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