Direct input dilemma

[james10pl]

I recently bought a tube amp, based on the assumption that I could us a direct input box like the Behringer DI-100 to put a signal straight to the computer and to the amp's speaker without interrupting the signal. I was told this was possible by a local music store's employee who appeared to have experience on the subject. After I bought the amp, I went to buy a Behringer DI-100 from the same store. A different employee, one who appears knowledgeable on that subject (being their repair guy), told me that that could damage the amp severely because of an issue with the signal impedence.

Is there anyone who either has direct experience with this, or certain knowledge on this issue, who can tell me whether it is possible to put a signal from a tube amp into a computer without modifying the signal impedence? That is, can I take the signal before it hits the speaker and just put it straight into the computer, without hurting the amp?

Thanks

 

[Halion]

I don't know where he got that knowlegde but I've never heard of harming something because the impendance was wrong? It might sound like crap, but I doubt your gonna do any harm to your gear.

I think what he might have meant is this:
Some people dissconnect to cable running from the power amp to the speaker, and run that to a DI box or computer. Now THAT is really not a smart thing. The signal is way to strong for that, because it is amplified by a power amp. You need to use a "direct out" or "line out" or something, then you'll be fine. NEVER EVER use a "speaker out" or "power amp out", they cary amplified signal that can destroy stuff.

One question though: why are you using a line-out when you have a tube amp? Most of the color in an all-tube amp comes from the tubes and the speaker. When you use a line out, you skip most of the tubes and the entire speaker. It's a big waste if you ask me. Also, the combination tube-amp/behringer DI don't seem smart to me. Tube amps are still expensive things with mostly high-quality component. Behringer DI's on the other hand, are not. Try putting a microphone infront of the speaker. That way your results should be good, if not great.

Also, don't ever trust what the guitar-store guys tell you. "Seeming" knowlegable is what they are best at. Beeing knowlegable is not.

 

[Adam P]

Never run a tube amp without a speaker load attached to it.
Always try to match impedance between your cab and your head...I'm fairly certain that if your cab is of a higher resistance (IE a 16 ohm Marshall 4x12 with a 4 ohm Fender Bassman head) it can damage the amp's output transformer. Don't quote me on that, though.

I'm pretty sure that that Behringer DI box you mention can be used in line between the head and the cabinet, running the head's speaker output into the DI, and then from the DI out to the cab. You should read its literature very carefully though to make absolutely certain that it is possible, because not all DI boxes can do this.

 

[sile2001]

I second that...

For the most part, solid state amps couldn't care less what load is attached to them and will just keep ticking. Tube amps, on the other hand, are extremely picky and can take serious damage if you don't match the impedances correctly. Over at the Peavey forum I've seen countless cases of dead output transformers and blown tubes due to impedance mismatches on cabs.

 

[Clive Hugh]

I am reading the Behringer DI 100 manual as I type and it says
"the 1/4 jacks (input and link out) and the Input XLR are wired parallel, so any connection as input will give the same performance" quote.

I take that to read speaker out into input, link(4) to speaker, this will still give the same impedance so the amp will be happy, then take the output XLR to your recording console.
One thing not covered there tho' the line from amp to speaker is not co-axial cable (ie guitar lead) as this is also a no-no, so make sure the connections fom amp out to DI 100 input are 2 wire, the existing speaker lead will be 2 wire so that will be ok.
The lead from DI 100 output to console , use standard XLR.
Hope that helps.

 

[sile2001]

One thing not covered there tho' the line from amp to speaker is not co-axial cable (ie guitar lead) as this is also a no-no, so make sure the connections fom amp out to DI 100 input are 2 wire, the existing speaker lead will be 2 wire so that will be ok.
The lead from DI 100 output to console , use standard XLR.
Hope that helps.

Using a coax cable for that isn't a no-no. You just have to make sure you use a cable with a heavy enough gauge to carry the load (i.e. no guitar cables). You need speaker cable with a heavy enough gauge for the output wattage of your amp.

 

[james10pl]

Thanks for all your suggestions, I think I'll try using the DI box, since the manual mentions specifically about impedence matching, with a heavy coax like sile2001 suggested.

 

[Armistice]

I guess you have some of us wondering why you actually do this? You will not get the benefit of having a tube amp from a recording perspective running through a Behinger DI. Unless you're also miking it and just having the DI as an extra feed to keep your options open.

Just curious...

 

[Clive Hugh]

Sile2001, I was referring to guitar leads generically as co-ax. Good point.
Clive