is the frequency of the iron tone. I don't think it would require much but would like some pointers from the technical minded members here. I can bread board something to test it out before finalizing the circuit and making it as small as possible to fit inside the housing of the CZ. It wouldn't have to neccessarialy be ajustable as long as I could swap out components to find the reduction of volumn I wanted, but adjustability of the volumn output of the iron freq would be nice, and it could/would be internal.

I would rather this be a passive design w/o the need for batteries.

Ideals?...

It's more likely to get results than your original idea. One thing you will need to know is the resistance of the headphones you intend using, and work out how they are connected to the detector circuitry - series or parallel. Then you can choose as a simple starting point a series capacitor that will allow the higher frequencies to pass while suppressing (a bit) the low freq. I suggest obtaining a stereo 1/4 inch plug and matching socket to make a break-in cable for the first tests. Capacitor values needed will likely be around 1 or 2 microfarad, ie. small (pea size) electrolytic types.
It's worth pointing out that this approach will affect all sounds coming from the detector, including those produced during pinpoint mode operation.



Edited 1 time(s). Last edit at 01/26/2013 08:49PM by Pimento.

Thanks Pimento. I'll put togather a break-in cable at work and give it a shot. My headphones will be the Auvio wireless which you helped me with on a voltage reducer for mounting it internally on my CZ using the 2 9v. batteries of the detector. I haven't installed the wireless headphones in my latest acquisition, a nice CZ6a, so I will test it first w/o the transmitter. I'm sure the capacitor will have to be changed once I go wireless.

You may have more success on the unit with the Auvio TX fitted. It depends on the input resistance of the Auvio - if it's high resistance, that gives you more possibilites circuit-wise.

I've tried to find the orginal spec sheet that came with my AUVIO Wireless Stereo Headphones Part # 33-283 but it's like Saul and "hid amongst the stuff". If anyone here has these wireless headphones and can find the spec sheet, please post the "input resistance" listed on it. ...well, I "hope" they have it listed :-) I've tried a search for the specs but am not having any luck.

Connor

Connor, here's a slightly different twist, concerning an external...if you could make up a real effective inline
EQ, likely it would be received widely...since there are many other brands/models that could benefit.
Just thought I would throw a curve ball....

Connor
If you haven't a;ready, you may want to post this on the Geotech forum. There's some brilliant guys over there that might have some idea's.

Tom

Steve...

I hadn't thought of that, but if in my working on the project I can come up with a way to make it in a small plug size, that might be a handy gadget for a lot of the guys needing to reduce the iron volume. The design would probably have to be specific to the detector as to the iron tone Htz and output impediance. Since I'm already involved with a CZ, and I think they all have a 200Htz iron tone audio, I would just have to make sure they all have the same output impedience. It would be nice if it could be enclosed inside a regular 1/4" phone plug and just replace the original plug on your headphones or it could be design to look like a 1/4" phone adapter and just plug the headphone into it. The adapter design would extend the plug about 2 inches, something I don't like, but some might rather put up with that instead of rewiring their headphone jack.

How about it Pimento, could this be small enough to fit inside a phone plug? We have some phone plugs at work that have a larger caseing for large speaker wire. I'm sure they would make them that size in a stereo configuration.

Great ideal Steve!

Turtleman, I'll post on the Geotech forum if someone here doesn't come up with specs on the wireless headphones. I have contacted a friend who has a Phd in electrical engineering and design to see if he can help me a little. He's retired but still designs projects for Boeing on the side.

In its simplest form, it would just be one component the size of a grain of rice.
Another thing that occurred to me is this: the audio signal is actually a square-wave tone (I think) so has a lot of harmonics. Even if you suppress the fundamental, and leave the harmonics, the brain 'fills in' the missing lower frequency note. This is why 2 inch loudspeakers are able to produce a reasonable sound, despite not being able to reproduce anything below 400Hz.

Good luck guys....remember companies don't like anyone but their tech's opening their units and may refuse to work on them if they go down.....opened a few in my day myself but just adjusted pots so no problems doing that....always remember the big big pro from way back when had a tab when broken they knew someone was inside...

The Auvio TX may have a DC-coupled resistive load on its input, try measuring the resistance from ground to tip (and ground to middle-ring) with a multimeter.

Hi Dan...

Not really concerned about warrenty on this 20 year old unit. It's not like I'd be screwing the electronics up on my auto and not be able to get to work for a month :-) I have several projects in different stages of modifying and don't expect the companys to warrenty any of them. I work on them as time and interest presents its self. The biggest project I have probably worked on was putting a V8 engine and auto transmision into a 1965 Mustang that originally had a straight 6 and 3 speed. I was succesful on that one, but I would never want to attempt it again! I'm just a modder at heart and have no hesitations about making things ...shall we say "better"? Some would argue that point with some of the things I have done :-) I design and make a good bit of the things I use, be it flashlights, knives, electronic mods, firearms, hoe handles :-)

I appreciate your concern thou. At least I'm not tinkering with atom smashers and uranium grade products :-)

Pimento.....

My friend contacted me today and recommend I look at the notch filter design number 7 on this site:

[www.linkwitzlab.com]

His email says...

{{{This is what I found on [www.linkwitzlab.com] , item 7.

Attached is a simple notch filter circuit. It's only requirement is R2 (the load) be much larger than R1 (the input resistor.) If you are feeding earphone directly then R2 will be low, so you will have to increase the impedance with a small audio transformer.

This filter is weak with only one active circuit. (About 1/4 the volume.) If you need additional filtering, then duplicate the circuit and put them in series.

The second attachment is this guys version that works at 291 Hz. You can scale either L or C by 1.455 (291/200) to get it to work at 200 Hz. Also smaller active circuits are shown.



BTW, since you are trying to kill of such a low frequency, these components are going to be fairly large.}}}




It sounds like you are recommending something a bit simplier. I like simple. What do you think?

I believe I was the one who suggested you use the small in line EQ...

I would still buy one ...there only less than 20.00 buck or so...see if they even work ...Before taking the idea further...

The one I posted on the original post is small enough to fit inside the earcup if you wan it out fo the way..just wire it in IF it is worthwhile...

Just a thought...

Keith

Keith Southern Wrote:
-------------------------------------------------------
> I believe I was the one who suggested you use the
> small in line EQ...
>
> I would still buy one ...there only less than
> 20.00 buck or so...see if they even work ...Before
> taking the idea further...
>
> The one I posted on the original post is small
> enough to fit inside the earcup if you wan it out
> fo the way..just wire it in IF it is
> worthwhile...
>
> Just a thought...
>
> Keith


I agree .

Connortn mod away my friend....just thought you had a new CZ3D...and my bad......with help from knowlegable forum members you should be good to go...and good luck in your modding as this is sure one hobby where its prevalent and fellas have come up with some good ones....

Keith, I don't believe the one linked to in the other post will work. It's a 3 band EQ probably covering 15Khz or close to it. That would mean the 1st band would be in the 200-1500 Htz or more, which would reduce all the tones of the cz's being that they lie between 200-1000 htz. I'm going to need a notch filter, one that is designed for one particular Htz (200) and won't influence the other tones of the cz. We have some 31 band EQ's at work which are rack mounted and if they go low enough, I can use one to test the project out before building anything, but even they may have too wide of a filter on the low band end.

Thanks for reminding me thou. If it had worked, I could have probably taken it apart and used the components to make the mod.

A passive ( ie.unpowered ) notch filter is only viable if the Auvio has a high input resistance. A plain high-pass like I am proposing you try, will work with headphones or the Auvio if it has a dummy-load type input.

Well, I got to do some testing before moding anything tonight. I picked up a few electrolectic caps at 1mf, 2.2mf and 4.7mf. They would reduce the volume but reduced all of the tones, not just the 200htz I was looking to lower. The audio was also very muffled in sound, not clear as when tested w/o the caps in the circuit. I tested with a pair of wired headphones and with the auvio wireless tx with same results. I tried measuring the input resistance of the tx but could not get a reading at all, so I must have being doing something wrong. Tested it with a Fluke meter in all variables I could think of, on and off.

I'm thinking that this may require a dedicated notch filter circuit, if it will work at all. I'll probably put this expirment on the back shelf till later and concentrate on installing the wireless tx inside the detector housing. It worked fine on another cz detector so shouldn't be a problem this time... I hope!

Thanks guys for all the help. I had hoped it would work not just for my benifit, but anyone else wanting to lower the iron tone volume on a CZ.

Being the CZ6a hasn't been manufactured for several years, maybe Dave Johnson could give us a tip or two about how to accomplish it. Don't know if it would be against Fishers policies for Dave to discuss it since it's no longer manufactured, but if it isn't a problem, and could be done fairly simple, I would sure appreciate any advise he has.

C.



Edited 1 time(s). Last edit at 01/29/2013 05:15AM by connortn.

I can't think why the sound would be muffled, the exact opposite is what I would expect. So you have the stereo plug and socket and made the break-in cable?

Yes.... and no. I made up a stereo plug with the 3 required leads and used jumper leads to put the caps in the circuit. I put the cap between the tip and ground, and sleeve and ground, one at a time. I could have shorted the tip and sleeve togather and tried that but in the configuration I used, I would get the muffled and somewhat reduced sound in my headphones from whichever side I had the cap in the circuit. I also tried putting them in line... putting the cap between the detectors tip and tx tip and sleeve to sleeve, which of course didn't ground the 200hz to anything :-)

It seemed that the cap acted like too wide of a filter. The only difference I could get was that the higher the mf, the more it would reduce the volumne... they all sounded muffled thou. But saying that, even the 4.7mf didn't reduce the sound quiet as much as I would have liked.

I'm use to using a cap to row off the lows on a guitar pot, which usually doesn't lead to a muffled sound. Should I try it with a pot/resistor?

...and any ideal why I couldn't get a reading while checking the resistance of the tx input? I didn't take a reading on the output of the detector.

Oh boy, I knew this was going to be a transatlantic pain. I've just looked back through the thread, and seen that I didn't actually tell you what I wanted you to do, because I was waiting for you to get the plugs/sockets etc first.
The capacitor has to go in series with the headphones. Connect the ground of the 'phones to the ground of the detector output. Connect the tip and middle-ring of the phones together. Then connect them to the tip or middle-ring of the detectors output via the 4.7 microfarad capacitor. At this stage it should behave close to normal - all tones normal volume. Then drop the cap value down, 2.2, then 1.0, and see if the iron tone reduces, but leaves the others little-changed.
The Auvio input resistance is probably capacitively coupled, then, in which case it will have a high-ish input resistance, which may help with filter design.

Let's see now... I take about a number 32 guage bare copper wire, wrap several turns tightly around the end of the frayed fuse of a cherry bomb, hook one end of the wire to the negative of a 9v battery and the other end to the positive! Then quickly put it in my pocket!

Got it!

Be right back.

:-)

Don't cut the red wire....no, the blue wire.... no, the ....

haven't heard from him, he probably didn't make it gallant effort, I love when you guys talk about this stuff, I don't under stand it, but I like it

DER [EMINTo,,,,,,,,,,,,,,,

wRON Wir... wsn,t Qik eNURF!!! wEll tyr aGIN 2moRrow. soRY 4 bAdd sPillin--- hArd 2 tpye WIf nOOSee!!!

Finally got my fingers bandaged up!


Pimento.... Something like this....?



Detector headphone output.... tip to ring... to 1uf cap... to tip (or ring) of headphone jack
Detector headphone output... ground.... to... headphone jack ground


I tried drawing a diagram using dashes and all those other strange looking symbols on my keyboard but when I previewed it, it looked worse than typing with my nose!

If this is correct, I tried it before I left work today and all I could get thru my headphones was a VERY VERY low volume on all tones. I could barely hear it using either 1uf or 4.7uf.

Maybe the audio out of the detector is between the tip and middle-ring, and ground is unused. In which case:
1 : connect tip of 'phones to tip of 'tector output, and connect middle ring of 'phones to middle-ring of 'tector output. No ground connections. Does this seem to work like normal? If so, then...
2 : Insert the 4.7 micro cap between tip and tip. Does it still sound normal? If so..
3 : reduce the cap value to 2.2 then 1.0 to see if the low frequencies become reduced.

Fisher uses the tip and ring as the output .. their as one,no right no left just Mono.......Ground is the sleeve...

Tesoro uses the same...

Wire the headphones in series and the volume will increase dramatically maybe enough for use with the cap in line..

Keith

That's what I was thinking they did, but something about connor's experiments with the Auvio cordless setup made me wonder if it may be different.
Looks like he may now have some success.

OK... Did as pimento says...(tip to tip. ring to ring, no ground). Detector worked as normally would with head phones plugged in. ...so evidently it doesn't use the sleeve for ground.

Put the caps in line between the tip to tip, no change. Tried ring to ring, no change. Tied both wired and wireless headphones with same results.

Put the ground to ground in circuit and no change... didn't think it would.

Shorted headphones tip and ring together, ran to tip(or ring) of detector, won't work w/o ground to ground, extremely weak sound other wise.

Have tried numerous variations of this (you can only do so much with 3+3 wires) and I get no sound, very very weak sound, or detector works as normal but putting the caps in line anywhere does nothing.

I picked the caps up at Ratty Shack. The package says electrolytic, but there's no + or - or any indication what the polarity is. Both ends of the caps have dimples, so no help there. I've been reversing the caps in each configuration that I tried and it made no difference.

I'm going to drop this mod as there's something we're not seeing and go ahead with the wireless transmitter install. I appreciate everyone's help on it. Maybe Fisher's new detector will have an iron audio volume control on it. If it doesn't, we should tie them up, put a pair of loud headphones on them and plug them into a detector under a swinging pendulum with a rusty nail taped to it for a few weeks :-)