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HELP! Recording with a tube amp

Discussion in 'Recording' started by spitfiresk822, Jun 14, 2007.

  1. hey, so basically i've heard a bunch of different ways for recording with a tube amp. I've heard the best way is just to mic it, but then I heard that you can run the speaker output into an interface and digitally record, but then i heard that will blow a transformer. So can someone please tell me if there is any way to record with a tube amp without micing it? thanks

  2. multoc

    multoc Active Member

    never EVER run a speaker output into a line/instrument plug, they run completely different ways and you would be STUPID to try it, you would run a direct out from the tube amp, though most don't have that option. So mic the thing
  3. Link555

    Link555 Well-Known Member

    Depending on the amp, the speaker output is capable of driving a Low impedance load (Like 8 ohms). THe input impedence of your pre-amp, will be much higher some are 1.2k some are higher. This means the speaker output transformer in your tube amp will have a unloaded secondary. That means the voltage will be much higher then it was designed for. And that the input of your pre-amp or A/D will have a much much much higher voltage then it wants to see. It will pop most likely.
  4. Boswell

    Boswell Moderator Distinguished Member

    Well, there are two issues here.

    Firstly, there is the question of whether to mic the amp or take a direct output from the speaker terminals. The results of the two cases will be quite different. The acoustic sound produced by a guitar amp is a function of the electronics inside and also the mechanical response of the loudspeaker in its cabinet. Different types of amplifier balance these two effects in different ways. If you just take the amplifier output, it will not sound like the full cabinet, which is the sound you would attempt to capture when you mic the cabinet.

    Secondly, there is the question of a safe way of extracting the output signal, should you wish to go that route. The important thing, if you are not driving the actual loudspeaker, is to have a dummy load in place of the loudspeaker of roughly the right impedance and with enough power handling capacity. Something like a 10 Ohm 50W resistor should work for small amps not turned up too far. For a large stack, a 2-bar electric fire will soak up the power and keep you warm. Bear in mind that you could have getting on for 100V of signal driving the load in these large amps, so a step-down transformer with its primary in parallel with the dummy load is the best for isolation and voltage reduction. I have used a single-ended valve output transformer as a makeshift DI box on a guitar amp with good results. The transformer output can safely go into the line input on your interface or mixer.

    However, I think you would be better off just miking the cabinet.
  5. RemyRAD

    RemyRAD Well-Known Member

    I think you are confused about the way in which to record guitar amplifiers?

    Sometimes, if you can get the guitarist to plug into an active DI (direct injection) direct box, you will be able to put a microphone on the amplifier and record the performance. At the same time, you are recording the guitar directly, without any amplifier interventions. It is that direct recorded channel that can now be folded back out from your recorder and back into another amplifier of your choice. That amplifier will faithfully reproduced what the guitarist bid including all feedback effects that were obtained utilizing their original amplifier. This technique is frequently referred to as "re-amping" which gives you the ability to experiment with different commonalities of different amplifiers.

    Conversely, you might want to try many of the software/plug-in amplifier emulators available on the market today?

    Looking for my box while trying to think about it
    Ms. Remy Ann David
  6. so it would be straight to run my head into a speaker, and run an output off the speaker into my computer? because the speaker wuld b taking the load away?
  7. Boswell

    Boswell Moderator Distinguished Member

    OK for load, but unless you know exactly what you are doing, it would be best to use either a transfomer (as described previously), or a DI box that can handle several tens of volts at the input.

    Your three different recording setups are:

    (1) Record the guitar pickup via a DI box in parallel with the input to the guitar amp. You can later re-amp the recorded track to get different effects. Methods 2 and 3 can be used on the re-amped signal.

    (2) Record the guitar amplifier output, as we've just been describing with associated caveats.

    (3) Mic the guitar cabinet.

    Each of these will produce a different sound, but can be done concurrently. You could have 3 tracks with the different methods and blend them at mixdown, or re-amp the first and get yet more different sounds. For example, you could mic the original cabinet and pan the track far left, then mic a different cabinet playing the re-amped signal and pan that far right.

    Lots of options, but just to re-iterate, do take great care when connecting directly to the cabinet's speaker terminals - its so easy to do damage.
  8. thanks a lot, im going to go out and buy a di box, but what is the difference between active and passive di boxes?
  9. RemyRAD

    RemyRAD Well-Known Member

    Back in the old days.....direct injection boxes were made from high impedance to low impedance, low level microphone type transformers. Quality transformers are not cheap. So the better transformer versions, available at most music stores start at about $45 US and up. Whereas the least expensive, bad sounding transformer direct injection boxes are available from Radio Shaft for as little as $13 US.

    Because a transformer is a passive device, it can be used in either direction. That's right. A high impedance to low impedance device can be used in reverse to create a low impedance to high impedance matching device. No external circuitry nor power is required for any type of transformer direct box.

    ACTIVE direct injection boxes offer a higher impedance input. Those types do not "load down" the pickups on guitars, and by not loading down the pickups, you will achieve a cleaner more opened sound. This is not as important with electronic keyboard outputs and other types of "active output pickup" guitars, that might require an internal battery such as some of the Paul Reed Smith, active output guitars and electric basses. An active direct box CANNOT be used bidirectionally, like a transformer can, since it is an active circuit inside the box with a very specific input and output. Just like any other commercial audio product, there are quality active DI boxes which can cost many hundreds of $US to as little as $15 for a crappy bargain type.

    Further differences include better transient response from the active type but can include terrible distortion artifacts.

    Transformer boxes offer electrical isolation which prevents a direct coupling of circuitry which can cause other types of problems.

    Most quality direct boxes of both varieties usually offer a "ground lift" switch which can help to thwart "ground loop" problems by disconnecting the grounded shield from the 3 pin output connector which is actually not always absolutely necessary in a balanced wired system. The audio is actually delivered on pins 2 & 3 only at the output.

    Most of the time, direct boxes are connected to very low level output devices such as an electronic keyboard or guitar output directly. Generally, a direct box is NOT connected to the output of a power amplifier or speaker. Some have that capability but unless there is a switch on the box that indicates "from Speaker" or, "from amplifier", they are not designed to belch high level power into. They are for teeny tiny voltages to only be converted so that a sensitive microphone preamplifier can accept the teeny tiny signal. Connecting to the output of a high power amplifier such as a guitar amplifier output could mean instant death of a DI box.

    Strangely enough, another interesting way to obtain a direct output from a speaker, without a microphone, can actually be accomplished through the use of a simple "telephone pickup coil". You know, with that little suction cup on it, that you find at Radio Shaft for about one dollar US. This device is actually half of a transformer and if it is brought close to another coil of wire, such as near the back of a speaker, near the voice coil, you can pick up what is coming out of that speaker, without microphone! The sound quality will depend on the orientation of the pickup coil near the speaker voice coil. And because it is a low impedance, unbalanced output, you would still need to topple that into a direct box (DI) so as to make it a balanced, microphone level output for your microphone preamp to accept. Conversely, if you keep your cable under 10 feet long, you might just be able to plug it in directly to your "mixer", without too many problems?

    I particularly like the Whirlwind, "Director", transformer DI boxes which can be plugged into the output of a high-power amplifier, which I've never done before.

    Both types have their pros and cons and while many people might feel that many of the active direct boxes "sound better", I prefer the electrical isolation from the transformers.

    Transformers are our friends!
    Ms. Remy Ann David
  10. cathode_ray

    cathode_ray Active Member

    If you're after the "goodie" from a tube amp (as opposed to a solid-state fizz box) you probably want the goodie from the speaker as well. If you want "crunch" at all you probably play fairly loud(or want people to think you are on recording). A speaker will affect an amps sound more than any other element you can change - find the right one.
    A guitar reacts to volume in a way you can never "simulate". The body/neck/strings all feedback(albeit not like Hendrix) in the presence of the amps vibrations. Stand in front of the amp to enhance this. But record the speaker !
    Note: IMHO (thought probably not very H...)

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