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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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21st May 2019, 12:06 pm | #1 |
Hexode
Join Date: Jun 2011
Location: Glossop, Derbyshire, UK.
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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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21st May 2019, 1:55 pm | #2 |
Dekatron
Join Date: Sep 2007
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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, GJ
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21st May 2019, 4:22 pm | #3 |
Moderator
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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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21st May 2019, 4:48 pm | #4 |
Octode
Join Date: Aug 2006
Location: Stoke-on-Trent, Staffordshire, UK.
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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 Trev |
21st May 2019, 5:03 pm | #5 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
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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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21st May 2019, 6:43 pm | #6 | |
Hexode
Join Date: Jun 2011
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Re: Quad 405 hum
Quote:
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21st May 2019, 11:12 pm | #7 |
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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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24th May 2019, 9:20 am | #8 |
Hexode
Join Date: Jun 2011
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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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24th May 2019, 11:37 am | #9 |
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Re: Quad 405 hum
That's good info!
There seem to be plenty of 405s around David
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24th May 2019, 1:28 pm | #10 |
Nonode
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Location: South Bradford, West Yorkshire, UK.
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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.
Keith |
24th May 2019, 5:24 pm | #11 |
Pentode
Join Date: Nov 2017
Location: London, UK.
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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. |
25th May 2019, 11:35 pm | #12 |
Octode
Join Date: Jan 2007
Location: Dorridge, West Midlands, UK.
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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.
Chris |
26th May 2019, 8:27 am | #13 | |
Hexode
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Re: Quad 405 hum
Quote:
Dave
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27th May 2019, 7:08 am | #14 |
Heptode
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Re: Quad 405 hum
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27th May 2019, 7:57 am | #15 |
Dekatron
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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 Last edited by Craig Sawyers; 27th May 2019 at 8:14 am. |
27th May 2019, 8:02 am | #16 |
Heptode
Join Date: Jun 2006
Location: Eindhoven, Netherlands.
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Re: Quad 405 hum
Thanks Craig,
In that case, I always calculate my designs with "audio grade" transformers. Jac |
24th Jun 2019, 9:25 am | #17 |
Hexode
Join Date: Jun 2011
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Re: Quad 405 hum
I have just won 2 transformers on ebay for £67 inc postage all I need now is the bracket has any one made it , if so do you have the size
Thanks Dave
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24th Jun 2019, 10:49 am | #18 |
Dekatron
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Re: Quad 405 hum
I had considerable success with TV transformers by heating them up then suspending them in a can of lacquer, cured most of them.
Peter |
7th Nov 2019, 4:38 pm | #19 |
Octode
Join Date: Nov 2013
Location: Penrith, Cumbria, UK
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Re: Quad 405 hum
I've got a pair of 405 mk1 that have been converted into monos, looks professional if not an actual Quad conversion, the boards look to have been serviced with replacement nichicon electrolytics in PSU and on the boards. They sound fine into a pair of ESL989 speakers soI think they must be fairly healthy.
However one in particular displays a really noisy buzzy vibration from the mains transformer but it dies down to a very low level that is tolerable and inaudible from 10 feet away.This seems to take an hour or two after the amp seems to have warmed through. It doesn't run hot so I don't think theres any circuit issues. Could it be just slack windings that the potting hasn't silenced and as it warms maybe expansion takes up the space? It's acceptable after running a while but annoying when just switched on and I don't like leaving gear powered up for various reasons of safety and economy. It does seem to be load related as the offending amp starts quiet on switch on and as the reservoir capacitors charge up and I assume the output stage starts conducting the buzz starts, at times very loud then abating before giving another loud buzz and an underlying continuous loud tizz. I have wondered if a bit of DC on the mains could cause this or some psu fault but it does abate after warming up. Any ideas? Or am I best replacing the transformer and would it be best to do both monos to keep them identical? I got them at a very good price so investing in a pair of transformers would be worth it looking at the mad prices on ebay etc. I have a scope and audio sig gen as well as good multimeters. Andy. |
7th Nov 2019, 7:23 pm | #20 |
Hexode
Join Date: Jun 2011
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Re: Quad 405 hum
If only 1 is faulty just change that one as they have gone up in price to £90.64 from RS https://uk.rs-online.com/web/p/toroi...rmers/2575231/ I have 4 from the 1980's and they do not hum it seams that few rogue TX got through Quads quality control
Dave
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