Quad Clone

[urant]

Hi.
I’m a new poster in this forum, even tough I have know about it for some time.
I’ve been meaning to build a small 50w amp for some while now, and the time is ripe to do it.
Now, I really like the idea of a Class A solid state amp…what I don’t like is all the wasted power. I live a city whose average summer temp is around 40C, so the idea of an amp/heater is not very pleasing.
The “current dump” concept that the old Quad amps used really looks nice…and I’m a bit more that curious to build one and see how they work.
Does anyone have a suggestion on which would be a good one to clone?

Thanks for you time

[Jan Dupont]

Maybe the 405

[analog_sa]

Maybe the 405

A fine amp, difficult to blow and well suited for tropical climate. But sounding as if it were class A it ain't.

[405man]

I would suggest you build a clone of the Quad 306 which with a proper split powersupply is capable of excellent results. This is very similar to the current and highly regarded 909 but with less power

Stuart

[Zombie]

Oh dear, analog_sa praising a Quad amp...what has happened?
Hope it doesn't snow on midsummer

Anyway, if you'll make a 405, take a look at another recent thread here, a guy from Romania? had some variations to his cloned 405-2...cleaner supply for the input opamp and class A amp...

[urant]

Hi ACD, thanks for your reply

Why do you recommend the 405?
Why not the 306 for example?

By the way, I have access to some really nice PCB software, and if anyone’s interested, I’ll post the finished artwork here

[analog_sa]

Oh dear, analog_sa praising a Quad amp...what has happened?

He,he,he. I built a few of these at the time - it was the only amp not blowing when my home made electrostats started sparking. Of course i built them with 'high-end' opamps (5534 was real good in 1984) and 3 separate PS, down to the transformers. Apart from an annoying power-on thump (different time constants) i thought it was a reasonable amp. Then again it was more than 20 years ago

[Zombie]

Not that I am an expert, but what's the use of cleaning up the supply to the opamp when the class A amp gets a lot of the crap anyway? Your solution with separate supplies helped a lot I can imagine?

But it seems the 909 looks pretty much like the 306, so much hasn't really happened with that amp in 20 years...or has it?

Cheers
T

[analog_sa]

Your solution with separate supplies helped a lot I can imagine?

It actually did. My main objection against the 405 at the time was the rather flat presentation - good image width but not much depth and especially height. Not too much cues of the recording venue, etc. First experiment was to separate the opamp supply; pleasant enough but not groundbreaking. The class A amp separation was indeed a monumental improvement. I might have also used parallel output transistors but can't say for sure. The case was Krell-sized as the main transformer was way oversized (650VA?).

I never experimented with later Quads. As the opamp is mostly taken out of the main signal path they might well sound better.

[urant]

Hi

The schematic I was planning to use is from
http://www.flashbacksales.co.uk/acat...zip/306cir.jpg

Analog_sa, is this the one you would build?
Do you mean a separate power supply for the OPAM and board and to optically link it to the clase A section via a fotodiode and fototransistor?

I was planning to use Mentor Graphics to draw the board since it can do PCB signal and thermal analysis<=

This is a bit off topic, but I’m beginning to design a digital amp: FPGA implemented DPS processor control, PWM modulated power supply, digital input (no ADC) thermally compensated output switching MOSFETS, a fuzzy logic based feedback-feedfoward error correction.

I’m pretty useless in analog, but in digital, that’s another story.