Still have sound through speaker with channel B gain input set to OFF

It sounds as if the input is too low. what happens if you plug whatever is going into the stereo channels into a pair of mono channels. Or are you taking about the phono stereo tape input?
The stereo channels are line level whereas the other channels have both line and mic level inputs, what are you trying to put through the stereo channels? You must make sure the gain switch is set to the -10dB to get the most sensitivity (the mono channels have about -132dB max sensitivity BTW) You probably need a different mixer or possibly a submixer if you are needing more than 4 low level inputs.

Where do you have the gain control set on the Mic channel ?
If you have no issues with either the speakers or the Mic, and the gain control for the channel you have the Mic plugged into is set at a somewhat "normal" position, you might have a problem with the mixer itself.

Where is the gain set for that input channel of the low impedance mics? If you have an unbalanced Hi-Z input sharing a channel with a low Z balanced microphone They are sharing the same gain stage op amp- in which case an unamplified microphone loses.

You've made a statement, please give full information if you would like help. Is the buzz heard from the speakers or the mixer? Do you get normal sound too? Is it there with no input? Does it change with the output setting? Help yourself to get help and let us know properly what's going on.

The amp has a failure. One side of the power amp is starting to draw excessive current to the point that the filter caps can't sustain the current so the ripple starts to be heard in the speaker. Continued use MAY burn up the speaker by sending DC through it as well as causing additional damage to circuit boards, etc..

Several things to do: Plugging into the tape type inputs... say the 7/8 channel.

The little button below the set you plug into needs to be pushed to the down position. This selects the "B" set which are the RCA jacks.

Below the set you are plugged into. Turn up the top knob "Gain" until the "clip" LED just isn't quite flashing.

At the bottom of that same column Turn up the "level" as needed for the mix.

Then of course, advance the Master level as needed.

gapoko

There is not enough info here to provide a complete answer, but let me give you some background:

There will always be some hiss. This is due to general amplification where a small amount of noise is amplified along with the general signal. In most cases, the signal is strong enough to overpower any noise that is present (vocals in your example). This noise should not be that noticable in normal cases. If there is an automatic gain control in the line, this could account for it as with "silent" times, the gain will automatically be increased potentially to the degree where the noise is noticable.

Barring that scenerio, if the input signal is too low, the overall gain necessary to produce reasonable volume at the speakers will also be such that the noise is noticable. In order to track this down, please provide details about the current setup including:

1) Microphone make and model being used
2) Input being used on the mixer
3) Gain level being used for the mic channel
4) Gain level being used at the master level.

Dan

The answer to your question is NO, there is NOT an internal adjustment.

For many mics the trim is used full clockwise. Some higher output mics I use the trims are run at 3 o'clock which is mostly turned up. This is NORMAL for most mixers. If you don't have enough mic gain relative to other inputs, the fault is balancing the other inputs down and using higher setting on your MAIN slider.

If you use 8 ohm speakers then you can expect to get about 200 Watts of audio per side with this amp. You can get about 400 Watts RMS (600 Watts peak) using 4 ohm speakers.

The efficiency of the speakers makes a lot of difference in the sound level output/

These are a real pain to open. You have to remove the front panel to remove a shield to remove the back amplifier power supply area. The power supply is a switching type and has lethal voltages present. Working on this should be done using an isolation transformer. With your symptoms, it is likely one side of the power amp MAY be blown, but do check that the wiring hasn't fallen off and the jack itself. Two pairs of wires come from the power amp to the front panel jacks. document location of ALL the cables you disconnect as they CAN be confusing to restore.