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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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16th Jul 2020, 12:21 pm | #1 |
Triode
Join Date: Aug 2019
Location: Basel, Switzerland
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Quad 303 thundering (in a bad way)
Ten minutes after turning on and listening to my old Quad 303 (one of a bi-amped pair) it did a realistic impression of a storm breaking overhead, as in deep rumbles followed by claps of thunder that got louder until they were deafening. Same again today. Not sure if it was both channels (amp drives one speaker with signal split high/low) but the claps were so convincing that I suspect it was. It's on at the moment to check that, but of course it's perfectly well-behaved just now.
I rebuilt it a few months ago with a Dada electronics kit, so main caps and lots of components on the power and driver boards are new. Sounded great, but now I'm now steeling myself to strip it all apart again. Could anyone suggest what I might be looking at and where to start the troubleshooting? Many thanks! |
16th Jul 2020, 12:29 pm | #2 |
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Re: Quad 303 thundering (in a bad way)
Is this the same Quad 303 which featured in this thread? You were offered advice, but never came back to us with an update:-
https://www.vintage-radio.net/forum/...d.php?t=158714
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17th Jul 2020, 8:40 am | #3 |
Triode
Join Date: Aug 2019
Location: Basel, Switzerland
Posts: 32
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Re: Quad 303 thundering (in a bad way)
Hi Graham, no, unfortunately I never got anywhere with that one. Sorry for not reporting back but after a few weeks of trying and failing to stop the main fuse blowing, I realised I wouldn't be up for risking another set of Dada boards in it even if I did make some progress. Consequently it's still in bits downstairs and instead I found a 303 with a battered case and started from scratch.
So the two amps I'm using have been good for the last six months, since their revision with Dada upgrades for the main caps, PSU and drivers boards. The problem is new and came on suddenly. I'll measure the voltages as soon as I have the time (a broken dishwasher needs me too) but just wondered if anyone has come across this problem before? |
17th Jul 2020, 1:33 pm | #4 |
Octode
Join Date: Jul 2011
Location: Staffordshire Moorlands, UK.
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Re: Quad 303 thundering (in a bad way)
Does the DaDa refurb kit include presets? If not then they would be my prime suspect. In any case you need to do some basic faultfinding like deciding if it's one or both channels and is the output of the PSU OK.
Steve.
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17th Jul 2020, 2:35 pm | #5 |
Nonode
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Location: Bristol, UK.
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Re: Quad 303 thundering (in a bad way)
Bi-amped, could be with / without active crossovers ?
Does one amplifier drive L only and the other amplifier R only (optimal) ? In any case I would try it with only 1 amplifier powered up at a time. dc |
17th Jul 2020, 3:14 pm | #6 |
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Re: Quad 303 thundering (in a bad way)
Take a few steps backwards.
Lose the active crossover, lose the good speakers. Try one 303 alone as a simple full frequency range stereo setup into some cheap (sacrificial) speakers. Get it going properly like this, then its compatriot, before trying to reassemble the biamp setup. There are fewer uncertainties to ponder this way, and clues are more easily interpreted. David
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17th Jul 2020, 5:55 pm | #7 |
Triode
Join Date: Aug 2019
Location: Basel, Switzerland
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Re: Quad 303 thundering (in a bad way)
Thanks everyone. It's a passive crossover set up, with one amp for each speaker so the faulty amp is easy to spot. The problem continued with it disconnected from the source. Great idea about the sacrificial speakers particularly as I can run them l/r instead of hi/low. It will make it more obvious if it's a single channel issue. Dada kit included handfuls of resistors, capacitors, diodes and two trim pots for each driver board, one for the PSU board.
The problem there as soon as I turned back on after a two minute break. Yesterday morning it took five minutes and having left them powered a few hours it was still silent as after an hour, but with no load. |
17th Jul 2020, 7:49 pm | #8 |
Pentode
Join Date: Feb 2020
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Re: Quad 303 thundering (in a bad way)
Steve, I believe you also asked a similar question in the Quad Dada forum some months back?
I agree with David that you need to return the units to their correct original set up before starting any debug activities. As suggested a good start is to ascertain which channel (or both) is faulty - then get back to this forum with some voltages etc, there's plenty of help available!
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17th Jul 2020, 8:18 pm | #9 |
Triode
Join Date: Aug 2019
Location: Basel, Switzerland
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Re: Quad 303 thundering (in a bad way)
Thanks Pete, different amp and problem but yes, will start to narrow it down with some testing and will report results.
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19th Jul 2020, 12:12 pm | #10 |
Triode
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Location: Basel, Switzerland
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Re: Quad 303 thundering (in a bad way)
10 hours of listening and it's not missed a beat. Beginning to believe I can fix things by staring at them really hard. I'll report back as soon as that changes!
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19th Jul 2020, 1:08 pm | #11 |
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Re: Quad 303 thundering (in a bad way)
The danger of that method is what they do when you stop staring at them.
It's very difficult fixing something while it's working properly. David
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20th Jul 2020, 2:19 am | #12 |
Octode
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Re: Quad 303 thundering (in a bad way)
In my experience, things which sometimes work and sometimes don't almost inevitably have some sort of physical reason for the failure; plain old fractured wires (the 303 has single strand wiring), weird dry joints, hairline cracks in pcb tracks, strange thermal effects in resistors and caps, even stranger failures of transistors.. etc. etc.
Get in there, switch it on and have a good old poke around and tap every component to see if you can provoke the fault. I remember a guitar amp which occasionally made noises - turned out to be a ceramic disc capacitor which, when I gave it a gentle tap with a screwdriver handle made a deafening noise. Steve.
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Those who lack imagination cannot imagine what is lacking... Last edited by fetteler; 20th Jul 2020 at 2:25 am. |
20th Jul 2020, 9:07 am | #13 |
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Re: Quad 303 thundering (in a bad way)
The key is in finding how to get it not working properly, and if the method of doing so doesn't directly reveal the fault, then at least you can get it sulking while you probe interesting places.
The insulated handles of a variety of sizes of screwdrivers down to little plastic trimming tools serve me as graduated clout generators. David
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20th Jul 2020, 1:38 pm | #14 |
Nonode
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Re: Quad 303 thundering (in a bad way)
Trying to provoke faults with hot / cold on a hair dryer is also worth trying!
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20th Jul 2020, 4:09 pm | #15 | |
Octode
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Re: Quad 303 thundering (in a bad way)
Quote:
Steve/
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20th Jul 2020, 6:02 pm | #16 |
Triode
Join Date: Aug 2019
Location: Basel, Switzerland
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Re: Quad 303 thundering (in a bad way)
Cheers for that. still short on time and holiday coming up fast but when I do get time to pull it apart I will torture it as directed. Currently it's still on its best behaviour.
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13th Aug 2020, 11:38 am | #17 |
Triode
Join Date: Aug 2019
Location: Basel, Switzerland
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Re: Quad 303 thundering (in a bad way)
Well, I've poked, prodded and listened for hours and haven't been able to provoke the thunder to come again. I should be pleased but I'd prefer to know what it was. Anyway, many thanks for the suggestions and if/when it returns I will let you know.
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13th Aug 2020, 1:36 pm | #18 |
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Re: Quad 303 thundering (in a bad way)
Well, if it's fixed itself then it still leaves you with that nagging uncertainty that you don't have a definite reason why it won't do it again.
I'm still wondering just what 'Thundering' was. The main issues I've had with 303s have been oscillations around 10MHz appearing only on part of the waveform of a audio signal (unstable triplet!) David
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13th Aug 2020, 6:23 pm | #19 |
Dekatron
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Re: Quad 303 thundering (in a bad way)
They were pretty sensitive to the fT of the 2N3055 output devices (they have a weird RCA all digit number). The original hometaxial base devices were really sluggish with an fT of 800kHz, whereas modern 2N3055's have an fT of 2.5MHz.
Craig |
13th Aug 2020, 11:28 pm | #20 |
Octode
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Re: Quad 303 thundering (in a bad way)
Steve
You have a private message. Mike |