Quad 33/303 earthing

[reddish75]

I'm looking to see if there's a way to use earthed mains cables with both the Quad 33 and 303 when there being used together without potentially inducing hum? Obviously the most direct way using the ungrounded sockets on the back of the 33 but this isn't up to modern standards and I'd like to avoid connecting this way if possible. Any ideas?

[Craig Sawyers]

Modern standards? If you are going for that, you need to rewire everything mains internally in both with double insulated wire. And shroud every connection with boots or shrink fit sleeving. And check for creepage and clearance distances.

I just use the mains connection that Quad specified and have done with it. No hum.

Craig

[GrimJosef]

You could break the ground loop by using a pair of isolating transformers in the signal links between the 33 and 303. When it comes to such transformers, you pretty much get what you pay for, although as always the law of diminishing returns sets in at the top end of the price range.

There is also some chance that if you earth the 33 you'll change the ground loop current which might flow between it and whatever sources you're using. If the signal levels are low there then even a relatively low level of new hum might degrade your signal-to-hum level significantly.

Cheers,

GJ

[reddish75]

Maybe poorly worded to say modern standards.

So no easy way to separate chassis and signal ground hum free in the 303 so a safety ground can be used?

If its the only way does anyone have s source for those two pin flat blade power connectors?

[Craig Sawyers]

I got mine from here https://shop.dadaelectronics.eu/quad...108463194.html but they are out of stock.

Craig

[GrimJosef]

I'm not familiar with the detailed grounding arrangements inside the 303, but the signal ground could probably be separated from the chassis if you were prepared to do some rewiring.

The first safety risk that you'd introduce would be that there would no longer be a path from the speaker -ve terminals to safety ground in the event of the 33 being disconnected. Since the speaker leads are easily accessible to you and to anyone else in the household you'd have to bear that in mind. You might reduce the risk using an 'earth lifter' (beefy anti-parallel silicon diodes) between the two grounds. There might also still be hum issues if there were capacitative coupling between the chassis and signal ground.

Cheers,

GJ

[Craig Sawyers]

Another one here http://www.quad-musik-shop.com/mains...-Bulgin-socket but not cheap!

Craig

[Craig Sawyers]

I suspect that it is actually a two pin US connector. All the commercial offerings have a captive two flat pin connector, which would figure. For example RS 870-2228.

If so, a Quad power cable can be made by chopping off the other end and wiring in a Farnell 313981.

Job done. Assuming you know how to solder.

Craig

[fetteler]

Like Craig, I use a Quad 33/303 very happily with the original power arrangement without any problems whatsoever. I feel there is little point attempting to change anything, these amps are used in their thousands around the world and if there were issues with safety I am sure they would be well documented and talked about.

In short, "If it aint broke, don't fix it!"

Sit back and enjoy the music

Steve

[reddish75]

Originally Posted by Craig Sawyers

I suspect that it is actually a two pin US connector. All the commercial offerings have a captive two flat pin connector, which would figure. For example RS 870-2228.

If so, a Quad power cable can be made by chopping off the other end and wiring in a Farnell 313981.

Job done. Assuming you know how to solder.

Craig

I looked at those from Rs but rated for 125v, sutible?

[fetteler]

American style 2 pin - Nema 1-15 (type A) is used in many countries on 230V.

See here:

https://www.netio-products.com/en/gl...lectrical-plug

HTH

Steve.

[Craig Sawyers]

I've measured the pins on a Quad two prong connector that goes into a 33, and it is definitely a NEMA 1-15P connector (blades 1⁄4 inch (6.4 mm) wide, 0.06 inches (1.5 mm) thick, 5⁄8–23⁄32 inch (15.9–18.3 mm) long, and spaced 1⁄2 inch (12.7 mm) apart).

And yes it is formally rated at 115V AC. But that is what Quad used. In the service manual it lists the lead as "lead - US two pin"

I'll bet that there has been no problem with that in practice in the many tens of thousands of 33/303 sold.

And of course the Bulgin mains input connector on the 33 and 303 are very far removed from anything that would pass modern safety standards!

So where do you stop with this? To bring a 33/303 up to modern safety standards would require major mechanical surgery to put IEC connectors on both, both for mains input, and the switched outputs on the 33.

But look - it is your gear, so you can do with it what you wish, and wire the mains as you think fit. Taking everyone's advice is not a requirement.

Craig

[McMurdo]

its a wonder they ever got away with it when new, I doubt it'd have passed a BEAB inspection even as far back as the 60's.

[Ted Kendall]

The 33/303 was of its time, no more and probably less dangerous than anything else on the market. Trouble is, as I find myself saying often, it is still a good bit of kit decades beyond its design life. You can't very well condemn it for not being what it couldn't set out to be in the first place.

[Hartley118]

Technical responsibility becomes an issue here once a modified piece of equipment is offered for sale, or even offered for use by a third party. As Ted makes clear ‘The 33/303 was of its time’. There’s always been conflict between technical earthing and safety earthing: I gained some of my grey hairs sorting out such issues in studio installations.

Once you modify the earthing on a piece of ‘of its time’ kit, you automatically assume personal responsibility for its safety, and often enough it’s impossible fully to get it to comply with today’s standards. Should a third party suffer a shock, you could get into legal arguments as to whether you employed ‘all reasonable endeavours’ to ensure safety. Better and safer to leave it ‘of its time’ with appropriate cautions.

Martin

[fetteler]

I suppose if the electrical safety of the 33/303 is of real concern then running the entire system from an isolation transformer is one option. The advantage is safety and simplicity without the need for any modifications and who knows - there may even be some audiopool related advantage to it

Steve.

PS RS Stock No. 278-7074 is a 100VA isolating transformer for £42.72 inc VAT. Compared to the trouble of modifying the amp that's pretty good value.

[Craig Sawyers]

There is a risk of overthinking this.

Back in the mid 70's we used 303's as disco amps, and a more beaten up clutch of them could not be imagined. The casework looked like they had been thumped liberally by a hammer. They had beer spilt in them (and worse) and they never failed once. I can't recall what the earthing arrangement was, but I'd be surprised if it was anything different to the manual standard way. And I don't recall any hum.

Craig

[GrimJosef]

Originally Posted by fetteler

... RS Stock No. 278-7074 is a 100VA isolating transformer for £42.72 inc VAT. Compared to the trouble of modifying the amp that's pretty good value.

Even better value might be to sell the Quad 33/303 to someone who's happy with them as they are and to buy a more modern amplifier. There's no shortage of them and it's quite possible to end up with cash left over .

Cheers,

GJ

[Synchrodyne]

Originally Posted by McMurdo

its a wonder they ever got away with it when new, I doubt it'd have passed a BEAB inspection even as far back as the 60's.

That’s hard to call. In a general sense, as individual pieces of equipment, both the 33 and 303 had three-pin power connectors, so with three-core power leads each would appear to have met the “Class I” (or whatever they were called at the time) requirements. At the time, the Bulgin three-pin power connector used might not have been irregular, so as to speak.

In those days, in domestic audio, the almost inevitable conflict between protective and functional earthing requirements was usually resolved in favour of the functional side. Thus the 33-to-303 power interconnect was of the two core type, with the assumption that protective earthing of the 303 would be handled by the signal interconnect, thus avoiding a potential hum loop. The 33 itself was normally connected to the power outlet by a three-core lead, inclusive of the protective earth, although that may have been varied in territories where, at the time, protective earthing via the power outlet was not always available. Usually it was the control unit or integrated amplifier of a component system that was protectively earthed, with the subsidiary components feeding it often relying on their respective signal earth connections to provide protective earthing. Even then there were other potential conflicts that could create hum loops, such as with tuners. An AM tuner might have its chassis connected directly to an RF earth, as well as being earthed by the signal interconnect. (These days, in some jurisdictions, that would be irregular in that it provides a forbidden alternative protective earth path.) An FM tuner might be connected to a coaxial aerial feeder whose braid was earthed at some point in its travels (such being required in some jurisdictions).

The move, in the 1970s I think, to double-insulated domestic audio equipment provided some relief. The Meridian 207 combination CD player/control unit of the 1980s was I think illustrative. Being double insulated, it did not need protective earthing. But the signal earth could be referenced to power supply earth via the three-core IEC power connector and associated lead. There was a ground lift switch on the rear panel that allowed this or not as required.


Cheers,