Whites 5900 sl and input amplification.

[scrungy_doolittle]

Years ago, I bought a 4 inch snooper, and it had an inline amp that made it very sensitive. Screwed up the ID a bit.

I have been hunting for a 5900 SL for a while, and found one, but it has a huge current draw.
Last week, I scored one off ebay, with no coil.,
Hooked it up and it works, except that in tr mode, one can't get the sound to go silent, which is the mode I prefer to hunt in.

I was under the impression that sigbal was essentially an amplifier, but now I am not sure.
Exactly what is the sig-bal block doing?

It looks like sigbal is used as a non inverting amp with a fixed gain. R2 is 6.34K R1 (Rf for the equation) is 34.8K 1+(rf/R2) looks like the gain is 1+(34.8/6.34) seems that the gain is 6.48. What does the pot on the + lead do?
What would happen if one changed R1 (34.8K to a similar configuration as the preamp to allow for a bit more gain?
What doe the R5 R3 resistor combination do here?
The output of the preamp is passed into sigbal, and it appears that R5 attenuates the signal some.


Second question, There is a pre-amp U1, a NE5534 that feeds everything. Looking closer, there is an R2 which is a 25K pot, and it appears to vary the feedback on the opamp. R3 is a 30K and feeds into the variable resistor R2. That would allow you to set the feedback from 30.1K up to 55.1K
given R1 is 825 1% resistor I am assuming that the gain of the amp is controlled by R2. IF R2 is removed, and measured, then attached to the box so it is accessible, can it be used to amplify the signal a bit more to get more depth like the external amp on the 4" sniper coil?

It looks like the gain can range from:

1+(55000/825) = 66.6
1+(30100/825) = 36.48
I have no idea what the actual setting is, and I assume it was set for specific output value by whites, and it is an on board trimmer.

IF R2 is removed, and measured, then attached to the box so it is accessible, can it be used to amplify the signal a bit more to get more depth like the external amp on the 4" sniper coil?

[scrungy_doolittle]

Carl, I am looking for your input here specifically.
Based on MR. Bills mods , I understand that changing R56 (a 220K) on the audio tuner will change the rate of the SAT signal is that correct?

I notice also, that there is no volume control.
based on the 6000 DI pro CB, it looks like one could lift the end of R59 or R114 and insert a pot in there to get a volume control to work. basically R114 14K ----100K pot----16.5K gnd

[Carl-NC]

Here is the front-end schematic:



The SigBal module is a variable attenuator G = R3/(R3+R5) followed by a fixed gain amp G=(1+R1/R2). The overall result is a variable gain amp. If you want to increase the gain I would suggest reducing R2.

On the preamp, R2 is probably used to trim the phase shift of the amplifier which trims the demod phases. You don't want to mess with R2 or R3 or it will alter the TIDs.

Yes, you can add a volume control exactly like done on the 6000. This is part of a retune circuit that includes R56 but it is not the SAT retune circuit. The SAT retune speed is set by R245. I have no idea what is involved in Mr Bill's mods, I don't think I've ever seen what they are.

[scrungy_doolittle]

They have been published on this forum... Grin.
For the classic 2, he moved the ground balance pot and one other to the top of the detector, and changed out the sat retune for a double pole switch that switched the 220k for a 375 K. Which schematic is this? Does not match my 6000/DI pro CB schematic,.
Fixed gain for the sigbal is 34.8/6.34 currently is 5.48+1 = 5.58. Replacing R2 in the dashed line, with a multiturn 10K pot would allow for tweaking the gain. What is that 11.3K R4 doing? I am guessing that might serve to alter the sensitivity of R5/R3 divider, since it is in parallel.
at maximum resistance of 10068 and 11.3K you have an effective resistance of 5324.24 and at minim, you have 68ohm so 11.2k and 68.1 is 67.57.

hmm. so if you wanted to set one up for the 4" coil only, you might be able to use R2 on the pre-amp to get the TIDs back to normal.... interesting.
I found a 1940s penny at a heavily hunted park, with the 4" coil right up next to a steel pipe, which is why I got the 4" coil.

I have about 4 or 5 of these old whites detectors. One 6000 di sl seems to have a short in it that I haven't tracked down.
I even have a hip mount that was working fine until it took a fall from a car hood. I haven't tried to get it working since.
With all the money I have put into these things, I could have gotten a VI3 ... grin....

Can you post the section of the schematic with R242? The sat has always confused me.