Discussion in 'Guitars' started by imacgreg, Mar 5, 2002.
Listen & learn what ribbon mics can do for you in your studio.
That and the previously surmised matching of level.
Excellent article in this month's EQ about re-amping. Addresses all of the issues and most of the products discussed above.
i just built a reamp box a couple months ago. it is possibly the simplest electronics project next to repairing cables. it is basically a transformer hooked up to some variable resistors. well... not 'basically'... it IS a transformer hooked up to a couple of variable resistors.
here's the schematic:
it has two dials: one for level matching and one for impedence matching and a ground lift switch. it's a passive device.
i used the jensen tranformer but you could likely swap in a cheaper one if you wanted. project cost me $100 Canadian ($90 of which was the transformer).
just used it last week... works great.
there are a host of schematics on the jensen site:
Thanks for the responses.
The very same #092-pdf was already on my table, together with I thought #04. In a book about guitar-electronics I've found some interesting impedance characteristics for several pickups,
so by adding say a cap and a coil the resonance of the impedance could be added as well.
Point is, when it works & sounds OK is _IS_ OK, but when I try to understand the function of adding the impedance when sending the signal back to the amp, I can only conclude it wouldn't be necessary.
Because: when DIY-ing the gtr (as when recording it dry to tape/disk) the influence of impedance is already taken into account. Note that I would do it like this: plug gtr into a very Hi-Z DI and feed/copy the direct (pre-DI) dry signal to the amp as well.
This way the DI is already 'sniffing' the interaction between gtr & amp-input. When reamping, all that seems to be needed is taking care the same voltage is present again at the amplifier-input.
Any oversights here ?
Parallel thread at:
(Dead Link Removed)
I know it's expensive (about 1g) but is way more than a reamp box....Millennia TD1.
I had to mention because I am a reamp freak and I am dreaming about this piece, sooner or later.
I received an E Mail from Millennia this morning regarding the TD 1. They say they are very backordered on the TD 1 at the moment but they promised me a unit as soon as they can get one to me.. Watch for a review.. Kurt
if they want I could review one for my own magazine too ask em if they are interested, I can wait as much as they need.
just joking I will waiting for your notes on that
Peter, i'm not really sure what you are getting at here but it's the impedance differential between the recording device's output, DAW or tape deck... Low Z and the guitar amp's input... High Z... that will be problematic when you go to rerecord the signal later. I notice a change in the tonal character and noise level even when i make adjustments to the pot controlling impedance on the jensen reamplification box... subtle but present.
I apologize if what i am stating is obvious... and certainly no one can argue with the "if it sounds good it is good" approach... if whatever you are doing is working then why add another box to the equation
except... of course... by adding another box to the equation you get to buy another box...
and then explain to all your bored looking friends what that little box is doing.
First of all, thanks for the responses, interesting subject.
W.r.t. impedance, I think there are two sides:
* First one is the actual adjustment/matching of the sending ('+4dBm') to the amp-input. I must admit I can't see any impedance problem involved - as long as the level is right and the signal is unbalanced and the plugs fit physically
I mean, I couldn't imagine a problem using a Hi-Z load for a source that now sees the Hi-Z instead of the usual 10k (or 600 Ohms) it usually sees. I may be wrong here, but higher loads (more Ohms) wouldn't hurt I guess.
* The second point is that the Re-Amp doesn't seem to address the 'real' source-impedance influence of guitar-pickups. Source impedance of a pickup is usually 'flat' (say 8 kOhms) and then has a sharp resonance peak at a few kHz.
Pickups can be made with this peak above the audible range but it would be a dull pickup, without much ;character'.
The TD-1 does seem to mimic this impedance-shape, with its Strat & LesPaul-outputs.
This second side of the impedance-story was the one I was having trouble-to-understand with: as I see it, the influence of this impedance-curve is already taken into account when recording the dry track - as long as it's done as described: using a DI with a very Hi-Z input and which senses the connection going to the amp. I'd say this arrangement already 'senses' the interaction between the guitar-pickups and the amp.
I tried out a bunch of the different units on the market (before the TD-1 was available), and the Little Labs stuff took the cake for me. I got the PCP and the Redeye, and I often wonder how I got along without them, especially for simple guitar pedal stuff. Highly recommended.
The TD1 has way more options AND a supercool mic pre intoit.
said that to me the best reamping devices are made by radial and little.
anyways I see a reamp like something that goes form +4 to -10 and possibly lower.
I guess that's indeed all there is to it.
Anything else in addition I couldn't really understand - unless some toneshaping is to be parked inside the re-amp box itself already.
As i understand it, the issue is that you are sending a low z source signal (low voltage, high current) to the amp which is expecting a hi z input (high voltage, low current).
So while you won't get the signal degradation that you get sending a high z signal into a low z input (guitar into mixing board without DI) you will have a voltage deficiency/weak signal which might result in additional noise/hiss . So while the guitar amp will 'see' all the frequencies,as you are suggesting, it will see them as very small. Which may add noise when you turn your guitar amp up.
This is just the issue... there will not be enough signal present even though the level might be fine... hence noise.
I would imagine that the degree to which this is a problem would depend greatly upon how well your guitar amp input is able to deal with the low voltage signal you are sending it. So it may sound fine without a reamp box if your amp is particularily forgiving... and i have heard of this happening.
Someone please correct me if i am mistaken as i am not an electrical engineer!
[ December 18, 2003, 03:13 PM: Message edited by: teleharmonic ]
The other missing piece is that impedance is both resistance and reactance.
I have no clue how reactance is playing into all this, if it is at all...
Getting a Reamp versus using a passive direct box
The Radial JDI direct box is sometimes suggested as a alternative to a proper Reamp. Although this is true, this may not be the best option. A passive Reamp and direct box like the JDI both employ a transformer as the motor that does the work. A direct box transformer is designed to capture an instrument level source - say between -20dB and -10dB and then convert the signal down to -30db or about the same level as a microphone. This enables the DI box to connect to a mic splitter on a stage or the mic input on a mixer or preamp. On a stage, having the ability to quickly swap cables around without worrying about signal levels can save a lot of time when trouble shooting. A Reamp is designed to take a +4dB line level source and bring it down to a guitar level (say -20dB) so that it sounds right in a guitar amp. Reamps all have variable output levels to compensate as needed.
The difference here is the type of transformer being used. With an instrument, a direct box transformer such as a Jensen JT-DBE has a 12:1 step-down turn ratio that no only changes the level and impedance, it also balances the signal. This is designed for instrument levels. Inside a Reamp, a 1:1 line level transformer is typically employed which also serves to unbalance the balanced line level signal from your recording system. You can turn the output level down on your recording system to use a JDI direct box backwards, but this will of course reduce the signal to noise (increase susceptibility to noise). You will also require a turn-around XLR connector to use the output as an input and once set up, this will force you to adjust the level gong into the amp at the console as there will not be a local volume control next to the guitar amp as found on a Reamp. In essence a JDI direct box and a Reamp are in many ways opposites!
Peter Janis - Radial Engineering
I got this one and get good results with my Vox AV60. Not expensive !
The New AT5047 Premier Studio Microphone
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