Hi,
i have a quad 520 power amp and recently moved - now when i turn off i get a farting crackle noise on the right channel, instead of the usual pop.
Plays fine.
I looked inside and the T2A fuse on the right channel has blown.
I've ordered a new fuse so will see what happens.
Just wondering what people think - could it be a one off or will it blow again? (i guess i'll find out when the fuses arrive)
i have a multimeter but not a lot of knowledge in this area.
I can't see anything else untoward on the inside.
thanks
i have a quad 520 power amp and recently moved - now when i turn off i get a farting crackle noise on the right channel, instead of the usual pop.
Plays fine.
I looked inside and the T2A fuse on the right channel has blown.
I've ordered a new fuse so will see what happens.
Just wondering what people think - could it be a one off or will it blow again? (i guess i'll find out when the fuses arrive)
i have a multimeter but not a lot of knowledge in this area.
I can't see anything else untoward on the inside.
thanks
a bit of an update - I'm told the fuse was for a centre tap, although i'm not sure exactly what that is or what the point of it is.
I replaced the fuse and now all is working fine.
I replaced the fuse and now all is working fine.
A centre tapped transformer provides a voltage reference for a split rail power supply
+V 0V(or voltage ref) -V Are there fuses on the +V and -V feeds as well?
Below is from a Google search.
A center-tap transformer is designed to provide two separate secondary voltages, VA and VB with a common connection. This type of transformer configuration produces a two-phase, 3-wire supply. The secondary voltages are the same and proportional to the supply voltage, VP, therefore power in each winding is the same.
+V 0V(or voltage ref) -V Are there fuses on the +V and -V feeds as well?
Below is from a Google search.
A center-tap transformer is designed to provide two separate secondary voltages, VA and VB with a common connection. This type of transformer configuration produces a two-phase, 3-wire supply. The secondary voltages are the same and proportional to the supply voltage, VP, therefore power in each winding is the same.
According to the manual the only fuses inside are the T2A ones and T6.3A - the latter are near the main power supply (for 220v).
i don't know much about electronics or amplifiers, but i just found it odd that a fuse had blown and the only consequence was the noise on turning off.
The person who told me it was centre tap could have been wrong.
i don't know much about electronics or amplifiers, but i just found it odd that a fuse had blown and the only consequence was the noise on turning off.
The person who told me it was centre tap could have been wrong.
Looked at the schematic --there is no "fuse in the centre tap" as there is no centre tap shown in any case.
One input fuse,
One HT (before FW rectifier ) fuse.
One input fuse,
One HT (before FW rectifier ) fuse.
Thanks - i guess the guy on another forum was wrong then.
I just remembered, and i'm not sure why i didn't connect the dots here, but after i moved i had no sound out of the right channel and i found it was the speaker cable (they were home soldered into an xlr plug and one of the connections must have broken in my move).
I guess this could be responsible for the fuse going?
Lateral thought here: A guy who describes a fuse (no mention of transformers) as centre-tapped is probably looking at the fuse wire inside the glass tube and realises that many "T" types have the fuse wire supported by another, rigid wire at the centre. Hence, he sees it as centre-tapped.
This is how many "time delay" fuses are constructed and for loads like amplifiers that have a high surge current at start-up that would blow a standard fuse if it were correctly rated to protect the amplifier against overloads.
This is how many "time delay" fuses are constructed and for loads like amplifiers that have a high surge current at start-up that would blow a standard fuse if it were correctly rated to protect the amplifier against overloads.
Could be.
I wonder if the 520f is centre tapped and he's looking at the wrong schematic - or the 510, or whatever the 520c is?
you don't see many of the straight 520's from my looking around.
I wonder if the 520f is centre tapped and he's looking at the wrong schematic - or the 510, or whatever the 520c is?
you don't see many of the straight 520's from my looking around.
My 520 schematic labeled M.12831 issue 1 shows the PTX secondary is centre tapped to ground via a fuse in both channels. This is the version with the LDR in the input circuit. I had such a one on the workbench a few months ago.
thanks.
yeah i showed the schematic to a friend who can read these things and he pointed out the centre tap to me so it definitely does have one.
i still find it odd that the only consequence that i could tell was the sound on turning off - is this normal and what you would expect?
cheers
yeah i showed the schematic to a friend who can read these things and he pointed out the centre tap to me so it definitely does have one.
i still find it odd that the only consequence that i could tell was the sound on turning off - is this normal and what you would expect?
cheers
According to hi-fi engine the schematic shown for the Quad 520 does not show any center taps on the mains transformer ,obviously various mark numbers /versions.
Ah ! there lies the difference --hi-fi engine has diagram-
M12828--ISS--7
I have downloaded it and looking at it as I type this post.
M12828--ISS--7
I have downloaded it and looking at it as I type this post.
i think thats the 520f - they look quite different inside.
here is what dada says:
The 520 differ on two major aspects from a 520f, a double conventional power supply instead of the power supply with the regulated earth to prevent any DC current through the loudspeaker, and discrete build current sources in the input circuit.
i don't know what significance this has.
here is what dada says:
The 520 differ on two major aspects from a 520f, a double conventional power supply instead of the power supply with the regulated earth to prevent any DC current through the loudspeaker, and discrete build current sources in the input circuit.
i don't know what significance this has.
You mean the LM334 current source ?
Being old school I am more used to the combination of two BJT,s but there are many variations on this .
A double conventional power supply is two identical power supplies not split rail .
Being old school I am more used to the combination of two BJT,s but there are many variations on this .
A double conventional power supply is two identical power supplies not split rail .
this is just what is said on this page:
Quad Spot: Revision of a Quad 520f
i'm not technical enough to actually know what it means 🙂
Quad Spot: Revision of a Quad 520f
i'm not technical enough to actually know what it means 🙂
When you swap the left and right loudspeakers, is the farthing sound still in the same channel?
I'm asking because of a problem with a Klein & Hummel OY active loudspeaker that seemed to be due to one of the built-in amplifiers, but in the end turned out to be due to the squawker's voice coil being disconnected. Multiway loudspeakers with a broken-down driver can present a very nasty load to the amplifier that may cause audible oscillations, either all the time or at power on or power off. It took me quite a while before I had the issue figured out.
The OY produced a weird squeaking sound at power off. Of course it also didn't work well when powered on, as its squawker didn't work, but the weird sound at power off was noticed first.
I'm asking because of a problem with a Klein & Hummel OY active loudspeaker that seemed to be due to one of the built-in amplifiers, but in the end turned out to be due to the squawker's voice coil being disconnected. Multiway loudspeakers with a broken-down driver can present a very nasty load to the amplifier that may cause audible oscillations, either all the time or at power on or power off. It took me quite a while before I had the issue figured out.
The OY produced a weird squeaking sound at power off. Of course it also didn't work well when powered on, as its squawker didn't work, but the weird sound at power off was noticed first.
Thanks for the link Aardvarky provides a lot of schematics ,now I see the version you have is the center tap transformer type .
£100 for a Quad 33 ??? --I had trouble selling mine decades ago as it wasn't exactly top end fidelity--times change.
I notice the article recommends getting the 520f but as I surmised a whole shop load of variations on the basic design .
Some good advice on updating them , I have to say I had never heard of DADA but they are a lot more open on providing schematics and conversion info, many commercial businesses aren't as open as that trying to make updating some kind mystery only the cognista can achieve.
£100 for a Quad 33 ??? --I had trouble selling mine decades ago as it wasn't exactly top end fidelity--times change.
I notice the article recommends getting the 520f but as I surmised a whole shop load of variations on the basic design .
Some good advice on updating them , I have to say I had never heard of DADA but they are a lot more open on providing schematics and conversion info, many commercial businesses aren't as open as that trying to make updating some kind mystery only the cognista can achieve.