Yamaha CA 800 right channel noise

dbdb

Member
Hey everyone.
I'd like some help diagnosing a hum (sounds more like white noise) coming from the right channel of my CA 800. I didn't notice it when I purchased it months ago because when the amp is cold it isn't audible. Hoping there's an easy enough fix for it.

Here's what I know:

-isn't audible for the first couple of minutes after power up
-right channel only
-noise drops slightly when I switch the audio muting to -20db
-noise gets way louder when I switch off the preamp coupler on the back
-no other switches or knobs change the noise
-I'm always running it in class A, but the noise is still there in class B

Really appreciate any advice on this. This amp sounds fantastic, otherwise.
Thanks!
 
Do you hear any music from that channel ?
Yes. It's not really noticeable at all when listening to most music. Quiet passages and silence are the only times I can hear it. I'm also not noticing any distortion at all in that channel. It's just noise at a low volume, and doesn't change volume when I turn the volume knob all the way up or down.
 
Yes. It's not really noticeable at all when listening to most music. Quiet passages and silence are the only times I can hear it. I'm also not noticing any distortion at all in that channel. It's just noise at a low volume, and doesn't change volume when I turn the volume knob all the way up or down.
But really I can only hear it when the room is silent. It doesn't really have any noticeable impact on the listening, I'd just like to fix it before it does, or potentially causes other problems
 
Could be and transistor , diode or cold solder connection within the right amplifier assembly.
Page 6 , step A . Check the voltage and try to adjust if needed. (primary stage Differential amplifier circuit current adjustment.)
Reading between the lines I think your about to jump on that poor C458 on the heatsink.
Maybe measure dc offset (mV, between red/black speaker posts) as per sm.
 
Reading between the lines I think your about to jump on that poor C458 on the heatsink.
Maybe measure dc offset (mV, between red/black speaker posts) as per sm.
Dc offset is not going to tell you squat about excessive floor noise in the amplifier assembly. I've never seen the thermal tracking C458 actually go bad in this model.I'm thinking a noisy transistor in the front end. Just wanted to see if the FET current was in the ballpark.
 
I would have thought that 200-300mV would be audiable?
Maybe time to buy that book and do some reading....
 
Hey again! Just seeing if I can revive this thread. Never got around to working on this amp until the other day (2 years later).
Checked the bias just as the manual says to, and found the idle current to be pretty far off. I maybe got a little hasty and dove right in to adjust the bias. Everything was going well, brought everything back to spec, hooked up speakers, and the noise that was there was almost gone on the right channel, and the left was perfectly quiet. Decided to open it up again to clean the bias pots thinking that might clean up the sound even more. I used crc qd electronic cleaner , gently worked the pots, and let it dry for a good 5-10 min before plugging it back in. I got everything close to perfect again on the right channel, and while adjusting the left channel in the normal A/B operation step, the two fuses on the right channel popped. I picked up some new fuses, but before I power it up again I wanted to get some opinions on whether I should check/test any specific components first. Nothing smelled bad and nothing looks burnt. Just don’t want to do any more damage (hopefully none has been done already besides the fuses).
Really appreciate any advice!
 
On the right channel outputs. Measure the resistance between the outputs cases(collector) and chassis ground. Should be infinite Ω's. (open) <------- Unplug the unit from the wall before doing this.
 
Did you re-install the mica insulators between the output transistors and the heatsink if you removed them?
 
On the right channel outputs. Measure the resistance between the outputs cases(collector) and chassis ground. Should be infinite Ω's. (open) <------- Unplug the unit from the wall before doing this.
I think I’m interpreting that correctly. I used the ground posts for the phono. Right channel red post shows infinite, and black terminal is showing 0.6 ohms
 
I think I’m interpreting that correctly. I
No....Clip your black test lead to the metal chassis(ground).. With the red test probe touch the output transistors metal cases one at a time..
 
Last edited:
Back
Top Bottom