Topic: Sharing power for pre amps and recorders (Interference)

[Phil Zone]

Hey all,

Anyone here use 1 battery to power both their pre amps and their deck? I am having a bit of low frequency buzz/hum when they are shared... It may have always been there and I didn't notice, but I'm not sure. Nothing really noticable, just there at -60-55db.

I have a talent cell with (2) 12v outs. One goes to my Littleboxes and the other to my DR-680. When I have everything on one battery it's a problem, split there is no problem. I'm sure it's some sort of impedance or resistance disparity somewhere causing it, but usually with DC it's less of an issue. Curious if anyone has any thoughts or has experienced this themselves.

It could be that there is a filter in my tascam that is on its way out, but I doubt it since it's 100% good on separate power.

[commongrounder]

You have created a ground loop. That happens when there is more than one ground connection between devices. Since one of the ground connections passes through the audio cable between your preamp and recorder, any ground current/noises from power supply circuitry or other hum fields is unfavorably impressed upon the audio signal. The solution is to break the ground somewhere. Assuming the audio connection between the preamp and recorder is unbalanced, using separate batteries may be your best, and simplest, solution. This is why balanced audio lines are so desirable. That type of connection (ideally) rejects hum and interference. One can even disconnect the shield(s) at one end of the cable to stop ground currents from flowing.

[Phil Zone]

You have created a ground loop. That happens when there is more than one ground connection between devices. Since one of the ground connections passes through the audio cable between your preamp and recorder, any ground current/noises from power supply circuitry or other hum fields is unfavorably impressed upon the audio signal. The solution is to break the ground somewhere. Assuming the audio connection between the preamp and recorder is unbalanced, using separate batteries may be your best, and simplest, solution. This is why balanced audio lines are so desirable. That type of connection (ideally) rejects hum and interference. One can even disconnect the shield(s) at one end of the cable to stop ground currents from flowing.

That makes a lot of sense!

[Gutbucket]

Commongrounder nailed it above.

Something to try- If you would like to carry only one Tallentcell battery, and if it is equipped with a 9V output port in addition to the 12V port, you might try powering the Littlebox with that (assuming 9V is enough for Littlebox). Reason being is there is likely to be separate voltage regulators supplying those output ports, which might serve to break the ground loop. This may or may not work, but is worth a try. 

[Gutbucket]

Rereading, it sounds like you are powering multiple Littlebox preamps, which may present a ground-loop in powering them both (3?) with a single supply.  Troubleshoot using only one as well as them in combination.

PS: The DR-680 is able to operate on 9V.  12V is preferable, but I ran mine for years that way off 9V DVD batteries with phantom engaged on all 6 channels.  Should be no problem with phantom provided by the Littleboxes.

[Phil Zone]

I tried both of those things even I first found it the 12/9v split actually made it much worse. Only thing I have found was totally discreet power...

Thanks for the help and ideas!

[goodcooker]

I have had great success running more than one device from a single battery including a DR680. I suspect the Littlebox may be the culprit here.
No troubles running a SD442 and DR701 from the same 5V Anker battery and I currently use a PMD661 or DR680 and either Wmod UA5 or a SD MixpreD powered from the same Talentcell battery.

Both of the Sound Devices preamps have transformers so they provide galvanic isolation in the signal path. Other difference would be the digital output to the decks from both of my current preamps doesn't complete the loop although I have used the analog out of the SD pre without trouble but it is transformer isolated.

I'm guessing your only solution is to use separate batteries for each device.