Moddeed Cambridge Audio 340A SE buzz problem

[mikesnowdon]

Originally posted by big1
I have a buzzing thought the tweeters if i undo the interconnections between the amp /pre/cdp . seems like a earth problem ,to fix it I fiddle with the interconnections till it go`s away.

Nice idea but the amp has this buzz even with nothing connected to it.

[Stream]

Try in another room

I took my 340 back, so i think at weekend i can measure any voltages, and carefully listen to find any buzzing

[big1]

Originally posted by mikesnowdon


Nice idea but the amp has this buzz even with nothing connected to it.

Mine too would buzz even with nothing connected. Thought two amps ,one for each speaker cleaned the ground wire /uplift the ground earth on one amp/ ajusted the IC`s no buzz.

[mikesnowdon]

Originally posted by big1


Mine too would buzz even with nothing connected. Thought two amps ,one for each speaker cleaned the ground wire /uplift the ground earth on one amp/ ajusted the IC`s no buzz.

Are you talking about rearranging the cables so no mains runs paralell to an IC etc...?

I'll give it a go then.

[mikesnowdon]

Originally posted by Stream
Try in another room

I took my 340 back, so i think at weekend i can measure any voltages, and carefully listen to find any buzzing

That would be interesting to see if you have any buzzing. I think yours is quite new? It should be quite silent really, i wouldnt expect it to buzz at all....

Have you made any modifications?

[mikesnowdon]

340A Power amp and PSU modding:

CA 340A SE LM3886 based amp - Upgrade advice please.

[Stream]

Hi. I tryed to listen my 340 in silence... It has not any buzzing. I hear very litle hissing from from very close distance to lodspeakers, but I dont her this from listening place

But my Audigy2 Value has one issue - it has buzzing+hissing on left channel, not constant and not loud... It is audible, when music is stopped, and also with high -gaine amps (i tryed with car Adagio 4ch.- amp)

[mikesnowdon]

regarding my buzzing problem:

Can anyone tell me what the "DC offset detect" circuit is doing? This is one area I havent investigated as a possible cause of buzzing. When I did the first round of mods I had a loud buzz on the first powerup. I shut it down and tried again with vol at zero - same thing happened. On the third attemp everything seemed fine until later that night I noticed this faint buzzing form one speaker. Could something have gone in the DC detect circuit which would cause a buzzing sound? (Details of what I have done so far to try and solve the buzzing can be found-here.

Also I would like to know if Im ok to disable the DC detect and how? This way I can easilly test if its the cause of my problem.

Thanks.

Mike.

(Reminder: I have the Service Maual if anyone would care to take a look. Thanks, Mike.)

[mikesnowdon]

Hi.

It seems the DC offset detect is part of a speaker protection function where abnornal DC offset triggers the output relay to fall open. Its unlikeley this would cause any buzzing then.

Im all out of ideas on how to solve this which is a real bummer as Ive been studying to circuit and theres lots of room for improvement in this amp. Ive allready bought some nice components to use but theres no point untill I get this buzz sorted. I have asked Brent @ audioupgrades.co.uk to take a look and hes cool with it. I just need to send it up to him.

Is there aything else I can try before I send it away to the hi-fi hospital?

Mike

[mikesnowdon]

Hi.

Ive finally got a service manual for the SE version. This has enabled me to study the i-Pod connection and its dedicated buffer cicuit. When an i-Pod (or other source) is connected via the front panel jack socket a realy switches in the opamp, also switching the selector ic and input buffer out of the signal path.

I plugeed in a phono lead with nothing connected, the relay clicked and I checked for the buzzing which was still there. This could indicate that the selector ic and input buffer circuit are actually fine, meaning there could be fault in the i-Pod buffer circuit? The only way to know for sure would be to disconnect the supplies to the selector ic and input buffer and disconnect them from ground. I'll also disconnect them from any signal traces and see if the buzz is still there.

I'll investigate when I replace some more components. I have new diodes and power caps for the poweramp PSU to fit.

Mike.