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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 7th Nov 2019, 7:51 pm   #21
bikerhifinut
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Default Re: Quad 405 hum

Thanks Dave,
I was recommended this company a while back by another forum member and their products look very good value.
I wonder if that would fit the bill being potted in epoxy and with internal screening etc.
https://sklep.toroidy.pl/en_US/p/TTS...ge-to-50V-/317

The price works out just shy of £49 at todays exchange rate with the Zloty.

Andy
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Old 7th Nov 2019, 7:59 pm   #22
nutteronthebus
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Default Re: Quad 405 hum

I know the RS one fits but you have to move the fuse holder look to the data sheets as the RS one is 115mm by 58mm where as the other one is 130mm by 44mm measure the Quad to see if it will fit and get the 2 X35v one

Dave
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Old 7th Nov 2019, 8:16 pm   #23
bikerhifinut
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Default Re: Quad 405 hum

yes I see, it would be tight so measure carefully first. I figure moving the fuse etc would be relatively easy and I was also looking to fit a power switch too. Not sure if there are fused IEC inlets that would fit the existing hole.
I've got a 405-2 also that's got a quiet transformer so I did wonder if it was a practical proposition to swap them over as a sort of test to make sure that it is the transformer at fault and not something else in the circuit doing it. Its weird that the noise diminishes as the amp warms through.
Thanks for the help Dave, much appreciated.

A.
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Old 7th Nov 2019, 10:48 pm   #24
greg_simons
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Default Re: Quad 405 hum

For what's it's worth i can confirm 405 transformers could be noisy, had to replace one in my own bought from new many years ago?
Greg.
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Old 7th Nov 2019, 11:28 pm   #25
bikerhifinut
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Default Re: Quad 405 hum

Quote:
Originally Posted by greg_simons View Post
For what's it's worth i can confirm 405 transformers could be noisy, had to replace one in my own bought from new many years ago?
Greg.
Thanks Greg,
Yeah it does seem the earlier 405 could do this as well as not being quite as refined and reliable as the late 405-2 but it also seems like most of them have been updated etc.
These are monobloc conversions that look very well done and I think they could well be official Quad jobs. Certainly the internal boards look serviced with no obvious toasted components and modern Nichicon electrolytics, all neat and tidy. I should check the board version next time the lids are off.
I suspect from the tired cosmetics that these have been "pro" used in a PA system and maybe that's why a rattly transformer has got through the net as it wouldn't be audible when these were pumping out 180 watts into an Auditorium?
It does settle after a while but in a domestic environment we need them to be up and singing as soon as they are powered up.
I am minded to swap the quiet transformer from my 405-2 stereo amp in and then see how things go, nothing to lose except an hour or 3 of my time. If that cures it then I can sort the 405-2 out or sell it on at a price reflecting any transformer noise. I got these monos for a song so I don't feel cheated and looking at the prices asked on the web for them I still will have come out on top. I'm very impressed with both the 405-2 and the monos especially driving big Quad ESL989s and I reckon they are as good as any modern power amplifier in this role. Horses for courses and all for a tiny fraction of buying the stuff new! Been an object of desire for most of my life and thankfully they haven't quite gone the way of the Valve stuff which is now beyond my means as an enthusiast and fan of the older audio gear.
But I digress.

A.
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Old 14th Nov 2019, 4:10 pm   #26
bikerhifinut
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Default Re: Quad 405 hum

When you fitted the toroid transformer, did you fit a varistor across the primary winding? I just wondered as a 300VA transformer might be capable of a huge voltage spike if switched off at the wrong part of the cycle?
For what they cost I think I would anyway.

I swapped the noisy transformer for the quiet one on my 405-2 stereo amp. It doesn't hammer quite as loud as before, mind you I did discover a couple of less than tight mounting screws but all the same it buzzes within a minute of switch on and then diminishes over the next 30 minutes as it warms up. So long term I think a replacement will be on the cards.
A.
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Old 15th Nov 2019, 5:57 pm   #27
bikerhifinut
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Default Re: Quad 405 hum

Quote:
Originally Posted by bikerhifinut View Post
When you fitted the toroid transformer, did you fit a varistor across the primary winding? I just wondered as a 300VA transformer might be capable of a huge voltage spike if switched off at the wrong part of the cycle?
For what they cost I think I would anyway.

I swapped the noisy transformer for the quiet one on my 405-2 stereo amp. It doesn't hammer quite as loud as before, mind you I did discover a couple of less than tight mounting screws but all the same it buzzes within a minute of switch on and then diminishes over the next 30 minutes as it warms up. So long term I think a replacement will be on the cards.
A.
That post could be a bit ambiguous, I meant to say that the monobloc with the quiet transformer out of the 405-2 is now as quiet as it should be, and the 405-2 which has the noisy transformer installed buzzes, albeit not quite as loud as it did before which I suspect was down to loose mounting screws at the front of the potting box. It still buzzes louder than I consider acceptable for a hifi amplifier in a domestic lounge though. But thanks to the info here it will be an affordable and worthwhile repair.

A.

Last edited by bikerhifinut; 15th Nov 2019 at 5:58 pm. Reason: wrong werd used.....
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