Getting distorted sound when connecting from mac pc headphone jack to 1/4" line in input

IF your Laptop has a stereo LINE 1/8" INPUT jack, you can take the Stereo ( Left & Right ) LINE outputs on your mixer and feed into this jack on your PC. You will need a 1/4" dual plug for the mixer end to a single 1/8" stereo plug on the PC end. I suspect the problem you are having is either related to your PC only have a MIC input jack or you have something set wrong in your PC's sound config. file. More information is needed to properly solve the problem.

are you going from the board to a 'mic' input, or a 'line input' on the Mac? you will need to attenuate the signal to a mic input. try reducing output from the board by 50% and reduce the input level on the Mac by 50%, and see if the distortion is lessened or eliminated. From there balance board output to Mac Input until you find what sounds good outta the Mac.

Simple: connect the headphones out (3.5mm jack) to the input jack of your fender (6.3 jack). By doing this you will loose one channel so you better generate a mono signal inside your computer before. Electrically this is no problem, nothing will be damaged. Turn the gain and volume knobs down and apply a signal from your Mac. Gently increase gain and volume. Et voila wonderful mono sound through a guitar amp

Check to make sure the problem is not with the headphone jack or the external speaker jack as these are in the circuit between the power amp chip and the built in speaker.

You can also trace through the circuit with a music source on the amp input and with simple headphones check the signal path through the circuit until the music disappears. To do this, take a headphone and set it up with 2 test leads on the ends- attach one to ground.

Now your TL072 op amps have 2 outputs, pin1 and pin 7. The inputs for pin 1 are pins 2 and 3, and the inputs for the amp section outputing on pin 7 are pin 5 and pin 6. If you get sound at pin 1 or pin 7, you move forward to the next TL072. Check for output. Then move to the power amp chip on the heat sink. Pin 1 should be the output and will be wired to the headphone jack first. The external speaker jack second and the built in speaker third. The input for that power amplifier chip is pin 7 or pin 8 depending how it is wired.

If the amp chip is blown, make sure to put an adequate amount of thermal grease on the back side of the IC in contact with the heat sink so it can operate as cool as possible.

You would NOT connect an audio signal to the "send" jacks... those are OUTPUTS... In doing so you are driving signal backward enough to get to the headphones. Sends and returns are NORMALLY used on a mixer for external effects. You should either be using a LINE input jack or one for "tape input".

There is NO way to select channels to "Source"... The selections on this mixer are to send the channels to SOLO, Sub1-2 or Sub 3-4 and/or main L-R. You should have the bottom button for each channel punched down to L-R. NEVER connect ANYTHING other than an external effects unit to the INSERT jacks!!!! These jacks are combined output/input jacks with send and return on the same jack. Special insert cables are used for these. An external drum machine should be connected to a line input for one of the channels USING a TRS balanced cable. Page 28 of your user manual shows the block diagram and signal flow diagram. The trim control is the input gain control. Start with those say at 12 o'clock and advance the fader for the channel of interest...you should get signal at the main outs. MAKE SURE that the lines from the mixer to the amps are BALANCED TRS type cables... You cannot use unbalanced cables for this. The user manual explains balanced cables and what they look like. I just repaired one of these mixers that some foolish people plugged stuff into the MAIN INSERT jacks and blew out the driver that drives the MAIN insert which kills the input to the MAIN output drivers. There is one small chip between the AMAIN fader and the sub next to it and one has to remove every knob and take the unit all apart to get to it... It is a tiny surface mounted part the size of a matchhead with 8 leads... not for the faint of heart to repair. As a test of this part, you can plug a st of headphones into the RIGHT MAIN insert jack and drive audio into a channel... turn trim control up fully for the channel and the fader on full, and set the PAN control to 12 oclock and punch down the L-R button for that channel. You should hear the audio in ONLY the left ear... Now try the phones in the LEFT INSERT jack... you again should hear the audio in the left headphone only (these jacks are not stereo like the headphones). If you cannot hear anything, then likely somebody has blown that driver in your unit... It is painful and time consuming to repair this... there are hundreds of knobs to pull off and put back on... dozens of screws and cables and to get it all back together. Also make sure ALL of your interconnected equipment is powered from a SINGLE receptacle or power module. Read your user manual thoughroughly. You can get one online download if you need it.

You can do a major amount of troubleshooting using tests from the many jacks on this unit.
I can walk you through a lot of those if you keep getting back to me with the results. First test: When the failure occurs does one or both sides of the headphones plugged in the headphone jack ALSO quit? Also does the level meter LED's reflect loss of signal? If these are still OK I want you to plug the headphones into the MAIN MIX MONO OUT jack. The headphone signal won't be very strong, but is it OK and not distorted.

I hope you have remembered to use BALANCED (TRS) audio interconnect cables and not plain mono cables from your mixer to the amps. Use of mono cables shorts out one side of the balanced output driving amps in the mixer. Also the other send of these MUST connect to balanced amplifier inputs... NOTE some amps don't have this and you have to use a BALUN or a DI at that end.

Lastly, ALL inteconnected equipment MUST be powered from the same source or receptacle for system safety.

Feel free to contact me via email or whatever.

try hooking headphones to the output and see if the crackling is still there.

then, try it with the speakers, at a lower computer voume level and higher speaker volume level. perhaps the headphone output is too loud and distorting in the speaker inputs.

Contrary to what's posted above, the Marshall MG series does not pass the speaker power output through the headphone jack, and inserting the headphones into the jack does not disable the speaker. The headphone amp is a separate circuit and it's input is taken before the master volume. So Jan's post is exactly right. Turn off the master volume and turn up all the other gain/volumes as high as they will go. The other issue is that the headphone jack's output does not drive low efficiency headphones well, so you need some headphones similar to Sony's MDR-V700s to hear it well. Earbuds just don't cut it.

Probably the easiest way would be to use a stereo receiver. You can run the headphone output of your ipod into a tape or cd input. The only thing to deal with will be adapting a stereo 1/8" (3.5mm) headphone type jack to 2 RCA type input jacks. You should be able to get this cord at radio shack. You might also be able to purchase a receiver that has a 1/8" input jack specifically for connecting things like an ipod. A receiver, by definition, has a tuner built into it. The alternative would be a tuner and an 'integrated amplifier' which has power amps to drive speakers as well as a pre-amp and input selection switching.