I have a Quad 33 / 303 / FM3 system. For some time I have been aware that there are unwanted sounds from the 33/303. I suspected that they were due to an ageing 303 power amplifier. However, yesterday evening I visited a neighbour who happens also to have a Quad 33/303 based system taking my 33 pre-amp and 303 power amp with me to try and isolate the problem(s).
On the basis of some experimentation and swapping units in and out I now get the impression that the problem lies not with my 303 but with my 33. The problem certainly followed my 33 back and forth and was not apparent when using his 33.
Aside from an initial "thump" on switch-on, there is a definite whooshing or rushing sound when I switch on the 33. It sounds somewhat akin to rushing water or a waterfall. This lasts for maybe a couple of seconds and then dies away.
There are a greater and longer-lasting range of sounds when I switch off the 33. These include rapid "clicking" sounds which gradually fade over about five seconds. I don't get the same effects when using the other 33.
For what it is worth, I use a Sony CDP-790 CD Player which has a variable line-out. I have tried playing this directly through the 303 and I get no extraneous noise at all.
Clearly my 33 needs servicing but I am curious to know what components may be causing this?
Any help and/or advice would be greatly appreciated.
On the basis of some experimentation and swapping units in and out I now get the impression that the problem lies not with my 303 but with my 33. The problem certainly followed my 33 back and forth and was not apparent when using his 33.
Aside from an initial "thump" on switch-on, there is a definite whooshing or rushing sound when I switch on the 33. It sounds somewhat akin to rushing water or a waterfall. This lasts for maybe a couple of seconds and then dies away.
There are a greater and longer-lasting range of sounds when I switch off the 33. These include rapid "clicking" sounds which gradually fade over about five seconds. I don't get the same effects when using the other 33.
For what it is worth, I use a Sony CDP-790 CD Player which has a variable line-out. I have tried playing this directly through the 303 and I get no extraneous noise at all.
Clearly my 33 needs servicing but I am curious to know what components may be causing this?
Any help and/or advice would be greatly appreciated.
Could be although I am not sure why the problem should clear up after a few seconds - insufficient time for components to "heat up"?
I am not so convinced about the poor connection idea; I have removed and reseated all five boards in the 33 and that has made no difference.
Are all these noises on one or both channels ?
(This can be the kind of fault where a little freezer spray comes into its own)
(This can be the kind of fault where a little freezer spray comes into its own)
Rotted PS caps ? the list could be long and expensive.
Possibly a good time/ opportunity to upgrade your Amp?
You Will get better sounds, with most any recent / semi recent equipment
Possibly a good time/ opportunity to upgrade your Amp?
You Will get better sounds, with most any recent / semi recent equipment
Good question and I am not sure, I will check and get back to you.
Even if I happened to have a can of freezer spray about, I wouldn't have any idea where to start - way beyond my pay grade.
The first question would be, is the noise audible on all positions of the input selector switch ?
I would certainly replace C500, C501 and C502, the PSU reservoir caps.
Modern equivalents would be 1000uF / 25V in all three positions.
The next question would be, is the noise audible in both channels ?
I wouldn't have thought that the transistors would be the cause of the problem, there are a few electrolytic caps on the amplifier boards which I would suspect before anything else.How good is your friend
If I remember correctly the two amplifier boards can be swapped over. Does the noise move L - R ? How good is your friend, try swapping them into his 33.
I would certainly replace C500, C501 and C502, the PSU reservoir caps.
Modern equivalents would be 1000uF / 25V in all three positions.
The next question would be, is the noise audible in both channels ?
I wouldn't have thought that the transistors would be the cause of the problem, there are a few electrolytic caps on the amplifier boards which I would suspect before anything else.How good is your friend
If I remember correctly the two amplifier boards can be swapped over. Does the noise move L - R ? How good is your friend, try swapping them into his 33.
Last edited:
Being an old amplifier you will find that modern electrolytics have different nominal values.
2.0uF can be replaced with 2.2uF
50uF can be replaced with 47uF
12uF can be replaced with 22uF
If you can't get the same voltage go for the next highest voltage, 16V will be normal.
2.0uF can be replaced with 2.2uF
50uF can be replaced with 47uF
12uF can be replaced with 22uF
If you can't get the same voltage go for the next highest voltage, 16V will be normal.
If its on both channels then you could be looking at a PSU or muting issue (something common to both channels)
Freezer spray is useful to just drip (not squirt or blast components off the face of the PCB 😉) a little on suspect parts that might 'heal up' when power is applied. No component should be affected by the chilling, if it is then you have found the fault.
Replacing the PSU smoothing capacitor/s is easy and not expensive.
Buy good quality (not fakes) commercial grade capacitors. Epcos are good.
Don't buy "Audio" grade at inflated prices.
Then retest.
Buy good quality (not fakes) commercial grade capacitors. Epcos are good.
Don't buy "Audio" grade at inflated prices.
Then retest.
If the OP would kindly answer this question, half these suggestions would be irrelevant.
OK, a bit of an update:
- It is definitely connected with the 33, not the 303 or the speakers.
- The problem only occurs on a single channel.
- I have removed and reseated all five boards - this hasn't changed anything
- No amount of playing with the Left & Right and "Mono" or the "Stereo" buttons makes any difference, it is always just one channel.
- Swapping the two internal Amplifier PCBs (12017) makes no difference. Looking at the circuit diagram I get the impression that the filter switches and volume control are all that come between these PCBs and the output to the 303?
A further observation - the rapid "clicking" sounds which gradually fade over about five (to ten) seconds seem to come from both speakers.
If you turn the volume down, does the 'rushing' noise reduce to zero ?
(the volume control is before the two 12017 boards and so that test splits the unit half as it were)
Assuming the volume control has no effect on the rushing noise, then the likely suspects (but not guaranteed) are the caps around the tone control feedback network. There's no point second guessing which it might be, it might be any of them. Those two 100uf caps would be an easy first swap too. The 0.033uf could be replaced one at a time.
The two channels are 'separated' by the balance control RV5. So try and determine which channel is the faulty one and then you are only working on that half of the circuit.
If you had your freezer spray then you could freeze each cap slowly in turn and see if the noise appears. Freezer is really expensive... cans of compressed air from Poundland used upside should work as a freezer substitute.
The clicking noise that's common to both channels is something to look at later. Judging by the documentation it seems there could have been several revisions of the circuit and so its not beyond the bounds of possibility that there is an inherent switch off noise problem.
(the volume control is before the two 12017 boards and so that test splits the unit half as it were)
Assuming the volume control has no effect on the rushing noise, then the likely suspects (but not guaranteed) are the caps around the tone control feedback network. There's no point second guessing which it might be, it might be any of them. Those two 100uf caps would be an easy first swap too. The 0.033uf could be replaced one at a time.
The two channels are 'separated' by the balance control RV5. So try and determine which channel is the faulty one and then you are only working on that half of the circuit.
If you had your freezer spray then you could freeze each cap slowly in turn and see if the noise appears. Freezer is really expensive... cans of compressed air from Poundland used upside should work as a freezer substitute.
The clicking noise that's common to both channels is something to look at later. Judging by the documentation it seems there could have been several revisions of the circuit and so its not beyond the bounds of possibility that there is an inherent switch off noise problem.
I am away from home now and will be for the next fortnight so I can't be entirely sure. However I am fairly confident that the "rushing" noise is not affected by the volume control.
Whereabouts is the "tone control feedback network"? Is that VR3, VR4 & VR6, VR7, etc.? Sorry, I am trying to learn here as I go along.
I take it that VR8 & VR9 are the "Slope" control and that RV5 is the component toward the top right of the circuit diagram between the two 100 "something" capacitors and the 100 Ω resistors?
All of these things seem to follow the Amplifier boards.
I know where the balance slider is so I will experiment with that when I get back. Once again, it is something that I tend not to adjust. In fact just about the only things I do use are the input selectors (Disc, Tuner & Tape for CD) and the volume control. It makes me wonder how I ever ended up with a Quad 33?
As to "freezer", would the stuff that plumbers use to avoid draining down systems work? It just so happens that I had a plumber in to replace a radiator recently and saw him use a can of that.
Whereabouts is the "tone control feedback network"? Is that VR3, VR4 & VR6, VR7, etc.? Sorry, I am trying to learn here as I go along.
I take it that VR8 & VR9 are the "Slope" control and that RV5 is the component toward the top right of the circuit diagram between the two 100 "something" capacitors and the 100 Ω resistors?
All of these things seem to follow the Amplifier boards.
I know where the balance slider is so I will experiment with that when I get back. Once again, it is something that I tend not to adjust. In fact just about the only things I do use are the input selectors (Disc, Tuner & Tape for CD) and the volume control. It makes me wonder how I ever ended up with a Quad 33?
As to "freezer", would the stuff that plumbers use to avoid draining down systems work? It just so happens that I had a plumber in to replace a radiator recently and saw him use a can of that.
The quality of the PCBs in Quad gear was never very good. Have a good look for dry joints and verdigre.
My 33 & 303 are at least 35 years old. I would have thought that dry joints would have shown up some time ago. Having said that, I guess that thermal shock may have had an effect on joints in that time?
I can't really comment on the quality of the PCBs but I would have to say that the edge connectors seem somewhat underwhelming.
I am certainly not an expert in this field but I would have thought that the symptoms sound like one or more capacitors failing somewhere?
I think you have already ascertained that one of the amplifier boards has developed a fault. I would certainly start by changing the electrolytics on that channel, buy twice ready to replace the same on the working channel but don't replace anything on that one yet.
I don't think I have.
I have swapped around the two internal Amplifier PCBs and the fault has stayed on the same channel. This would suggest to me that the problem in not associated with either amplifier board.
If I am wrong, please explain.
- Status
- Not open for further replies.