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

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Old 21st May 2019, 12:06 pm   #1
nutteronthebus
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Default Quad 405 hum

Hi I have been doing those round tuit jobs of upgrading 6 Quad 405 for resale ( new power caps replace R7&8 etc ) and whilst 4 are great and look good as I have had the cases sandblasted and power coated (they were all different colours and few rusty ) 2 sound good but have a mechanical hum from the transformers . Is this one from RS ok or do the wisdom of the forum know any better one https://uk.rs-online.com/web/p/toroi...rmers/2575231/


Thanks Dave L
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Old 21st May 2019, 1:55 pm   #2
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Default Re: Quad 405 hum

I haven't checked the 405's electrical requirements against the RS part but the obvious question, to which it might be hard to get a definitive answer from the spec sheet, is "How loud does it hum ?". The description says 'Very low induced noise (hum)' but I don't know if this means that it doesn't couple stray 50Hz magnetic field into the signal circuitry or that it doesn't buzz of its own accord.

On the basis of past good experience with them I would recommend talking to Canterbury Windings http://www.canterburywindings.co.uk/standard_range.html. They specialise in toroidal transformers for audio equipment and they do understand the need for negligible noise in all respects. Perhaps the TM105A or TM301A parts from their Audio Grade list would be suitable ? Just to be clear, I have no connection with Canterbury except as a satisfied customer. But I have found them very helpful to deal with.

Cheers,

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Old 21st May 2019, 4:22 pm   #3
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Default Re: Quad 405 hum

My experience is that the designers of ordinary grade toroid mains transformers look at the higher flux levels they can run the cores to, exclaim "Oh goody!" and proceed to drop the number of turns per volt to save winding time and copper. The high flux levels mean plenty of acoustic noise from magnetostriction in the core and winding clatter.

I agree with GJ. If you want to use a toroid in your living room, you need a manufacturer who can exercise self restraint.

David
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Old 21st May 2019, 4:48 pm   #4
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Default Re: Quad 405 hum

I used to retail the 405 back in the day changed loads of transformers they used to hum !
Never did try the dc blocker with them this may be the problem The transformers are not a toroid in that the are oblong rather than a doughnut
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Old 21st May 2019, 5:03 pm   #5
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Default Re: Quad 405 hum

The very early 405 transformers often used to vibrate. A bit surprising as they are potted. Quad supplied replacements then for those affected. They soon got it sorted so only the odd one made any noise.
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Old 21st May 2019, 6:43 pm   #6
nutteronthebus
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Default Re: Quad 405 hum

Quote:
Originally Posted by GrimJosef View Post
I haven't checked the 405's electrical requirements against the RS part but the obvious question, to which it might be hard to get a definitive answer from the spec sheet, is "How loud does it hum ?". The description says 'Very low induced noise (hum)' but I don't know if this means that it doesn't couple stray 50Hz magnetic field into the signal circuitry or that it doesn't buzz of its own accord.

On the basis of past good experience with them I would recommend talking to Canterbury Windings http://www.canterburywindings.co.uk/standard_range.html. They specialise in toroidal transformers for audio equipment and they do understand the need for negligible noise in all respects. Perhaps the TM105A or TM301A parts from their Audio Grade list would be suitable ? Just to be clear, I have no connection with Canterbury except as a satisfied customer. But I have found them very helpful to deal with.

Cheers,

GJ
The 2 that I have sound like wasps in a bean tin it is worse when the lid is on as that to vibrates as well even with the damping pad fitted . Quad used to replace them as a matter of course but they are well out of any warranty by now . As Trevor and Vidjoman say most have been changed by now
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Old 21st May 2019, 11:12 pm   #7
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Default Re: Quad 405 hum

THe wasps in a bean tin comment makes me wonder if you have a snare drum effect with a cabinet part vibrating in the field.

One trick is to wrap thick copper foil around the OUTSIDE of the lamination stack, over the bulge of the windings and to solder it as a 'shorted turn' around the outside of the transformer. Being on the outside, it doesn't muck with the main field in the transformer, but it does act to cancel stray field leaking out.

David
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Old 24th May 2019, 9:20 am   #8
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Default Re: Quad 405 hum

I have found out that this part RS Stock No. 223-8235 Mfr. Part No. 0300P1-2-035 is the one that will work and at 56.54 each plus having to make a mounting bracket not a bad price ( thanks to Red Hill Audio )
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Old 24th May 2019, 11:37 am   #9
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Default Re: Quad 405 hum

That's good info!

There seem to be plenty of 405s around

David
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Old 24th May 2019, 1:28 pm   #10
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Default Re: Quad 405 hum

That's a lot cheaper than the Quad price! I had to replace the transformer on my 405 about 20 years ago and it was about 100. I hate to think what it would be now.

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Old 24th May 2019, 5:24 pm   #11
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Default Re: Quad 405 hum

For what it's worth, I've just fitted a 280VA audio grade toroid with two secondary windings into a Beomaster 4000. It was made to order by Canterbury Windings with whom I have no connection. It cost 101 including UK delivery.

It is totally silent even under load, so I can thoroughly recommend them.
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Old 25th May 2019, 11:35 pm   #12
chriswood1900
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Default Re: Quad 405 hum

For what its worth I have also repaired my humming 405 with one of those toroid transformers successfully and it was quiet and has been reliable.
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Old 26th May 2019, 8:27 am   #13
nutteronthebus
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Default Re: Quad 405 hum

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Originally Posted by chriswood1900 View Post
For what its worth I have also repaired my humming 405 with one of those toroid transformers successfully and it was quiet and has been reliable.
Chris
Did you use the RS one and how easy was it to fit as I have 2 that need them

Dave
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Old 27th May 2019, 7:08 am   #14
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Default Re: Quad 405 hum

Quote:
Originally Posted by Krolroger View Post
For what it's worth, I've just fitted a 280VA audio grade toroid with two secondary windings into a Beomaster 4000.
Stupid question perhaps, but what is an "audio grade" toroid?

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Old 27th May 2019, 7:57 am   #15
Craig Sawyers
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Default Re: Quad 405 hum

Ususally with an oversized core, and specifically arranged to have minimum acoustic hum.

For a domestic power amp playing music (rather than continuous sine, or some other artificial signal), the supply can be 70% the rating needed for the nominal power output. So a 2x100W amp will only formally need a 140VA from the supply.

Now a simple supply (bridge and reservoirs) pulls pulse-like current out of the transformer, so it needs to be 50% higher VA rating than the 70% rule - so say 200VA for a 2x100W amp.

In higher quality audio gear, (or pro audio which is turned up to 11), the transformer is significantly larger than that formally needed. This is to compensate for real loudspeaker loads, which have significant impedance (including phase) variation, and so can suck significant current.

So audio grade transformers tend to be much larger VA rating (and smoothing caps of larger value) than you might expect from a naive calculation. In the above case of 2x100W you might typically fit a 300-400VA transformer.

A good (and over the top) example is the Naim Statement, where each monoblock power amp can produce 746W into 8 ohms, 1450W into 4 ohms and 9kW pulsed into 1 ohm. That uses a 4kVA transformer. Each one (there are two of course) weighs a total of 100kg, a decent chunk of which is the transformer and the rest of the power supply.A fair chunk of the rest is the massive convection cooled heatsinks, which if you run the thing at 1450W into a 4 ohm dummy load will have to cope with ~600W of waste heat. (class B is ~60% efficient at full whack)

Craig

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Old 27th May 2019, 8:02 am   #16
Jac
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Default Re: Quad 405 hum

Thanks Craig,

In that case, I always calculate my designs with "audio grade" transformers.

Jac
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