Hi guys. Welcome to WillyBoy Audio blog!

In this first post I will show you the inside of a popular amplifier among the budget crowd: The Kinter MA-170. Not only that, I will show you how you can mod it and turn it into something decent, without going overboard and spending more than you paid for the amp. Yep I know us gearheads/DIY geeks/name-your-title here tend to do that, don’t we?

Alright. Now about the actual amplifier. The Kinter MA-170 is available from websites like Parts Express or eBay and AliExpress for around $10. Here in Indonesia, I bought it for an equivalent of $6. I’ve seen Lepy (another name for Lepai) offers something really similar for even cheaper. So I conclude that this is just a generic design that is being offered by a number of manufacturers. My flatmate has one of these, and he uses it to power his kitchen mini-system. Just recently, I started making miniature speakers from carton boards, and I needed a small amp to play with it. That’s how I got into this mess.

Let me tell you the first interesting fact: They updated their product from time to time. The earliest version of this amp, let’s say before 2014 uses TDA7266 class A/B chip. Then, sometime later, users reported that the amp uses LA4625 chip, which I think was designed by ON Semiconductor, but also manufactured by Sanyo.

I borrowed his, and opened it up. Alright, not too bad. I can deal with this chip. More importantly, I immediately see things I can mod to improve the amp! So I splurge all that burger-and-coke money into this amplifier. Didn’t even turn it on when I got home, I immediately reached to my screwdriver and behold:

Ever feel pleasantly surprised? That’s how I felt! My online reading hasn’t mentioned anything about TDA7297, so I am really pleased to see this. In addition, there are also some changes in PCB design.

Yep. Those Chinese manufacturer do listen to all you guys yappin’ about in online forums about their products!! They replaced ordinary ceramic caps with multi-layered ones, and some with mylar ones. Still the same 16V-rated no-name electrolytics, and carbon resistors. I didn’t take a photo of the solder side of the board, but I can tell you they did a good job.

Although the following photos will show you the newer one, the principles still apply for the older versions. I know replacing the resistors with some low noise 1% tolerance metal film will make them quieter, but I concluded the noise from poor grounding and poor RFI insulation will not justify that. So don’t ask me about resistors, please.

The left pot is the treble tone control, and you can see the treble section uses two 100nF and two 10nF capacitors. I will be replacing these with some MKT capacitors. Next we look at the bass section.

It uses some 47nF MLCC here, again, will be replaced with some MKT capacitors. Here’s where the headache starts. Look at the 100pF ceramics. Look at the op-amp. Look at that, my friend. No self-respecting DIY-er will keep anything like that in their amp.

Here’s the op-amp that came with the amp, next to some known genuine op-amps. You be the judge whether or not it’s a fake.

The electrolytics actually play some important part. The 220uF cap is connected to V+ of the op-amp, so it’s crucial to the stability of voltage supply to the op-amp. The 470uF cap is the signal input side of the op-amp, and the 470nF is connected to the output. Yes, they are actually in the signal path, so give some attention in those areas. The following pictures will show you the difference in quality between the stock electrolytic and a decent film cap.

Actual capacitance 447.3nF and ESR= 8 Ohm! Let’s see how the film capacitor fare in this test:

If only all caps measure this well! That low ESR (Equivalent Series Resistance) means your signal is dancing and flying faster, due to the lower resistance! In addition, I always buy more than I need for a project so I can hand-match them for perfect balance between left and right channel. The electrolytic has 5.7% tolerance from rated capacitance, which is pretty good if you think about it, but it pales in comparison compared to the 0.12% tolerance of the film cap. This is no snake oil mantra, just honest, objective engineering.

Here’s a comparison between some of the old parts and their replacements. For this build I use film caps when I can, and C0G ceramic for the small value. It’s not worth using Cornell-Dubilier silver mica cap or anything exotic here, the C0G will serve you just fine. For the electrolytics, I use Rubycon YXF series for the small values, and Nippon-Chemicons for bigger ones. The old 1N5401 diode gets replaced with the ultrafast MUR460. I won’t hear any difference in sound, but I figured I’ll do that for bragging rights. LOL.

Finally everything is installed back, and I managed to operate on this board without ruining the traces. I fortified some paths by connecting the component leads directly to the neighboring contact point for additional assurance. To refresh our memory, here’s a before and after shot:

I carefully slid the board back in the case, and put some thermal paste on the chip. It came from the factory with none, so I made sure I put some before I closed up the case.

I haven’t tell you my biggest secret yet: I changed the LED to bright white. I can’t stand that color-changing LED that it came with. This is how you turn a $10 amp into a $20 one.

Look at that proud little fella.