# Arc Audio 4050 - one of four channels is boosted



## aaron_T (Sep 5, 2011)

I'm hopeful for some assistance with an Arc Audio 4050 XXK v2 amplifier. It's a 4 channel amp and was purchased used via this forum several years ago. I've had it in service during this time and have always thought something is up with the balance on the rear output channels. Today I pulled it to take some measurements as follows:

- amp powered on bench with a 12V battery
- set amp to 2 channel input mode, 4 channel stereo output
- crossovers set to full, bass boost 0db

- phone connected to front input of amp
- played 800Hz sine wave with Audio Tool app
- phone volume set full
- varied amp gain for front and rear channels equally
- measured AC voltage of amp output channels

My suspicions are confirmed. The Rear Left channel is boosted compared to the other three as follows when increasing gains:
FL, FR, RR = 1.0VAC ---> RL = 1.9VAC
FL, FR, RR = 1.5VAC ---> RL = 2.35VAC
FL, FR, RR = 2.0VAC ---> RL = 3.0VAC

I'm not afraid to get inside the amp to take additional measurements and hopefully make a repair, but this is not my area of expertise.

Can someone provide some guidance on what to check next or some ideas on how to repair this amp? Thanks for replies.


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