Playing Directly Through The Power Amp?

KingRazor · #1 08-31-2011, 05:10 PM

Is it possible to plug a passive bass directly into a power amp hooked up to a cab? As in, skipping the preamp stage altogether?

Infidelity · #2 08-31-2011, 05:12 PM

Possible(adding a passive DI) but you'll lose all the flexibility of a pre-amp..

M0ses · #3 08-31-2011, 05:16 PM

Depends on the power amp. I don't think any are idealized for it, though, and you'll probably lose substantial fidelity.

BurningSkies · #4 08-31-2011, 05:16 PM

Won't work. A passive bass doesn't produce enough signal...even active basses don't produce enough signal.

pedulla1 · #5 08-31-2011, 05:19 PM

Do you usually set your pre-amp flat?

KingRazor · #6 08-31-2011, 05:23 PM

Quote:

Originally Posted by pedulla1

Do you usually set your pre-amp flat?

I usually play with a combo amp. But yeah, I go flat.

Thankfully I have a preamp I can use, I was just wondering if it was possible or even a good idea to play straight through a power amp. My preamp can be bypassed, so I should still be able to get an "uncolored" tone.

Bassmec · #7 08-31-2011, 05:30 PM

A passive bass has an output impedance of circa 50,000 Ohms
at no more than 300 mw output, a power amp needs a 600 Ohm matching input impedance and more than 775 mw to drive
it properly.
So the answer is absolutely not.

GrowlerBox · #8 08-31-2011, 05:32 PM

Quote:

Originally Posted by KingRazor

I usually play with a combo amp. But yeah, I go flat.

There is almost always a big difference between "flat" as measured and represented on a frequency response curve, and "all EQ knobs nooned/centred". You may, of course be referring to either, but the distinction is worth mentioning as there is often some confusion about this.

**colcifer** · #9 08-31-2011, 05:36 PM

Quote:

Originally Posted by Bassmec

A passive bass has an output impedance of circa 50,000 Ohms
at no more than 300 mw output, a power amp needs a 600 Ohm matching input impedance and more than 775 mw to drive
it properly.
So the answer is absolutely not.

Sounds about right.

JHAz · #10 08-31-2011, 05:37 PM

The problems are, as discussed above, the bass won't have enough output to get anything like full power from the power amp, and AFAIK, a passive bass will be a bad impedance match, resulting in changes in tone.

And while I hadn't thought much about it, a brief look at the various bass gear magazine tests show that preamp controls set flat does not mean the amp is flat. For example, it looks like the GK tone stack that I like and live with has quite a boost centered around 40 Hz when set flat, plus a couple of other anomalies. ANd the Orange amp they tested in the last issue requires 2 of the 3 EQ controls to be set at "zero" (IIRC) to be optimally flat(!) Unless you know and use the "optimally flat" settings for your amp, you're not actually flat . . . .

Phalex · #11 08-31-2011, 05:38 PM

You can do it, but it'll suck. Preamp or DIE!

seanm · #12 08-31-2011, 05:42 PM

You *can* do it, but you won't hear anything

If you want no EQ, even a cheap mic pre like the ART MP will work. I used one to drive a power amp at a jam space and it worked great.

Josh Pelican · #13 08-31-2011, 05:44 PM

I tried plugging directly into a preamp and nothing came out. Once in a while I could get a note or two, but that's it.

Alex1984 · #14 08-31-2011, 05:56 PM

You would need a DI like a SansAmp, Tone Hammer, Bass Buddy, etc. Or if you have a SUPER hot active bass, it might work.

will33 · #15 08-31-2011, 06:21 PM

The problem with that is voltage. Your pickups put out signal that can be measured in millivolts (1000ths of a volt). You need the preamp to boost that signal up to 1-1.5 volts which is what a poweramp needs as input to get anything approaching volume as output.

That said, you can plug into a cheap little mic pre like a tubemp just to boost the power. Downside is you have no tone controls other than what's on the bass. Kinda like running a dry, pre eq di, just louder.

rummy · #16 08-31-2011, 06:26 PM

Don't do it.

Mingo Sanders · #17 08-31-2011, 06:40 PM

Quote:

Originally Posted by BurningSkies

Won't work. A passive bass doesn't produce enough signal...even active basses don't produce enough signal.

I've plugged an L-2500 (Tribute) and an L-2000 (USA) directly into a Crown DC-300A driving a Berg HS210. It was about as loud as a laptop at 50% of full volume. So, yes, it is audible, but no, it has no practical volume.

seanm · #18 08-31-2011, 06:43 PM

Quote:

Originally Posted by Mingo Sanders

I've plugged an L-2500 (Tribute) and an L-2000 (USA) directly into a Crown DC-300A driving a Berg HS210. It was about as loud as a laptop at 50% of full volume. So, yes, it is audible, but no, it has no practical volume.

They are active, a passive bass will be much much worse. An active bass at least has a low output impedance that will be a closer match to the power amp.

KingRazor · #19 08-31-2011, 10:59 PM

To the people commenting on "flat" settings: I obviously am referring to simply setting the knobs on the amp to the center position. Setting my EQ perfectly "flat" would be difficult without at least some RTA software.

My preamp is a Behringer Bass V-Amp Pro and it's got amp modeling, so I can try a number of different amps, or simply bypass the preamp altogether.

I plan on getting a multi-band fully parametric EQ. If I can't find one I'll get one of those 31-band graphic EQs. The standard bass, mid, treble knob set up is much too limiting for me.

Son of Bovril · #20 09-01-2011, 02:55 AM

you could probably run your bass straight into the EQ and then into the Poweramp (many eq's can drive a poweramp, if you wanted to lose the V-amp, otherwise just use the V-amp as the pre