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Pre / power set up advice please!


Craig Robinson
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Hi all 

Looking for a little advice/input about preamps mostly. I have a Thomann t-amp 800 power amp, which, when used as a pa amp is really great. When on the other hand I use it with a preamp for just my bass , with a Behringer BDI 21 pedal wise, and I have also tried line out of my old Laney G 300 both give limited volume? Not unusable like there us a fault but just not what I would be able to use effectively.

I am running the amp in bridge mono but have tried in both modes to no avail. Will a new pre of better quality, preferably in pedal form provide the kick in volume I require or is it something else entirely. Dont want to shell out for the same end result.

Any thoughts most welcome.

Craig.

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A pedal or pre that gives line level output (which is intended to be routed to the front end of a standard head/combo) will not provide sufficient output to drive a power amp sufficiently. Check the input sensitivity of your power amp. It will probably need around 1.75 volts to deliver full output. Full rack type pre's are probably going to be your best bet. They are intended to drive a power amp directly.

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I had a similar experience recently with my Helix Stomp going in to the power stage of my GK head. Noticeably quieter than going in to the preamp.

My output setting on the Stomp was set to Instrument, which i guess is the standard stomp pedal level. Changing to Line level brought the volume level back up to a much more usable level.

Unfortunately you cant do this change this on the BDI21. Did you try both XLR and normal out? Although i have this pedal ive not used it in years so cant remember if there is a difference.

Edited by dave_bass5
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4 hours ago, Craig Robinson said:

Hey bud 

Thanks very much!! Not going to pretend to understand but knowing a rack pre is appropriate will save me a lot of money and misery 😖😖😀😀😀

Cheers 💪💪

Craig 

 A pleasure. In basic terms, you need something with a high enough output. Some pedal type pre's may give that and enable you to drive a power amp directly, but you will need to check the specs. Your power amp will need something that gives around the same output level as a mixing desk. Here's a handy and brief article about line and mic levels from the Audio Technica website - https://blog.audio-technica.com/audio-solutions-question-of-the-week-what-is-line-level-and-what-is-mic-level/.

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In very approximate values 

bass/guitar/mics have outputs of around 1/1000th of a volt

PA amps have a standard input of just under a volt

Instrument amps tend to have inputs of around 1/4 of a volt into the power amp section, but that varies a lot.

All you need is something with a little gain obviously the dedicated pre's will do all that for you but if you want a low cost solution and you want to keep using your BD121 then almost any little mixer will give you plenty of gain https://cpc.farnell.com/qtx/mm41/4-channel-mini-mic-mixer/dp/DP35486 for around £15 is small enough to fit on a pedal board and there are probably pedals that will do it. A lot of modellers will give out enough to drive straight into a power amp too

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