How to design an amplifier

[TonyD'Amore]

Since the unveiling of our A series amplifiers and before, I get the occasional email that reads "hey, I know you're busy, but could you design a few amps for me real quick" It usually makes me giggle a little and then smh. It takes me back to 1999 right before I started with RF. I also had no idea what was involved designing an amplifier from the ground up.

No disrespect intended if you are reading this and have asked me to make you some amps before. How would you know what is involved if you haven't done it before? This has prompted me to go through literally thousands of photos on my phone and pull off any amplifier design pictures that have to do with the new amplifiers we just introduced. I will make my best attempt at posting them here in chronological order, and make some brief comments here and there. I also threw in a few pictures of my daughter taken during those times as a measure of time.

The A series amplifiers are a direct COPY of the home audio amplifier I designed for my own use (changed power supply to 12VDC, added fans, remote turn on, balanced/unbalanced input and ability to put it into Class A/B mode (home amp is always class A)) so I have included the photos of designing that as well because all of the time I spent developing the circuits went directly into the mobile amplifiers. Ok enough of me talking..

On with the show!

Before I build any circuit I like to try to simulate it in PSPICE, here you see a nice clean output and the predicted distortion

My daughter was born during this time

Here you see the power supply for the home amp. AC to DC supplies like this are very easy to design. The small circuit board is the input stage and voltage amplifier stage. This is where a lot of the magic is and many months of reading and testing were done to get it to work. Unfortunately I couldn't find any pictures during that time. We went through at least 3 different voltage amplifier designs, PCBs and testing before we came up with what we use today.

Moved tested input stage and voltage amplifier stage onto main PCB instead of it having it's own PCB. (In the car amp it still has its own PCB for the least amount of noise possible) Each tiny resistor and transistor has been studied for voltage, current, and power dissipation.

Prototyping the current amplifier stage

It works! Now lets build 2 voltage amplifiers, 2 current amplifiers, connect them together and add a power supply! We also added a prototype SMD VU-DIN meter for S&G.

Ok let's put this contraption in some kind of case so we can move it around without breaking anything. A SMD AD-1 Amp Dyno prototype case worked well

Keeping the same case, I designed a simple face plate for it and had my machine shop CNC it.

We put it all together with some prototype meters. Shown here on the distortion analyzer making a sweet ass sine wave with only 0.0068% THD! WHOA! Cleanest amp i've ever tested, home, pro, or car.

Edited January 18, 2016 by TonyD'Amore

[2loud4uboyz]

Sir your on another level than us. You may be from another planet is what I am think. Tony You are the MAN. Yeah I'm a fan in a half of you.

Edited January 17, 2016 by 2loud4uboyz

[Airborne]

Niice,

[OrionStang]

Well shit,,,,

can you design some amps for me?

[Airborne]

So cool to see, I am such a nerd for this sort of thing

[TonyD'Amore]

Time to give props where they are due. I've learned a lot about amplifier design over the years from some of the best. Besides the books shown here I also worked with Jim Strickland and Mark Albers daily for years

.

The next step here is to design some heatsinks, make them, dump heat into them and see how they react. I don't have pics from that time but this is the result, the tunnels increase the surface area of the heatsinks big time! Surface area is what you need to move the heat to the atmosphere. The holes are 0.750" diameter. So the surface area lost by having the holes is (.750 / 2) ^2 * pi x 2 (top and bottom) = about 0.88 square inches x 39 holes = 34 square inches. BUT the amount of surface area gained is (.750 * pi * 7 inches deep = 16.5 square inches x 39 holes = 643 square inches! So each hole effectively gave us 20x the surface area. Not to mention a great chimney effect that starts to flow air without a fan.

Lets make a set of mechanical and have them anodized black

Now we need to loose all the prototype stuff and design the actual PCB that will contain the voltage stage, current stage and sit nicely on our new heatsinks

[MrSkippyJ]

This is amazing. It's hard to argue against the price of your products when you see that it is truly isn't off the shelf parts.

[TonyD'Amore]

I send my PCB design files off to the PCB house along with some $ and in a week I have some PCBs! During this waiting time we ordered up all the components for the PCB so they arrive about the same time. I choose the best capacitors I could find for the audio paths, Nichicon FG (fine gold) and Nichicon Muse (green). My partner Juan is magical with a soldering iron and debugging so it's his turn now.

Let's drill these new 'sinks for the PCB mounting holes and transistor mounting holes

Proud papa Magic Juan

Testing the supply, only 180V DC

[ShadeTreeMechanic]

Thanks for the inspiration! That prototype has me thinking!

[TonyD'Amore]

Let's test it.

Wait what? Only 0.0095% THD at 20kHz! That is nuts! I bet it's amazing at 1kHz! (Distortion always goes up with frequency, always)

Here it is at 1kHz

I was just as skeptical but didn't have any better test equipment at this time. So we trusted it as the truth and moved on. Let's play some music already!