Noise during recording

[brentandang]

I have an Ampeg svt4 pro. I was trying to record using the balanced output on the back. However I got had noise in the line and was picking up an audio transmission. How can I eliminate picking up the interference?

[billfitzmaurice]

Getting noise on a balanced line is hard to do. Almost impossible, actually. Is the input to whatever it was feeding balanced? If not that would explain it.

[BassmanPaul]

Try using one of the transformers that are used to connect a low impedance microphone to a PA that only has 1/4" phone high impedance inputs. They only cost a few bucks at a music store.

[T-Bird]

Hi.

You'll usually need galvanic isolation between two different non-matched equipment.

You also usually need to match the impedances, with a transformer preferably.

Most people use a DI box for those exact reasons, whether it's a live situation, or studio.

Regards
Sam

[Jerrold Tiers]

The 4PRO already has transformers to balance and isolate the "DI" outputs......

Were you using the XLR or the phone plug outputs?

The phone plug outputs have a ground connection, but pin 1 of the XLR is open so as not to create a ground loop .... i.e. it is in "ground lift".

Use the XLR and make sure the receiving end shield is connected to ground. or use the phone plug, but make sure teh amp end is NOT grounded, if it was originally grounded.

[bassmeknik]

"picking up an audio transmission" should have someone asking if your preamp tubes are microphonic or worn out.

Jerrold Tiers would know if this was a possible cause of RF interference but I had similar issue with my SVT4pro until I replaced the tubes (4pro has a tube pre-amp)


AT&T cell phones WILL interfere with many types of audio equipment I had to keep it away from the stage altogether until switching carriers. Every amp in the place would pick up signals a second or two before a call would come in.

[billfitzmaurice]

Originally Posted by bassmeknik

"picking up an audio transmission" should have someone asking if your preamp tubes are microphonic or worn out.

If that was the case he'd hear it in his speaker as well. I assume he checked that. OTOH if he didn't connect his balanced output to a balanced input then the common mode rejection of the balanced line would be defeated, opening the door for noise and interference, potentially making the cable an antenna.

It never ceases to amaze me how many people will give advice about something they know nothing about.

+1.

[bassmeknik]

Thanks Mr. F I am aware the tubes are ahead of the DI stage and noise would pass through the amp to its speakers as well as the DI out. Experience has taught me to resist making assumptions.

Since the OP mentioned recording it would be natural to think it was noticed whether the noise was in the 4pro's speaker as well as the DI, but I really don't know what level of engineer they have and if they are pro or like most TBers still trying to make it with less than pro support.

To the OP: More information is needed to accurately diagnose this issue. What was the DI hooked to. Please describe the board or recording device and detail the manner of connection. Also is this a new problem in an existing recording set-up or is this a first time using these pieces of equipment together?

[BassmanPaul]

Originally Posted by bassmeknik

It never ceases to amaze me how many people will give advice about something they know nothing about. SVT4pro is common

"picking up an audio transmission" should have someone asking if your preamp tubes are microphonic or worn out.

Jerrold Tiers would know if this was a possible cause of RF interference but I had similar issue with my SVT4pro until I replaced the tubes (4pro has a tube pre-amp)


AT&T cell phones WILL interfere with many types of audio equipment I had to keep it away from the stage altogether until switching carriers. Every amp in the place would pick up signals a second or two before a call would come in.

I just love it when someone comes out of the blue with a post like this. Especially the first statement.

Why on earth would a faulty or microphonic tube suddenly decide to pick up PFI? If it did the entire signal chain would amplify the result.

Cell phones of all stripes interfere with high gain electronics not just AT&T.

[chadds]

Originally Posted by brentandang

I have an Ampeg svt4 pro. I was trying to record using the balanced output on the back. However I got had noise in the line and was picking up an audio transmission. How can I eliminate picking up the interference?

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