Changing a Quad 405-2 transformer that has a buzz/hum

[high.spirits]

My Quad 405-2 transformer has a buzz/hum (mechanical), so looking to change out.
Has anyone used an RS transformer (toriodal transformer - RS part no 223-8235) in their 405-2?

If so, how did it perform and what wiring connections were used?
Thanks

[tubehunter]

Hi Martin

In my experience with the Quad 405's replacing the bridge rectifier with a 35A 400v can calm down the buzz from the transformer.

If you go ahead and change the transformer, a better model is the 223-8910 part no RS.

These encapsulated transformers are very quite.

The reason I'd go for a 500va rating is that the original is rated at 350va so a nice upgrade.

Happy days

[high.spirits]

Hi Martin

In my experience with the Quad 405's replacing the bridge rectifier with a 35A 400v can calm down the buzz from the transformer.

If you go ahead and change the transformer, a better model is the 223-8910 part no RS.

These encapsulated transformers are very quite.

The reason I'd go for a 500va rating is that the original is rated at 350va so a nice upgrade.

Happy days

Hi Duncan

Thanks for the feedback.
Have you changed the transformer to the larger one and did it fit o.k., as I have read upgrading to a larger rated one can be an issue getting the lid back on?
Did you parallel up the secondary windings?

Also have you details of the bridge rectifier you mention.

So many questions before I take the plunge :)

[danilo]

IF mine ? I'd consider remote mounting your Existing transformer. Fit it into a small box, even wooden may do.
Then Simply run wires from it's output (secondaries) into the Amp case.
Use an XLR plug if you feel the urge for it to be detachable .. Or hard wire it on.
Bit of a pain but easier than sourcing/paying for a replacement Tx, then trying to stuff it in.
Often one Tx will buzz while another identical one doesn't. Happens more often with the Square frame types rather than Torroids
There Is a wee add on circuit one Can diy to subdue the buzz (google for it)
I also wouldn't recommend the Audio Weenie; 'Bigger is better' notion.
Often causing..more.. issues than it claims to 'address'.

[high.spirits]

IF mine ? I'd consider remote mounting your Existing transformer. Fit it into a small box, even wooden may do.
Then Simply run wires from it's output (secondaries) into the Amp case.
Use an XLR plug if you feel the urge for it to be detachable .. Or hard wire it on.
Bit of a pain but easier than sourcing/paying for a replacement Tx, then trying to stuff it in.
Often one Tx will buzz while another identical one doesn't. Happens more often with the Square frame types rather than Torroids
There Is a wee add on circuit one Can diy to subdue the buzz (google for it)
I also wouldn't recommend the Audio Weenie; 'Bigger is better' notion.
Often causing..more.. issues than it claims to 'address'.

Thanks Danilo

I had not considered that. However I do not want any more boxes and I think the hum will still be there from the transformer windings in the frame.
Will google the other mod. cheers

[danilo]

Welll.. it's IMO a decent solution.. An Audio Weenie approved one too. More boxes are a Badge of Honor.
Those pesky Tx's often Hum into the Amp casework, Mains power, 50 or 60hz, geography dependant.
Isolating the rascals .. rubber pads Work.. on the Hummmm.
But it can Bite one, did for me .. sending the buzz into the circuitry ultimately the speakers. Far worse.
If the Tx is in a stand alone box then it can happily Hummm away.
Placing the humming box on a towel or something more elegant if you prefer.. Works!

[HarryCrumb]

Hope you don't mind me resurrecting an old thread Martin but I'm just about to order the torodial transformer that you suggested to me in my classified add a few weeks ago. I'm not confident working with transformers though so I wanted to get some advice on how to wire this one in.

It's the Nuvotem Talema 230ac 2 x 35v. I'm fairly sure that I should be wiring each of the secondary positives to the rectifier, and then binding the negatives together and grounding them, in my case to a bridge between the PS smoothing caps.

Because I'm new to electronics, and because I'm aware of there being different ways to wire a transformer up, and certainly because I don't want to blow anything up, I would appreciate anyones thoughts here.

https://i.postimg.cc/3RgjtKFk/Screen-Shot-2020-09-16-at-18-30-08.png

[high.spirits]

Let me dig out the paperwork tomorrow and I will see if I can find the original photos showing connections to the existing transformer wiring. A picture paints a thousand words!


Hope you don't mind me resurrecting an old thread Martin but I'm just about to order the torodial transformer that you suggested to me in my classified add a few weeks ago. I'm not confident working with transformers though so I wanted to get some advice on how to wire this one in.

It's the Nuvotem Talema 230ac 2 x 35v. I'm fairly sure that I should be wiring each of the secondary positives to the rectifier, and then binding the negatives together and grounding them, in my case to a bridge between the PS smoothing caps.

Because I'm new to electronics, and because I'm aware of there being different ways to wire a transformer up, and certainly because I don't want to blow anything up, I would appreciate anyones thoughts here.

https://i.postimg.cc/3RgjtKFk/Screen-Shot-2020-09-16-at-18-30-08.png

[spendorman]

I bought my 405 new in 1976, the transformer had a bit of mechanical noise, but not too bad. I didn't use the amp much and later found out that Quad were providing free replacements. I didn't bother. Strangely, the mechanical noise reduced with time and usage.

Some time later I upgraded the op amps and this improved the sound quality noticeably and very cheaply.

In 1987 I upgraded the 405 with the Quad -2 kit. The mechanical noise was pretty well not detectable, however, the sound was not really different to the upgraded op amps stage.

I still have the amp, and it's still quiet.

[Barry]

I have five Quad 405s, all having had various modifications and tweeks applied to them, but all use the original potted bi-limboid transformer and none of them hum or buzz.

But I have heard of others experiencing this problem with the Quad mains transformer.

If you use the toroidal transformer cited above, the black and yellow leads should be connected together to the 0V rail (the green wires), and the red and orange leads connect to the bridge rectifier.

[spendorman]

It was fairly early on in production that this mechanical noise was reported, I think Quad soon got to grips with it. I was disappointed with mine as it was the first brand new piece of Quad equipment that I bought, and it was not cheap. I am very happy with it now though!

[high.spirits]

Let me dig out the paperwork tomorrow and I will see if I can find the original photos showing connections to the existing transformer wiring. A picture paints a thousand words!

Just had a look to see what I had done and I have connected the following wires to the existing transformer wires. If you have the Quad wiring diagram the transformer terminals are numbered. This has illiminated the voltage switching so permantly 240v.

Torodial Orange & Black to Quad xformer green wire (terminal 7A linked 6A, 7B, 6B on xformer)
Torodial Yellow to Quad yellow (outer terminal 5B linked to 8A)
Torodial Red to Quad yellow ( inner 8B linked to 5A)

I hope that helps.

[Barry]

Thanks, that confirms what I wrote in post 10.

[HarryCrumb]

Martin, thank you for checking. The way you describe your wiring is different to how Barry describes in post 10. Or is that essentially the same thing? His description is how I would have thought best to do it - Red and Orange to Rectifier. Black and Yellow form centre tap to ground.

I've just spoken to Quad and double checked the price of a replacement transformer. It's not as much as I seemed to remember, coming in at £90 inc vat. The torodial that we are discussing comes in at £86 (plus a little to have a mounting plate made) so I'm currently mulling over my options. The torodial would be the better transformer in theory, but the original style may be a safer bet in terms of fit, and possible re-sale (though I have zero plans to sell my 405's).

I've got four 405's and really love them as amplifiers. They sound great with my speakers and are a joy to tinker with or work on. I would be interested to know if anyone has noticed an audible difference with a torodial?

[spendorman]

That Quad price for a replacement transformer seems pretty good, I'd go for that, but others probably will have different views.

[Barry]

Martin, thank you for checking. The way you describe your wiring is different to how Barry describes in post 10. Or is that essentially the same thing? His description is how I would have thought best to do it - Red and Orange to Rectifier. Black and Yellow form centre tap to ground.

I've just spoken to Quad and double checked the price of a replacement transformer. It's not as much as I seemed to remember, coming in at £90 inc vat. The torodial that we are discussing comes in at £86 (plus a little to have a mounting plate made) so I'm currently mulling over my options. The torodial would be the better transformer in theory, but the original style may be a safer bet in terms of fit, and possible re-sale (though I have zero plans to sell my 405's).

I've got four 405's and really love them as amplifiers. They sound great with my speakers and are a joy to tinker with or work on. I would be interested to know if anyone has noticed an audible difference with a torodial?

I think Martin and I are saying the same: Black and Yellow joined together to form a centre tap to the 0V rail (green wire on the Quad transformer), with the Red and Orange wires going to the bridge rectifier and replacing the yellow wires on the Quad transformer.

I have three stereo 405s (with various levels of upgrade and improvement) and two of which have been 'monoblocked' (i.e. converted to single channel amplifiers) and extensively modified. However, in all of them the potted Quad transformer has been retained (and all are mechanically silent).

If it was up to me - I would replace your buzzing transformer with a Quad replacement. The cost is virtually the same, the new transformer is guaranteed to fit, and more importantly the resale value of your amp would be preserved.

[HarryCrumb]

Thanks for everyones comments. I was in the neighbourhood on Monday...sort of.... So I called in at IAG House and picked one up. Not quite as new and shiny as the torodial may have been, and I will forever wonder how it would have looked, but there you go. I agree that a guaranteed fit and re-sale value are important enough.

I'm going to bypass the voltage selector as I don't see any benefit of having it wired in, and I'm going to hard-wire it for 240v as per the later Quad 405-2. Diagram below;

https://i.postimg.cc/rmHF5y8T/Screen-Shot-2020-09-24-at-18-23-33.png