Bad buzz with audio recorded to laptop

[Tracyp]

Hey guys 🙂

Great suggestions thanks 🙂

Epicyclic, thats a good point about the USB mic input only being mono...I'll make up a single mono RCA to mono 3.5mm jack for this coming Sunday and run that instead of the stereo.

Turk182, Yep got a digital multimeter. What tests should I perform on the amps RCA outs?

thanks
Tracy

 

[turk 182]

unplug the PMX see if there's any continuity between the RCA shell and the ground pin of the AC cord and tell us the value.

then plug in a set of cables to the "out" jacks and at the open end check resistance between the ground and the tip pin of the plug what do you have?

then while you have your multimeter out re-read post 16 with respect to the isolator and let us know what you find there, ok?

 

[turk 182]

are you in fact using a 3.5 mm "line in" on your laptop? if it's a "mic" input than the gain structure is wrong and the resultant noise floor will be raised and noisy.
pre tell what make and model laptop do you have?
and just what software are you using for recording?

a USB interface could indeed be an alternate solution/workaround.

 

[MAAC0]

When I asked to You to use a non-balanced cable, I meant connecting the RCA's to the speaker, not the main outs. Try and post results. By the way, try to record from an mp3 player or cd player. Try Audacity, but select line-in and not mic input, since line-in disables mic bias found on laptop inputs.

 

[Tracyp]

Thanks guys, great helpful stuff 🙂

I will run the multimeter over the amp this sunday.

The laptop is a Toshiba satellite... with one of those annoying all-in-one 3.5 sockets that require a special adapter cable 🙁 hateful darn things!!!

Hence why I got the USB adapter. The specs of it are as follows:

- Convert a USB port to audio port.
- Aluminium housing.
- USB v2.0 provides stable data transmission and audio output.
- Compliant with USB audio transmission revision 2.0.
- Support I2S/PCM/TDM.
- DAC supports up to 192KHz 16/24bit output.
- ADC supports up to 96KHz 16bit output.
- Energy saving, eco-friendly.
- Crystal clear audio output.
- Plug and play, no need to install a driver.

Specifications
Product Dimension
46 x 28 x 12 (mm)

Upstream
USB2.0 A-Male

Downstream
1 x DC3.5 Input (Microphone)
1 x DC3.5 Output (Headset)

The software is M00O recorder which is nice and simple for our "users" to use.

 

[epicyclic]

When you make up the RCA to 3.5mm mono lead use a stereo ( TRS ) 3.5mm jack but only use the tip and sleeve , leave the ring disconnected . The 5V power feeding for electret microphones comes out of the ring and you don't want or need this .

 

[Cableaddict]

That's very common on Laptops. I believe it's caused by a ground loop.
You even hear the mouse moving and HD spinning.
Connect the laptop to a non-earthed outlet, or use a non-grounded PSU. (Try a cheater plug). Don't tell me about safety and FCC regulations. All mobile DJ's I know do it.

Buzzing is never caused by a ground loop. That would be 60 cycle hum.

But yes, laptop buzzing is very common..Normally the first thing you look at is the PSU. Cheap ones can have no shielding, and o electronic protection. Also no ferrite beads.
---------------------------

But the OP says he tried a different supply. Assuming it was a name brand supply, then the other main cause, and very hard to fix, is an OPEN ground somewhere on the chassis.

I had this problem once, and found the solution online after a long search. Sadly I can't remember the details, but I think I had to add / replace a screw, or maybe solder a wire. Anyway, the thing was, the chassis was not connecting to my drive housing, or CD housing. Something like that, and so part of the internals had no faraday shield.

Some heavy Googling might bring more details.

 

[Cableaddict]

Oh, I just skimmed some other responses.

If you are using a USB interface, make SURE you have ferrite beads on both ends of the USB cable. Those things act like antennaes, picking up all sorts of EMI and RFI.

 

[Tracyp]

Awesome 🙂 thanks for that 🙂

When you make up the RCA to 3.5mm mono lead use a stereo ( TRS ) 3.5mm jack but only use the tip and sleeve , leave the ring disconnected . The 5V power feeding for electret microphones comes out of the ring and you don't want or need this .

 

[Tracyp]

Ok thanks will do 🙂

Oh, I just skimmed some other responses.

If you are using a USB interface, make SURE you have ferrite beads on both ends of the USB cable. Those things act like antennaes, picking up all sorts of EMI and RFI.

 

[MAAC0]

I own a Toshiba p70 and can record in stereo, and I don't need an adapter. Make sure recording is set to line in and not mic. Audacity let's You do it, and turns mic bias off. Audacity is a good software and free also.