Quad 303 - earth and ground question

[mikmas]

I’ll start with the short question and then give the lengthy background for those who have the interest, time and patience to read on….

OK – here’s the thing … I am running a set up involving a satisfactory ground loop in the component chain (Mac > DAC > passive pre > Quad 303) The sound is brilliant and I have noticed no discernible adverse affect audio-wise but wonder about a potential H&S risk in that none of the electrical components have a connection with the mains earth. This situation could be remedied quite quickly and at low cost by aquiring an earthed Bulgin lead for the 303 but my question is really whether it’s essential or desirable.

As I understand it, Quad advised NOT to have separate earthed mains supplies for the 33 and 303 (as this can potentially induce hum) but to use the switched supply from the 33 to power the 303. Circuit ground requirements are taken care of through the 4 pin connector lead.

In my current (and provisional) set up, my music path begins with an optical out from my Mac -> Beresford 7520 DAC -> fixed output to DIY passive (10k Alps) -> Quad 303. At the moment the 303 is powered from the switched 33 output which is on but has no connection with the whole chain other than the 2 pin mains lead (I am using it for the inbuilt switch suppression)

Quite happy to clarify any points but thought it best to keep this brief….

[Firebottle]

For safety I would fit a three cord lead to the 303.
Modern regulations insist on any metal cased mains powered equipment to have a dedicated earth connection.

With no other unit having an earth connection it is very unlikely that you will be troubled by hum due to an earth loop ;)

:cool: Alan

[Oldpinkman]

For safety I would fit a three cord lead to the 303.
Modern regulations insist on any metal cased mains powered equipment to have a dedicated earth connection.

With no other unit having an earth connection it is very unlikely that you will be troubled by hum due to an earth loop ;)

:cool: Alan

+1. You have to have an earth. The comment from Quad relates to the preamp having an earth connection - so the power amp is earthed via its connection to the preamp.

[Gordon Steadman]

I'm glad you raised this and that Alan answered it. I have the 303 fed by a passive at the mo and I'm therefore in the same situation. I have the 303 on all the time though so don't need the switch suppression. I'll find a suitable lead!!

I'm liking the 303 more and more. It is not quite as good as the Stereo 20 but is clean and clear and lets me enjoy the music. It will be interesting to compare it with the 306:eyebrows:

[Firebottle]

It certainly will be interesting to have a 303/306 comparison, can't recall reading one before?

:cool: Alan

[Gordon Steadman]

It certainly will be interesting to have a 303/306 comparison, can't recall reading one before?

:cool: Alan

I'll bring the 303 up with me in Feb and we can have a play!! (Oh and the 33 of course for a quick wave of the magic soldering iron:))

[mikmas]

Thank you chaps for the swift confirmations - twas as I feared....
Ah well - another tenner flies out the door :roll eyes:

Don't suppose anyone has a spare set of 33 push switches kicking about a kitchen drawer :D

[DSJR]

Quad coupled the signal and chassis earths together in their power amps I recall (definitely the 405mk1 series) and this was why the 33/303 from the mid 70's certainly, had just a two core mains lead from the 303 to 33 preamp, as the 303 chassis earth was taken via the signal screens, NOT a very satisfactory solution these days. I think Naim did the same, but can't remember now for certain.

Hope I'm right with the above, but it's a while since I got inside a 33 and 303 to check.

Have a word with the Dada guys, or join the Yahoo Quad group. Loads of genuine experienced experts posting there who can help.

[Light Dependant Resistor]

Quad coupled the signal and chassis earths together in their power amps I recall (definitely the 405mk1 series) and this was why the 33/303 from the mid 70's certainly, had just a two core mains lead from the 303 to 33 preamp, as the 303 chassis earth was taken via the signal screens, NOT a very satisfactory solution these days. I think Naim did the same, but can't remember now for certain.

Hope I'm right with the above, but it's a while since I got inside a 33 and 303 to check.

Have a word with the Dada guys, or join the Yahoo Quad group. Loads of genuine experienced experts posting there who can help.

The Quad 303 arranged its ground return via the signal lead Pin 2 of its din input socket when partnered with the supplied AC cords and used with a 33. Their intention was two part that I see partially to have a star earth with the preamp being that point, and at the same time also to have AC supply from the 33. There is difference of 2.2 ohms arranged by R115 between the input grounding and the output stage fed by the regulator collector transistor TR 3, so it was Quads design intention to have its output stage and regulator lifted by R115 and this remains when a 3 wire cable is correctly used.

The 303 arranges its earth correctly back to the Bulgins mains connector, and in the case of later models to the IEC socket, So there are no safety concerns with the 303 if used with a three wire mains plug - be it Bulgins or IEC.

However if your set up has it partnered with a two wire AC cable back to the 33 or to other equipment, this should be changed to be a three wire cable in order to comply with safety standards.

Further information is here: http://quadrevisionspot.blogspot.co.nz/2009/03/hum-most-of-hum-problems-are-related-to.html

[mikmas]

Thank you David and Chris for the great responses and the info links, I had actually read the DADA article before which kind of prompted my original question. The situation I have at the moment is a bit of a different one in that I am currently (and temporarily) using the 303 as power amp with no connection to the 33 bar the 2 pin switched lead. I figured it would be wise to therefore get a second earthed lead for the 303 to use it in the combination given above and switch it seperately before using that set up any further. I can of course use the 33 mains lead but want to keep the 33 ready to go so I can change back to routing the DAC via the 33/303 combo - simply because unplugging the Bulgin from the 303 each time is a pain in the butt given where it is located on the housing.

This leads on to another question of whether a mains earthed 303 (used without the 33 at all) will require an isolated ground loop with the DAC and passive pre to prevent a whole different issue cropping up (mentioned in the responses on the DADA site) - i.e. meltdown!!!

I think for the moment I'll flip back to the 33/303 combo while I wait the postman with a 3 pin lead and look out for more info on using the 303 as a stand alone.

[Light Dependant Resistor]

Thank you David and Chris for the great responses and the info links, I had actually read the DADA article before which kind of prompted my original question. The situation I have at the moment is a bit of a different one in that I am currently (and temporarily) using the 303 as power amp with no connection to the 33 bar the 2 pin switched lead. I figured it would be wise to therefore get a second earthed lead for the 303 to use it in the combination given above and switch it seperately before using that set up any further. I can of course use the 33 mains lead but want to keep the 33 ready to go so I can change back to routing the DAC via the 33/303 combo - simply because unplugging the Bulgin from the 303 each time is a pain in the butt given where it is located on the housing.

This leads on to another question of whether a mains earthed 303 (used without the 33 at all) will require an isolated ground loop with the DAC and passive pre to prevent a whole different issue cropping up (mentioned in the responses on the DADA site) - i.e. meltdown!!!

I think for the moment I'll flip back to the 33/303 combo while I wait the postman with a 3 pin lead and look out for more info on using the 303 as a stand alone.

I will be very surprised if you get anything but perfect results with your DAC , passive pre and 303 with a 3 pin mains lead, however follow the advice of using a single power point. A LDR based preamp has the ability to
give you next to total silence, and this is the next path for you to take as it will reveal far more from your system than the usual losses associated with either switched resistors or L Pad potentiometers.

Cheers / Chris