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Old 16th November 2011, 04:40 PM   #1
methc is offline methc  Guyana
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Default Line out from Guitar Amp

Not sure if I am posting to the right place! Sorry if I am not...

I have a guitar amp (bass Roland Cube 30Watt) I want to tap a line out from the speaker wires so I can send the output signal into my Mixer PA system.

Any simple schematic you guys could offer? If the circuit had an on/off switch and a POT to adjust the signal out level that would be great.

Thanks guys.
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Old 16th November 2011, 04:56 PM   #2
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Dont try to tap off the speaker for a line out. The level is too high and could damage the PA. Much better would be somewhere in the pre-amp section. Do you want the sound level sent to the PA to be controlled by the volume on the amp? If so, come off the center of the volume control with a coupling cap and send it two a jack on the back of the amp. This is what I would suggest.
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Old 16th November 2011, 05:02 PM   #3
methc is offline methc  Guyana
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Quote:
Originally Posted by firechief View Post
Dont try to tap off the speaker for a line out. The level is too high and could damage the PA. Much better would be somewhere in the pre-amp section. Do you want the sound level sent to the PA to be controlled by the volume on the amp? If so, come off the center of the volume control with a coupling cap and send it two a jack on the back of the amp. This is what I would suggest.
Thanks for the reply!

Coming off the vol control of the amp will mean every time the bassist fools around on the amp it will affect the sound/vol level on the PA. I'd much rather the volume level on the PA is fixed unless I adjust it on the Mixer.

Where in the pre-amp section of a Roland Cube 30x Bass amp would I tap?

Not much of a pro in this kinda stuff. But I really need my bassist to be heard past the stage.
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Old 16th November 2011, 05:10 PM   #4
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Doesn't your Cube 30 already have a "Recording Out/Phones" 1/4 inch jack? The manual says it does.
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Old 16th November 2011, 05:14 PM   #5
methc is offline methc  Guyana
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Originally Posted by leadbelly View Post
Doesn't your Cube 30 already have a "Recording Out/Phones" 1/4 inch jack? The manual says it does.
Yes my friend it does, good eye... However the issue is when I plug the 1/4 in jack in there it turns the speaker off. I need the speaker to work so the bassist can monitor himself while still sending a signal to the Mixer/PA.

Questions:

A) Is there a way to bypass this 'switch' in the headphone 1/4 jack?
B) Will that signal be too large to just send straight into my Mixer (it shouldn't right, since it's meant for a headphone)
3) Will any damage be caused to the amp circuitry or the speaker if I did manage to disable the 'switch' in the headphone jack?

Thanks guys.
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Old 16th November 2011, 05:58 PM   #6
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A) Is there a way to bypass this 'switch' in the headphone 1/4 jack?

Yes - you will need to get inside and solder a jumper onto the phones jack. This level output should do nicely for what you are looking for. Now one way we could help is if you could take pictures of the inside, and someone could talk you through it. This is not hard to do, but I dont want your to get shocked or to break something. Im sure your agree.
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Old 16th November 2011, 06:03 PM   #7
methc is offline methc  Guyana
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Quote:
Originally Posted by firechief View Post
A) Is there a way to bypass this 'switch' in the headphone 1/4 jack?

Yes - you will need to get inside and solder a jumper onto the phones jack. This level output should do nicely for what you are looking for. Now one way we could help is if you could take pictures of the inside, and someone could talk you through it. This is not hard to do, but I dont want your to get shocked or to break something. Im sure your agree.
Thanks for the reply.

I'm savvy enough not to get shocked and break something I know the basics, enough to get by... If a picture is all you need to help me out then I'll get you that come this friday when I go the band rehearsal again. So I'll be taking a pic of the headphone 1/4 jack assembly? Yes?

Thanks again...
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Old 16th November 2011, 06:17 PM   #8
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Yea- The inside or back of the headphone jack.
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Old 16th November 2011, 06:24 PM   #9
methc is offline methc  Guyana
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Originally Posted by firechief View Post
Yea- The inside or back of the headphone jack.
Report back to you guys in a few days when I have the pictures. Please 'watch' the thread so you'll get my reply

Thanks man...
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Old 16th November 2011, 09:33 PM   #10
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How far a line do you want to run to the board?

A direct box with an internal transformer would allow you to plug the bass guitar into the direct box and the direct box's balanced low-impedance output into the board. This allows you to run long balanced lines. The level will be pretty low, but more than a mic.

Coming straight off the preamp gives you a hotter unbalanced high-impedance line. That might do, but could introduce ground loops, rf and emi, and you may need to pad the board input and such a hot channel may bleed to others in a long snake. A truck with a CB and linear can ruin your show. That might do for a very short run to a small on-stage board or to a stage box A/D for a digital fiber-optic snake. But most shows only use balanced inputs with a ground-lift switch and a pad at the board. An effects send or pre-out or a cap and resistor network off the volume hot or wiper are good outputs to feed into a direct-box transformer, so that again you have balanced low impedance. If your snake's board-box has splitter transformers you may be able to wire into that channel in reverse if you don't want bass in the stage monitors anyway.

You also have to consider whether you want any of the amp's own sound signature.
The speaker output is also pretty low-impdance and not very high in voltage, so it's also suprisingly common to feed that into a direct box so the transformer again gives you a balanced low-impedance line. You may need a pad or voltage-dividing resistors to optimize the drive level for the particular transformer. You may be surprised at the treble noise in a bass guitar amp that you don't normally detect because the speakers don't reprooduce it, so you will want to fiddle with the boards' EQ on any direct line.

And if you really want the amp's real sound, a large-diaphragm dynamic mic works great. Some guys mount a gooseneck directly to the speaker, which picks up some cabinet resonance but less floor noise.

If you're serious about PA, get a direct box...or a few. Guitar Center sometimes has cheap ones advertised as "loss leaders" to get you into the store, in which case they cost less than you can get just the transformer for. A few Christmases ago they had them for $10. And if you're REALLY serious, look at Deane Jensen (rip) brand transformers. You can also add switches or pots before the transformer so that the input level doesn't saturate the transformer, especially with a small cheap transformer. A Deane Jensen BM output transformer, level control, and balanced XLR jack built into the amp is a really classy way to go.

Good luck.
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