Hi,

have a Quad 520f in the workshop for a minor repair after 32 years of service in a home installation. I believe the owner imported it here ( Sydney) himself.

It uses 3 pin XLR connectors for input and speakers, but is in no way "balanced". The wiring of these is atypical, done to an IEC standard to please the BBC.

Contrary to published schems and pics found on-line, input pin 1 is not connected and pin 2 is signal. This is as labelled on the back and has always been that way ( no solder on the internal pin).

PITA on the bench since it did not work properly with the usual tests leads.
I service XLR based gear almost every day and for over 40 years so the 520 is definitely an odd ball.

Anyhow, after soldering a few dodgy crimp connectors on the PCBs all is well and it meets original specs for THD etc. Only grumble is the 500VA toroidal power tranny with NO soft start system fitted.
Creates a 100A plus peak surge at switch on.

....... Phil

On Thu 28/04/2022 04:14, Phil Allison wrote:
> Hi,
>
> have a Quad 520f in the workshop for a minor repair after 32 years of service in a home installation. I believe the owner imported it here ( Sydney) himself.
>
> It uses 3 pin XLR connectors for input and speakers, but is in no way "balanced". The wiring of these is atypical, done to an IEC standard to please the BBC.
>
> Contrary to published schems and pics found on-line, input pin 1 is not connected and pin 2 is signal. This is as labelled on the back and has always been that way ( no solder on the internal pin).
>
> PITA on the bench since it did not work properly with the usual tests leads.
> I service XLR based gear almost every day and for over 40 years so the 520 is definitely an odd ball.
>
> Anyhow, after soldering a few dodgy crimp connectors on the PCBs all is well and it meets original specs for THD etc. Only grumble is the 500VA toroidal power tranny with NO soft start system fitted.
> Creates a 100A plus peak surge at switch on.
>

Maybe a silly question Phil but many years ago I got over a switch-on
surge issue on a piece of equipment by fitting a solid-state relay on
the input and driving that by other means. SSRs switch on zero crossing
so surely that would dampen if not nearly eliminate such a large
switch-on surge?

In article <06f11f56-c1cf-46f2-ad46-35aecb7d9014n@googlegroups.com>,
Phil Allison <pallison49@gmail.com> scribeth thus
> Hi,
>
>have a Quad 520f in the workshop for a minor repair after 32 years of service in
>a home installation. I believe the owner imported it here ( Sydney) himself.
>
>It uses 3 pin XLR connectors for input and speakers, but is in no way
>"balanced". The wiring of these is atypical, done to an IEC standard to please
>the BBC.
>
>Contrary to published schems and pics found on-line, input pin 1 is not
>connected and pin 2 is signal. This is as labelled on the back and has always
>been that way ( no solder on the internal pin).
>
>PITA on the bench since it did not work properly with the usual tests leads.
>I service XLR based gear almost every day and for over 40 years so the 520 is
>definitely an odd ball.
>
>Anyhow, after soldering a few dodgy crimp connectors on the PCBs all is well and
>it meets original specs for THD etc. Only grumble is the 500VA toroidal power
>tranny with NO soft start system fitted.
>Creates a 100A plus peak surge at switch on.
>
>
>
>...... Phil
>
>
>
>
>
>
>
Oddly enough got a couple of them here Phil, they have input XLR's and
have a small board thats got a Line transformer on it.

I don't think outside perhaps the BBC there are or were, many of them
about!. That version was probably made for the BBC or similar
broadcasters, maybe studios....
--
Tony Sayer

Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.

Woody wrote:
--------------------
Hi,
> >
> > have a Quad 520f in the workshop for a minor repair after 32 years of service in a home installation. I believe the owner imported it here ( Sydney) himself.
> >
> > It uses 3 pin XLR connectors for input and speakers, but is in no way "balanced". The wiring of these is atypical, done to an IEC standard to please the BBC.
> >
> > Contrary to published schems and pics found on-line, input pin 1 is not connected and pin 2 is signal. This is as labelled on the back and has always been that way ( no solder on the internal pin).
> >
> > PITA on the bench since it did not work properly with the usual tests leads.
> > I service XLR based gear almost every day and for over 40 years so the 520 is definitely an odd ball.
> >
> > Anyhow, after soldering a few dodgy crimp connectors on the PCBs all is well and it meets original specs for THD etc. Only grumble is the 500VA toroidal power tranny with NO soft start system fitted.
> > Creates a 100A plus peak surge at switch on.
> >
>
> Maybe a silly question

** Not at all.

> but many years ago I got over a switch-on
> surge issue on a piece of equipment by fitting a solid-state relay on
> the input and driving that by other means. SSRs switch on zero crossing
> so surely that would dampen if not nearly eliminate such a large
> switch-on surge?

** Zero crossing reduces the peak inrush current from a capacitor bank.

HOWEVER - it makes the huge, magnetic saturation surge from the transformer primary the worst possible - every time the AC is applied.
Why you never see it used that way.
Peak switching would reverse the order of the above.

..... Phil

tony sayer wrote:
==============
>
> Phil Allison
> > Hi,
> >
> >have a Quad 520f in the workshop for a minor repair after 32 years of service in
> >a home installation. I believe the owner imported it here ( Sydney) himself.
> >
> >It uses 3 pin XLR connectors for input and speakers, but is in no way
> >"balanced". The wiring of these is atypical, done to an IEC standard to please
> >the BBC.
> >
> >Contrary to published schems and pics found on-line, input pin 1 is not
> >connected and pin 2 is signal. This is as labelled on the back and has always
> >been that way ( no solder on the internal pin).
> >
> >PITA on the bench since it did not work properly with the usual tests leads.
> >I service XLR based gear almost every day and for over 40 years so the 520 is
> >definitely an odd ball.
> >
> >Anyhow, after soldering a few dodgy crimp connectors on the PCBs all is well and
> >it meets original specs for THD etc. Only grumble is the 500VA toroidal power
> >tranny with NO soft start system fitted.
> >Creates a 100A plus peak surge at switch on.
> >
=======================================================
>
> >
> Oddly enough got a couple of them here Phil, they have input XLR's and
> have a small board thats got a Line transformer on it.
>

** Yes, that is an option, also a soft state PCB is too.

> I don't think outside perhaps the BBC there are or were, many of them
> about!. That version was probably made for the BBC or similar
> broadcasters, maybe studios....
> --

** That may be the case with this one.
The owner is a professional guitarist - he played with the Renee Geyer band in the past.
Picked the 520f up in the UK.

( Or stole it ? )

BTW

Think is is a very cool amp, like a Quad 360 on steroids.

Even has a nice carry handle on the back !!!.

https://pinkfishmedia.net/forum/threads/2x-bbc-quad-520-series-power-amps.235054/

..... Phil

Phil Allison wrote:
-----------------------------

** Re the Quad 520f
>
> Think is is a very cool amp, like a Quad 306 on steroids.

** Bugger.....

....... Phil