Arcam D290 Right Channel fault?

[IansMusical]

Hello Everyone,

Can anyone shed some light on this problem please?

I have two Arcam D290s used in a bi-amp setup driving a pair of Acoustic Energy AE109s. Obviously the top amp is driving the tweeters and the bottom amp the bass. Both amps have the Direct button on, so bypassing the tone controls.

What I've found is that the output on the right channel of the bass amp is about 3dB lower than the left channel bass. To put another way it's like someone has turned the bass control down on that speaker! The tweeters both left and right are not affected in anyway, so I'm presuming I have a fault on the bass amps' right channel?

I do have the circuit diagrams but not sure where to start :-) Have verified the cable link between the amps and the speakers themselves by swapping the inputs etc.

Has anyone experienced this or know what the fault could be???

Thanks for any help,

Ian

[anatech]

Hi Ian,
Any way to send the diagram? My email is bhome at sympatico dot ca .

I am thinking the cap in the feedback circuit to ground is going open. I don't know if your amp uses it, but it is common. The diagrams will confirm or deny this. If it's something else, we need to look at the diagram for sure.

-Chris

[jaycee]

Does the sound crackle if you wiggle the Direct button about ? If it does, it's as simple as a dirty switch.

[IansMusical]

Hi Jaycee!

Thanks for your response and sorry for my delay in checking for postings!

I've tried wiggling the direct button but I'm thinking that it won't be in the circuit on the bass amp as it is this amp that's in power amp mode... being fed from the treble amp. Therefore I think whatever comes in through the power amp in sockets is directly amplified. I know for example that the tone controls do not operate but of course they will on the treble amp.

Thanks,

Ian

[anatech]

Hi Ian,
If you have an oscilloscope, look at the output of the DC servo (pin 6 NE5534). Look to see how much audio there is there (should be none or very, very little). You could also run a frequency generator in to see if the gain loss is frequency dependant.

If that's okay, check the ratio of R23 and R24. They set the gain.

-Chris

[IansMusical]

Hi Chris,

Thanks for getting back me :-) Unfortunately I don't have an oscilloscope or access to one (knew I shouldn't have sold the one I had!)

I did try listening regards frequency response, obviously only bass and mid frequencies are present but I noticed that it's only the lowest ones that are missing, so those covering the bass guitar or those that shake the floor for example ;-)

Is there any mileage without having an oscilloscope in comparing voltages between the two amps with them being identical and with no signal going in etc?

I should also point out that the left speaker is in an alcove, whereas the right isn't. However, I've moved the left one out and it didn't really make any difference as I know alcoves enhance bass.

With this information do you have any further ideas?

Thanks again,

Ian

[anatech]

Hi Ian,
Place the speakers beside each other to compare.

To run frequency tests, you need a full range speaker and signal sweep. It's meaningless otherwise. An oscilloscope and oscillator are the tools of choice here. A sound card and oscillator program will work.

I don't trust most meters for AC frequency response, the 87 series from Fluke is an exception. The rest you may as well just make the numbers up.

See if you can borrow a 'scope and oscillator. Strange, once a person owns an oscilloscope, they'll never be without one. It's a basic tool that I could not do without. I made sure I kept my test equipment when I sold my shop.

-Chris