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Monday, 28 August 2017

Sinclair Stereo Sixty Amplifier.

Colin popped by, with an unusual amplifier under his arm.

Chap's bought this off me, can you take a look?

Yeah, why not...

It's a Sinclair (Sir Clive... think of the ZX 80, 81 and Spectrum computers, and the C5 electric tricycle, yeah, that bloke) "Stereo Sixty" Amplifier.



Now back in the 60's and 70's, before Sir Clive hit the big time with home computers, Sinclair sold electronic kits, and the Stereo Sixty was the preamplifier part of "Project Sixty", which consisted of a Stereo Sixty Power pre-amp, a Z8 power supply and a Z30 or Z50 Stereo amplifier module.

There was also a "Filter module"... and a quick web search show's it looks nothing like the module fitted to this module, but does show a similar one in "Project 80", although not available as a separate unit....








Lid off, and it's definitely home-built.... Coax used to get the audio from the din plugs, what looks like coax screening stripped off and used to screen the mains cable to and from the switch (?!) ...









and some rather too short wiring between some badly fitting phono sockets, to an attenuator hovering above the board ....









Gently powering the thing up produces some audio, and quite a bit of hum ...

That big red capacitor is open circuit...

Note the "Nomark" pass transistor, and the bridge rectifier shaped like a nut!








Dated Nov '71 ... it's almost as old as me, no wonder it's knackered....









There's a few other caps that are a touch low... these are replaced.

There are two output capacitors, each 1000uF, 63v, which read perfectly.... Sadly they can't be trusted. If they fail short, it's good-bye output stage, so they're replaced...








The dodgy mains-switch wiring is replaced... Someone was obviously paranoid about hum pick up... screened indeed!









The pre-amp is removed, and checked through.











The pots are horribly noisy, but clean up well. The co-ax is removed, along with the wiring that's too short ....













... and that floating attenuator replaced with something much nicer...










and lashed up for testing ....












All cleaned up and back together. I quite like it's blue and grey case ....










So... how's it sound?

I expected to be typing "of it's time" , but I think it deserves better than that , I was pleasantly surprised  ... It's quiet, and I enjoyed a couple of Matt Berry albums in the workshop whilst it was soak testing.

Of course, being a home built kit, this would vary dramatically on how it was put together in the first place. Whoever built this example was obviously paranoid about hum pickup. It's got a reasonable star-earthed design.

The bass control's centre frequency is far too high for my liking, and the PU input (for turntable pick up) seems very "flat", I suspect it was designed for a ceramic cartridge. Other than that, a talking point for Sinclair collectors everywhere, and very usable.





















2 comments:

  1. Aah I remember making up amps using those modules compaired to today it was steam driven technology. Now you buy a black blob the size of a postage stamp and 5 legs to 8 legs and you have everything inside the blob. I still have one of the Z30/50 modules complete with the red edge connector from Radio Spares. I will have to fire the beast up :)

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  2. Built one of the Sinclair systems in 1970 at age 15!, cut a hole in Mum's coffee table to fit the Garrard turntable in, I built my own pre-amps as I wanted to keep the whole thing 'flat' under the table, so the pots were on the table top. I had a box of components, my Mum and Dad looked at them, looked at me and smiled, they never thought it would ever work (but didn't say so until afterwards!). 2 weeks later, all completed, ready for switch-on!. Mum loved Mantovani, I switched it on, stroked the styles on the cartridge, nice rumble, so put on a record, and Mum burst into tears, she never thought it would ever work!!, Dad was a bit more positive, but they were astonished I had done it and they had many years of music from the system!. After that, they knew I was deeply into electronics. Loved the Sinclair stuff, made a second on with the Sinclair pre-amp control unit for myself when I got married, great times!!. Ah well, back to the Chinese built 2018's. Rob.

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