Best mods to the Surf PI kit??

[Bart]

Hello, I'm just curious what the best modifications I could make to the Surf PI kit I ordered from Silverdog? I've read on other forums of converting the Surf PI to the Pro model, or close to it to detect small gold pieces. Any info would be greatly appreciated!

[mikebg]

Hello, I'm just curious what the best modifications I could make to the Surf PI kit I ordered from Silverdog? I've read on other forums of converting the Surf PI to the Pro model, or close to it to detect small gold pieces. Any info would be greatly appreciated!

Bart, I have read in this forum for 4 very important modifications for detecting small gold, however they need aditional PCBs. The modifications are:
1. Using DOD (twin loop induction balanced) search head.
2. Place TX end stage near to (or inside) search head.
3. Place preamp of RX near to (or inside) search head.
4. Use two stage preamp.
The mentioned modifications makes the circuit to operate as fast network.

[DIRCEU]

Bart, I have read in this forum for 4 very important modifications for detecting small gold, however they need aditional PCBs. The modifications are:
1. Using DOD (twin loop induction balanced) search head.
2. Place TX end stage near to (or inside) search head.
3. Place preamp of RX near to (or inside) search head.
4. Use two stage preamp.
The mentioned modifications makes the circuit to operate as fast network.

Hi! Mikebg

How to make two stage preamp.?
Please, sugest a schematic.; What the best opamp gain combination
Coment more... it's very interesting.

Many thanks in advance,

DIRCEU

[mikebg]

Hi! Mikebg

How to make two stage preamp.?
Please, sugest a schematic.; What the best opamp gain combination
Coment more... it's very interesting.

Many thanks in advance,

DIRCEU

Dirceu, this was explained in the forum by Carl Moreland. To design a faster preamp circuit, it is better instead an opamp with gain for example 60 dB to use two opamps with gain 30 dB.

[6666]

And check out the schematic in post one,
for two stage preamp

Quote from Carl

The MAX412 was chosen because I've found it to be one of the best for PI preamps. I think only the MAX414 (quad version) is being discontinued, and probably because it's a 2-chip hybrid. The MAX410 & 412 are extremely popular opamps and shoud be around for a long time. Yes, you can use other opamps; any wideband in a standard dual pinout (NE5532, etc).

http://www.geotech1.com/forums/showthread.php?t=15732

[DIRCEU]

Hi!

Many Thanks! Guys.

Dirceu

[Tepco]

Hello, I'm just curious what the best modifications I could make to the Surf PI kit I ordered from Silverdog? I've read on other forums of converting the Surf PI to the Pro model, or close to it to detect small gold pieces. Any info would be greatly appreciated!

I just wonder why no one answered this in more details. Modification steps:

#1 Be sure your detector is operating optimally, good fast coil, minimal delay and dumping R properly adjusted. Whit fast coil, changing U2 whit something faster is good idea.

#2 Next step is to "upgrade" to Surf PI pro, twice integrator gain, twice threshold amp gain, and only 5 components to change. Add sens control too, may be needed. (increasing already excessive gain even further, thing that really should be modified first is Surf audio response)

#3 timing modification: lazy man's way, brute force: increase pulse width (and current consumption), this will buy you next few cm, or try this:

#3a total timing modification, decrease pulse w. 3 times, shorten sampling pulses to 20uS or so, increase freq. to 5+kHz, fix audio, increase C4/R12 rolloff ten times. This mod can give you 3 main advantages compared to original, alone this will increase range by 20-25%, most effective so far. Only the Surf may not be the optimal platform for this.

Whit all this in place you will end up whit detector having 10+ times more "system" gain compared to original. Then, every imperfection, mechanical, electronics, shield, ground, interference etc, being below threshold level before, now will be clearly audible. At the end, you may have more trouble whit all this instead of any real benefits. Goes just like this: unproportional increase in gain is needed for just modest performance increase. For small gold, fast coil and fast sampling is most important, concentrate your effort on this, modify latter. Best mod for Surf is probably 100% redesigning it from ground

[plumabob]

Please in detail. What 5 components need to be changed for Surf PI Pro upgrade?

Bob

[6666]

Which C4/R12 on which schematic ?

if its 100nF and 10k thats about 160Hz HPF and you want that reduced by 10 times ?

[Tepco]

Which C4/R12 on which schematic ?

if its 100nF and 10k thats about 160Hz HPF and you want that reduced by 10 times ?

Yes, when operating detector @5kHz. This will reduce powerline interference and cut off large part of low frequency corner noise region of input amp.

[Tepco]

Please in detail. What 5 components need to be changed for Surf PI Pro upgrade?

Bob

Referred to original Surf schematic: R16&R15: increase from 220K to 470K, C6&C5 decrease from 470nF to 220nF. This will double integrator (U3B) gain, leaving time constant unchanged. R22 (100K in original) increase to 220K, this will double threshold amp. gain(U3A). If you need sens control, add it like on PI pro schematic, otherwise just leave as is. Few other components are different in PI pro, say C8 is now 47nF, not 100nF, R20 is 47K, not 22K, but this is not so critical, you can leave old values.

[WM6]

Great advice Tepco, thanks.

Which Surf PI schematic is regular one and which Surf PI PRO? Can you post here both?

[plumabob]

Thanks for that Tepco I will give it a try.

Bob

[Tepco]

Great advice Tepco, thanks.

Which Surf PI schematic is regular one and which Surf PI PRO? Can you post here both?

This one is "original", probably zillion times posted so far, PI pro is here (scaled down version):

http://www.geotech1.com/forums/showp...4&postcount=13

[Bart]

Thanks for the info Tepco... Thought I had some of those resistors, all of mine are 20%ers so... Looks like I need to get a few spare parts.