Yamaha DSP A2070
 

Just to say thanks to all for the tips - a couple of 10µF electrolytics
mounted on the PCB sorted it.

Only thing is what to do with it now - it's a great lump of a thing. Ebay?

--
*Why do we say something is out of whack? What is a whack? *

Dave Plowman London SW
To e-mail, change noise into sound.

Yamaha DSP A2070
 

On Sat, 21 Nov 2009 13:20:40 +0000 (GMT), "Dave Plowman (News)"
wrote:

Just to say thanks to all for the tips - a couple of 10µF electrolytics
mounted on the PCB sorted it.

Only thing is what to do with it now - it's a great lump of a thing. Ebay?

Sounds like a good idea. It was interesting to see how a real consumer
manufacturer approaches the tricky business of cost-cutting. And I
wonder how many died through oscillation. Warrantee repairs are
horribly expensive things to deal with.

d

Yamaha DSP A2070
 

In article , Don Pearce
wrote:
On Sat, 21 Nov 2009 13:20:40 +0000 (GMT), "Dave Plowman (News)"
wrote:

Just to say thanks to all for the tips - a couple of 10µF
electrolytics mounted on the PCB sorted it.

Only thing is what to do with it now - it's a great lump of a thing.
Ebay?

Sounds like a good idea. It was interesting to see how a real consumer
manufacturer approaches the tricky business of cost-cutting.

There may be swings and roundabouts. Many years ago I decided to avoid
using rail-ground-rail caps on the amp board as they tend to inject
distortion from half wave ripple into the amp via any ground imperfections.
But you then need to ensure the amplifier has an inherently high ability to
ignore rail variations.

And I wonder how many died through oscillation. Warrantee repairs are
horribly expensive things to deal with.

Given the above was the cause of the problem I'm curious as to why the
oscillations waited until after warranty. :-) Gives me the feeling that
something else has degraded.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Yamaha DSP A2070
 

"Don Pearce" wrote in message
...
On Sat, 21 Nov 2009 13:20:40 +0000 (GMT), "Dave Plowman (News)"
wrote:

Just to say thanks to all for the tips - a couple of 10µF electrolytics
mounted on the PCB sorted it.


Dear oh dear, when is it ever anything else other than caps or dry joints?



Only thing is what to do with it now - it's a great lump of a thing. Ebay?

Sounds like a good idea.



You think so, do you? There's one on eBay in the West Midlands (collect
only) still at *99p* for the next two and a bit days:

120494159176

Or, if you can't be asked to go yourself (or put a courier in) to collect
and want it delivered, there's one in Claremont NH for a whole 27 quid and
*only 280 quid* shipping, but be quick, there's only an hour left on it:

280422224601


I got a better idea, but he'll need a length of rope with a noose in it and
he'll have to haul it up to the Thames....


:-))


Note to self: if it gets any sillier than this in here, then the plug
*must* be pulled - it's a *terrible waste* of one's lifespan...

Yamaha DSP A2070
 

On Sat, 21 Nov 2009 13:54:53 +0000 (GMT), Jim Lesurf
wrote:

In article , Don Pearce
wrote:
On Sat, 21 Nov 2009 13:20:40 +0000 (GMT), "Dave Plowman (News)"
wrote:

Just to say thanks to all for the tips - a couple of 10µF
electrolytics mounted on the PCB sorted it.

Only thing is what to do with it now - it's a great lump of a thing.
Ebay?

Sounds like a good idea. It was interesting to see how a real consumer
manufacturer approaches the tricky business of cost-cutting.

There may be swings and roundabouts. Many years ago I decided to avoid
using rail-ground-rail caps on the amp board as they tend to inject
distortion from half wave ripple into the amp via any ground imperfections.
But you then need to ensure the amplifier has an inherently high ability to
ignore rail variations.


That is where really well designed grounding is vital. Stars rule!

And I wonder how many died through oscillation. Warrantee repairs are
horribly expensive things to deal with.

Given the above was the cause of the problem I'm curious as to why the
oscillations waited until after warranty. :-) Gives me the feeling that
something else has degraded.


If oscillation started because of the inevitable degradation of a
component (a cap losing value somewhere, maybe?) then they didn't go
through the design centering stage of development. A "what happens
if..." scenario chase is really quite important.

Here's a little stability thought I've been pondering - and modelling
in Spice. Cdom goes around the voltage amplifier, then the output
stage follows. Now, if the output stage is simply a voltage follower
with no gain or inversion, why would I not connect Cdom to the output
of that stage, rather than just the one transistor's collector? Would
that not give an advantage for HF distortion suppression, since it
would not matter that the overall feedback was degraded by lost HF
gain in the V amp...


d

Yamaha DSP A2070
 

In article , Don Pearce
wrote:
On Sat, 21 Nov 2009 13:54:53 +0000 (GMT), Jim Lesurf
wrote:

There may be swings and roundabouts. Many years ago I decided to avoid
using rail-ground-rail caps on the amp board as they tend to inject
distortion from half wave ripple into the amp via any ground
imperfections. But you then need to ensure the amplifier has an
inherently high ability to ignore rail variations.


That is where really well designed grounding is vital. Stars rule!

Ideally. The snag is ensuring that the stages well clear of the chosen
point are still happy with ground or rail impedances at ultrasonic/RF that
aren't zero. I used to deal with that by making as many stages as I could
either common mode differential, or hang via constant current or current
mirrors. Then the rails can flap about all over the show, but provided they
have voltages that are 'enough' the amp can ignore all the flapping. :-)

And I wonder how many died through oscillation. Warrantee repairs are
horribly expensive things to deal with.

Given the above was the cause of the problem I'm curious as to why the
oscillations waited until after warranty. :-) Gives me the feeling
that something else has degraded.


If oscillation started because of the inevitable degradation of a
component (a cap losing value somewhere, maybe?) then they didn't go
through the design centering stage of development. A "what happens
if..." scenario chase is really quite important.

Well, to be fair, you can always find failure modes once you accept that
eventually a component will fail or change.

Here's a little stability thought I've been pondering - and modelling in
Spice. Cdom goes around the voltage amplifier, then the output stage
follows. Now, if the output stage is simply a voltage follower with no
gain or inversion, why would I not connect Cdom to the output of that
stage, rather than just the one transistor's collector? Would that not
give an advantage for HF distortion suppression, since it would not
matter that the overall feedback was degraded by lost HF gain in the V
amp...

Not sure ATM. TBH I never used to approach design of power amps that way.
:-)

If you look back at the 700 amp design there isn't an explicit Cdom cap
shoved in at the end of the voltage gain sections. Instead I put a snubber
on the front long-tailed pair and got it to be stable with that.

That said, I also linked the drivers to the output so they could shunt past
the output devices if they weren't able to keep up with any HF. I also
though this would help to 'fill in' as a quasi-class-A stage driving the
output. Bit like current dumping.

I know Doug Self did a lot of models, etc, of various o/p arrangements. But
I found the above simply worked better even if his results indicated
otherwise. Presumably because this all depends on the specific details of
the devices, etc, etc. I also found that tiny movements of the wiring loom
altered the performance. Can't recall anyone in a book dealing with that.

IIRC I tended to dislike having large caps in the output area as it seemed
to just give problems with slew limiting. But I am trying to recall decades
ago, so I'm sure I've forgotten most of this! :-)

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Yamaha DSP A2070
 

In article ,
Don Pearce wrote:
On Sat, 21 Nov 2009 13:20:40 +0000 (GMT), "Dave Plowman (News)"
wrote:

Just to say thanks to all for the tips - a couple of 10µF electrolytics
mounted on the PCB sorted it.

Only thing is what to do with it now - it's a great lump of a thing.
Ebay?

Sounds like a good idea. It was interesting to see how a real consumer
manufacturer approaches the tricky business of cost-cutting. And I
wonder how many died through oscillation. Warrantee repairs are
horribly expensive things to deal with.

To be fair it did work just fine for some 15 years.

d

--
*A conscience is what hurts when all your other parts feel so good *

Dave Plowman London SW
To e-mail, change noise into sound.

Yamaha DSP A2070
 

In article ,
Keith G wrote:

"Don Pearce" wrote in message
...
On Sat, 21 Nov 2009 13:20:40 +0000 (GMT), "Dave Plowman (News)"
wrote:

Just to say thanks to all for the tips - a couple of 10µF
electrolytics mounted on the PCB sorted it.


Dear oh dear, when is it ever anything else other than caps or dry
joints?

Expert now, are you? Try reading the rest of the thread before jumping in
with your pearls of wisdom.



Only thing is what to do with it now - it's a great lump of a thing.
Ebay?

Sounds like a good idea.



You think so, do you? There's one on eBay in the West Midlands (collect
only) still at *99p* for the next two and a bit days:

120494159176

Which part of 'well used' 'getting on a bit' 'sold for spares or repair'
didn't you understand?

Or, if you can't be asked to go yourself (or put a courier in) to
collect and want it delivered, there's one in Claremont NH for a whole
27 quid and *only 280 quid* shipping, but be quick, there's only an
hour left on it:

280422224601

No manual or remote and sold by a dealer in junk.

There are two others (in the UK) described as being in good condition
which have several days to run. I'll see what they make.


I got a better idea, but he'll need a length of rope with a noose in it
and he'll have to haul it up to the Thames....

If it was attached to you it would be worth every penny. ;-)

--
*There are two kinds of pedestrians... the quick and the dead.

Dave Plowman London SW
To e-mail, change noise into sound.

Yamaha DSP A2070
 

Dave Plowman (News) wrote:
In article ,
Don Pearce wrote:
On Sat, 21 Nov 2009 13:20:40 +0000 (GMT), "Dave Plowman (News)"
wrote:

Just to say thanks to all for the tips - a couple of 10µF electrolytics
mounted on the PCB sorted it.

Only thing is what to do with it now - it's a great lump of a thing.
Ebay?

Sounds like a good idea. It was interesting to see how a real consumer
manufacturer approaches the tricky business of cost-cutting. And I
wonder how many died through oscillation. Warrantee repairs are
horribly expensive things to deal with.

To be fair it did work just fine for some 15 years.

Yeah, Ive got two Yam AX-496 85 watt/channel amps, both still pumping out a fine
sound (IMHO) all these years later.

Yamaha DSP A2070
 

"Dave Plowman (News)" wrote in
message
Just to say thanks to all for the tips - a couple of 10µF
electrolytics mounted on the PCB sorted it.

You're saying that it is now working 100% - none of the origional
symptomology?