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Booster to drive a PA power amp?

K

kucor

Aug 26, 2011
159
40
EU
#1
Hi TB, can you please recommend me a clear, high quality booster pedal to drive a PA power amp. I need at least 25dB; 30dB or more would be optimal.

I have a pedal preamp but it has no juice enough to drive a power amp. Don't wanna buy a new pedal preamp as I really like the EQ and the way this one sounds.

so, the idea is: bass (active or passive)->pedal preamp->booster->PA power amp->bass cab.

ps, will this work at all with standard guitar booster? no impedance mismatch with pa power amp, or whatsoever?

thanks!

cheers!
 
#5
kucor said:
Amp has a 20Kohm/1,25V input
Click to expand...

This means that a 1.25Vrms input signal will drive the amp output to full power.

Something to consider with the amp's 20K input impedance... you will need a booster that can provide 1.25Vrms into a 20K load. This is the minimum criteria that you should be looking for. I would suggest that you contact the boost manufacturers you are interested in and ask if the output has the ability to drive at least that much. If the boost pedal has larger output drive capabilities, let's say 2Vrms into a 10K load, then that would be something better to consider.

With the amp's 20K input impedance, the output impedance of the boost pedal can be a limiting factor on the level of the signal that the amp input sees.

-Frank
 
#7
kucor said:
Thanks Frank. Let's say I wanna do this simple: if I decide to go with a mic preamp like mentioned ART MP or similar, do I still have to worry about gain and impedance?
Click to expand...

The best way to get what you need, is to look at it from the preamp output first. Find a preamp that can easily drive at least a 1.25Vrms signal into 20Kohms. You will need to qualify the preamp output signal level by using the amplifiers input impedance. Example: If the preamp can only deliver 1.25Vrms into 100Kohm loads, then it will not be able to drive your amp to full power with its 20K input load. OTOH, If the preamp can deliver 1.25Vrms into a 10K load, then it will be good for what you are looking for.

Then you will need to determine if the preamp has enough gain to amplify your instrument signal to the 1.25Vrms level the amp needs for full output power. More gain than necessary is usually a good thing, unless it is crazy high and causes your level adjustments to be overly sensitive (difficult to adjust).

IMO, That's the minimum that you should be looking for.

Good luck on your search.
-Frank
 
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#9
Gremson said:
I was considering doing something similar. Wanting to use my Radial Bassbone as a preamp, and thought a zvex SHO would do the trick. But I'm no bass physiscist like some folks on here....
Click to expand...

Power amplifiers have different sensitivity ratings and input impedance's.

You can trial and error to find something that works well, or get the numbers and quickly narrow in on a target.

-Frank
 
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#10
FWIW, almost every mic preamp (having a 1/4" DI input) has both plenty of gain AND an ideal output impedance for driving even the most finicky PA power amps. If you just don't have the patience or technical aptitude for figuring out the details of the various pedals, get a mic pre.

I've had a few boost and OD pedals that did a great job driving power amps, but I would say more than half of the ones I've tried were not ideal for that application--and none of them came with documentation that would have answered the question before buying and trying them out.
 
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#11
Here's the manual:

Link Removed

As bongo points out, the text claims it can drive a power amp. As per my earlier question, I strongly recommend using the pedal's 1/4" output on the right to feed the amp, not the XLR DI. It will be a matter of experimentation, mind you. On the bright side, mic preamps are quite reasonable if required.

Riis
 
#12
I bought a Behringer ADI21 and like it with my bass. I just joined a new band and wanted a cheap rig for practice. I have an old Carver power amp and last week I used one channel of the bands mixing board to drive my power amp. Sounded great and the other band members complimented me on the sound. I am now looking for either a used Art MP professional (tube pre-amp) or a (very) basic mixer to use as the "booster" to get from instrument level of my ADI21 to line level to drive my power amp. With the stereo power amp ($100 used), ADI21 ($30 new), and a cheap Art or Behringer pre/mixer (hope to get one for about $20-40). This means I will have another stage rig (2 x 400w rms) for less than $200. That is about a 1/4 of what my primary rig cost me used and it sounds great...

The signal chain on this rig will be: bass---ADI21---preamp/mixer---power amp. I will use the ADI21 output as a effects loop send and the preamp/mixer input as the effects loop return...
 
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#14
Well the real difference has to do with the difference between mic, instrument, and line level. Most of the pedal pre's have a instrument level output (-10dbu) where mic pre's and most rack mount pre's have line level (USUALLY 0dbu but varies from manufacturer to manufacturer). This lack of industry standard and the lack of data available for the consumer makes for a lot of confusion. I only recently experienced this when I was doing my research in preparation to buying the ADI21. I knew it wouldn't drive the power amp by itself (fortunately) and had to come up with a simple work around. That seems to be a simple mic pre, either a channel strip (line out from a single channel to your power amp) or small mixer or something like the Art MP tube preamp that can reach 0dbu (about 1.2 volts rms).
 
#15
Many power amps have internal jumpers to adjust input sensitivity, so you may not need as much gain as you thought. The Crest CA9 for example, can adjust down to .775V.

If you use just a clean boost pedal, you risk adding noise into your signal.

You should also check that your power amp has an input impedance at least 10X the output impedance of the preamp or pedal it is feeding into it. Is that 20K input impedance specification for a balanced or unbalanced signal? A typical spec for a power amp may be balanced line 20K, and unbalanced line 10k. A pedal's 1/4 line is an unbalanced signal. The last pedal in my chain has output impedance of 2.5K. So for me, my pedal would be a poor match impedance-wise, resulting in loss of the signals full bandwidth.

You could do a search here for pedal to power amp, or something similar.
Google>>pedal to power amp site:talkbass.com
 
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#16
Wow, lot of good and helping information here, thanks guys. I did a search already but didn't find good explanation regarded to boosters/mic preamps.

My amp is simple, 1/4 stereo inputs, no jumpers for sensitivity.

I really think Art tube should do the trick. It is cheaper than most boosters too, so I'm gonna give it a try. It is for my second bend and I don't wanna spend much money for new rig.

Actually I just ordered Avalon U5 for my main rig, and am pretty much broke at the moment:D
 

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