[I tried posting this message before but it seems to have been lost in
the ether]

Does anyone have any advice to prevent the output stage from blowing
on these amps during regular (ie low volume) use. Mine has went a
couple of times (one channel dead each time). It's currently fixed and
I'd like to keep it like that.

Each time the problem occured was on power up (ie turned amp on and
one channel dead - on both times I had been listening at low volumes
the last time it was used).

I've heard various hypothetical reasons for why the problem that may
cause this - having a active source input when amp is off, setting a
selector to 'mute' etc. but as this is a fault that has been discussed
on the groups, does anyone have any experience in this area?

Also has anyone seen any similar problems on the later Cyrus Amps?

If the unit is old then the main rail smoothing caps are possibly low/leaky
and you would get rather a lot of ripple for the first few seconds after
switch on. This could cause instability and cause the outputs etc to fail.
re the need to have input muted- unnecessary- certainly the power amp
section can't get a signal if the volume is at the bottom. I suppose its
possible that if the input signal was at max amplitude the instant you
turned on it may allow some sort of pulse through- but the volume would have
to be turned up also!.
I'd get someone with a scope to check the ripple at switch on- the caps will
dry up with age and if you don't have smooth DC- but instead AC effectively
then the amp will/can protest.
Hope that helps
Andrew

"B." wrote in message
m...
[I tried posting this message before but it seems to have been lost in
the ether]

Does anyone have any advice to prevent the output stage from blowing
on these amps during regular (ie low volume) use. Mine has went a
couple of times (one channel dead each time). It's currently fixed and
I'd like to keep it like that.

Each time the problem occured was on power up (ie turned amp on and
one channel dead - on both times I had been listening at low volumes
the last time it was used).

I've heard various hypothetical reasons for why the problem that may
cause this - having a active source input when amp is off, setting a
selector to 'mute' etc. but as this is a fault that has been discussed
on the groups, does anyone have any experience in this area?

Hi JVC Dude,

Thanks for the info - this is consistant with my failures. The 2
smoothing Caps (rails post rectifier bridge but pre regulators) are
470uF marked as C67 and C68 on the board incase anyone else is
interested.

Also from the transformer (between Vcc and ground and -Vcc and ground)
there are a pair of 40V Slit Foil Electrolytic 7000uF caps. There are
also two 6.8nF non electrolytics's across the same rails - I assume
thes are to suppress spikes.

Finally, beyond the regulators (between Vreg and ground and -Vreg and
ground), there are also two 22uF electrolytics's across these rails.

Would you consider these sets of caps to be likely to cause any
problems also? [I can imagine the advice to be replace any
electrolytics..]

cheers for the info either way,
B.

The 470u and 22u are certainly worth replacing- it will improve the sound
also since each rail is better stabilised. You may even increase the value
slightly!! no more than double- since modern caps usually have a smaller
footprint for the rating.
As for the big 7000u again worth changing if 10yrs+ old. These beasties
don't fail that often but when they do its with catastrophic results.- as
you seem to have experienced already. Thats why its worth checking the
ripple present on a scope first to confirm. Even so the cost of £10-£15 for
ea isn't too expensive
Its not usually worth replacing ALL the caps- the vast majority of small
ones never have problems.

AW

"B." wrote in message
om...
Hi JVC Dude,

Thanks for the info - this is consistant with my failures. The 2
smoothing Caps (rails post rectifier bridge but pre regulators) are
470uF marked as C67 and C68 on the board incase anyone else is
interested.

Also from the transformer (between Vcc and ground and -Vcc and ground)
there are a pair of 40V Slit Foil Electrolytic 7000uF caps. There are
also two 6.8nF non electrolytics's across the same rails - I assume
thes are to suppress spikes.

Finally, beyond the regulators (between Vreg and ground and -Vreg and
ground), there are also two 22uF electrolytics's across these rails.

Would you consider these sets of caps to be likely to cause any
problems also? [I can imagine the advice to be replace any
electrolytics..]

cheers for the info either way,
B.