Arcam Alpha 8R that sounds harsh

[theFan667]

Hi,

I've got an Alpha 8R integrated amp and also the matching Alpha 8 power amp.

I was originally biamping some Kef Q900 speakers with the integrated on the high frequencies and the power amp on the low frequencies but i soon felt like the sound was kind of hurting my ears - the high frequencies made me wince. It wasn't obvious and I thought it might be that the speakers needed breaking-in (i bought them new) but it didn't go away.

I removed the power amp and used the only the integrated - the harshness was still there.

I used the integrated solely as a preamp into the power amp and the harshness disappeared which tells me the issue is likely in the power amp section of the integrated.

According to the service manual the power amp circuit of the integrated is the same as the power amp's circuit.

Does anyone have any suggestions as to what i should try first? Maybe this symptom commonly points to a specific problem?

The service manual specifies a bunch of test points and their expected voltages so without any further info this would be my first step - testing the voltages to see if they match the service manual.

I'm an electronics engineer but haven't done much analog stuff since i left school but i do have a scope/dmm/decent soldering gear.

Any advice would be appreciated.

Thanks,
Tim

 

[JonSnell Electronic]

Are you using an active or passive crossover or no crossover?

 

[theFan667]

Are you using an active or passive crossover or no crossover?

The Kef Q900 have a passive crossover internal to the speaker cabinet that i haven't touched. They also each have 4 binding posts for bi-amping but in my latest tests I added the jumpers and used only a single power amp:
- integrated (alpha 8R) -> speaker is harsh
- integrated's pre-out (alpha 8R) -> seperate power amp (alpha 8) -> speaker is not harsh

I'm not 100% sure i'm understanding your question.

 

[JonSnell Electronic]

Just making sure no bass is getting to the tweeter because that would cause a harsh sound if the crossover was not stopping LF to the tweeter.

 

[Ian Finch]

Both 8R and 8P amplifiers are stereo so it begs the question as to whether the harshness is with one or both channels. 'Easy enough to listen to both channels alternately, ideally with a with a mono signal, and post.

 

[AndrewT]

The one or both channels will be useful feedback.

I would suggest you take those test point measurements for all 4 channels and post here.

But be careful, a slipped probe could seriously damage the amplifier.
Insulate the exposed metal legs of the probes to leave just about 1 to 2mm at the ends.

The scope will show up early clipping of a test signal.
It will also show up excessive overshoot and/or ringing of the test signal.

Unfortunately it alone cannot show excessive harmonic distortion, nor crossover distortion.