GOLDSCAN 5 SCHEMATIC QUESTION

[Op04]

That blocking diode I solved with TVS before goes to LT1226 still one.of the best preamp, I loose 2 chip before that. In case anyone have same problem.

[Op04]

1n4148 has far less capacitance which you'd want for those diodes. Sticking to 2x or 3x configuration of 1n4148 is best.
I buy packs of x100 1N4149 (fairchild/on) from mouser which are rated 500mA / 4A continuous current.
After I started using those I've never had a deffective piece which happened all the time with cheaper alternatives if they are used on the edge of their specification, sometimes even 1/2 of that would make them pop.

I just blown 1N4149 by doing some experiments on traditional PI. If I can have 20ns diode higher rated current. Can this diode use without smoke? Since it five time slower. Any help highly appreciated.thanks

[Carl-NC]

Hello Carl...thanks for all the answers...i think the original manta had the bi polar coil drive as in a scope diagram i saw on this site it showed both positive and negative pulses...

Alexandre had dabbled with bipolar but I assumed the original manta was unipolar. At least the first one I ever saw was.

[Carl-NC]

So the bottom right-hand control has a dual function (main sample delay, and adjustment of the pulse repetition rate)?
I was misled into believing the Reject control was the the main sample delay. Presumably the FREQ adjustment can be made when the bottom left-hand control is in position two?

Correct on both.

[daverave]

Hello 6666 Many thanks for the discrimination table

[6666]

Hi Qiaozhi....ive found the 8 uS can be a bit of a draw back at times as it picks up very tiny little pieces of junk you can hardly see

Keep your tiny junk, and experiment with delay and see where it disappear's , dont go below that,

[daverave]

Hi Qiaozhi....ive found the 8 uS can be a bit of a draw back at times as it picks up very tiny little pieces of junk you can hardly see

[Qiaozhi]

Hello Carl...thanks for all the answers...i think the original manta had the bi polar coil drive as in a scope diagram i saw on this site it showed both positive and negative pulses...my tdi's work down to 8 uS and i found on some parts of the beach i get some chatter and some other area's a lot better in that respect...i wondered sometimes how the tdi beach hunter is so stable at higher sens setting considering the control box is plastic with no screening.

Usually the recommended delay for hunting in the surf is between 10us and 15us. From your experience (and the Fisher AQ) it looks like 8us is on the limit.

[daverave]

Hello Carl...thanks for all the answers...i think the original manta had the bi polar coil drive as in a scope diagram i saw on this site it showed both positive and negative pulses...my tdi's work down to 8 uS and i found on some parts of the beach i get some chatter and some other area's a lot better in that respect...i wondered sometimes how the tdi beach hunter is so stable at higher sens setting considering the control box is plastic with no screening.

[Qiaozhi]

The pulse delay (7-11.5) is in microseconds. The iron reject is just an arbitrary range, is is akin to the GB control on a TDI but used in a slightly different way.

So the bottom right-hand control has a dual function (main sample delay, and adjustment of the pulse repetition rate)?
I was misled into believing the Reject control was the the main sample delay. Presumably the FREQ adjustment can be made when the bottom left-hand control is in position two?

[dbanner]

Well there you have it, clear as a midsummer day.

[Carl-NC]

someone told me the whites tdi sl has a fake threshold that gives a more stable threshold

No, the threshold is real. I think the improved stability was largely due to a better layout and more attention to detail. The Impulse AQ is even better than the SL, again largely for the same reasons.

on youtube some claim they can use a delay of say 7 uS on wet sand using the fisher AQ which has a bi polar coil drive from what i see...so im a bit confused

The AQ is not bipolar.

Hello Qiaozhi....its just all confusing as i asked someone on youtube who was using a fisher AQ about the 7 uS delay setting and they told me they could use the 7 uS setting on wet sand without chatter but they said in the surf if the coil is swept in the waves then the detector will chatter

I have also used the AQ in wet salt sand at 7us. It takes a lot of care in how you swing the coil. In the surf I got some noise but I could still hunt through it, although 8-8.5us was a better setting.

There's nothing on the front panel that indicates micro-seconds.

The pulse delay (7-11.5) is in microseconds. The iron reject is just an arbitrary range, is is akin to the GB control on a TDI but used in a slightly different way.

[Altra]

In the sale brochure it claims "as low as 7us". I recall the designer stating that careful construction of the coil and digital processing allowed for short delays in wet salt. Also the AQ is not bipolar, Tartar said he has one in the works. Carl could clear all this up.

First post in the link has a sales brochure

https://www.detectorprospector.com/forums/topic/13215-fisher-impulse-aq-essential-information/

[green]

There's nothing on the front panel that indicates micro-seconds.

https://www.geotech1.com/forums/attachment.php?attachmentid=53777&d=1606133374

Wondering if pot(lower right)isn't labeled in micro seconds

[Orbit]

someone told me the whites tdi sl has a fake threshold that gives a more stable threshold

No it's not a fake threshold , the threshold is real!