My take on the HH2

[Carl-NC]

Do you think gain of final stage should be 1 to do final subtraction or it's better like other 100?

It can be 1 or it can be higher. It depends on the overall design.

Do you think i should put C39 or doesn't need?!

Generally it will help.

Where/how are you implementing ground balance control?

[h9361]

It can be 1 or it can be higher. It depends on the overall design.



Generally it will help.

Where/how are you implementing ground balance control?

Thanks dear Carl.
My GB pot is here.
I want to add it to your HH1, can you suggest me 1 or higher gain?

[Carl-NC]

You can try that but I think it's not going to work.

[h9361]

You can try that but I think it's not going to work.

Is it possible to tell me why it is not going to work?
Can you tell me your reason?

[h9361]

Actually, i'm going to add two other sampling to my HH1.
According to your information, i can fix gain of S2-S4 (like S1-S3) but i change sample width of S2 and S4 as GB pot.
Do you think which of method will work?
Off course, i forgot to tell you. I want to use Mr. Mdtoday's Audio for out of my GB
Thanks

[h9361]

I think your meant is use of a separate variable gain like the attached, is it true?

[Carl-NC]

For GB to work it is critical to match the delays of the TGT and GND channels. Yes, you can add a variable gain to the GND channel but you need to add an equal-delay fixed gain to the TGT channel. You also might consider adding a SAT circuit to both channels. Yes, you can also vary the GND sample pulses for GB but probably you still want some extra gain in the GND channel, otherwise the pulse width can get very wide.

[h9361]

For GB to work it is critical to match the delays of the TGT and GND channels. Yes, you can add a variable gain to the GND channel but you need to add an equal-delay fixed gain to the TGT channel. You also might consider adding a SAT circuit to both channels. Yes, you can also vary the GND sample pulses for GB but probably you still want some extra gain in the GND channel, otherwise the pulse width can get very wide.

Before everything, thank you for your clear explanation.
I think your final schematic is like it.
According to GB discussions, there is two idea about using sample width:
1- All of four samples use an identical sample width, like TDI.
2- Only S2 and S4 (S2-S4) use a wider sample width.
Do you think which of them is better performance, or What is difference between them in practice??!

[Carl-NC]

Using a wider GND sample will improve noise performance.

[h9361]

Using a wider GND sample will improve noise performance.

Thanks dear Carl for your valuable information.

[h9361]

Hello
Dear Walter
I have a question about your final Gain stage (R37), do you remember your gain?
Do you think the gain can affect over depth?!
I remember that i used your VCO part over my HH1 (After R36 in HH1), sensitivity of your VCO was low. Do you think i should increase gain of final stage like you (HH1 is 100, your gain is variable near 200)?
Thanks.

[waltr]

Been long time since building this.
What I remember is the pot for variable gain did very little so just put in a fixed resistor.
Don't remember if it's 100k or 200k but thinking probably 200k.

This gives +5 to -5V out of the SAT stage when a largish target passes the coil.

[h9361]

Been long time since building this.
What I remember is the pot for variable gain did very little so just put in a fixed resistor.
Don't remember if it's 100k or 200k but thinking probably 200k.

This gives +5 to -5V out of the SAT stage when a largish target passes the coil.

Thanks dear Walter for your guiding

[h9361]

Sorry, for my request.
You have written that we should adjust R20 for base voltage of Q9 (your VCO). Do you think the R20 is related to sensitivity of your Audio?
Thanks

[waltr]

My VCO uses the SAT output through a 2:1 Voltage divider into an ADC input of a PIC12F1501.
The Q9 and the 555 are not used. The PIC output, audio tones then goes into R48, LPF, to Q11 &Q12.

The PIC12F1501 is on a PCB with a header that plugs into the 555's socket for power and audio out. Another lead connects to TP9 to pick up the SAT output stage.WR-PIdet-sh2.pdf

That PIC12F1501 VCO is in the upper left corner of this picture.


I also use a 1000 Ohm to 8 Ohm audio transformer from audio transistor Q12 for isolation and Impedance transformation to headphone jack.
This then goes to a Blue Tooth Transmitter for use with Blue tooth headphones.

All of this is in this thread but you must read the entire thread to follow the changes made.