These are all jack-to-jack cables, but they’re not wired the same. To record from a headphone output to an audio interface’s input, you’ll usually need the bottom one, often known as a ‘Y-cord’ or ‘insert cable’.
I’m looking for guidance on why I can’t record from my guitar amp directly to my audio interface. i’m working with two small amps, a marshall and a cabinet, and trying to record a signal from the headphone outputs of the guitar amps through a focusrite scarlett 2i2 interface. originally i thought the headphone jacks on both amps might be broken but when i plugged in a pair of sony headphones the sound was perfectly clear. then i thought the problem might be that the headphones had a quarter inch trs connector instead of ts, so i took one of those and tried to connect the amp to the interface that way. no dice.
Reading: Guitar amp headphone out
However, I don’t get total silence – if I turn the amp up high enough, I get very crackly audio that sounds like it has a high pass filter. your guidance would be greatly appreciated!
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sos forum post
sos tech editor hugh robjohns replies: while headphone amps aren’t technically the best output source for a recording, you should capture something reasonable if you use the right cables. but the problem here is that the seemingly similar quarter-inch sockets on the amp and interface are wired very differently and therefore carry/expect differently formatted signals.
The headphone output is unbalanced and is wired to be compatible with stereo headphones, even though the guitar amp produces a mono signal. that means the unbalanced amp’s output signal is connected to the tip and ring contacts on the headphone jack, with a common ground on the sleeve. the interface input expects a balanced line level signal, meaning it only responds to the difference between the signals at the tip and ring contacts.
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with a trs-trs cable connecting the amplifier’s headphone output to the interface’s balanced line input, the signals on the interface’s tip and ring contracts are identical; there is no difference, so it will appear that there is no signal. all you’ll hear, as you describe, is the very small error signal that results from an imperfectly balanced input amplifier, which is typically a very quiet sibilant, spitting, toppy sound (see figure 1).
with a ts-ts (instrument) cable connecting the amp’s headphone output to the interface’s balanced line input, there is no ring contact, so the ring output terminal on the headphone jack it is shorted directly to ground by the plug sleeve. inside the amp I suspect the headphone jack tip and ring contacts are connected directly to each other (as opposed to having a true stereo output amp) as there is only a mono source. this means that the act of inserting a mono ts plug will actually cut the entire output of the headphone amp to ground, leaving no signal to send to the interface! (see figure 2.)
The only viable solution, if you want to record from the headphone output, is to use a “y-cable”, which consists of a trs connector at the amp end and two ts connectors for the interface end. it is often sold as an ‘insert patch cable’ or a ‘stereo to dual mono output splitter cable’. When using this type of patch cord, the TRS plug provides the signal from the tip of the headphone jack to the tip of one TS plug and the signal from the ringer to the tip of the other TS plug. if you then plug one (or both) of these ts sockets into the balanced line input(s) of your interface, the balanced input circuit looks for the difference between the signals at the tip and sounds again, but this time the sleeve shorts ts the ringer signal to ground, and the desired headphone output signal is applied between tip and ground, so all is well. (See Figure 3.) Hello, done! everything will work as you want and expect…
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