Pre-amp/DI connection query

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KeithJ
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Pre-amp/DI connection query

Post by KeithJ » Tue Oct 01, 2019 8:32 pm

Nerdy gear question for you guys, since I can't find an answer after much googling: if I have an old solid state bass amp head with no DI plug for the sound guy, but it has a pre-amp out on the back, can the sound guy just plug into the 1/4" pre-amp plug, OR could I plug a DI box into it and let the sound guy plug into the DI box? Or is it neither and I'm screwed?

I feel confident that plugging a DI into it would kill the DI box, but fingers crossed!

For the curious ones, the head is a 70s (I think) Traynor Group II B, if that helps anything.

Thanks all!!

Keith <3

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Larsongs
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Re: Pre-amp/DI connection query

Post by Larsongs » Tue Oct 01, 2019 8:47 pm

I don't know about that but I've run Guitars to Art Tube Pre Amps into the Input Jack on a SS Fender Amp.. With good results. It made the annoyingly shrill wimpy SS Amp sound more like a Tube Amp & gave it a much needed Power Boost... Be cautious about overloading the Speaker...

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marqueemoon
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Re: Pre-amp/DI connection query

Post by marqueemoon » Tue Oct 01, 2019 9:18 pm

It looks like it’s an effects loop (preamp out/power amp in).

If your DI has a parallel 1/4 output I bet to you could you just run 1/4” into the DI, and out of the DI to Power Amp In. Then use the XLR on the DI to send to FOH.

Or just place the DI between your pedals (if you use them) and amp.

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Embenny
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Re: Pre-amp/DI connection query

Post by Embenny » Tue Oct 01, 2019 9:39 pm

DI boxes convert a hi-Z/unbalanced signal (instrument) to lo-Z/balanced so that they "play nice" with the inputs on studio/PA gear. A low impedance (lo-Z) signal prevents an impedance mismatch that "loads down" the signal and degrades its frequency response. A balance signal is less susceptible to noise (e.g. hum) than an unbalanced one, especially but not exclusively over long cable runs.

Your 1/4" preamp output on your amp is lo-Z, so that's one issue solved. It's not balanced, but that's not necessarily going to be a problem for you. It's also probably line level, which is way higher than the instrument level that comes straight from the instrument.

One of the advantages (but not the only one!) of a balanced signal/cable is that, if you're about to run your signal through a gain stage, like one designed to bring an instrument level signal up to a line level one, the improved signal:noise ratio means you avoid boosting that noise/hum along with it. Since your preamp output is already line level, it's not going to need the same kind of boosting once it reaches its destination at the mixer.

If it's not going to be a huge cable run, using an unbalanced cable from the amp to mixer probably isn't going to be a huge deal. But there's a reason people use DIs - if you were recording, or sending that signal down a 200-foot snake to the mixing booth in a huge venue, the SNR of a balance cable run is going to be advantageous.

If you want to use a DI so that you can enjoy all the benefits of a balanced signal via XLR to the mixing desk, you just need one that can accept a line level signal. The DIs marketed specifically to guitarists/bassists don't always have this feature, but many/most DIs do. They do, however, pad (reduce) the output down to "mic level" which is not something you have to worry about if you're not manning the desk.

TLDR - you're fine to give the sound guy your amp's preamp output, but if you run into noise or other performance issues, you can get a DI that accepts line level signals, and plug into that, with the XLR output of the DI going to the desk.

Your instinct is correct that you should never plug a line level output into a DI designed exclusively for instrument level signals, but you're fine as long as the DI is designed for it.

It also depends on whether you want the coloration of the preamp. Like marqueemoon said, you could plug into an instrumental-level DI input if it has a parallel 1/4" instrument level output, send that output to your amp, and your bass' direct tone to the board, if that's your preference. If you like what the preamp does for your tone, then sending that to the board is a fine way to go.
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marqueemoon
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Re: Pre-amp/DI connection query

Post by marqueemoon » Wed Oct 02, 2019 5:43 am

In my experience the person running sound is going to do it however they want to do it.

As mentioned above sometimes a line out is noisy or just plain doesn’t sound good, but it’s worth experimenting with.

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Re: Pre-amp/DI connection query

Post by somanytoys » Wed Oct 02, 2019 10:11 am

Great info. Levels can be hard to figure out with differing applications, and it’s so easy to fry things.

A good DI is never a waste of money, for practice, recording or live. It’s amazing how many situations it can really be useful in, or even required in, and can save your ass.

I have 2 dual DI boxes. Because if it isn’t overkill, it just isn’t enough.

Edit: also, an alternative if the DI only takes instrument level could be something like an Ebtech line level shifter. It may be cheaper to get a good DI box, but that is an alternative, with both 1/4” and xlr connections that can be converted with the signal.
-David

It's a boost booster, to boost your boost - it makes your tone much muchier.

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KeithJ
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Re: Pre-amp/DI connection query

Post by KeithJ » Wed Oct 02, 2019 4:43 pm

Holy cow, thanks for all the great info you guys!! This has been super helpful!

I do have an MXR DI box that sounds amazing on its own, and I've run it in the FX loop off another amp, but I basically just wanted the sound of this new - to - me amp coming through the house sound system.

I guess in the worst case scenario I can put the MXR between the bass and the Traynor head and it will still sound good, it just won't sound like this awesome old ugly amp! 😂

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