headphone amp output to shop bought power amplifier

Status
Not open for further replies.
S

SimonW

New Member
Dear Friends,

I made the below circuit from a kit which I bought from

**broken link removed**

(both mics are electret types)

I know the circuit is working good when I connect the output with a headphone.


when I try connect output to a household shelf Power amplifier I get a noise on speakers.....

the noise is present even if I turn RV1 A/B up or low


I think it is got something to do with impedance matching.... which is set by
the R8+R13 and R7+R11??

I read somewhere that an L pad circuit might help?

Hope someone can help!

Thanks

Simonw
 
Last edited:
Do you power the thing with a battery?
Also what kind of noise? Hiss, rumble, or high pitched squeal?
 
Last edited:
SimonW said:
I think it is got something to do with impedance matching.... which is set by
the R8+R13 and R7+R11??
Click to expand...

No, it's nothing to do with impedances - which is set by the output impedance of the opamp, plus the 8.2 ohm in series.
 
Of course the "noise" is acoustical feedback howling or squealing because the microphones hear the speakers and the amplified sounds go around and around.

To eliminate feedback then the mics and speakers should be in separate enclosed buildings far apart.
Or you can record the sounds then play them back later.

The "noise" can also be mains hum if non-shielded cables were used.
 
Many think for your replies,

I am using a el cheapo wall adaptor converting to 4.5v DC

what is the minimum distance needed between this circuit and the power amp.... in inches, cm,mm

I think that it might be main hum, the power cable is very close to the audio cables

I have recorded the noise onto a *.wav file..... it is in the noise.zip
(rest assured there is no virus, trojan etc..... as I am in the need of help)
 
Last edited:
SimonW said:
Many think for your replies,

I have recorded the noise onto a *.wav file..... it is in the noise.zip
(rest assured there is no virus, trojan etc..... as I am in the need of help)
Click to expand...

hi Simon,
Change the wave file extension to .txt and you can upload to your post as an attachment
 
SimonW said:
Thanks Eric..... the noise.zip is really *.wav file.....
Click to expand...

Its 50Hz mains Hum, you have a ground loop signal break thru

E

EDIT:
Do you have a 4.5V battery you could use in place of the 4.5V wall wart, for test only?
 
Last edited:
Where is a description of the "noise" (the attachments do not work)?
Is it acoustical feedback howling or mains hum?
 
The low frequency noise is mains hum.
Maybe your power supply output is AC instead of DC?
Maybe your AC to DC power supply has a filter capacitor value that is too small?
Maybe the cable feeding the power amp or preamp is not a shielded audio cable?
Maybe you built the circuit on a breadboard and all the contact strips and very long connecting wires pickup mains hum?
 
Status
Not open for further replies.

Similar threads

S
  • Question
Amplifier shutting down
Replies
19
Views
3K
Nigel Goodwin
S
  • Question
Amplifier aux switch
Replies
11
Views
2K
S-fr
S
V
  • Question
How to convert stereo audio signal into mono out for mono amplifier
Replies
16
Views
3K
audioguru
  • Question
What is the drop in load voltage and output voltage of the power supply during loading؟
Replies
10
Views
2K
crutschow
S
  • Question
Amplifier ic change
Replies
1
Views
1K
Tony Stewart
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…