Shshshshshs on Out put

[aljamri]

Happy New Year for everybody,

It is me again but with good news this.

I've added a pre-amp as Nigel suggested using TL071 as audioguru suggested and the voice became quite good that made me to reduce the PA volume which resulted in low noise at output ( but not zero ). so I told myself why not to check jumids suggestion and put a piece of aluminum underneath the circuit, isolate it and connect it to ground. This made noise to ZERO. So my circuit has no hiss and no need to put your mouth on the Mic.

Thanks all of you again (Radio Ron, jumides, Nigel Goodwin, audioguru and Hero999 for you valuable participation to my circuit.

 

[aljamri]

Hi everybody and happy new year,

I don't know if it is OK to continue on another issue for the same circuit here in the same page or i should start a fresh one ? for now i'll ask here in the same page and If i'm wrong please anybody tell me to immegrate to a new one.

I added a switch to my reverb circuit to switch it off when not in use ( Thumbnail01). The problem is that when i switched it ON/OFF while the PA is ON, a bang nose is heard out of the speaker. Similar devices uses JFET switch instead. Is it possible for me to connect one here? In my hand a 2N5457 is O.K. for this purpose ( Proposed Circuit Thumnail 02, Datasheet Att.03 ).

Thanks

 

[audioguru]

I am amazed that you used a lousy, noisy old 741 opamp and it doesn't cause hiss. I would use a low noise TL071 opamp for a mic preamp.

I don't think the POP comes from the opamps because their Vb slowly drops when the power is turned off.
I think the POP comes from the echo IC. The circuit must be observed on a 'scope to see if it abruptly goes high or goes low. Then a FET can be added to disconnect it when the power is removed.

 

[aljamri]

I am amazed that you used a lousy, noisy old 741 opamp and it doesn't cause hiss. I would use a low noise TL071 opamp for a mic preamp.

Sorry, I have not used 741 in my circuit, at the beginning I used LM358 and you suggested me to use TL07 Family ( The old thread follows )
https://www.electro-tech-online.com/threads/pt2399-echo-processor.33044/

In my last working fine circuit, I used TL071 as per your recommendations.

I don't think the POP comes from the opamps because their Vb slowly drops when the power is turned off.
I think the POP comes from the echo IC. The circuit must be observed on a 'scope to see if it abruptly goes high or goes low. Then a FET can be added to disconnect it when the power is removed.

I see, so do I have to connect at the + supply to 2399?

Thanks for all

 

[audioguru]

The type of FET you use and how it connects depends on the polarity of the POP.

 

[aljamri]

The type of FET you use and how it connects depends on the polarity of the POP.

POP ?! the one i heared, how i know its polarity?

 

[audioguru]

POP ?! the one i heared, how i know its polarity?

Look at it on an oscilloscope.

 

[Hero999]

If you don't have a scope you could connect a pair of LEDs wired in reverse parallel to the output.

 

[aljamri]

If you don't have a scope you could connect a pair of LEDs wired in reverse parallel to the output.

Like the attached connection ?

 

[Hero999]

Yes.



.

 

[aljamri]

I've connected the attached circuit between the output and the Ground and used a 2khm: variable resistor set at 50% at the begining and switch on the reverb supply. i've got no indication, gradually i reduce the resistance and try again until reach around 500hm: where i got the forward bias LED on when i switch the reverb on.

is that enough to know which JFET to be used to stop the pop sound ?

 

[aljamri]

Sorry This is the circuit i used for the test.

 

[audioguru]

You have a positive-going POP when the power supply is turned on. Then you could add a resistor in series with the output and a P-channel Jfet with its drain at the resistor and its source connected to ground. Its gate voltage is 0V when the power supply is turned on so its channel is a low resistance which will attenuate the POP. Then use a resistor from the positive supply to its gate and a capacitor to ground to slowly charge and allow the sound to pass through.

But the jfet might still conduct a little during sounds which will cause distortion. And the series resistor increases the output impedance of the circuit.