[dcs]

Hi,

A quick question - during bias setup I noticed that when the power to the amp was turned off, the offset voltage rose from around 130mv to about 11V.  Is this to be expected? Is it correct to assume that this voltage would be drained by the speaker load under operating conditions?

Many thanks,
Dave

P.S. If I am going to get as much enjoyment from listening to this beast as I have had so far in building it, then it will have been the best investment I have made in a long time! Many thanks are due to Hugh.

[AKSA]

Dave,

Yes, offset does rise at switch off.

However, it is infrasonic, no noise is produced, and dissipation in the voice coil is 12W for around half a second.

Since most speaker drivers will handle at least 40W continuous for hours on end, this is never a problem, even for a Lowther, and you can safely ignore it.  The cone will move to its full excursion, but this will not in any way damage the speaker because it's happening so slowly and for such a short duration.

I'm delighted you enjoyed the build!

Cheers,

Hugh

[andyr]

Hi,

... during bias setup I noticed that when the power to the amp was turned off, the offset voltage rose from around 130mv to about 11V.

Dave, if your output offset is 130mV BEFORE you switched off then I would've thought this needs some resistor adjustment to get it down to the figure which Hugh recommends ... less than (preferably a LOT less than) 50mV.

Hugh's instructions tell U what U need to do.

Regards,

Andy

[dcs]

Wow - thanks for the prompt replies, and thanks for the answer - my curiosity is salved (for now).

Dave