Shshshshshs on Out put

[aljamri]

Merry Christmas to everybody,

I've built the attached circuit and it works fine. The only problem is at the output, a low Shshshs sound is there, if you talk into the input or not.

What can be the problem. Please help me.

Sorry for not using the proper AUDIO terms.

Thanks and happy new year.

 

[RadioRon]

Your schematic diagram is incomplete, missing useful information. For example, what is the part number for the delay line IC and what is the part number for the unidentified op amp?

Also, I don't quite understand the point of the 9V battery. It appears to subtract 9V from the 9V supply rail to insure that the ring connection of your jack is at zero volts. That can't be right, is it?

 

[audioguru]

It seems to use a microphone that is not the normal electret type. A dynamic microphone? They normally feed a low impedance amplifier, not the 1M in parallel with 510k like this preamp.

The Shshsh hiss might be caused by the unknown input opamp.

The circuit has the input opamp feeding directly into the output opamp without any lowpass filter.

 

[jumides]

it looks like guitar preamp to me.

 

[Nigel Goodwin]

Yes, it's a guitar preamp with reverb - no idea what the delay chip is, but I would expect the noise is from the BBD delay device, as it shifts data through itself.

 

[aljamri]

sorry guise ! i forgot to put the IC number it is TL072. And i used a dynamic Mic as what Audioguru expected. Jumids circuit it is simmilar to mine but i am not using it for guitar, it is for speaking/singing only.

thanks for all.

 

[jumides]

sorry guise ! i forgot to put the IC number it is TL072. And i used a dynamic Mic as what Audioguru expected. Jumids circuit it is simmilar to mine but i am not using it for guitar, it is for speaking/singing only.

thanks for all.

hi aljamri,
It was not similar, but it was your diagram/circuit and add some wiring for the completeness of the circuit, sorry for editing your diagram. Those circle "mark" are base only on my experience during repair works.

Yes, it's a guitar preamp with reverb - no idea what the delay chip is, but I would expect the noise is from the BBD delay device, as it shifts data through itself.

I agreed to Nigel Goodwin's idea.

Another source of "hiss" are PCBoard, lack of grounding/earth and metal shield, be sure to used good shielded wire from mic to preamp to amplifier.

 

[Nigel Goodwin]

sorry guise ! i forgot to put the IC number it is TL072. And i used a dynamic Mic as what Audioguru expected. Jumids circuit it is simmilar to mine but i am not using it for guitar, it is for speaking/singing only.

If you're using it with a microphone then add a mike preamp to the front end, it's not suitable for mike level signals, and that would be a major reason you're hearing the switching noise from the BBD - because you're operating at MUCH too low a signal level.

As we've suggested, it looks more like a guitar circuit, with actually zero gain, and about 400Kohm input impedance.

Actually, after a few seconds thought, it's actually a guitar reverb foot pedal - switched by plugging the quitar in, and with a bypass switch operated by your foot, and a gain of zero so it doesn't alter volume when you switch.

 

[audioguru]

I didn't notice that the circuit has no gain.
It certainly needs a microphone preamp that is designed for a low impedance dynamic mic.

 

[aljamri]

Your schematic diagram is incomplete, missing useful information. For example, what is the part number for the delay line IC

its 2399 ( Echo processor )

Also, I don't quite understand the point of the 9V battery. It appears to subtract 9V from the 9V supply rail to insure that the ring connection of your jack is at zero volts. That can't be right, is it?

no it is the whole circuit supply, and wherever 5V required it comes from the 7805 regulator.

Thanks

 

[aljamri]

If you're using it with a microphone then add a mike preamp to the front end, it's not suitable for mike level signals, and that would be a major reason you're hearing the switching noise from the BBD - because you're operating at MUCH too low a signal level.

You are right again, I used it as a pre amplifier for TOA PA Ampliger Model A-1061 where i control the output to the loud speakrs and adjust Bass and Tereble.

By the way what is BBD ?

 

[Hero999]

I didn't know they still used BBDs for delays, I thought digital signal processing units are more common nowadays.

 

[audioguru]

The PT2399 echo IC is not a BBD. It has an ADC, digital processor and DAC.
It has fairly low distortion and low noise.

 

[Nigel Goodwin]

You are right again, I used it as a pre amplifier for TOA PA Ampliger Model A-1061 where i control the output to the loud speakrs and adjust Bass and Tereble.

By the way what is BBD ?

It's a Bucket Brigade Device, but now you've given us it's number we know it's not one of those.

 

[aljamri]

The PT2399 echo IC is not a BBD. It has an ADC, digital processor and DAC.
It has fairly low distortion and low noise.

yes all that information as per its datasheet but unfortunately i cannot attach it here.

but as i said guise, it is working fine, just the little hiss which prevent it to be perfect, what can be adjusted even as trial step

 

[Nigel Goodwin]

yes all that information as per its datasheet but unfortunately i cannot attach it here.

but as i said guise, it is working fine, just the little hiss which prevent it to be perfect, what can be adjusted even as trial step

Like I said (twice), it's a GUITAR effect pedal, you need to run it at a MUCH higher signal level than a microphone provides - add a preamp to the front, and turn down the gain on what it's feeding.

 

[aljamri]

Like I said (twice), it's a GUITAR effect pedal, you need to run it at a MUCH higher signal level than a microphone provides - add a preamp to the front, and turn down the gain on what it's feeding.

I got it this time, i'll try and let you know.

Thanks . happy Christmas and new year for all.

 

[aljamri]

Like I said (twice), it's a GUITAR effect pedal, you need to run it at a MUCH higher signal level than a microphone provides - add a preamp to the front, and turn down the gain on what it's feeding.

Can i use this circuit:

https://www.electro-tech-online.com/threads/electret-mic-preamp-questions.34575/

in addition to the suggested pre-amp it is good to get more than one MIC inputs.

thanks

 

[Nigel Goodwin]

That's specifically for an electret mike, I thought you had a dynamic one?. What impedance is it?, and is it balanced or not?.

 

[audioguru]

Can i use this circuit:

https://www.electro-tech-online.com/threads/electret-mic-preamp-questions.34575/

in addition to the suggested pre-amp it is good to get more than one MIC inputs.

That circuit uses the 10k input resistor to power an electret mic. The circuit will work with a dynamic mic if the 10k resistor is removed.
Use a TL071 single opamp instead of the TL072 dual opamp. Its pins are different, see its datasheet.

Use a mixer circuit and more preamps if you want more than a single microphone.