IDX-PRO+VDI

[Koala]

Tried everything different ferrite over soil and over concrete pretty constant 30K-32K

Reading this post I might have the wrong coil. Can't read the stamp on the left lug but may be 6B blue max coils are 8B apparently not interchangeable and give ground balance problems according to the post. I thought all Classics had the same main board so would use the same coils apparently not.

Assuming that is my ground balance problem the the poor volume is the only thing that need fixing Could the fact I used BCX38C for MPSA13 causing a problem

[golfnut]

I dont think anyone knows why you need 30k instead of 25k

Maybe your cap that goes with it is a little out? Or the freq is off.


Did you try it over soil or just ferrite.

[Koala]

This is identical to mine from md4u.ru
Yesterday went to the exploration of the cop. Dirt in plowed fields almost linear in the knee, you can get caught up seriously, in addition a lot of snow But I tested and found out that the MD must be finalized. The sound volume urgent need to increase, very quietly responds to relatively deep end.

don't understand the fix it's got lost in the translation
After replacing the speaker on vosmiomny, consistent with the installation of 3.6 ohm resistor, the volume was enough.

Davor you could be right it's not stainless steel but may be something similar. I can detect it fine now in all metal mode.

[Koala]

Mmmmmm Both go to the white mark easy in the photo above (on headphones) can get an extra bit if you listen really hard in all metal mode. Blue was best with reverse diode in Disc all metal mode is about the same but tone is better now. Would like to keep zener as spring is easy detectable but detector was silent with the reverse diode.

[golfnut]

The PP has CH has lower gain than geb/Disc combo look the resistor ratio on U5 post mixer/det and has wider BW so it wont have the same range.

lower gain and wide band is more noise and lower gain.

S

[Koala]

No short.
Forget the comment about the detector is now more unstable. The batteries were down to 9v. Put some fresh in and its back to rock steady. All Metal is now greater than Disc. All Metal is now more linear in the sound drop off. Detection range is 2 1/4" less than with the revered diode but the usable range is about the same. Overall pleased. Would like the volume louder in all modes and know why it neads 30k to ground balance.

[golfnut]

Is this pcb one of the ones with the error - where there is a short between two vias?

The ones which were later sold off cheap


S

[Davor]

If it is stainless steel - it is kind of expected behaviour. Some alloys of stainless steel do that. More grown-up rigs have problems with stainless steel.

[Koala]

Blue mark is with the reversed diode in Disc Mode. The white one is with the zener, All metal mode and Disc Mode are the same

This peg spring was not detected by this detector or original "classic I" now detects okay with the zener 2.7 in all metal mode. Detector is now more unstable and in disc mode you have to be very close to the coil for a clear tone

[golfnut]

In disc mode vol is ok.

You cant influence vol level in disc mode using sens control ? I can - It depends what you call sens pot I guess. (I call Threshold pot the one on the dual comparator .)


I call sens the one on the op amp at the top of the schematic VR4 on U5 - it influences the DC conditions of U5 input. If this pot is at 0 targets are quieter in disc mode.
If this pot is at 10 targets are louder.


~In PP I need to advance sens until I get just below the annoying tone - then most sensitive in PP mode.

In PP the Disc CH outputs are disabled.


Can you be certain that the PP CH is live? It appears the Disc CH is going off - this is correct - but the PP CH may have a fault -


Post decent images of board.

Can you see a signal on all 3 Channels as you pass a target with a scope or a multimeter meter on ac in Disc mode with the sens full

S

[Koala]

Just testing at the moment so board is just loose on the table. Sound is fine in Disc Mode. I thinking Q3 Q4 and surrounding components are okay. In post 1307 reiv added a volume control by lowering the value of R40 tried it and it makes it worse. Post 1306 seems to have the same problem but don't see what fixed it. I use a home made set of headphones made out of some ear defenders same problem with the headphones and speaker. Is it worth trying a 2.7 zener there is a Maplins near me and could get one today. There is a video on Youtube lost the link but they are testing the pinpoint mode and have the same problem there other video shows Disc Mode and has twice the range.

[golfnut]

Be aware that the speaker returns to battery -ve terminal and NOT the 0 Volt rail - which ia up at 4volts wrt to batt -Ve !!!


If you have a metal cas, the chassis is often 0V - or the same as the coil ground but beware, this gound is actually +4 VOLTS above batt -Ve terminal.

The speaker return or headphone return cannot touch the chassis..

Make double sure you havent made this error !!




I dont have an external speaker currently, I like the bud type in ear phones with vol slider in the cord. Maxell do a suitable one for under a fiver in Sainsburys
I had to use an insulating bush on the panel so the gnd lock ring of the stereo jack socket didnt short out the +4v to the batt -Ve


S

[Koala]

Hi tried all pots in all positions nothing helps. Been playing around some more now I have moved VR3 detection in Disc mode is superb. Put the coil back on the "Classic I" and the detection range is almost twice. Volume is good in Disc mode. In All Metal mode volume is very faint. Detection range is almost as good but because the volume is so low you would walk passed. Speaker was 32 ohms so I have tried a 8 ohms no differance. To hear from the speaker you have to put your ear to it.

[golfnut]

In PP you need to advance the sens pot to just below tone boundary. If you dont it will be quiet.

S

[Koala]

cheers I am testing with 2 factory coils 8 inch that ground balance fine on a 6000d. Tried with 2 types of ferrite and the ground all ground balance fine but at around 30K. Played with VR3 thought it only affected a display set at 1K the sens pot is working correctly now unless I have knocked something. Volume is very low in pinpoint mode but fine in disc mode. Will do some more testing. Disc mode is great much better than a genuine Classic.