SO!….. I decided to build an amplifier. From Scratch…. Mostly… I have no electrical training (apart from soldering stuff and wiring LED’s and computer stuff…. and hanging out with the repair guy next door). I have just read a literal shit tonne of information on amplifiers and power supplies and capacitors etc etc and so on…
My colleague, Adam, had already built a little Class A Single Ended Triode valve amp. It is in the shop, and to be fair, it is a kit amplifier. It sounds gorgeous even with the 8 watts it is capable of. He had everything supplied for him in one box, and there were masses upon masses of forums available for him to read and reference.
I decided “I wanna build a Class A amp… 4 of them…. for my pair of 2 way bookshelf speakers”… Holy shit I did not know what I was in for. I originally bought 4 15W Class A Hiraga kit amplifiers (PCB’s and components) from Jims Audio on Ebay. Excellent store, very helpful people there, highly recommend them. Those 4 amplifiers cost me about $260 or so.
Right off the bat, I asked him “What transistors can I use instead of the provided ones that would be better? What is the best I could put in?”. So he told me to get some particular ones (which I have forgotten the model of) which cost me around $80 for the set of 8. Compared to the equivalent $25-30 of the original ones, I have high hopes for them. Soldering all the boards up, I then had to figure out the power supply. I have read that these kits can handle anywhere between +/-12V DC to +/-35V DC… depending on heat sinks. Which I had plenty of (donated chassis with heat sinks on side panels).
The power supply has had me in a bit of a pickle though. The simple way would be to get the largest toroidal transformer I can find, wire a set of bridge rectifiers to it, and I’d have a simple but powerful unregulated power supply (meaning big power draws would give me voltage drops). But I want the power supply to be STIFF. With as many caps as possible to make it not bend…. I need my power supply to be made of some kind of Unbendium… Going against the accepted approach of a linear analog power supply, I decided to go for a noisy trashy switch mode power supply… Originally by tying two 24V switch mode power supplies with all the current. Turns out because they ground to their own chassis, I cannot easily create a center tap (0V). Sooooo… for the time being, I just have one of them running, cranked to max voltage output (29V) and splitting it into two rails with a pair of resistors. It mostly works, but it is not where I want it to be. Technically I am using a +/- 14.5V power supply this way, and it sounds absolutely massive… It is not what I wanted.
Consulting a power supply manufacturing company somewhere in the world (I have no idea where they are… probably China), I found they build a 2000W switch mode supply specifically for audio. At much higher voltages than I would want… BUT THEY CUSTOM MAKE THEM. Asking them if they would do around +/-24V, they said yes, but it is limited to about 1500W… which would still give me all the headroom I could possibly want. This is exactly what I need.
It is common in the Audiophile circles to shun switch mode supplies and class D amplification because of the switching noise that is common to that technology. The shit I have learned however is that switch mode supplies are perfect for class A amplification due to the constant draw. Switch mode power supplies only introduce noise in audible frequencies when there is very little current draw. Class A amplifiers always draw significant current, so that noise is pushed well past audible frequencies. That combined with a set of ceramic filtering caps should help resolve the near insignificant ripple and noise left. The noise I am getting through the shoddy LED driver supply is practically nil from what I can hear anyway, so an audio specific one should do even better.
With a traditional transformer supply, the ripple and noise is usually at the 100Hz range (50Hz from the wall, and after the bridge rectifiers, both sides of the wave form are on the positive side. 100Hz). Filtering that is fairly easy, but with big power draw, you need a huge amount of capacitance to cope with the voltage drop. With a switch mode supply, the frequencies can be into the 100kHz range, and not many electrolytic capacitors can filter those frequencies. Instead of the ripple being tens of volts (or more), the ripple with a smps can be as little as a few hundredths of a volt. I am still using a large number of capacitors to handle big current draw faster than the smps can respond, but the supply will respond with the current demand much MUCH faster than a traditional supply.
The new power supply has arrived, and I installed it in my amplifier last night. I was worried about the heat output from it considering the size of the heat spreader on the side. I mounted it directly to the heat sink of the power supply chassis and having it run for HOURS… it was barely warmer than the unused sink on the other side. Having the higher voltage (+/-26.9V) did make the amplifiers heat up a fair bit more (still able to touch the heat sinks without burning myself over a long period of time). One issue with this power supply I did discover is the over-current protection kicks in on start up… Playing with the power switch a bit will get it to kick over, but ultimately, I need to put in a soft start circuit (already ordered one from eBay). Once she is running though, it is smooth sailing.
At this stage, my amplifier is running and I am getting a sound I am LOVING. But ultimately, it has been an absurdly long process with plenty of trial and error, and there are still bugs I have to iron out. To build audio components from scratch, many tools are required, as well as a good understanding of what you are doing. I will not recommend building a big class A amplifier as your first project, it can be difficult to stay motivated over a long period of time. I DID THE WHOLE THING ON MY LIVING ROOM FLOOR! And I had to cut, drill, and modify big chunks of aluminium too.
Moral of this story: you can get excellent results cheaper than retail components, but it will screw your head in sideways and take a bloody long time… Not to mention the inherent danger in operating on electrical circuits running off 230V AC, and the sheer frustration of trial and error, and the gargantuan mess you will make.