In article , Trevor Wilson
wrote:
On 31/05/2016 9:13 PM, Dave Plowman (News) wrote:
In article ,
Phil Allison wrote:
** The simple solution is to add a DPDT relay to mute both inputs of
the 405 whenever there is no AC power.

Ideally, a miniature sealed type with gold contacts powered by
rectified AC from the secondary of the transformer - plus a suitable
series resistor.

You can use the contacts to either ground the two signals or open
circuit them.

Snag is this squawk happens immediately at switch off. So the relay
would have to operate extremely quickly.

**Phil's idea is a good one. I used exactly that solution a short time
back with a Sony integrated amp. The preamp section was going unstable
at switch-off. The job was rapidly becoming unviable, so, after
consultation with the client, he agreed that a fast operating relay
would be acceptable. I used it to short the output of the preamp to
earth at switch-off. Perfect solution. Not ideal, but it does work well.

IIRC The Quad 34 has a circuit that clamps the output to ground as soon as
the rails start to fall when you switch it off.

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

In article ,
Jim Lesurf wrote:
I was more hoping someone could come up with why some of these
crossovers squawk, but some not.

I guess that we can't say much more than the obvious. i.e. that
something is different between examples of amps and crossovers/speakers!
Not exactly news for you. :-/

I've never seen an AM8/16 so have no idea what changes the BBC people
may have made. I can't tell if the 'quawk' is due to a protection
circuit rattling on and off, bursts of RF instability, or what. Might be
fixable by a bigger output inductor or a cap in just the right place.
But where?...

Thought I'd made it fairly clear. If you remove the power to the crossover
PCB while leaving the amp powered up, you get the squawk. Leave the power
off that PCB, and the Quad part powers up and off normally.

Ideally, you'd be best asking in some place were ancient BBC engineers
are listening. But again, I'm not sure where to suggest!

Finding one who knows the design intimately is the problem. As an aside,
noticed the Keith Snooks site seems to have disappeared too. Everyone is
getting old.

--
*All those who believe in psychokinesis, raise my hand *

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

In article ,
Trevor Wilson wrote:
Snag is this squawk happens immediately at switch off. So the relay
would have to operate extremely quickly.

**Phil's idea is a good one. I used exactly that solution a short time
back with a Sony integrated amp. The preamp section was going unstable
at switch-off. The job was rapidly becoming unviable, so, after
consultation with the client, he agreed that a fast operating relay
would be acceptable. I used it to short the output of the preamp to
earth at switch-off. Perfect solution. Not ideal, but it does work well.

But not really an answer to my question, thanks.

It's an fairly obvious 'cure' although might well not be perfect in
practice.

--
*ONE NICE THING ABOUT EGOTISTS: THEY DON'T TALK ABOUT OTHER PEOPLE.

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

In article , Dave Plowman (News)
wrote:
I've never seen an AM8/16 so have no idea what changes the BBC people
may have made. I can't tell if the 'quawk' is due to a protection
circuit rattling on and off, bursts of RF instability, or what. Might
be fixable by a bigger output inductor or a cap in just the right
place. But where?...

Thought I'd made it fairly clear. If you remove the power to the
crossover PCB while leaving the amp powered up, you get the squawk.
Leave the power off that PCB, and the Quad part powers up and off
normally.

OK. Then maybe a circuit on the *input* of the 405 that duplicates what it
sees from the output mute on the 34 might help? IIRC this just clamps the
signal line to ground using a bipolar.

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

In article , Dave Plowman (News)
scribeth thus
In article ,
Trevor Wilson wrote:
Snag is this squawk happens immediately at switch off. So the relay
would have to operate extremely quickly.

**Phil's idea is a good one. I used exactly that solution a short time
back with a Sony integrated amp. The preamp section was going unstable
at switch-off. The job was rapidly becoming unviable, so, after
consultation with the client, he agreed that a fast operating relay
would be acceptable. I used it to short the output of the preamp to
earth at switch-off. Perfect solution. Not ideal, but it does work well.

But not really an answer to my question, thanks.

It's an fairly obvious 'cure' although might well not be perfect in
practice.



Seems that this is in the BBC designed bit of the amp?.

Have you got the circuit for that particular variant unit Dave;?..

Phil's idea is a good one but in this instance there is another fault
thats causing a problem that shouldn't be there.

Makes me wonder if thats having an effect on the signal path?

Got a sack of mini relays made by Pickering used by Neve and Audix if
you want a few, only problem is there're 24 volt ones....

--
Tony Sayer

Ideally, you'd be best asking in some place were ancient BBC engineers
are listening. But again, I'm not sure where to suggest!




Finding one who knows the design intimately is the problem. As an aside,
noticed the Keith Snooks site seems to have disappeared too. Everyone is
getting old.



His phone number is on here..

As to ageing your bloody right there...


http://www.dc-daylight.ltd.uk/
--
Tony Sayer

In article ,
tony sayer wrote:
But not really an answer to my question, thanks.

It's an fairly obvious 'cure' although might well not be perfect in
practice.



Seems that this is in the BBC designed bit of the amp?.

Yes.

Have you got the circuit for that particular variant unit Dave;?..

I think so. I have three versions of the schematic but this amp is a
fairly late one and appears to have the latest of the ones I've seen.
That's not to say there isn't an even later version.

If you'd like it, I'll post a link to it - but you've probably got it
anyway.

Phil's idea is a good one but in this instance there is another fault
thats causing a problem that shouldn't be there.

Quite.

Makes me wonder if thats having an effect on the signal path?

Got a sack of mini relays made by Pickering used by Neve and Audix if
you want a few, only problem is there're 24 volt ones....

Got loads of suitable relays here too.

Not a lover of relays in a signal path, though.

We had an inline monitoring 48/4/2 Neve at Thames with thousands of the
bloody things always giving problems. ;-)

--
*Caution: I drive like you do.

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

On 2/06/2016 9:42 AM, Dave Plowman (News) wrote:
In article ,
tony sayer wrote:
But not really an answer to my question, thanks.

It's an fairly obvious 'cure' although might well not be perfect in
practice.



Seems that this is in the BBC designed bit of the amp?.

Yes.

Have you got the circuit for that particular variant unit Dave;?..

I think so. I have three versions of the schematic but this amp is a
fairly late one and appears to have the latest of the ones I've seen.
That's not to say there isn't an even later version.

If you'd like it, I'll post a link to it - but you've probably got it
anyway.

Phil's idea is a good one but in this instance there is another fault
thats causing a problem that shouldn't be there.

Quite.

Makes me wonder if thats having an effect on the signal path?

Got a sack of mini relays made by Pickering used by Neve and Audix if
you want a few, only problem is there're 24 volt ones....

Got loads of suitable relays here too.

Not a lover of relays in a signal path, though.

We had an inline monitoring 48/4/2 Neve at Thames with thousands of the
bloody things always giving problems. ;-)


**I'll bet they weren't decent, hermetically sealed, gold contact types,
nor were they used to short the signal to earth. If such relays are used
in that type of application, they almost never exhibit problems.
Whenever I see a product with those clear topped, non-sealed DIL relays,
I know exactly what needs to be done. When the relay is replaced with a
proper one, I never see the job back. There are relays and there are
decent quality relays.

--
Trevor Wilson
www.rageaudio.com.au

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Trevor Wilson wrote:



Got a sack of mini relays made by Pickering used by Neve and Audix if
you want a few, only problem is there're 24 volt ones....

Got loads of suitable relays here too.

Not a lover of relays in a signal path, though.

We had an inline monitoring 48/4/2 Neve at Thames with thousands of the
bloody things always giving problems. ;-)


**I'll bet they weren't decent, hermetically sealed, gold contact types,
nor were they used to short the signal to earth. If such relays are used
in that type of application, they almost never exhibit problems.



** Pickering (of the UK) relays are ALL reed types - so have glass encapsulated contacts. They feature Mu-metal shielding and are rated for millions of operations - certainly not a cheap component.

http://www.pickeringrelay.com/


Whenever I see a product with those clear topped, non-sealed DIL relays,
I know exactly what needs to be done. When the relay is replaced with a
proper one, I never see the job back. There are relays and there are
decent quality relays.

** The non sealed types I have come across develop bad contacts ( high resistance) and cleaning them is PITA.


..... Phil

On Thu, 2 Jun 2016 04:29:14 -0700 (PDT), Phil Allison
wrote:

Trevor Wilson wrote:



Got a sack of mini relays made by Pickering used by Neve and Audix if
you want a few, only problem is there're 24 volt ones....

Got loads of suitable relays here too.

Not a lover of relays in a signal path, though.

We had an inline monitoring 48/4/2 Neve at Thames with thousands of the
bloody things always giving problems. ;-)


**I'll bet they weren't decent, hermetically sealed, gold contact types,
nor were they used to short the signal to earth. If such relays are used
in that type of application, they almost never exhibit problems.



** Pickering (of the UK) relays are ALL reed types - so have glass encapsulated contacts. They feature Mu-metal shielding and are rated for millions of operations - certainly not a cheap component.

http://www.pickeringrelay.com/


Whenever I see a product with those clear topped, non-sealed DIL relays,
I know exactly what needs to be done. When the relay is replaced with a
proper one, I never see the job back. There are relays and there are
decent quality relays.

** The non sealed types I have come across develop bad contacts ( high resistance) and cleaning them is PITA.


.... Phil

Mosfets are an excellent alternative to relays these days. On
resistance of a few milliohms in cheap packages.

d

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