XLR Out For Tube Amp?

[Hammertone]

_One_ reason that tube amp designers don't put XLR outs on their amps is that users might be tempted to use the amps without speakers connected because they are going direct to the board/PA. The problem with using a tube amp without speakers, of course, is that the output transformer (OT) has no load--it senses a load, rather, of infinite impedance, which is reflected back to the power tubes. The amp attempts to power this "load" by ramping up the voltage to the point where the OT and/or the tubes self-destruct. YOU SHOULD ALWAYS OPERATE A TUBE AMP INTO AN APPROPRIATE IMPEDANCE LOAD, I.E., INTO A SPEAKER....[ ]...

Unless it's a Koch tube amp, of course, which almost always has a switch to allow it to run with a dummy load if no cab is connected.

[Greentone]

Yep, a built in dummy load will work.

[DRS]

My Mesa MkV25 has a cab emulated XLR out that gives you the choice of either an open or closed back cab emulation. It sounds pretty good.

[helios]

My Mesa MkV25 has a cab emulated XLR out that gives you the choice of either an open or closed back cab emulation. It sounds pretty good.

The Mark V 35 has a similar "cab clone" feature (Closed Back, Open Back, Vintage). It works quite well, not as good as a high-quality mic in front of the speaker, but about as good as you'll get for a line out:

[M.T.Pilot]

_One_ reason that tube amp designers don't put XLR outs on their amps is that users might be tempted to use the amps without speakers connected because they are going direct to the board/PA. The problem with using a tube amp without speakers, of course, is that the output transformer (OT) has no load--it senses a load, rather, of infinite impedance, which is reflected back to the power tubes. The amp attempts to power this "load" by ramping up the voltage to the point where the OT and/or the tubes self-destruct. YOU SHOULD ALWAYS OPERATE A TUBE AMP INTO AN APPROPRIATE IMPEDANCE LOAD, I.E., INTO A SPEAKER.

With solid-state amps, however, it's okay in general, to turn on the amp without a speaker connected. Just using the amp head as a signal source for the XLR-out will work. (Do look at your operating manual, however, to confirm this.)

I'm using a Koch Jupiter 1x12 combo. It is a hybrid, but with special design; it has a tube in the pre-amp and one in the power-section (and then some mosfets). That way, you get the tube-amp feel and sound, without it being an all tubes amp. It also has a record out (1/4") which sends an emulated signal to the mixing-board. In the manual, it specifically says that you can unplug the speaker without causing any problems.

[bluefonia]

All 1/4" jacks that I've ever seen look the same from the outside. You have to be able to see the contacts inside to know whether it's stereo or not, and I've seen lots of guitars and amps with TRS jacks that are only used for TS applications, probably because it's often cheaper and easier to use the same jacks for everything. You cannot tell by looking at an installed jack from outside.

Sometimes pictures are better than words :-). Just for clarification: For a jack-plug to work as balanced it needs to be stereo. A normal guitar cable has mono jacks. And they look different from the outside - stereo/balanced on the small pict. and mono/unbalanced large pict.

[geoff23]

A simple way to get an XLR output on a valve amp is to use a Palmer PDI 09 (Palmer PDI 09 Passive DI Box for Guitars: Amazon.co.uk: Musical Instruments). This is a small passive box (no batteries needed) that is wired in parallel across your speaker connection and provides a line-level facimile of your amp sound on an XLR output.

The way I use this with my Princeton Reverb Reissue is to feed it from the Princeton’s parallel speaker extension jack. I leave the Palmer semi-permanently installed inside the back of the amp using velcro.

It sounds pretty good to my ears when fed into the PA - as good as mic’ing up with a SM57 for clean sounds (maybe not quite as good for dirty sounds) and a lot more convenient than a mic, and with no danger of spurious stage noise or people kicking a mic over!

With these you do have to be very careful to connect them properly so that, as discussed above, you don’t run the amp without a load - this box in itself doesn’t provide a load so you do need to keep the speaker connected.


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[newsense]

Koch do an excellent dummy load with either XLR or line out, plus power soak options.

Koch Dummybox Studio / PA - Koch Amps

Koch Dummybox Home - Koch Amps

I use the DummyBox Home for silent practice and recording. The cab emulation is not the greatest and I use Digitech's cab IR pedal to hone the final sound.

[sgosnell]

Those are plugs. Jacks are the female part they plug into. Mistaking plugs for jacks can cause confusion. Jacks all look the same from the outside, but it's easy enough to spot stereo or mono, (TRS or TS) plugs.

[sgosnell]

This is a jack:

[bluefonia]

yes, sorry - I made my post pretty early this morning and was probably still half asleep and simply forgot about the female part of a jack connection. Indeed, here it is pretty hard to see the difference between bal. and unbal. from the outside