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
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
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
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
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
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.
Hi
The schematic I was planning to use is from
http://www.flashbacksales.co.uk/acatalog/manualzip/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.
The schematic I was planning to use is from
http://www.flashbacksales.co.uk/acatalog/manualzip/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.
Looks to me that the constant current diodes (I suppose?) in 306 onwards should serve to clean up the class A supply.
I have a late 405-2 and just put in new caps in it, when I saw the Net-audio kit for separating the PSU for each channel. Very tempting to try it and take out a separate supply for the class A and opamp from there...
The late 405-2 circuit (M12333 ISS 10) is a lot simpler that earlier ones and the 306. Ripping out the current limiting "chips" makes it even simpler.
Would try that one first if to clone smth, also look at what Keith Snook and Berndt Ludwig suggest for the 405 in terms of input stage, bridge mods and low impedance drive.
Check tvicols schematic: http://www.diyaudio.com/forums/showthread.php?s=&threadid=51036&highlight=
Cheers,
tom
P.S. Must say I enjoy Quad II a lot more, though
I have a late 405-2 and just put in new caps in it, when I saw the Net-audio kit for separating the PSU for each channel. Very tempting to try it and take out a separate supply for the class A and opamp from there...
The late 405-2 circuit (M12333 ISS 10) is a lot simpler that earlier ones and the 306. Ripping out the current limiting "chips" makes it even simpler.
Would try that one first if to clone smth, also look at what Keith Snook and Berndt Ludwig suggest for the 405 in terms of input stage, bridge mods and low impedance drive.
Check tvicols schematic: http://www.diyaudio.com/forums/showthread.php?s=&threadid=51036&highlight=
Cheers,
tom
P.S. Must say I enjoy Quad II a lot more, though
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