BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

I've just been lucky enough to have purchased a pair of the stunning
Rogers/BBC LS5/8 speakers, complete the with a pair of the BBC modified
Quad 405 frequency splitting amps (actually, one 405 and one 405-2...
no idea why!)

The main problem is that both amps exhibit a low level but perfectly
audiable mains hum - even with their gains right down and nothing
plugged into the (XLR) inputs. Am I right in thinking it's reasonably
easy to fix by changing some capacitors? Any help greatly appreciated!!

Many thanks.....

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

spwyatt wrote:

I've just been lucky enough to have purchased a pair of the stunning
Rogers/BBC LS5/8 speakers, complete the with a pair of the BBC modified
Quad 405 frequency splitting amps (actually, one 405 and one 405-2...
no idea why!)

The main problem is that both amps exhibit a low level but perfectly
audiable mains hum - even with their gains right down and nothing
plugged into the (XLR) inputs. Am I right in thinking it's reasonably
easy to fix by changing some capacitors? Any help greatly appreciated!!

Any 405 is pretty ancient by now. You should consider replacing all the
electrolytic caps.

Graham

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

"spwyatt" wrote in message
oups.com...


** Groper alert !

I've just been lucky enough to have purchased a pair of the stunning
Rogers/BBC LS5/8 speakers, complete the with a pair of the BBC modified
Quad 405 frequency splitting amps (actually, one 405 and one 405-2...
no idea why!)

The main problem is that both amps exhibit a low level but perfectly
audiable mains hum - even with their gains right down and nothing
plugged into the (XLR) inputs. Am I right in thinking it's reasonably
easy to fix by changing some capacitors? Any help greatly appreciated!!



** The hum is almost certain to be a result of the internal modifications -
ie, it has been built in due to earth loops or magnetic field injection from
the mains transformer.

Likely very difficult to fix with the mods still in place.

Find a good service tech and let him have a look.




........ Phil

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

"spwyatt"
The main problem is that both amps exhibit a low level but perfectly
audiable mains hum - even with their gains right down and nothing
plugged into the (XLR) inputs. Am I right in thinking it's reasonably
easy to fix by changing some capacitors? Any help greatly appreciated!!



** This article is worth reading:

http://www.mhennessy1.f9.co.uk/rogers/ls58.htm


Even if only as a warning.




........ Phil

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

In article .com,
spwyatt wrote:
The main problem is that both amps exhibit a low level but perfectly
audiable mains hum - even with their gains right down and nothing
plugged into the (XLR) inputs. Am I right in thinking it's reasonably
easy to fix by changing some capacitors? Any help greatly appreciated!!

Failed electrolytics are a common fault on these. Remember they could be
near 30 years old. I'm sure if you Google you'll find details on the best
replacement makes, etc.

--
*Most people have more than the average number of legs*

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

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

In message .com,
spwyatt writes
I've just been lucky enough to have purchased a pair of the stunning
Rogers/BBC LS5/8 speakers, complete the with a pair of the BBC modified
Quad 405 frequency splitting amps (actually, one 405 and one 405-2...
no idea why!)

The main problem is that both amps exhibit a low level but perfectly
audiable mains hum - even with their gains right down and nothing
plugged into the (XLR) inputs. Am I right in thinking it's reasonably
easy to fix by changing some capacitors? Any help greatly appreciated!!

Many thanks.....

The 100uF 6.3V capacitor C2 on the input I.C. is the usual culprit for
hum. But as others have said, I would change all the electrolytics on
the PCB.
--
Kevin Seal (at home)
F800ST
{kevin at the hyphen seal hyphen house dot freeserve dot co dot uk}

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

"Kevin Seal"


The 100uF 6.3V capacitor C2 on the input I.C. is the usual culprit for
hum.


** That ( tantalum) cap has nothing to do with any hum problem.

http://www.geocities.com/quad_esl63/...c/power405.jpg

It is a response setting cap for the DC offset servo.


But as others have said, I would change all the electrolytics on the PCB.


** Which will have no effect on the OP hum issue.

His 405s have been modified in a way that is highly prone to creating hum.




........ Phil

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

In message , Phil Allison
writes

"Kevin Seal"


The 100uF 6.3V capacitor C2 on the input I.C. is the usual culprit for
hum.


** That ( tantalum) cap has nothing to do with any hum problem.

http://www.geocities.com/quad_esl63/...c/power405.jpg

It is a response setting cap for the DC offset servo.

Apologies, I meant C5. It usually pops it's can and dries out, I've
changed it in about 30 amps so far with great reduction in hum.

In every amp I've dealt with , C2 is an NP electrolytic. Never seen one
with Tants in.


But as others have said, I would change all the electrolytics on the PCB.

Still maintain that all the electros should be replaced in old 405's.

** Which will have no effect on the OP hum issue.

His 405s have been modified in a way that is highly prone to creating hum.

Enlighten me.
--
Kevin Seal (at home)
F800ST
{kevin at the hyphen seal hyphen house dot freeserve dot co dot uk}

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

"Kevin Seal"
Phil Allison

The 100uF 6.3V capacitor C2 on the input I.C. is the usual culprit for
hum.


** That ( tantalum) cap has nothing to do with any hum problem.


It is a response setting cap for the DC offset servo.


Apologies, I meant C5. It usually pops it's can and dries out, I've
changed it in about 30 amps so far with great reduction in hum.


** Even with C5 removed the result is a barely audible, 5 mV rms hum.


In every amp I've dealt with , C2 is an NP electrolytic. Never seen one
with Tants in.


** A tantalum is the usual & specified part used.

http://quad405.com/405-1schematic.pdf

See C2 on the parts list and diagram.

It is marked as being 3 volt, 100uF, polarised and having a tolerance of
10%.



His 405s have been modified in a way that is highly prone to creating
hum.

Enlighten me.


** Try reading the heading, the original post and this link I posted two
days ago:

http://www.mhennessy1.f9.co.uk/rogers/ls58.htm

The "mod" consists of a PCB of similar size to a power channel board, fitted
with an input transformer all crammed into one end of the already cramped
case.

BTW

You can cleary SEE a tantalum capacitor ( blue in colour) in the pic of the
405 PCB about half way down the page.




........ Phil

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

In article , Phil Allison
writes

"Kevin Seal"
Phil Allison

The 100uF 6.3V capacitor C2 on the input I.C. is the usual culprit for
hum.


** That ( tantalum) cap has nothing to do with any hum problem.


It is a response setting cap for the DC offset servo.


Apologies, I meant C5. It usually pops it's can and dries out, I've
changed it in about 30 amps so far with great reduction in hum.


** Even with C5 removed the result is a barely audible, 5 mV rms hum.


In every amp I've dealt with , C2 is an NP electrolytic. Never seen one
with Tants in.


** A tantalum is the usual & specified part used.

http://quad405.com/405-1schematic.pdf

See C2 on the parts list and diagram.

It is marked as being 3 volt, 100uF, polarised and having a tolerance of
10%.



His 405s have been modified in a way that is highly prone to creating
hum.

Enlighten me.


** Try reading the heading, the original post and this link I posted two
days ago:

http://www.mhennessy1.f9.co.uk/rogers/ls58.htm

The "mod" consists of a PCB of similar size to a power channel board, fitted
with an input transformer all crammed into one end of the already cramped
case.


"Input" transformer in a power amp eh?.

Not too clever an idea shirly??..
BTW

You can cleary SEE a tantalum capacitor ( blue in colour) in the pic of the
405 PCB about half way down the page.




....... Phil





--
Tony Sayer

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

"tony sayer"


"Input" transformer in a power amp eh?.

Not too clever an idea shirly??..



** Not related to Tony Greig or Gary Player, by any chance ?




........ Phil

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

In article , Phil Allison
writes

"tony sayer"


"Input" transformer in a power amp eh?.

Not too clever an idea shirly??..



** Not related to Tony Greig or Gary Player, by any chance ?




....... Phil


Nope.. Nor Leo Sayer either......
--
Tony Sayer

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

"tony sayer"
Phil Allison


"Input" transformer in a power amp eh?.

Not too clever an idea shirly??..


** Not related to Tony Greig or Gary Player, by any chance ?


Nope.. Nor Leo Sayer either......


** Ah - Young Leo is living in Aussie these days.

One of my best customers provides live sound reinforcement for him from time
to time.

Just thought I detected a cute "Sou-fafrican" accent is your spelling
anomalies.






........ Phil

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

In article ,
tony sayer wrote:
"Input" transformer in a power amp eh?.

Not too clever an idea shirly??..

It's an elderly BBC monitoring active loudspeaker with a balanced input.
So a transformer.

--
*Middle age is when it takes longer to rest than to get tired.

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

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

In article , Phil Allison
writes

"tony sayer"
Phil Allison


"Input" transformer in a power amp eh?.

Not too clever an idea shirly??..


** Not related to Tony Greig or Gary Player, by any chance ?


Nope.. Nor Leo Sayer either......


** Ah - Young Leo is living in Aussie these days.

One of my best customers provides live sound reinforcement for him from time
to time.

Just thought I detected a cute "Sou-fafrican" accent is your spelling
anomalies.



Just a joke in our local news group .. almost always misspelt that way.

Cambridge born and bred, never been to SA !.....




....... Phil






--
Tony Sayer

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

In article , Dave Plowman (News)
writes
In article ,
tony sayer wrote:
"Input" transformer in a power amp eh?.

Not too clever an idea shirly??..

It's an elderly BBC monitoring active loudspeaker with a balanced input.
So a transformer.

Perhaps fine done if you know what your doing, tho as a DIY project?.
And hum should never be an issue with power amps at all!...
--
Tony Sayer

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

In message , Phil Allison
writes

"Kevin Seal"
Phil Allison

The 100uF 6.3V capacitor C2 on the input I.C. is the usual culprit for
hum.


** That ( tantalum) cap has nothing to do with any hum problem.


It is a response setting cap for the DC offset servo.


Apologies, I meant C5. It usually pops it's can and dries out, I've
changed it in about 30 amps so far with great reduction in hum.


** Even with C5 removed the result is a barely audible, 5 mV rms hum.

I've never measured the hum, I just used my ears.
On all 30 of the foldback amps I've repaired, replacing the duff C5 has
resulted in a total reduction in the hum fault reported.

In every amp I've dealt with , C2 is an NP electrolytic. Never seen one
with Tants in.


** A tantalum is the usual & specified part used.

http://quad405.com/405-1schematic.pdf

See C2 on the parts list and diagram.

It is marked as being 3 volt, 100uF, polarised and having a tolerance of
10%.

Quite right, and on the 405-2 which is the OP's second amplifier, C2 is
an NP electrolytic.


His 405s have been modified in a way that is highly prone to creating
hum.

Enlighten me.


** Try reading the heading, the original post and this link I posted two
days ago:

http://www.mhennessy1.f9.co.uk/rogers/ls58.htm

The "mod" consists of a PCB of similar size to a power channel board, fitted
with an input transformer all crammed into one end of the already cramped
case.

The main problem with hum as described on that web page is to do with
the fact that the amp had been fitted with a toroidal transformer before
it was purchased for the project.
Nothing else is mentioned about the extra mods causing hum.
--
Kevin Seal (at home)
F800ST
{kevin at the hyphen seal hyphen house dot freeserve dot co dot uk}

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

"Kevin Seal

In every amp I've dealt with , C2 is an NP electrolytic. Never seen one
with Tants in.


** A tantalum is the usual & specified part used.

http://quad405.com/405-1schematic.pdf

See C2 on the parts list and diagram.

It is marked as being 3 volt, 100uF, polarised and having a tolerance of
10%.

Quite right, and on the 405-2 which is the OP's second amplifier, C2 is an
NP electrolytic.


** So you have never seen an original Quad 405.

Hardly surprising you don't know what is in one.




His 405s have been modified in a way that is highly prone to creating
hum.

Enlighten me.


** Try reading the heading, the original post and this link I posted two
days ago:

http://www.mhennessy1.f9.co.uk/rogers/ls58.htm

The "mod" consists of a PCB of similar size to a power channel board,
fitted
with an input transformer all crammed into one end of the already cramped
case.

The main problem with hum as described on that web page is to do with the
fact that the amp had been fitted with a toroidal transformer before it
was purchased for the project.
Nothing else is mentioned about the extra mods causing hum.


** If you cannot imagine how adding such mod to a 405 could easily result
in creating a background hum, there is no point me trying to " enlighten "
you.

It is permanently dark where you have your head stuck.





........ Phil

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

In message , Phil Allison
writes

"Kevin Seal

In every amp I've dealt with , C2 is an NP electrolytic. Never seen one
with Tants in.


** A tantalum is the usual & specified part used.

http://quad405.com/405-1schematic.pdf

See C2 on the parts list and diagram.

It is marked as being 3 volt, 100uF, polarised and having a tolerance of
10%.

Quite right, and on the 405-2 which is the OP's second amplifier, C2 is an
NP electrolytic.


** So you have never seen an original Quad 405.

Hardly surprising you don't know what is in one.

No, having read and re-read the posts, I've never said I haven't seen a
405-1. Please do not assume what isn't there.




His 405s have been modified in a way that is highly prone to creating
hum.

Enlighten me.


** Try reading the heading, the original post and this link I posted two
days ago:

http://www.mhennessy1.f9.co.uk/rogers/ls58.htm

The "mod" consists of a PCB of similar size to a power channel board,
fitted
with an input transformer all crammed into one end of the already cramped
case.

The main problem with hum as described on that web page is to do with the
fact that the amp had been fitted with a toroidal transformer before it
was purchased for the project.
Nothing else is mentioned about the extra mods causing hum.


** If you cannot imagine how adding such mod to a 405 could easily result
in creating a background hum, there is no point me trying to " enlighten "
you.

You said..
Quote
** The hum is almost certain to be a result of the internal
modifications -
ie, it has been built in due to earth loops or magnetic field injection
from the mains transformer.
/quote

As I said, the hum described on the web page you cited was caused by a
*different* mains transformer, and states that as the Quad transformer
is screened, it will not suffer from hum.

It is permanently dark where you have your head stuck.

Insults, the last defence.
--
Kevin Seal (at home)
F800ST
{kevin at the hyphen seal hyphen house dot freeserve dot co dot uk}

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

"Kevin Seal the ****head "


In every amp I've dealt with , C2 is an NP electrolytic. Never seen
one
with Tants in.


** A tantalum is the usual & specified part used.

http://quad405.com/405-1schematic.pdf

See C2 on the parts list and diagram.

It is marked as being 3 volt, 100uF, polarised and having a tolerance of
10%.

Quite right, and on the 405-2 which is the OP's second amplifier, C2 is
an
NP electrolytic.


** So you have never seen an original Quad 405.

Hardly surprising you don't know what is in one.


No, having read and re-read the posts, I've never said I haven't seen a
405-1.


** Never seeing a tantalum cap in a 405 tells the story - ****head.


Please do not assume what isn't there.


** Go **** yourself - ****head.



** If you cannot imagine how adding such mod to a 405 could easily
result
in creating a background hum, there is no point me trying to " enlighten
"
you.


As I said, the hum described on the web page you cited was caused by a
*different* mains transformer, and states that as the Quad transformer is
screened, it will not suffer from hum.


** The URL for that (very long) page was supplied since it showed the PCB
that has to be installed for the x-over mod, plus a pic of the disputed tant
cap. No other reasons.

Please do not assume what I did no say - ****head.





........ Phil

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

In message , Phil Allison
writes

"Kevin Seal the ****head "



** Go **** yourself - ****head.

As I said, insults, the last resort.
When they know they are wrong, but can't admit it, they resort to
insults.


Please do not assume what I did no say - ****head.

It's sad isn't it, but having done a bit of Googling, it appears to be a
typical theme.
--
Kevin Seal (at home)
F800ST
{kevin at the hyphen seal hyphen house dot freeserve dot co dot uk}

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

"Kevin Seal"

As I said, insults, the last resort.



** Not at all - there is no such reality on usenet.

When publicly insulted one is entitled to insult back - with knobs on.

When dealing with arrogant half wits on a NG - there is no need to
prolong the agony by being polite.

Time for YOU to go back to you pommy ****heads perched on yellow motorbikes
NG.

ARSEHOLE !






.......... Phil

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

In message , Phil Allison
writes

Nothing of interest.
--
Kevin Seal (at home)
F800ST
{kevin at the hyphen seal hyphen house dot freeserve dot co dot uk}

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

"Kevin Seal ****ing ****head "


Just another, know nothing, pommy ****HEAD.

This one rides a yellow motorbike.

Must look like a canary with a fat cockroach on its back.

LOL




....... Phil

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

In message , Phil Allison
writes

....a factually incorrect nothing of interest.
--
Kevin Seal (at home)
F800ST
{kevin at the hyphen seal hyphen house dot freeserve dot co dot uk}

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

"Kevin Seal"
Phil Allison

Just another, know nothing, pommy ****HEAD.

This one rides a yellow motorbike.

Must look like a canary with a fat cockroach on its back.

LOL


...a factually incorrect nothing of interest.



** Quote from the Google Archive:

--------------------------------------

"uk.rec.motorcycles"

Kevin Seal

May 15, 2006

Yellow 51 plate registered in Feb 2002, it's the one with the better
lights and pointy fairing.
26,500 miles. Bit tatty round the edges now, i.e. paint chipping off the
engine and radiator. Crack in fairing below the RHS indicator and
scratched/re-painted clutch cover where it fell over.
New rear tyre last month.
It's had replacement down pipes fitted last year.
I think their is a full service history available for it, taxed till Jan
'07, MOT till Feb '07.
Located in North London.

Pics can be emailed if you're interested.
I'd like anything over £1600 for it.


email me at kevin at the-seal-house dot freeserve co uk.
--
Kevin Seal (at home)
FZS600 in Banana
{kevin at the hyphen seal hyphen house dot freeserve dot co dot uk}

----------------------------



** A cockroach riding a banana ....

ROTFL



........ Phil

BBC/Rogers LS5/8s plus modded Quad 405s - mains hum
 

In message , Phil Allison
writes

"Kevin Seal"
Phil Allison

Just another, know nothing, pommy ****HEAD.

This one rides a yellow motorbike.
^^^^^^^

Must look like a canary with a fat cockroach on its back.

LOL


...a factually incorrect nothing of interest.



** Quote from the Google Archive:

--------------------------------------

"uk.rec.motorcycles"

Kevin Seal

May 15, 2006

Yellow 51 plate registered in Feb 2002, it's the one with the better
lights and pointy fairing.
26,500 miles. Bit tatty round the edges now, i.e. paint chipping off the
engine and radiator. Crack in fairing below the RHS indicator and
scratched/re-painted clutch cover where it fell over.
New rear tyre last month.
It's had replacement down pipes fitted last year.
I think their is a full service history available for it, taxed till Jan
'07, MOT till Feb '07.
Located in North London.

Pics can be emailed if you're interested.
I'd like anything over £1600 for it.

As I said, a factually incorrect, nothing of interest.
--
Kevin Seal (at home)
F800ST
{kevin at the hyphen seal hyphen house dot freeserve dot co dot uk}