Mooly great.
Understood - will do it after Corrie !!
Ha !
If the Quad is silent will I have to create a star earth in the passive ?
Cheers
Understood - will do it after Corrie !!
Ha !
If the Quad is silent will I have to create a star earth in the passive ?
Cheers
Confession.
I didn't short them properly the first time - hence the silence.
Now that I have the hum is still there in the same musical key of A and without the wasp.
Re connect the passive and the wasp is back.
I shorted the whole of the inputs and grounds and no change.
Maybe your a bit sick of this thread now and I should just change the C5 and all the caps and see what happens.
It's no problem, I've had hours of your help on this and feel pretty bad now
Thanks
Andrew😱
I didn't short them properly the first time - hence the silence.
Now that I have the hum is still there in the same musical key of A and without the wasp.
Re connect the passive and the wasp is back.
I shorted the whole of the inputs and grounds and no change.
Maybe your a bit sick of this thread now and I should just change the C5 and all the caps and see what happens.
It's no problem, I've had hours of your help on this and feel pretty bad now
Thanks
Andrew😱
Hi Andrew,
Can I ask how you are shorting the inputs. Are you using shorting plugs or bits of wire etc.
Hum with no harmonics -- 50 Hz fundamental -- can be caused by the magnetic field from the mains transformer inducing a current into the internal wiring. The problem shows when a "loop" is formed and the current can then develop a small volt drop along the legth of wire. When the loop is broken no current flows hence no volt drop, no hum.
Harmonics present come from the charging currents in the PSU and are at 100 Hz fundamental but have a very harsh edge to them. This occurs because the charging pulses of the bridge etc are contaminating the signal grounds.
It sound a bit like you have a combination of the two.
Just to recheck then, shorting just the signal and ground of each input, step 1 only in my previous picture, done right on the amp sockets themselves. The amp case etc isn't signal ground, you have got to use the ground wired to the socket. If that gives hum there is an internal amp problem.
Can I ask how you are shorting the inputs. Are you using shorting plugs or bits of wire etc.
Hum with no harmonics -- 50 Hz fundamental -- can be caused by the magnetic field from the mains transformer inducing a current into the internal wiring. The problem shows when a "loop" is formed and the current can then develop a small volt drop along the legth of wire. When the loop is broken no current flows hence no volt drop, no hum.
Harmonics present come from the charging currents in the PSU and are at 100 Hz fundamental but have a very harsh edge to them. This occurs because the charging pulses of the bridge etc are contaminating the signal grounds.
It sound a bit like you have a combination of the two.
Just to recheck then, shorting just the signal and ground of each input, step 1 only in my previous picture, done right on the amp sockets themselves. The amp case etc isn't signal ground, you have got to use the ground wired to the socket. If that gives hum there is an internal amp problem.
Hi
I made shorting plugs from an old apir of Maplins phono plugs with the +'ve and negative legs soldered together.
My interpretation of your drawing was to connect left and right
signal inputs whilst the shorting plugs were in the sockets.
Hum still present though without the harshness that I attempted
to describe as ' wasp ' ish.
Pre back in and the harshness returned.
Sorry for the delay ( done 500 miles today )
Regards
Andrew
I made shorting plugs from an old apir of Maplins phono plugs with the +'ve and negative legs soldered together.
My interpretation of your drawing was to connect left and right
signal inputs whilst the shorting plugs were in the sockets.
Hum still present though without the harshness that I attempted
to describe as ' wasp ' ish.
Pre back in and the harshness returned.
Sorry for the delay ( done 500 miles today )
Regards
Andrew
Hi Andrew,
If you have plugged in two shorted phono plugs( that's perfect by the way ) and the pure 50 hz hum is present that's a problem internal to the amp. It sounds like a wiring issue really. Is the hum the same level on both channels.
Leaving those plugs in if you now short them one to another does the hum change. Does the "wasp" appear.
It sounds like your passive is perhaps picking up hum but first job has to be to get the amp silent if that's possible. If it's been modded anything could be different from the original.
If you have plugged in two shorted phono plugs( that's perfect by the way ) and the pure 50 hz hum is present that's a problem internal to the amp. It sounds like a wiring issue really. Is the hum the same level on both channels.
Leaving those plugs in if you now short them one to another does the hum change. Does the "wasp" appear.
It sounds like your passive is perhaps picking up hum but first job has to be to get the amp silent if that's possible. If it's been modded anything could be different from the original.
Thanks
I'll go through the process you desribe tonight.
On the passive - it's silent with the gainclone and another
power amp I converted from an old 70's Denon dual mono integrated.
Diffferent topologies I suppose but it's quiet nonetheless.
As far as ' modded ' is concerned you simply wouldn't recognise the boards as being for Quad 405's - such is the difference.
Explanation - same size boards but every component is in a different place, no op amps and a third triac or ' something ' where there are normally two large wirewound resistors side by side - near the Ali plate that holds the the MJ15003's.
I really should take some pics - your eyes would pop !!
Back soon with some answers
And
I'll go through the process you desribe tonight.
On the passive - it's silent with the gainclone and another
power amp I converted from an old 70's Denon dual mono integrated.
Diffferent topologies I suppose but it's quiet nonetheless.
As far as ' modded ' is concerned you simply wouldn't recognise the boards as being for Quad 405's - such is the difference.
Explanation - same size boards but every component is in a different place, no op amps and a third triac or ' something ' where there are normally two large wirewound resistors side by side - near the Ali plate that holds the the MJ15003's.
I really should take some pics - your eyes would pop !!
Back soon with some answers
And
The manual for the 405 states that the amp should either be grounded via the power cord, OR via the interconnects (via the pre-amp), but not both!
You may need to break power ground for one component. With a passive pre I guess the other ground connector must be the source component.
Just wanted to add this info to all good suggestions here.
You may need to break power ground for one component. With a passive pre I guess the other ground connector must be the source component.
Just wanted to add this info to all good suggestions here.
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