I recently posted a thread about a humming Avondale modified Quad 405 power amp - plenty of readers but no answers.
Has anyone else had a 405 modded by Avondale that hums ?
The main ps caps are about 10 years old as are the Avondale mods.
It get's quite warm too particularly on the right channel.
Any simple but effective component change suggestions
out there to make it quiet ?
Thanks
Andrew
Has anyone else had a 405 modded by Avondale that hums ?
The main ps caps are about 10 years old as are the Avondale mods.
It get's quite warm too particularly on the right channel.
Any simple but effective component change suggestions
out there to make it quiet ?
Thanks
Andrew
I can remember working on a 495 with an intermittent hum ! The problem was traced to a poor connection on one of the psu capacitors merley touching the connector could stop it humming
regards Trev
regards Trev
Andrew,
why not give Les at Avondale a ring? He has been known for the good support of his creations...
Best,
Oliver
why not give Les at Avondale a ring? He has been known for the good support of his creations...
Best,
Oliver
Quad 405 Hum
Thanks for the replies !
To Mooly - I got it pre modded and therefore have no experience or knowledge of how it used to be.
The boards look like no other I've viewed - completely different.
It does use MJ 15003 x 4 successfully and when playing music
it sounds OK when the volume is above the hum level.
It's also quite a bit warmer on one side of the heatsink than the other.
To Latala - The connections to the PS supply caps are all good.
I did attempt to agitate them ( gently ) whilst the amp was at idle
and there was no change. - thanks for the suggestion though.
To Roger Gustavvson - I'll do C5 as soon as possible and report back - many thanks
To Core Dump - I think your suggestion is probably the way to go
ultimately as I'm not completely comfortable with ' tech ' stuff.
I've built a 3886 based Gainclone ( with good instructions and diagrams ! ) and built a couple of nice passive attentuators but that doesn't qualify me at all when things get complicated.
I'll try Roger's C5 suggestion and then make the call to Les !!
Many thanks to all for doing some thinking for me !!
Regards
Andrew
Thanks for the replies !
To Mooly - I got it pre modded and therefore have no experience or knowledge of how it used to be.
The boards look like no other I've viewed - completely different.
It does use MJ 15003 x 4 successfully and when playing music
it sounds OK when the volume is above the hum level.
It's also quite a bit warmer on one side of the heatsink than the other.
To Latala - The connections to the PS supply caps are all good.
I did attempt to agitate them ( gently ) whilst the amp was at idle
and there was no change. - thanks for the suggestion though.
To Roger Gustavvson - I'll do C5 as soon as possible and report back - many thanks
To Core Dump - I think your suggestion is probably the way to go
ultimately as I'm not completely comfortable with ' tech ' stuff.
I've built a 3886 based Gainclone ( with good instructions and diagrams ! ) and built a couple of nice passive attentuators but that doesn't qualify me at all when things get complicated.
I'll try Roger's C5 suggestion and then make the call to Les !!
Many thanks to all for doing some thinking for me !!
Regards
Andrew
Does it hum with no inputs connected or more specifically with the inputs shorted. Are you actually sure it is the power amp. Worth asking.
If one side is warmer than the other that suggests the outputs on that side are drawing more current for some reason, unless there is some other component ( regulator been added or something ) that is causing it. The original 405 runs at fixed and what is really zero bias, so should run cold.
It's an unknown quantity I'm afraid.
If one side is warmer than the other that suggests the outputs on that side are drawing more current for some reason, unless there is some other component ( regulator been added or something ) that is causing it. The original 405 runs at fixed and what is really zero bias, so should run cold.
It's an unknown quantity I'm afraid.
Quad 405 Hum
Mooly thanks.
Absolutely no hum with nothing connected to the inputs
and speakers connected.
What's odd is that I'm running it with a passive stepped attenuator PRE that's completely quiet with another power amp.
Only other active component in the chain is the CD player.
Regards
Andrew
Mooly thanks.
Absolutely no hum with nothing connected to the inputs
and speakers connected.
What's odd is that I'm running it with a passive stepped attenuator PRE that's completely quiet with another power amp.
Only other active component in the chain is the CD player.
Regards
Andrew
That sounds odd. You need to short the power inputs ie signal input to signal ground to be sure.
Sound like it may not be faulty at all.
Connect just the preamp and disconnect the CD player, so that is to say you have just the Quad and it's preamp connected, nothing else. Any hum ?
Sound like it may not be faulty at all.
Connect just the preamp and disconnect the CD player, so that is to say you have just the Quad and it's preamp connected, nothing else. Any hum ?
Mooly Hi
Tried it and it's still there.
Thats is to say, passive and power connected and no CD
player.
Are you suggesting I put a resistor from signal positive to ground ?
Can you suggest a value ?
I've ordered some metalised polyester caps - 0.01 uf 400 v
and I'm going to apply them across the PS caps and the IEC
mains inlet.
If no change then renew every cap I see - from suggestions elsewhere.
They are all old now maybe that'll do it.
The extra heat from one channel is bothering me.
Could the outputs on the hot side pull more current if the cap is knackered
Appreciate your input on this and sorry for just not ' getting it ' yet .
Thanks
Andrew
Tried it and it's still there.
Thats is to say, passive and power connected and no CD
player.
Are you suggesting I put a resistor from signal positive to ground ?
Can you suggest a value ?
I've ordered some metalised polyester caps - 0.01 uf 400 v
and I'm going to apply them across the PS caps and the IEC
mains inlet.
If no change then renew every cap I see - from suggestions elsewhere.
They are all old now maybe that'll do it.
The extra heat from one channel is bothering me.
Could the outputs on the hot side pull more current if the cap is knackered
Appreciate your input on this and sorry for just not ' getting it ' yet .
Thanks
Andrew
I agree with Mooley, the hum probably originates elsewhere.
Is this a d.i.n. input or RCA socket? Past experience says you may have a missing ground connection or poor ground connection at the output of your passive preamp. No hum without inputs connected to any amp usually means the fault lies elsewhere.
These amps usually run warm to the touch.
Regards
Barry
Is this a d.i.n. input or RCA socket? Past experience says you may have a missing ground connection or poor ground connection at the output of your passive preamp. No hum without inputs connected to any amp usually means the fault lies elsewhere.
These amps usually run warm to the touch.
Regards
Barry
Hi Andrew,
Right 🙂 , you can have an internal wiring problem that causes the amp to be silent until the inputs are ( effectively ) shorted together by the preamp etc. But if that is the case that's a problem with incorrect internal grounding.
The nature of the hum tells a lot. Is it a deep, pure sounding 50 hz hum or is there any harshness to it ? That's a big clue. How loud are we talking here.
What I was getting at before was that if the amp alone is connected to the mains and you are using a passive preamp then an external ground loop can not exist. This leaves either something like the passive preamp "picking up" stray hum which is certainly possible, or some other problem.
The next test has to be to simply "short" the inputs on the back of the amp together. Left signal ground to left signal input. Same for the right channel.
It will either still hum or be silent.
Caps !! I suspect these are not the problem. It wouldn't be silent on it's own. The amp should reject ripple on the PSU and the wiring should be correct so that ripple currents can not enter the signal path.
Right 🙂 , you can have an internal wiring problem that causes the amp to be silent until the inputs are ( effectively ) shorted together by the preamp etc. But if that is the case that's a problem with incorrect internal grounding.
The nature of the hum tells a lot. Is it a deep, pure sounding 50 hz hum or is there any harshness to it ? That's a big clue. How loud are we talking here.
What I was getting at before was that if the amp alone is connected to the mains and you are using a passive preamp then an external ground loop can not exist. This leaves either something like the passive preamp "picking up" stray hum which is certainly possible, or some other problem.
The next test has to be to simply "short" the inputs on the back of the amp together. Left signal ground to left signal input. Same for the right channel.
It will either still hum or be silent.
Caps !! I suspect these are not the problem. It wouldn't be silent on it's own. The amp should reject ripple on the PSU and the wiring should be correct so that ripple currents can not enter the signal path.
Quad 405 hum stopped
Mooly erm....
When I shorted the RCA's it all stopped - what the@(*&^^%%%%$ ?
You are now going to tell me that the earth or screening
is suspect on the passive - right ?
OK, the box is a cast aluminium one and I've used pure silver teflon coated cable throughout.
The RCA's on the back are grounded directly to the case ( no insulation between input socket and case )
I deliberately did not create a star because of this.
The Alps Black B is grounded to the base of the case as is the ELNA selector switch.
Singal path less than three inches ( 1.5 in and 1.5 out )
Do I make a dedicated star earth for all components and input / output sockets ?
I'm so sorry for all this - I'm frankly stunned at the faint hiss
I now hear - it's really faint !
What a plonker.
Thanks
Andrew
Mooly erm....
When I shorted the RCA's it all stopped - what the@(*&^^%%%%$ ?
You are now going to tell me that the earth or screening
is suspect on the passive - right ?
OK, the box is a cast aluminium one and I've used pure silver teflon coated cable throughout.
The RCA's on the back are grounded directly to the case ( no insulation between input socket and case )
I deliberately did not create a star because of this.
The Alps Black B is grounded to the base of the case as is the ELNA selector switch.
Singal path less than three inches ( 1.5 in and 1.5 out )
Do I make a dedicated star earth for all components and input / output sockets ?
I'm so sorry for all this - I'm frankly stunned at the faint hiss
I now hear - it's really faint !
What a plonker.
Thanks
Andrew
Not at all 🙂 Do you mean it's OK now with the preamp back in circuit. Dicky connection ? Or do you mean the power amps OK but the hum is still there with preamp wired in ?
I'll post this anyway.
It still could be the amp, unlikely but possible.
Having shorted the inputs and finding all OK you now have to connect those input grounds together. This is where any wiring problem in the amp will show. It's not easy to explain this !
So that's all shorted as in the previous post, but then connect the left and right channel inputs together. The lot, grounds and signal inputs. It should still be silent.
If it is the amps fine, if it isn't the amp isn't.
If it's OK it's stray hum pickup in the preamp or poor shieding somewhere.
It still could be the amp, unlikely but possible.
Having shorted the inputs and finding all OK you now have to connect those input grounds together. This is where any wiring problem in the amp will show. It's not easy to explain this !
So that's all shorted as in the previous post, but then connect the left and right channel inputs together. The lot, grounds and signal inputs. It should still be silent.
If it is the amps fine, if it isn't the amp isn't.
If it's OK it's stray hum pickup in the preamp or poor shieding somewhere.
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