Not so DC waveform of minus 5 volt rail at the ne5534 - could this be cause of noise problems

[waltr]

Been thinking of what might be the problem.
One thing is the possibility that the AC coupling Cap from Pre-amp to Integrator is causing the issue. Maybe this cap is the wrong type, quality.
With many, many cap types the capacitance changes with Voltage and we know the Voltage at the pre-amp output goes rail to rail.

Exactly what cap is used here?

[kt315]

interesting thing i though... i did bara board to decise all problem of people... but sametime George also run in the process...
strange enough that problems are still not fixed and only growing up )))

[green]

Quote from green post #17
"Wondering if high frequency signal matters. Looks like low frequency signal is more than 6 times high frequency signal. Could you repeat scope picture with persistence off and 200msec/div instead of 200usec/div? Channel 1 only."

Yes, of course! here you go:

[ATTACH]42722[/ATTACH]
[ATTACH]42724[/ATTACH]

Both are without trace persistance.

What is the best test procedure to determine the cause of noise and how to minimize it? My thoughts, maybe someone that knows could suggest the correct procedure.
Pin 7 of U7 is the important test point to monitor, 200msec/div. Noise pickup from coil would vary with location so testing with coil disconnected would be best. Lifting one end of R16 or C15 would remove amplifier noise. Record p-p noise at U2 pin6 to see if noise is near what expected could be a place to start.

[waltr]

The second sampling looks pretty noisy compared to the first sample.
It does seem the two samples are doing what they should in the scope trace on the Integrator output in Post #14. !st sample increase signal, 2nd sample decrease signal.

Now trying to not get your project confused with someone else's (the MPP rev E) but could have a similar problem.

Possible the wobbling is due the AC mains interference. Have you taken the detector far from the house and AC mains?
If the wobbling goes away then that is the problem. My HH detector does this when the heater kicks on a few feet away in my shop but is fine when away from the house.

Another possibly thing to try is increase the delay a few usec. You do have the 1st sample a bit early and sampling a little later may help.

Also possible one or both the JFETs are not working properly OR U7 needs better caps on its power pins (adding caps may help).

[Polymer]

Ahhh...if Damping R is not connected then the pre-amp was probably getting overloaded for too long.
Good find and fix.

Only my reference to rev D (was thinking of the MPP rev E thread). The rest is valid to be checked.

Battery connection diagram looks good. You now see how to get a Negative Voltage using two batteries.

Thank You!

I ran the detector with batteries only without the lt1054.
The detector works just like before, wobblenoise included!

So for now the lt1054 is not part of my threshold jumpiness problem.
Maybe I can't see what other noise it may be causing at the moment, but that's something for another time.

I probed the Q2 jfet like you advised. I also probed Q3 as a comparison.

Both gate signals look good to me coming from pin 10 & pin 12 of the 40106.

The output of Q2 (second sample) does not look good to me.
It's in the right position timewise though. But who am I to say ... Here's the pic:



Here the screenshot of the measurement of the main sample at Q3.
Looks somewhat "better", but the signal shape is odd to me nonetheless.
I have no reference scope pics of them working at "nominal" value.



Just a somewhat wild guess here from what I have learnt so far about jfets:

- They may be ESD partially damaged
- The wide range of Upinch in these components may be causing problems

What is your take on these signal shapes?

I did read "My take on the HHII". It's a veeery long read and a lot to digest for me.
Chock full of interesting knowledge. Those posts I will be reading again. Learning ....

[waltr]

Is the damping resistor in place as it should be, then that funny signal is very small, like in Qiaozhi's measurement.
Sorry, my mistake ...

Is the entire middle text part invalid or just the reference to "RevD"? Thanks for correcting this, I have not looked at this yet.

Finally the knot in my head has unravelled. Your battery connecting information did it Yippee! THANK YOU!

I will be grabbing a bag of batteries tomorrow and powering with that. Don't have enough new ones around right now.

Here a picture of how I understand it, just to be sure:

[ATTACH]42721[/ATTACH]

Ahhh...if Damping R is not connected then the pre-amp was probably getting overloaded for too long.
Good find and fix.

Only my reference to rev D (was thinking of the MPP rev E thread). The rest is valid to be checked.

Battery connection diagram looks good. You now see how to get a Negative Voltage using two batteries.

[Polymer]

I'm sure it doesn't matter. On my Geotech Baracuda board I shorted out R22, and reduced the 4mV ripple to zero. There was no detectable difference in the preamp output. This is exactly the same power supply filtering arrangement as the Hammerhead design, and there's no problem there either.

Polymer appears to have an error on his board somewhere.

You're right, I had an intermittent Rdamp connection causing the excessive -5v noise at the 5534. The wonkiness is still there though ... grumble ...
The hunt shall continue ...

Thank you for putting the GeoBara on the bench!

Could you, please, please, make a scope shot like green is suggesting in post #17 !!!!!

Now where's the emoticon "pretty please with a cherry on top" ...

[Polymer]

Quote from green post #17
"Wondering if high frequency signal matters. Looks like low frequency signal is more than 6 times high frequency signal. Could you repeat scope picture with persistence off and 200msec/div instead of 200usec/div? Channel 1 only."

Yes, of course! here you go:




Both are without trace persistance.

[Polymer]

Sounds like either R22 (27 Ohm) value is not correct as has been suggested (did you check?) or the 47uF cap is NOT a Cap. Adding a 100uF seems to have fixed this so that should be good enough.

Your scope capture of U7a Output (pin 1) looks like the Offset from the Pre-amp is not adjusted correctly- but the pre-amp is AC coupled (cap) so can not be the case here.
OR - the second Sampling switch (Q2) is not working correctly.
Re-check the second sample pulse and Q2 is switching. Scope probe on Q2-R26 connection should show a change of Voltage level when Q2 switches on.
Look at Q3 output and the RevD to see what this point should look like.

We were suggesting using a second battery instead of the LT1054 Voltage inverter. To do this remove the LT1054 and connect a 7-15V battery into pin 5 (B-) and pin 3 (B+) to power the 79L05 (negative regulator). This second battery's Positive goes to 0V (Ground).
The 12V batter still connects to +VB & 0V to power the 78L05 (positive regulator).

I did check the 27 Ohm resistor. It is so.
There is one thing I noticed when taking the temporary 100uF bypass cap off and measuring again with only the 47uF in place.
That is, that the funny signal on the -5v at pin 4 of the 5534 was still gone, although only the 47uF was now in place.
You having mentioned it maybe not being a capacitor had me poking around quite a bit.

From what I found, one of the damping resistor wires had a faulty, intermittent connection.
When the damping resistor is not connected, the funny signal on the -5v line of the 5534 is hefty, like in the scope picture.
Oddly enough the added 100uF capacitor mitigated this effect.
Is the damping resistor in place as it should be, then that funny signal is very small, like in Qiaozhi's measurement.
Sorry, my mistake ...

Is the entire middle text part invalid or just the reference to "RevD"? Thanks for correcting this, I have not looked at this yet.

Finally the knot in my head has unravelled. Your battery connecting information did it Yippee! THANK YOU!

I will be grabbing a bag of batteries tomorrow and powering with that. Don't have enough new ones around right now.

Here a picture of how I understand it, just to be sure:

[green]

I'm sure it doesn't matter. On my Geotech Baracuda board I shorted out R22, and reduced the 4mV ripple to zero. There was no detectable difference in the preamp output. This is exactly the same power supply filtering arrangement as the Hammerhead design, and there's no problem there either.

Polymer appears to have an error on his board somewhere.

Could you post a scope picture like I asked Polymer in reply #17 to compare with Polymer's picture. I'm interested in what the low frequency noise signal looks like, less than 10Hz since that is what we are trying to detect.

[Qiaozhi]

Bara_Geo_pin7_lf412_persistance 5s.png from reply #14

Wondering if high frequency signal matters. Looks like low frequency signal is more than 6 times high frequency signal. Could you repeat scope picture with persistence off and 200msec/div instead of 200usec/div? Channel 1 only.

I'm sure it doesn't matter. On my Geotech Baracuda board I shorted out R22, and reduced the 4mV ripple to zero. There was no detectable difference in the preamp output. This is exactly the same power supply filtering arrangement as the Hammerhead design, and there's no problem there either.

Polymer appears to have an error on his board somewhere.

[green]

Bara_Geo_pin7_lf412_persistance 5s.png from reply #14

Wondering if high frequency signal matters. Looks like low frequency signal is more than 6 times high frequency signal. Could you repeat scope picture with persistence off and 200msec/div instead of 200usec/div? Channel 1 only.

[waltr]

Please ignore the revD comment- I mixed your posts with someone else.

[waltr]

Sounds like either R22 (27 Ohm) value is not correct as has been suggested (did you check?) or the 47uF cap is NOT a Cap. Adding a 100uF seems to have fixed this so that should be good enough.

Your scope capture of U7a Output (pin 1) looks like the Offset from the Pre-amp is not adjusted correctly- but the pre-amp is AC coupled (cap) so can not be the case here.
OR - the second Sampling switch (Q2) is not working correctly.
Re-check the second sample pulse and Q2 is switching. Scope probe on Q2-R26 connection should show a change of Voltage level when Q2 switches on.
Look at Q3 output and the RevD to see what this point should look like.

We were suggesting using a second battery instead of the LT1054 Voltage inverter. To do this remove the LT1054 and connect a 7-15V battery into pin 5 (B-) and pin 3 (B+) to power the 79L05 (negative regulator). This second battery's Positive goes to 0V (Ground).
The 12V batter still connects to +VB & 0V to power the 78L05 (positive regulator).

[Polymer]

When the -5V drooping is Synchronous with the TX pulsing then it should NOT effect RX noise. Since the -5V out of the regulator has no droop and there is a series resistor to the neg rail pin of the op-amp means that op-amp is drawing a good amount of current. The Vdrop times the series resistor value (27 Ohm) equals the current draw. This is when the TX is ON which is then OVER VOLTAGING the Op-amp (driving its output to the power rails which is drawing more current. This is what you see.

It may be possible that the NE5534's Bypass caps are not being effective. Maybe try a different 47uf (or other value) & 100nF caps.

What does the output of the Integrator stage (U7a) look like on the scope?


You can wire in a another battery to supply all the Voltages without the LT1054. Just ensure you get the battery polarities correct and also still have the 5V regulators.

As for the 'wobbling' of the final output & audio- I can have this issue in the Hammer Head I build (see the thread "my take on the HH2" in the HH II sub-forum). I did two things that helped decrease this:
1- adjusted the PPS rate so remove AC Mains beat.
2- decreased the Gain of the SAT stage (U7b on the Barra).
There is still a little wobbling but not enough to cause real issues.
If I ever find a better solution I will be posting that in my thread.

Thank You waltr! It's a consolation to know I am not the only one with this problem.
It has been dogging me for quite some time, nearly having me throw all this stuff to the dogs ...

I have put another 100nF ceramic cap directly from pin 4 of the 5534 to the ground plane of the 1k resister next to it.
That didn't change anything. I then popped in a 100uF cap in the same position.
Didn't want to unsolder the 47uF first to find out it's not the problem.
The DC signal at pin 4 of the 5534 is for what I can see, quiet now , so that is solved.

The wonkiness of the output is still the same though .... aaarghhhh.

Here's the output of pin 1 of the LF412 like you asked (This is the output of the integrator stage U7a I believe)

The first pic is the signal in normal display mode.
The second pic is the signal in persistance display mode (5 seconds) to easily see the amplitude of the wonkiness here.
The jumpiness is already in that stage, with the threshold loudspeaker output dancing to this signal.




here's another on from pin 7 of the LF412



I have not gotten my head around connecting two battery supplies to this, as I get all mixed up with which potential should be where.
What has me puzzled the most is where to connect the ground plane on the pcb.
If I say connect that to the centre of two 7.5v batteries (-7.5v -- Ov -- +7.5v),
then I would only have 7.5v across the coil. Would that be right?
Hope I haven't lost you, because I am, my heads in knots now ...

To be continued ...

I have been reading up on the 5534 and its apparent quirks, most is written by Douglas Self
and I hope to find a solution (or least a partial one) there ... may this not be a wild goose chase ... again ...