Enter the MAK
I started this blog a long time ago and posted a few amplifier designs with the plan of keeping up to date. Life has been happening, so I didn't keep to this. I have, however, built many amplifiers since my last updated post. I built the 10-14 W class A amplifier and the 21 W class AB amplifier. The 21 W is sweet, but maybe there are simpler designs...
Anyway, I have built a 120W, a revamped version - around 130W and now I'm revamping it again - 140W. I'll post a page dedicated to that when it's done. I don't have the money for all the parts at once, so I'll start the build in a little while. The design for the 120W was slightly modified and built by a friend some years ago. Output on that one is in the region of 150W and he built it for an uncle, who uses it on a pair of Kef IQ9's. That amplifier sounds fantastic!! Kudos to my friend for the build quality. The size of the amplifier is mind-blowing - I can't fathom how he made it as small as he did. The entire amplifier is somewhere around 40 cm x 25 cm. Unbelievable.
In addition to that amplifier, my brother has a 35 W stereo running a pair of Monitor Audio BX2's - very beautiful speakers those. The amp was originally built about 6 years ago (2009) and is still going strong. I built a similar spec for myself, which has been thrashed and is running like cream. I built that in 2008 about. Lovely amplifier! And it's still running my Celestion F20's. I've built a few amplifiers here and there. My latest one being a 65 W for a friend for whom I am building a PA type speaker to amplify his drum kit. The 65 W doesn't sound like all that much, but it's truly a no mucking about amplifier! It uses large heatsinks and a big transformer and very large power supply capacitors. I'm proud of this amplifier - while setting it up it handled 16A bias current and didn't sweat.
So, MAK? Yes - my flagship hi-fi amplifier is a 50W, which has been used in a guitar amplifier I have called the MAK. Now I know the common guitarist is all about tubes, but they haven't heard the MAK. The amplifier itself is designed with overrated components - enough for a 100W amplifier easy and a power supply that is big enough for 4 50W amps (no jokes). There is certainly good reason for this and I'll get to it in a minute. The preamplifier is quite simple, although very many hours of design have gone into it. Basic tone control, a simple gain control and volume control. The gain control is super-simple, but took me 6 years to develop. And this preamplifier is the heart of the MAK, driving 90 W easily into the Celestion G12H75 Creamback at full gain.
Why such a big power supply?
The supply uses a 160 VA transformer and almost 20 mF power supply capacitance. The reason is that if you are playing heavy, you want the amplifier to keep up with your power demands. This power supply will never collapse and thus, you will always be reaching your desired power without causing the amplifier to clip. I've tested it. 90W pushed the Celestion to almost 120 dB at 1 m. To explain this, the very ground shakes violently and your pants around your ankles moves (vibrates?) quite a lot too. You can literally feel the power in your body. It feels like you're being choked. And it's wonderful! Anyway, it (the amplifier) handles the power no problem. It just shoves more and more power into the speaker, which after a short while smells like it's burning. The speaker can take 75 W continuous, so the amplifier was indeed pushing the 90 W as mentioned. If the speaker impedance drops to around 6 ohms at certain frequencies, the amplifier can quite easily push 125 W. So that's why.
Preamplifier - the heart of the beast
The tone control is nice. You can bump up a muddy guitar to ring a bit more or you can sound like a bass guitar (although why?). The gain control is where the magic happens though. Normally two diodes (sometimes 3 and sometimes 4) are used opposing one another to "soft clip" the signal. Meh - it sort of works, but it's actually not great. You get the Orange amplifier overdrive sound: clean until it's dirty - not a smooth transition from clean to dirty. And it sounds dead and amateur. This is the MAK! I wanted it to sound like something that when you use it, people come to you to ask about the amp. I used a simple transistor configuration of two specific complement transistors to get a wave shape extremely similar to vintage 60s style valve amps. You can set the gain to give a clean, but shaped wave, so you get a sweet, smooth tone somewhere in your sweet spot, so you get that valve-like control over your overdrive. So now I have an amplifier which costs a third of the price of an equivalent quality valve amp, but sounds BETTER. You want the design for the gain control? No. Sorry - it's something I'm holding onto. It's stupid simple, but I'm very proud of it, and I haven't even come close to finding a remotely similar circuit online (and in books).
Here's the FFT of the fully overdriven sine wave. The key things are that higher harmonics decay quickly - this is characteristic of soft valve-like clipping and the little bit of 2nd harmonic there indicates slightly asymmetrical clipping, just like 60s valve amps. :)
Oh, the wave looks like this:
With slight overdrive, you can see the wave is still shaped nicely - typical transfer function of valves.
Things about guitar amps
The thing is that normally transistor amps are chip amplifiers and the design is usually cheap - small power supply capacitors (usually general purpose) and a layout that makes amps freakin' noisy! One of my power supply capacitors is almost 4 times the physical size of Chinese made (British and German designed) amplifiers' power supply capacitors! And I use 4, where these amps use two, and I use more capacitance per capacitor! And the amps in question have higher power ratings! My MAK amp is constructed in such a way that it has no noticeable noise whatsoever. Really - you can't hear it with your ear next to it. And the speaker is 100 dB/W @ 1 m! No, the MAK is in another universe in comparison. So there's something to add - truly, the high quality amps use valves and the low quality amps use transistors. There's no denying it. But the MAK uses high quality components, high quality design, high quality construction (did I mention 22 mm solid wood - Bubinga or Saligna) and a very high quality speaker. So the MAK is a high quality SS amp, yes, it will blow your mind.
Here are some quick vids of the amp - not great playing, but you can hear what I'm on about.
(it now has a nicer handle...)
More to come in the near future, including the amplifier design, PCB layout, and a few pics.