Solution for line level into bass amp
 

Hi. I alternate between bass guitar and keyboard bass during gigs, so I connect my bass guitar into the active input of the amp and the keyboard bass sound (coming from an audio interface) into the passive input.

The problem is that I get a bad buzz sound from the keyboard bass, probably because it's a line level being plugged into an instrument level input. Is there any way to solve this, using any sort of device before connecting to the amp? (hopefully cheap)

Thanks!

PS: the amps is a Hartke LH1000 head with a Hydrive 410.

Have you tried plugging it into the effects return input?

I think that input takes line level.

Tried switching the inputs? Bass into passive, keys into active?

Any other usuable options for keyboard output? As well as making sure it's a mono output that you're using?

Thanks guys.

I haven't tried the effects return. I just plug it in there? That's all?

I did try switching between the passive and active inputs. Same problem.

if you plug something into the effects return, that's all the amp will do.

a little mackie notebook mixer might be the ticket, you could plug the keys and the bass (if it's active, or going through pedals) into it, balance them out, and from there into the amp.

as for the buzz, that's likely a ground loop problem. maybe try a signal cable with the ground disconnected on one end.

TRy plugging in the keyboard only and see how it sounds. If it's ok then it's a ground loop issue as walterw mentioned.

Hi guys. Thanks for your help!

I tried the effects return. Keyboard sounded ok, but the bass wouldn't sound at all.

I tried plugging the keyboard only through the main inputs but the problem continues.

Also tried going through a guitar pedal (with the effect off), but didin't help.

Anyone know of a device that I could plug it through to eliminate the buzz, or convert the line signal to instrument, if that's the problem?

Thanks again!

You might have a ground loop, if the keyboard ground is connected to both the amp and the mains ground. Try a ground loop isolator (aka noise canceller). It's a passive circuit, a transformer only.

They are cheap, I guess around 30-40 dollars or so.

Check out for example the Behringer hum destroyer hd 400.

A reamp box would work.

Does the keyboard have a volume control? I've noticed almost universally that the outputs of digital keyboards are too "hot" for the inputs of typical amps and PA systems. It's a hassle.

I play bass guitar and synth, but always use 2 seperate rigs. For synth, it's just a small head and 2x10, used as a stage monitor. A mixer should help you out, but I'd consider not trying to play 2 different instruments through the same rig. A Roland KC350 would work well for the keys.

You could pad down the output of the keyboard and then feed it into the instrument input on your amp.

http://www.uneeda-audio.com/pads/

If you are using a keyboard its one thing but when i read "audio interface" i read "laptop" and so we are not talking keyboard..we are talking computer... and that raises a large number of issues...

1. power connections to laptop and amp must be on same power strip to avoid ground loops

2. an audio interface with a wall wart may be not have polarised plug.. turn it around. it may have a noisy power supply regardless.

3. switching noise from the laptop power supply can be injected into an audio interface via the usb.. try unplugging the laptop power supply and run on batteries.

4. the ground on a computer rig is not quiet. there is significant digital noise.. a quality external audio interface will have balanced outputs.. that you can then put into a DI before the amp.

and thats the start...

at the end of the day..if you are going gig regularly and wish to use one power amp with two instruments you need a mixer with balanced inputs in the fx loop..

Radial makes a box called a Reamper. It sells for about $200 though. There are less expensive alternatives that convert line to instrument level.

You have to determine what you problem really is. As was mentioned a ground loop can cause noise. So can an incompatible signal.

Thanks everyone.

Yes, the keyboard bass sound is coming from a VST on a laptop, then out of an audio interface into the amp via 1/4" cable. Everything's on the same power strip. The laptop ground issue was taken care of previously with a cheater on the power plug. The audio interface's power plug is not grounded. Therefore I'm guessing it's just the characteristics of the line signal?

BAce mentioned a pad. Or a DI box. Maybe these could be cheap solutions.

putting everything on the same strip does NOT stop ground loops.
try ground lifts on everything BUT your amp

Yeah for the keyboard I would bypass the amps pre by using a power amp in or effects return (depending on the amp). I do that to use separate pre amps with my swr head.

Plug the bass into the amp as normal, then plug the effects send into a mixer. Keyboard into mixer, too. Mixer out into effects return. Can then adjust levels in the mixer to balance them.

you need to break the ground connection from the audio interface to the amp..pure and simple.. you are transitioning from a ground buried in digital noise (hello!..its a computer!) to the ground on an amplifier... and putting the laptop on a cheater plug removes its protection (really not smart) and will do nothing for this issue...

again..if you are going to be giggin regularly.. you need a mixer with balanced inputs in the fx loop and either an audio interface with balanced outputs, or a transformer coupled DI unbalanced>balanced for the interface outputs.

ground loops require a ground differential voltage.. this is highly unlikely on the same power strip unless you have faulty equipment..but quite likely when using a socket on a separate spur from the breaker panel.