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View Full Version : FS: Quad 520C Dual Mono Rack Mount Power Amp



twotone
23-03-2025, 19:20
For sale is a Sound association variant of the Quad 520C PA.

I'm looking for £230 posted to a UK postcode or £200 picked up from me here in Glasgow.

Payment by bank transfer or cash on collection.

I bought the amp last week from a seller on AV forums and have decided to move it on.

The amp works perfectly but after comparing it to my Marantz NR-1200 and connecting the pre outs to the Quad there really isn't a great deal of difference.

The amp comes with all of the cables and a kettle type power cable.

No original box but it was well packed when I received it last week so I can use that packaging that the amp arrived in.

The previous owner is an electronics engineer and he upgraded the amps to work with modern equipment.

Here's the specs and comments from the previous owner etc from the advert.

"Quad SA520C 2U rackmount amp, Sound Associates edition built by Quad used in Odeon Cinemas.
Based on the most recent rev 8 520 board and power supply.
Mainboard Electrolytic capacitors upgraded."

"All Quad amps are dual mono, single transformer but dual windings, dual power supplies."

"I did the upgrade myself, I'm an Electronics Engineer, this is why I bought them originally, the Quads are very easy to get parts for and repair, unlike most more modern amps.

I replaced the main power supply Electrolytic Capacitors when I bought the amp.

I added multiturn input attenuators, these Quad amps operate on 0.5v signals and modern preamps and processors output 1v, some up to 4v.

I changed the input filter capacitor resistor network to the same later design as the Quad 707 & 909, this gives a better frequency response below 50Hz, useful if the amp is used without a subwoofer for stereo."
Specifications​
Power output: 100 watts per channel into 8Ω (stereo) (140watts into 4 Ohms)

Frequency response: 20Hz to 20kHz

Total harmonic distortion: 0.1%

Input sensitivity: 0.5V (modified, adjustable from 500mv to 4v)

Signal to noise ratio: 115dB

Dimensions: 482.6 x 88 x 310mm

Weight: 12.5kg

https://i.imgur.com/Ks1Yf8f.jpeg

https://i.imgur.com/7c7I9xX.jpeg

https://i.imgur.com/sFl5lur.jpeg

https://i.imgur.com/RGn7ZlM.jpeg

https://i.imgur.com/oHqszQS.jpeg

Barry
23-03-2025, 19:33
That's a bit of a bargain Tony.

With the added (internal?) input attenuators and other modifications it turns the power amplifier into a 'breathed on' Quad 520f, which is already a very good design.

Good luck with the sale.

twotone
23-03-2025, 20:32
That's a bit of a bargain Tony.

With the added (internal?) input attenuators and other modifications it turns the power amplifier into a 'breathed on' Quad 520f, which is already a very good design.

Good luck with the sale.

Thanks Barry, I bought it last week for that price from a very nice guy on AV forums.

Bought it to try with a Marantz NR1200 pre-outs going into the Quad as I've a pair of speakers that are 8ohms but only 86db and to be honest there wasn't a great deal of a difference between the Marantz on it's own or through the Quad.

They're real sleepers these amps.

twotone
24-03-2025, 09:07
Some internal photos guys and some additional information.

The amp has the 12828-8 PCB per the below link.

The Quad 510 and 520 were the first professional current dumping amplifiers. Produced from 1984 until 1995.

Production numbers:

Quad 510 Mono 19" Rack Amplifier(Pro), produced from 1984-1989 numbers: 3200
Quad 510 Mono 19" Rack Amplifier(Neutrik)Pro), produced from 1989-1995 numbers: 600
Quad 520 Stereo 19 " Rack Amplifier(Pro), produced from 1984-1986 numbers: 4000
Quad 520f Stereo 19 " Rack Amplifier(Pro), produced from 1986-1989 numbers: 7500
Quad 520f Stereo 19 " Rack Amplifier(Neutrik)Pro), produced from 1989-1995 numbers: 3000

https://quadrevisionspot.blogspot.com/2010/04/revision-of-quad-520f.html

https://i.imgur.com/T8EaaZD.jpeg

https://i.imgur.com/67tPd6D.jpeg

https://i.imgur.com/hxUt3qF.jpeg

https://i.imgur.com/oKAWQvU.jpeg

https://i.imgur.com/755VKu0.jpeg

twotone
24-03-2025, 15:01
Sold Subject to the usual guys.

Barry
24-03-2025, 15:06
Well done. I was on the verge of buying it myself, to add to my collection of Series 5 Quad amps, so I have now been saved from the disapproval of my partner!

twotone
26-03-2025, 09:59
Well done. I was on the verge of buying it myself, to add to my collection of Series 5 Quad amps, so I have now been saved from the disapproval of my partner!

Aye it went fairly quickly on PFM one of the members on here, who I sold speakers to years ago, bought it.

BTW, if you're serious about buying one of the amps the guy on AV forums who I bought it from has four of them left, two Quads and two SA amps the Quad amps are the first version of the 520 amps but the sellers modded them to work with modern equipment. Happy to pass on his details, someone has already asked for his details on PFM.

Barry
26-03-2025, 22:23
Thanks for that Tony, and whilst I was thinking of buying your amplifier it would have been an extravagant and non-essential caprice.

To give you an idea of my collection of Quad gear, I have 30 items:
2 off 510 monophonic amps (used with Quad ESL-57)
1 off 520f amplifier (used with B&W DM2a speakers)

5 off 405-2 amplifiers (2 of them 'monoblocked' and upgraded to Keith Snook Level 3, and with improved power supplies)
1 off 303
1 off 303J
4 off 50E single channel amplifiers

1 off 33 preamp
1 off 44 preamp

5 off Quad tuners.

So to buy any more Quad gear would have been almost immoral.

twotone
28-03-2025, 16:27
Quadtastic Barry:eek:

grog
03-04-2025, 08:35
you need a 240 to complete the series!

Barry
03-04-2025, 08:55
The Quad 240 power amplifier is one of the rarest products Quad made.

Essentially a Quad 306, but with a beefier power supply and fitted into a 1U 19" rack mounting case. Obviously intended for professional use, many of them were used by the BBC in their outside broadcast vans, presumably to power their LS3/5A speakers.

But despite their fine performance and almost indestructible construction, I have no compelling wish to own one.