One of the Quad 405 amps driving my LS5/8 makes the most enormous 'bang'
through the bass unit about once a day. Wondered what it was first time I
heard it - thought something very heavy had fallen over. Now I know what
it is, it is preceded by low level hum for a few seconds then the bang - I
assume a cap discharging. Allegedly, the amps had a full overhaul before I
bought them including all new electrolytics. I suppose the power supply
ones can be ruled out since it's only the bass amp. Of course it might be
one in the crossover. Am I right in thinking it's more likely to be an
electrolytic? And presumably near the front end if it's producing a near
full power thump?

--
*Rehab is for quitters

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

"Dave Plowman (News)"

One of the Quad 405 amps driving my LS5/8 makes the most enormous 'bang'
through the bass unit about once a day.

** Quad 405 mk1 or mk2 ?


Wondered what it was first time I
heard it - thought something very heavy had fallen over. Now I know what
it is, it is preceded by low level hum for a few seconds then the bang - I
assume a cap discharging.

** Very unlikely.


Allegedly, the amps had a full overhaul before I
bought them including all new electrolytics. I suppose the power supply
ones can be ruled out since it's only the bass amp.

** It's not a bad electro cap at all.

Of course it might be one in the crossover.


** FFS - unplug whatever is feeding the 405.

It must make the noise all on its own or it is not faulty.


Am I right in thinking it's more likely to be an electrolytic?


** No.

And presumably near the front end if it's producing a near
full power thump?

** No again.

Be smart to put a 1A fuse between each channel of the 405 and your woofers
until you have found the problem.


.... Phil

In article ,
Phil Allison wrote:

"Dave Plowman (News)"

One of the Quad 405 amps driving my LS5/8 makes the most enormous 'bang'
through the bass unit about once a day.

** Quad 405 mk1 or mk2 ?

Think they are MK1. But modified by the BBC (over the years) so may not be
exactly that now.

Wondered what it was first time I
heard it - thought something very heavy had fallen over. Now I know what
it is, it is preceded by low level hum for a few seconds then the bang - I
assume a cap discharging.

** Very unlikely.


Allegedly, the amps had a full overhaul before I
bought them including all new electrolytics. I suppose the power supply
ones can be ruled out since it's only the bass amp.

** It's not a bad electro cap at all.

Of course it might be one in the crossover.


** FFS - unplug whatever is feeding the 405.

The crossover is internal. Unplugging the signal feed makes no difference.
The 'noise' is being generated within the 405 + crossover.

It must make the noise all on its own or it is not faulty.


Am I right in thinking it's more likely to be an electrolytic?


** No.

And presumably near the front end if it's producing a near
full power thump?

** No again.

Be smart to put a 1A fuse between each channel of the 405 and your
woofers until you have found the problem.

It isn't over driving the bass unit.


Thanks for the answer - but it's been of no help whatsoever.

--
*Velcro - what a rip off!*

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

"Dave Plowman (Nutcase ****head)"

One of the Quad 405 amps driving my LS5/8 makes the most enormous
'bang'
through the bass unit about once a day.

** Quad 405 mk1 or mk2 ?

Think they are MK1. But modified by the BBC (over the years) so may not be
exactly that now.

** That is no help at all - ****head.



Wondered what it was first time I
heard it - thought something very heavy had fallen over. Now I know
what
it is, it is preceded by low level hum for a few seconds then the
bang - I
assume a cap discharging.

** Very unlikely.


Allegedly, the amps had a full overhaul before I
bought them including all new electrolytics. I suppose the power supply
ones can be ruled out since it's only the bass amp.

** It's not a bad electro cap at all.

Of course it might be one in the crossover.


** FFS - unplug whatever is feeding the 405.

The crossover is internal.

** Now you tell us .......


Unplugging the signal feed makes no difference.
The 'noise' is being generated within the 405 + crossover.

** That is no help at all - ****head.


Am I right in thinking it's more likely to be an electrolytic?


** No.

And presumably near the front end if it's producing a near
full power thump?

** No again.

Be smart to put a 1A fuse between each channel of the 405 and your
woofers until you have found the problem.

It isn't over driving the bass unit.


** So ****ing what ?

What it has done so far is no predictor of what it will do next.

Make my day - let it kill one of your antique woofers.


Thanks for the answer - but it's been of no help whatsoever.


** There is no way to "help" a know nothing ****head like you.

And not good reason to either.



.... Phil

In article , Dave Plowman (News)
wrote:
One of the Quad 405 amps driving my LS5/8 makes the most enormous 'bang'
through the bass unit about once a day. Wondered what it was first time
I heard it - thought something very heavy had fallen over. Now I know
what it is, it is preceded by low level hum for a few seconds then the
bang - I assume a cap discharging.

I don't know the cause. But I've been wondering if it might be something
like an intermittent connection of a power rail or ground that doesn't go
totally open, but very resistive, then clears again abruptly.

Have you opened it up to see if there is something obvious like a
rail/ground connection that needs tightening or resoldering? I'd check
things like any pushon connectors for rails/ground on the PCBs / reservoir
caps, diode bridge, etc. But I've not looked at the diagram and can't
recall any details. Nor have a 405.

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 ,
Phil Allison wrote:
** That is no help at all - ****head.

Says it all. Anyone who knows the 405 and has some ideas?

--
*If you must choose between two evils, pick the one you've never tried before

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

On Thu, 08 Aug 2013 17:02:27 +0100, "Dave Plowman (News)"
wrote:

In article ,
Phil Allison wrote:
** That is no help at all - ****head.

Says it all. Anyone who knows the 405 and has some ideas?

I can't offer any advice regarding the amp problem but, if it's any
consolation, that response by Phil is typical of him in most, if not
all, the groups he's posted to.

He seems to regard himself as an expert who "Doesn't Tolerate Fools
Gladly" and decides that, whenever he sees a posting from a percieved
'fool', he is duty bound to respond with a scathing reply.

It might be more effective if he didn't make the mistake of resorting
to words such as "****head" and the like which simply make him look
like your bog standard internet troll.

He does seem to have some knowledge of the subjects concerned but you
know what they say about the dangers of having a little knowledge...
--
Regards, J B Good

In article ,
Johny B Good wrote:
On Thu, 08 Aug 2013 17:02:27 +0100, "Dave Plowman (News)"
wrote:

In article ,
Phil Allison wrote:
** That is no help at all - ****head.

Says it all. Anyone who knows the 405 and has some ideas?

I can't offer any advice regarding the amp problem but, if it's any
consolation, that response by Phil is typical of him in most, if not
all, the groups he's posted to.

Oh indeed. Seen it for years.

He seems to regard himself as an expert who "Doesn't Tolerate Fools
Gladly" and decides that, whenever he sees a posting from a percieved
'fool', he is duty bound to respond with a scathing reply.

Funnily those who say they don't suffer fools gladly usually have some
massive personality problem. And he certainly proves that theory. Sad
lonely little man.

It might be more effective if he didn't make the mistake of resorting
to words such as "****head" and the like which simply make him look
like your bog standard internet troll.

He does seem to have some knowledge of the subjects concerned but you
know what they say about the dangers of having a little knowledge...

Can't see why he bothers replying if he has nothing constructive to say.

--
*Time is the best teacher; unfortunately it kills all its students.

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

In article ,
Jim Lesurf wrote:
In article , Dave Plowman (News)
wrote:
One of the Quad 405 amps driving my LS5/8 makes the most enormous
'bang' through the bass unit about once a day. Wondered what it was
first time I heard it - thought something very heavy had fallen over.
Now I know what it is, it is preceded by low level hum for a few
seconds then the bang - I assume a cap discharging.

I don't know the cause. But I've been wondering if it might be something
like an intermittent connection of a power rail or ground that doesn't
go totally open, but very resistive, then clears again abruptly.

Have you opened it up to see if there is something obvious like a
rail/ground connection that needs tightening or resoldering? I'd check
things like any pushon connectors for rails/ground on the PCBs /
reservoir caps, diode bridge, etc. But I've not looked at the diagram
and can't recall any details. Nor have a 405.

I'll have a look at all of those, Jim. It uses miniature spade connectors
for most the connections to each board. Dunno why. It's not an amp I'm
familiar with either - hence the question. Was hoping someone had come
across just this fault before and could put their finger on the cause.

--
*It sounds like English, but I can't understand a word you're saying.

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

On 8/08/2013 8:41 AM, Dave Plowman (News) wrote:
One of the Quad 405 amps driving my LS5/8 makes the most enormous 'bang'
through the bass unit about once a day. Wondered what it was first time I
heard it - thought something very heavy had fallen over. Now I know what
it is, it is preceded by low level hum for a few seconds then the bang - I
assume a cap discharging. Allegedly, the amps had a full overhaul before I
bought them including all new electrolytics. I suppose the power supply
ones can be ruled out since it's only the bass amp. Of course it might be
one in the crossover. Am I right in thinking it's more likely to be an
electrolytic? And presumably near the front end if it's producing a near
full power thump?


**Assuming it is not whatever is connected to the amp, then it is most
likely a semiconductor. Pull it out of the system, put it on the bench,
connect to a dummy load and a pair of speakers, through a couple of 100
Ohm resistors. Hit each semiconductor with your freezer spray. That
should isolate the faulty component.

--
Trevor Wilson www.rageaudio.com.au