Gain
- Thread starter Dsparil
- Start date
pulltabMiner
Forum Supporter
Yeah! I would like to know too!
My best understanding in reference to MD is that the lower the gain is set, the bigger the discrepancy in volume between weak (i.e. deep) signals and strong (i.e. shallow) signals. With the gain set high all signals will report back at relatively the same volume. With the gain set lower, weak signals will report back at a lower volume that strong signals.
That's my understanding, in any case. Anyone with better info is free to correct me!
That's my understanding, in any case. Anyone with better info is free to correct me!
Rudy
Admin
What you refer to is known as modulated audio. Some detectors (like the MXT for instance) have modulated audio and behave as you describe. Other detectors do not have modulated audio and will sound off with the same volume regardless of how deep the target was.
Rudy
Admin
The problem with a reasonable explanation is that there are several "gain" areas in a metal detector.
In general gain refers to amplification of a signal. The first gain stage in a VLF MD is usually the pre-amp gain. This is the amplification of the raw signal present at the output of the coil and before it goes into the discrimination circuit.
The next gain stage is the amplification of the signal at the discriminator output. Usually, but not always, there is another gain stage which amplifies the audio output before it is fed to the speaker or earphones.
Some of these gain stages may have fixed amplification or it may be variable depending on the design.
In general gain refers to amplification of a signal. The first gain stage in a VLF MD is usually the pre-amp gain. This is the amplification of the raw signal present at the output of the coil and before it goes into the discrimination circuit.
The next gain stage is the amplification of the signal at the discriminator output. Usually, but not always, there is another gain stage which amplifies the audio output before it is fed to the speaker or earphones.
Some of these gain stages may have fixed amplification or it may be variable depending on the design.
sllingshot47
Elite Member
Well, this gives me the perfect opportunity to ask a question I've always wondered about. Part of the success of the Compadre is due to the fact that it doesn't have the high-gain, low-noise circuitry. How would this affect a detector's response to say, gold chains?
Actually it does or it would not pick up anything. However it's response to gold is more of a function of the frequency of the machine.
Jerry
Basically speaking this means you can use the Gain control to lift or brighten the response from a signal, a little like increasing the volume of your detector but in a more dynamic way. However Gain can also correspondingly increase everything else in the audio train, so ground noise, interference from other detectors, EMI etc will all add their weight to the audio information pouring from your machine.
sllingshot47
Elite Member
Then why does the Compadre pick up a fine gold chain while discriminating a paper clip but the Silver umax won't do it in it's a/m mode?
If it is in all metal mode, either should pick up both. If not then I would suspect the way it is ground balanced for one.
Added comment: The Silver umax has an operating frequency of 10.6 Khz and the Compadre is 12 Khz. Not all that far apart. But for my original point, the Lobo, which is advertised as a Gold machine operates at 17.5 Khz.
pulltabMiner
Forum Supporter
I've always said this forum is Metal Detecting University.
Good info!
Good info!
sllingshot47
Elite Member
I will add to my original comment: actually I got it from Monte and am not saying he knows everything but it proved true in my tests. The Compadre, which doe NOT have high-gain, low-noise circuitry, is able to find a gold chain, whereas the new high-gain, low-noise Tesoros cannot. This seems to be the case, as my Silver umax SLAMS on a coin whereas the Compadre just gives a good strong sound.
The detector does not see the entire chain en mass, it sees individual links. A small target.
The larger the coil for any detector, deeper it will go but will be less responsive on smaller target than a small coil. You did not say if your detectors are using similar coils or not.
Also the higher frequency is more suited for small bits of gold which is why you see the gold machines operating at higher frequencies than coin machines.
All of the detectors I have that operate at 14 - 15 Khz are better at detecting gold, large or small than the one's that run at 5 and 6 khz. Some of the them are old true non motion VLF and some are new micro-processor controlled and they all seem to behave in this manner, including one that I built
I could go on but this is already starting to get long and it is getting late
Jerry
The larger the coil for any detector, deeper it will go but will be less responsive on smaller target than a small coil. You did not say if your detectors are using similar coils or not.
Also the higher frequency is more suited for small bits of gold which is why you see the gold machines operating at higher frequencies than coin machines.
All of the detectors I have that operate at 14 - 15 Khz are better at detecting gold, large or small than the one's that run at 5 and 6 khz. Some of the them are old true non motion VLF and some are new micro-processor controlled and they all seem to behave in this manner, including one that I built
I could go on but this is already starting to get long and it is getting late
Jerry
sllingshot47
Elite Member
Yeah, we're beating this thing to death, and the original poster's question has been answered. For what it's worth, the Silver behaved the same way with the 5.75" coil. The Compadre is just a different animal and I was trying to figure out if maybe the low-noise components made the fine chain harder to detect, as I COULD rub the chain on the coil and pick it up.The detector does not see the entire chain en mass, it sees individual links. A small target.
The larger the coil for any detector, deeper it will go but will be less responsive on smaller target than a small coil. You did not say if your detectors are using similar coils or not.
Also the higher frequency is more suited for small bits of gold which is why you see the gold machines operating at higher frequencies than coin machines.
All of the detectors I have that operate at 14 - 15 Khz are better at detecting gold, large or small than the one's that run at 5 and 6 khz. Some of the them are old true non motion VLF and some are new micro-processor controlled and they all seem to behave in this manner, including one that I built
I could go on but this is already starting to get long and it is getting late
Jerry
ToddB64
Elite Member
Gain and Sensitivity
Hi Jerry !
Being a determined cuss, I've spent several hours on the Internet searching for a positive statement confirming that in context with metal detectors Gain is synonymous with Sensitivity. But, despite having read something to that effect in the past, I couldn't find a positive supporting statement at this time.
From my search I did learn that within some modern metal detector circuits there are several different areas/applications in the total circuit where Gain controls are used, but I don't know if all of these Gains can be termed synonymous with a Sensitivity control.
Your use of the word colored blue in the above quote, makes me think you might agree that Gain and Sensitivity are synonymous, or at least thought of as being synonymous in the general metal detecting community.
Whatcha think ?
ToddB64
Hi Jerry !
Being a determined cuss, I've spent several hours on the Internet searching for a positive statement confirming that in context with metal detectors Gain is synonymous with Sensitivity. But, despite having read something to that effect in the past, I couldn't find a positive supporting statement at this time.
From my search I did learn that within some modern metal detector circuits there are several different areas/applications in the total circuit where Gain controls are used, but I don't know if all of these Gains can be termed synonymous with a Sensitivity control.
Your use of the word colored blue in the above quote, makes me think you might agree that Gain and Sensitivity are synonymous, or at least thought of as being synonymous in the general metal detecting community.
Whatcha think ?
ToddB64
DIGGER27
In Memory Of
You will have to yell louder.
Jerry hasn't been on this forum since the middle of October 2012.
Jerry hasn't been on this forum since the middle of October 2012.
ToddB64
Elite Member
Gain and Sensitivity
Hi Digger27 !
} Jerry !!!!!
Whoops ! I should have checked his Profile before posting.
Thanks for the heads-up.
If you feel like tackling the question in my post to Jerry, great ! Otherwise, if I don't see an answer in several days, I'll re-write it on another website for the general public....no problem.
ToddB64
Hi Digger27 !
} Jerry !!!!!Whoops ! I should have checked his Profile before posting.
Thanks for the heads-up.If you feel like tackling the question in my post to Jerry, great ! Otherwise, if I don't see an answer in several days, I'll re-write it on another website for the general public....no problem.
ToddB64
