Quad 303 & Recovered Memories

[kchap]

Silicon Chip Jan 2024, page 92 has an article on restoring the Quad 303 and companion Quad 33 control unit. Unfortunately the web site does not give much information, but the article was justification enough to buy a copy.

While reading about the restoration it triggered memories of my attempt to build an amp inspired by the Quad design: Pratical Electronics - Gemini. I only built the power amp as it was too hard to get the parts for the preamp in Australia. Three and six (actually more like $1 AU) was a lot of money for a young lad back then

The Gemini was a pretty good design, I never got it to work; too inexperienced. I did have a crack at building the ETI mosfet amps a few years later. That worked, just do not look too closely at my workmanship.

 

[sergeauckland]

I built the Gemini, both pre and power, in my last year at University to replace a pair of Mullard 5-10 valve amps I built in my last year at school.
I thought it was a pretty good amp, albeit not very reliable. In particular, it had a stabilised power supply where the series stabiliser transistor would blow to protect the fuse!

In common with solid-state power amp designs of that era, it didn't provide a lot of current so struggled with loudspeakers that dipped well below 8 ohms, even below 4 ohms.

I used it happily for about 5 years, but when I bought a pair of IMF TLS50s, it clipped horribly, (expect current rather than voltage was the limiting factor) and I replaced it with a much higher power design based on a Linsley Hood circuit.

S

 

[kchap]

I built the Gemini, both pre and power, in my last year at University to replace a pair of Mullard 5-10 valve amps I built in my last year at school.
I thought it was a pretty good amp, albeit not very reliable. In particular, it had a stabilised power supply where the series stabiliser transistor would blow to protect the fuse!

Yes that's the reason you used power transistors, fuse protection

A few years years later just about every amp used a long tail pair input stage. Good CCMR and PSU immunity meaning no regulated power supply.