Hi all, I'm after some help from the experts if i may. Ebay special, quad 99 power amp, the amp will not come out of standby. Im going to use as a stand alone amp so i have the selector on the "Input" but the red light stays a constant red.
I have attached some photos of the board, which it appears to me, has had a mod of some sorts. can anyone confirm what the mod is for? and by chance could this be to bypass the selector switch???
Any thoughts gratefully received. Thanks.!
PS thanks for the group!
current equipment: 2x 405's dada mods and re cap, 2 x 306 dada recap 1 x useless 99 😁
I have attached some photos of the board, which it appears to me, has had a mod of some sorts. can anyone confirm what the mod is for? and by chance could this be to bypass the selector switch???
Any thoughts gratefully received. Thanks.!
PS thanks for the group!
current equipment: 2x 405's dada mods and re cap, 2 x 306 dada recap 1 x useless 99 😁
Attachments
Hello ITCSUK,
first of all, I would clean the circuit board from the dirt (brush and spirit) there may still be a hairline crack on the soldering. Then repair properly again and check the through-plating from the lower to the upper layer on a board with a double layer.
I was just looking at the board and saw two spots that I would take a closer look at. Firstly, the resistor (marked red), which looks a bit stressed, and the marked connection on the right capacitor (where the other side was patched) looks a bit rough and may have suffered from excessive stress. Maybe everything is unimportant because repairs are out from afar are always kinda bad
Good luck and have a pleasant day
first of all, I would clean the circuit board from the dirt (brush and spirit) there may still be a hairline crack on the soldering. Then repair properly again and check the through-plating from the lower to the upper layer on a board with a double layer.
I was just looking at the board and saw two spots that I would take a closer look at. Firstly, the resistor (marked red), which looks a bit stressed, and the marked connection on the right capacitor (where the other side was patched) looks a bit rough and may have suffered from excessive stress. Maybe everything is unimportant because repairs are out from afar are always kinda bad
Good luck and have a pleasant day
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These have an underrated capacitor across the muting power supply, first thing after the diode from the mains transformer. It needs to be 100uF 100V and it is found on the later units as 50V. It goes leaky, pulls down the muting voltage, so it would not come out of mute. C146 on the mono version, dunno on the stereo one.
Oh, that sounds like a good shout. Do you know when it’s in mute mode is the LED on the front solid red?
what puts the unit into mute? I presume a signal from the 99 pre amp.
The literature says that the solid red light is standby, do you think standby and mute are the same thing?
Sorry for the questions, and thanks for the suggestion I will follow it up.
I find it a bit strange, information on these amps is like searching hens teeth. There is lots on the preamp but very little on the power amps a schematic would come in really handy right now, but can’t find one anywhere.
what puts the unit into mute? I presume a signal from the 99 pre amp.
The literature says that the solid red light is standby, do you think standby and mute are the same thing?
Sorry for the questions, and thanks for the suggestion I will follow it up.
I find it a bit strange, information on these amps is like searching hens teeth. There is lots on the preamp but very little on the power amps a schematic would come in really handy right now, but can’t find one anywhere.
Yes they are the same thing. I should probably have said 'standby', but I seem to remember the signal is called 'Mute' on the schematic. I believe the LED should go red on standby, but I'm not 100% certain.
On the preamp at least, 'standby' only means muting, and turning off the display. All other power is still being drawn.
Information on the 99 amplifier is indeed very scarce. I don't have a schematic, and I still don't know who designed it, or indeed why, when Quad already had a perfectly good current-dumping design. This one was a brand new class B design.
On the preamp at least, 'standby' only means muting, and turning off the display. All other power is still being drawn.
Information on the 99 amplifier is indeed very scarce. I don't have a schematic, and I still don't know who designed it, or indeed why, when Quad already had a perfectly good current-dumping design. This one was a brand new class B design.
I thought that the current dumping design was carried forward into the 707 and 909 power amplifiers and left out of the 77/99?
The muting thing is definitely a good start as Quad liked throwing micro controllers at things although looking at the pictures this could all be based on simple logic gates instead.
Another possible suspect would be if any of the rail voltages were faulty. I don't know how much power management monitoring the amplifier does to prevent the system from unmuting.
Muting, in this case, isn't the typical relay disconnecting the output of the amplifier from the speakers as you can see the output inductors are wired directly to the terminals. This is the same as the 77. I've got a 77 integrated and when you turn that on you get a turn on thump through the speakers even though it's still in standby. If the 99 power amplifier does the same thing then you'd be able to check for DC offset on the outputs of the amplifier. If it's below ~50mV then the power amp circuitry itself would appear to be functional. If DC offset is only a few mV then you could connect the amp to a cheap speaker, power it on, and see if you get the typical power on thump. If you do then that would indicate that the power amplifier circuitry is fine.
Looking at the PCB you can see differential line receivers. Now Quad only provided one set of additional single ended inputs for non Quad systems but they are clearly using balanced connections through their Quad link thingy. It wouldn't be too hard to modify the amplifier for a pair of balanced inputs I don't think.
Moving on from that. If the power amplifier circuitry is working correctly, and you cannot get the amplifier to come out of standby, then theoretically all you'd need to do is find out where the signal is being muted (following the path of the single ended inputs) and then bypass it.
The modification on the underside of the board definitely looks like a repair job.
The muting thing is definitely a good start as Quad liked throwing micro controllers at things although looking at the pictures this could all be based on simple logic gates instead.
Another possible suspect would be if any of the rail voltages were faulty. I don't know how much power management monitoring the amplifier does to prevent the system from unmuting.
Muting, in this case, isn't the typical relay disconnecting the output of the amplifier from the speakers as you can see the output inductors are wired directly to the terminals. This is the same as the 77. I've got a 77 integrated and when you turn that on you get a turn on thump through the speakers even though it's still in standby. If the 99 power amplifier does the same thing then you'd be able to check for DC offset on the outputs of the amplifier. If it's below ~50mV then the power amp circuitry itself would appear to be functional. If DC offset is only a few mV then you could connect the amp to a cheap speaker, power it on, and see if you get the typical power on thump. If you do then that would indicate that the power amplifier circuitry is fine.
Looking at the PCB you can see differential line receivers. Now Quad only provided one set of additional single ended inputs for non Quad systems but they are clearly using balanced connections through their Quad link thingy. It wouldn't be too hard to modify the amplifier for a pair of balanced inputs I don't think.
Moving on from that. If the power amplifier circuitry is working correctly, and you cannot get the amplifier to come out of standby, then theoretically all you'd need to do is find out where the signal is being muted (following the path of the single ended inputs) and then bypass it.
The modification on the underside of the board definitely looks like a repair job.
I guess that is what you said but I interpreted it in a different way.
The way you said it made it sound like they'd dropped the current dumping design altogether. Whereas Quad had decided to save that for the flagship power amplifier and go with something cheaper/simpler for the less expensive amps.
The way you said it made it sound like they'd dropped the current dumping design altogether. Whereas Quad had decided to save that for the flagship power amplifier and go with something cheaper/simpler for the less expensive amps.
Can't understand that interpretation. It isn't what I said, and it isn't what I meant.
The only way I can interpret what you've said here, with it being a bad thing that they came up with a new class B design, is if they had stopped producing a product based on current dumping and you could no longer get it. You're basically complaining that Quad came up with a simpler design for a lower price point and there's no reason why anyone would complain about this unless you thought they'd stopped making the current dumping amplifier as a result. So I figured you weren't aware of the fact they still produced the current dumping amplifier.
It's like saying information on the Tesla Model 3 is indeed very scarce. I don't have a service manual and I still don't know who designed it, or indeed why, when Tesla already had the Model S. It's like why are you complaining about the introduction of a cheaper product when you can still get the more upmarket version too?
So I suppose I should really be asking you why did you complain about the cheaper 99 amplifier design, in the quote above, if you can still get the current dumping 909?