The beast has been tamed. It sounds good too, although my headphones are cheap Sennheisers. The headamp is enclosed in a Hammond enclosure, using the aluminium casing as heat sink, it gets hot. It makes for a nice way to keep the coffee warm by placing the cup on top of the amplifier.
Q6, Q8, Q15, and Q17 are the output transistors, and needs heat sinks, I have not calculated the exact size needed, but the bigger the better. I use the aluminium chassis of a Hammond 1455N2202 with the transistors mounted on the bottom, and it gets warmer than I like. Never test the amp without proper heat sinking in place, as the output section will most certainly release the precious blue smoke.
Power supplyI have used a 2X12V toroid, a rectifier bridge, and 4700uf on each supply rail. Each channel draws about 200mA.
GroundingSome attention is advised when wiring the ground, my first ground layout resulted in a nasty saw-ish 50Hz hum from the amplifier. I now connect the separate grounds from the input RCA connectors to their respective ground pads, next to the input pads. The power ground are connected to a star ground between the 4700uf power supply capacitors, as well as the ground wire from the headphone jack.
In the 3020i there a two thermal fuses (E401, E402) in the output circuit, you can take these out if you are certain, that you will never short circuit the output. On the earlier original model I believe this protection is done using a relay, and an integrated circuit, I think you will be able to rip out the relay in these versions.
I just ripped out these thermal fuses and replaced them with a piece of SILVER (you have to shout that word to make sure it's stays audiophile) wire, that my good friend Peter gave me.
I do believe this further cleaned up the bass output, of the thing, so much that I will have to find means to reconnect my sub woofers soon. This means that the bass output is now at "normal" and acceptable levels. I'm not working at optimal listening conditions as a friend of mine is playing Battlefield right beside me, but I do believe these thermal fuses had a higher sonic impact, than I would have thought, then maybe again it's the SILVER.
Build the last simulated version of the SE class a headamp today, on breadboard. It works as an amplifier, it is class A, it is hot, and it is oscillating. I have to read a little more about taming the beast, did try some tricks, and it helped. Also I have to try some other transistors in the output stage, I have two different brands of BD139. I was unable to measure the hFE of the ones of which I have the most, even though the other brand measures fine. Since this was a prototype, I used the strange ones, maybe they are bad to the bone.
NOTE: I found this thread at diyaudio.com read through, it's really nice stuff: Pure Class A Single End Amplifier Idea!
I have had this baby sitting on a shelf for a couple of years, getting more and more sick, to the point where it would skip through a CD in about 1 minute, very annoying. I needed something for my DAC to compete against and tried the SONY CDP-228ESD I had around, this uses a SONY digital filter and 2xPCM58P-J, but it was really no match, and I have never liked the sound of the thing. I must say, that I like the construction, this SONY, is surely made to be above average, but for me it didn't do the trick sound wise.
Back to the DCD-3560, I tried the adjustment procedure outlined in the service manual, with no success. So, back to the conclusion, that the laser was dying, fast. The laser is a KSS151A, from SONY, and of course out of production! Costing on the wrong side of 100EUR it wasn't really an option to just buy a new one. Secondly, things are a little more complicated with the KSS151A than a most other lasers I have seen, throwing out a lot of money, only to wreck the player completely, didn't seem like the way to go Until
I realised, that the SONY machine had the same laser, unfortunately, this means, that I've killed it, not in cold blood, but still the SONY is now very dead. After sweating 5 litres of nervous sweat, loosing a screw in the actuator, and readjusting the DCD-3560, which by the way, went smother with the new laser. The tracking gain was impossible to get right, with the old laser. Well the DCD-3560 is running smoothly again. Now there is nothing to do but hope the laser will last a long time.
John Linsley Hood Class A amplifier. Distortion figures and PSRR look quite nice, but the circuit has only been simulated, I have a TDA1545 DAC to finish If I could only keep my mind on a single project. If my calculations are correct, the amp will deliver 250mW into a 32Ohms load in class A.
PS: Sorry for the extra ground symbol.
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