Threshold Pot doesn't work

[h9361]

Hello
Dear All
Before everything, i have to thank Mr. Walter, Carl and Surfdetector for their helps.
Now, i'm using HH1-Rev-C2-VCO version. First, i had a poor detection problem but finally i could solve it via Mr. Carl and Walter helping.
Anyway, now i have an another problem and that is my R31 (threshold pot) doesn't affect over Audio.
I checked values of R30, R31, R32 and R33 and all of them is true. According to users suggestion, i checked TP9,TP5 and TP4 by DVM, voltage of the points are 0.
Do you have any suggestion for check?
Thanks.

[waltr]

Does the op-amp output DC Voltage change when you turn the Threshold pot?
This is what the pot does, creates a DC offset on the op-amp output.


Thanks for creating a new thread in HH1. Now all of your questions and the answers will be in one thread and easier to follow.

[h9361]

Hello
Dear Walter
Thanks for your replying.
As you remember, i'm trying to change audio part of HH1 (VCO) for using 8-Ohm speaker. After searching, i copied Technik of the Polones detector (see attached).
But i have a problem, my audio is muted. What is interesting is that i touch my audio part, its audio is heard.
I think my threshold problem was for my previous audio amplifier (LM358, i had shared in your thread before), so i decide to change my audio amplifier.

[waltr]

If touching the circuit makes a change then something is not right.

I never had luck getting Carl's 555 VCO working properly. That is one reason I did the PIC12F1501 VCO on my HH2. The switch, two transistor, 555 & amp were replace with an 8-pin PIC processor and code.

[Carl-NC]

1. If you vary R31 the offset voltage at TP19 should vary. If it does not, something is wrong around IC8b.

2. The base of Q6 should be -0.8V and the emitter should be 0V. If they are not, make sure N7 is high.

3. IC9-pin3 should have a rectangular waveform on it. If it does not, something is wrong around IC9.

4. For more volume you probably want the speaker on the collector side of BD140, with the emitter grounded.

[h9361]

1. If you vary R31 the offset voltage at TP19 should vary. If it does not, something is wrong around IC8b.

2. The base of Q6 should be -0.8V and the emitter should be 0V. If they are not, make sure N7 is high.

3. IC9-pin3 should have a rectangular waveform on it. If it does not, something is wrong around IC9.

4. For more volume you probably want the speaker on the collector side of BD140, with the emitter grounded.

Thanks dear Carl for your guiding.
I will check and tell here.
Please see attached, is your mean this?

[Carl-NC]

Please see attached, is your mean this?

Yes.

[h9361]

Yes.

I checked R31 in TP9, it changes DC voltage of the point.
Base of my Q6 is incorrect, it's -0.024V, instead of -0.8. I checked R50 for N7, with/without of R50, no difference in base of Q6.
As soon as touching between of Q5 and Q6, my VCO audio is heard!
Voltage of pin 9 of ic7-c is 2.5V.

[Carl-NC]

Base of my Q6 is incorrect, it's -0.024V, instead of -0.8. I checked R50 for N7, with/without of R50, no difference in base of Q6.
As soon as touching between of Q5 and Q6, my VCO audio is heard!
Voltage of pin 9 of ic7-c is 2.5V.

Sounds like IC7c might be dead. Short IC7 pins 8 & 9, that will put 0V on Q5-emitter which is what you want.

[h9361]

Sounds like IC7c might be dead. Short IC7 pins 8 & 9, that will put 0V on Q5-emitter which is what you want.

Thanks dear Carl.
I shored IC7 pins 8 &9, but i have a full horn and my BD140 gets hot so that you can smell it.

[Carl-NC]

Probably you want to add some series resistance to the speaker. To finish debugging the circuit you might want to replace the speaker with, say, a 1k resistor. Measure all the voltages & waveforms to ensure everything is correct.

Also, I suspect the way you implemented Volume will be ineffective. You might try adding a series fixed resistor and a series Volume pot to the speaker. The fixed resistor sets the maximum volume. You will need to experiment to get the values you want.

[h9361]

Sounds like IC7c might be dead. Short IC7 pins 8 & 9, that will put 0V on Q5-emitter which is what you want.

Hello
Dear Carl.
Is your mean a direct connection between +12V (+VB) to Q5-emitter?

[Carl-NC]

Yes

[h9361]

Hello
Dear Carl.
I did a lot of trying, but i couldn't solve my audio problem. According to your advice, i added fixed resistors + Vol pot in series speaker but my BD140 is still hot!!!
I tested it with 4R speaker, it made no difference. I measured DC voltage of TP9 via threshold pot, that is -0.6 to 1.2V!
For more testing, i built Mr. Walter audio+BD140 (attached), it works but sensitivity of my audio is low (i think i should increase Gain of IC8b from 100 to 200).
Now, i'm going to build MiniPulse audio, i hope it works (attached).
I checked my TP9 when a target is near my coil, it clearly shows targets.

[h9361]

I even made HH1 separately (attached), but i did not hear any audio or low growl!
I think my problem is Q5+Q6 method. Since i connected emitter of Q5 to +12V, my BD140 gets very hot. I checked connection of Q5 and Q6 more and more, they are OK.
What is interesting is that Mr. Walter's audio works, but it's not low growl mode and has low sensitive than TP9. Other words, i have a detection from a good distance in TP9, but Walter's audio has action from half distance than TP9.