RFI/EMI interference

[drummerman]

 

[drummerman]

I've got hold of some Ferrite clamps and fitted them on every cable entering the amplifier, including speaker leads and interconnects but not the power cable. Here if fitted the core to the internal powersupply cabling leaving the transformer.

I then shielded internal cabling from alps pot the the pcb and speaker terminal to pcb carefully with copper tape. I also shielded the RCA sockets internally.

Result; Unfortunately I dont have the equipment to measure this but subjectively at least ... cleaner treble, less hash, less harshness and more dimensionality to sound. This was no more apparent than on the interconnect from cd player to amplifier (a wide band design).

Of course this could be a placebo effect without the benefit of an abx test but I somehow doubt it. It is not subtle.

Next, I will experiment with bias idling current. I measured DC offset and the bias current (low) and would say there are most probably some benefits to be gained. I am aware of some theories that there is an 'ideal' bias adjustment but I believe it is not as clear cut and simple as that and there is enough evidence around to suggest it is worth experimenting with this aspect. Whilst any deviation from the spec sheet may be a compromise and could potentially be offset with an increase in distortion elsewhere in the spectrum it could be very beneficial to raise current. Longevity or amplifier failure can be an issue if done wrong so dont try this yourself unless etc etc . - I will give it a go and report back on this. Most commercial amplifiers are factory set at a save level which is often below ideal.

Forgot to mention, the amplifier is not Class A by design so comparativly small heatsinking and the output devices heat dissipation ability will limit what can be done. Results to follow.

regards

 

[chebby]

Forgot to mention, the amplifier is not Class A by design so comparativly small heatsinking and the output devices heat dissipation ability will limit what can be done. Results to follow.

 

[drummerman]

I am wearing my lucky beanie ...

regards

 

[drummerman]

Well, happy Sunday everone!

On a less happy note, chebby's dooms day prediction came true ... she blew ...

Not perhaps for the reasons expected but by being ham fisted :O

I was happily adjusting the idle current and after some time reached a state which didn't get the heat sinks cooking. This was some 35% above factory setting and still within what shouldnt affect long term operation.

Then I slipped a probe.

The result, a shorted rectifier diode. There may be more damage but thats as far as I got. Currently over at DIY Audio to try and find a match as the things this amplifier uses are rather hard to obtain.

As to sound quality with the increased bias, difficult to describe precisely in the short time I enjoyed it (!) but it seemed subjectively like everything was just a little 'tighter and faster' with a little bit less grain. The difference wasn't huge but it was there.

I'll give an update when I replace the rectifiers and do some more testing ... very carefully.

regards