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fisher 1200 series modds?
Posted by: amcjavelin
Date: February 05, 2016 09:03AM
hello there been a while since I've visited here and was wondering does anyone here no anyone that has added a G/B mod to there unit? or any other internal mods?

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Re: fisher 1200 series modds?
Posted by: MarkCZ
Date: February 05, 2016 11:22PM
Quote
amcjavelin
hello there been a while since I've visited here and was wondering does anyone here no anyone that has added a G/B mod to there unit? or any other internal mods?

The 1200 Series uses what the manual describes as "Automatic Ground Cancelation" I know, that doesn't reveal much and it doesn't actually say auto ground balancing. But, in their day the 1200's ran deeper than about all of the other brands and models that used (or needed) manual ground balancing, even in todays standards the 1200's (or the later ones) are pretty darn deep!
Automatic ground cancelation might also mean that it don't have an internal pot that's preset like some models.

But to answer your question,
I've never seen or heard of anyone adding a manual ground balance control, I'm not sure about any other mods?

Mark



Avatar, Me and my two brothers from left to right!

WV62 - MarkCZ - Still Looking 52

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Re: fisher 1200 series modds?
Posted by: thump7
Date: February 08, 2016 08:43AM
I've checked the ground balance on the 1265 at almost every site I've used it at. It is always dead on, other preset ground balance machines I've used are usually close, sometimes way off. I've come to believe the 1200 series do have auto gb, it's just always set at the right ground balance.



Edited 1 time(s). Last edit at 02/08/2016 08:43AM by thump7.

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Re: fisher 1200 series modds?
Posted by: MarkCZ
Date: February 08, 2016 11:46AM
I've seen statements in manuals like,
Preset,
Fixed, (non adjustable) and
Automatic Ground Balance.

But the manual for the 1266 doesn't really say any of the above!
See picture below.

Mark




Re: fisher 1200 series modds?
Posted by: Dave J.
Date: February 08, 2016 12:08PM
The automatic tuning and automatic ground rejection are both accomplished with two stages of differentiation (not by adjusting phase, which is fixed).

In theory you could bring the internal ferrite phase tweak out and call it a "ground balance knob", but you'd likely be disappointed in the results. Adjust it just a little too far or use it in rocky ground and the machine's gonna become noisy as heck.

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Re: fisher 1200 series modds?
Posted by: MarkCZ
Date: February 08, 2016 12:43PM
Quote
Dave J.
The automatic tuning and automatic ground rejection are both accomplished with two stages of differentiation (not by adjusting phase, which is fixed).

In theory you could bring the internal ferrite phase tweak out and call it a "ground balance knob", but you'd likely be disappointed in the results. Adjust it just a little too far or use it in rocky ground and the machine's gonna become noisy as heck.

Thank You Dave, as deep and reliable as the 1200's are I never felt that there was anything to gain by twisting and screwing around on the inside.

Hey Dave, let me ask you this while we have you on the line so to speak. On the first release of the 1266 it had what I would call "Double Stacked Circuit Boards" the later releases had only a single board (mine has the double boards) What was the reason for the change? and was there any gain or loss in the change?

I pray all is well with you and your family!

Mark



Avatar, Me and my two brothers from left to right!

WV62 - MarkCZ - Still Looking 52

Re: fisher 1200 series modds?
Posted by: Dave J.
Date: February 08, 2016 02:55PM
We went to the single board to cut manufacturing cost; and at the same time there were several design improvements, stuff you probably wouldn't notice unless you were working on salt water beaches.

When you're operating in discrimination mode, depth is determined primarily by the discrimination channel and fiddling with the phase of the resistive (all metals) channel has almost no effect on depth. This is why most older metal detectors that had a ground balance knob, reverted to fixed phase operation when in discrimination mode. Most of our computerized metal detectors built on the T2 and later platforms that have manual and/or pushbutton ground balancing do use the ground balanced signal for control in addition to the fixed phase resistive signal: in some ground this provides a slight improvement. And, it's "just software", what could be lower cost than that? [AARGH! if you only knew how expensive software really is.....]

Re: fisher 1200 series modds?
Posted by: amcjavelin
Date: February 08, 2016 08:23PM
well hey guys thanks for clarifying all this and you too espeacially Dave J I guess I was interested in was looking for more tweeking with the 1236x2 more than anything

Re: fisher 1200 series modds?
Posted by: JJdigs
Date: February 10, 2016 08:29PM
Quote
Dave J.
We went to the single board to cut manufacturing cost; and at the same time there were several design improvements, stuff you probably wouldn't notice unless you were working on salt water beaches.

When you're operating in discrimination mode, depth is determined primarily by the discrimination channel and fiddling with the phase of the resistive (all metals) channel has almost no effect on depth. This is why most older metal detectors that had a ground balance knob, reverted to fixed phase operation when in discrimination mode. Most of our computerized metal detectors built on the T2 and later platforms that have manual and/or pushbutton ground balancing do use the ground balanced signal for control in addition to the fixed phase resistive signal: in some ground this provides a slight improvement. And, it's "just software", what could be lower cost than that? [AARGH! if you only knew how expensive software really is.....]

I guess I missed my calling....instead of playing bass in bands in my teens and twenties....I wish I was learning the tech in metal detectors.....I bought my first detector when I was 32 and got hooked hard....But my love for local history and science has had my mind traveling so many different ways. Dave how did you find your path on the metal detector design world ? If you don't mind me asking. I have used and bought 60+ detector in the past five years.....Vintage to the etrac and in-between I loved them all....of course I don't have that many now....I like to flip them ! So my question is .......How did you end up designing Detectors.......I hope someday soon I find my life pasion when it comes to a day job. Do you consider this to be yours. Either way thanks for your contributions to this hobby and man have you helped us find some serious cool things in the ground and great relationships !

Re: fisher 1200 series modds?
Posted by: Dave J.
Date: February 10, 2016 10:49PM
Quote
JJdigs
Dave how did you find your path on the metal detector design world ? If you don't mind me asking.

As a kid, one of my hobbies was electronics (back then, vacuum tubes and crystal radios). Built some neat stuff. Didn't go to college. Got drafted and became a medic. After I got out of the Army I took up electronics again as a hobby, this time with transistors and the occasional IC. Timing was perfect, I learned about CMOS within weeks of its being introduced and never had to screw around with TTL. Was hired by CALTRANS to do traffic studies, but I saw the need for electronic stuff that didn't exist and began screwing around with that. My first "metal detector" was an experimental portable low-power unit I developed for detecting vehicles on the freeway using roadway loops, so we wouldn't have to be hauling 100 pound boxes of lead acid batteries to power the regular units they use on traffic signals. Quite to my surprise it discriminated between cars and trucks, because trucks have steel frames but cars have body pans, same thing you see in a regular metal detector with nails reading ferrous and flat steel (e.g. bottlecaps) usually reading nonferrous. Unfortunately it was too drifty to be practical and without a clear picture of how to make it stable I abandoned the project.

Later, I designed and built newfangled traffic signal controllers and traffic analysis and control analog computers for doing real-time ramp metering in San Jose. With no college education, got to play real games with real freeway rush hour traffic according to rules I invented, achieving uniformity of flow and increased throughput that the old school engineers said was never going to be possible. Then two successive Governors, Reagan (through massive corruption) and Moonbeam (through outright stupidity) wrecked CALTRANS and I left.

A couple months ago I was going through old photos and documentation and realized that what I did working for CALTRANS was actually the best engineering work I ever did, better than what I later did in metal detectors. What I've done in metal detectors, there are other engineers who have done comparably good stuff, but what I did working for CALTRANS nobody else did and nobody else could have done. To my knowledge 40 years later it still hasn't been replicated.

For years I tried to find employment in the natural sciences but the first thing they ask is where's your degree, and that was a showstopper. But back then, electronics was still "are you any good at it?" The closest I got to a career in the natural sciences was a one year stint with the State Climatologist of Arizona doing solar radiation instrumentation. I eventually added up the evidence: no matter what line of work I was hoping to get, whenever I actually found gainful employment electronics was either a part of it or was the whole thing. From then on out I did electronics. Feb 8 1981 I went to work for Fisher in Los Banos, introduced the revolutionary 1260-X about 15 months later, and that's when and where my beeps career actually began.

--Dave J.

Re: fisher 1200 series modds?
Posted by: 88junior
Date: February 11, 2016 03:21AM
Very cool life story Dave J. Thanks for sharing your story. I would love to work for FTP making detectors that would be my dream job!! I work in industrial maintenance for the world's largest carpet manufacturer Shaw Industries I work on electronics and huge industrial air compressors. I'm currently learning a lot about automation and PLC programming.



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Re: fisher 1200 series modds?
Posted by: JJdigs
Date: February 12, 2016 07:55PM
Thanks so much Dave J. I find you story so very interesting and inspiring. Thank you very much for putting in the time to write back.

to dave j.
Posted by: alex74
Date: February 14, 2016 03:57PM
dave, you became a medic? what kind of?
regards, alex (a medic)



Edited 1 time(s). Last edit at 02/14/2016 04:00PM by alex74.

Re: to dave j.
Posted by: Dave J.
Date: February 14, 2016 04:36PM
Quote
alex74
dave, you became a medic? what kind of?
regards, alex (a medic)
Just regular Army medic. 2-year draftee.

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WOW... I am more impressed now by you than I was. And trust me it was considerable ..N/T
Posted by: Elton
Date: February 14, 2016 06:52PM

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