Basic Amplifier Mods for Dummies

Posted on Sunday, 10th May 2009 by Auw Jimmy

I have received so many emails asking about how to do the mods. Why I do this? Why I do that? Etc… Ok, I will spend my lazy evening to use one good example and write a simple tutorial here. Just enjoy.
I look around my room to find a good and easy example to support this tutorial. Then, my eyes stunned to my old Simbadda CST z120 Dual-O speaker set. Well, it a small speaker, you can’t call it audiophile or even near it. I open the case and find that this small “thing” could become our perfect object.

You can get at your near computer retailer for very cheap price, less than US$10, I think. Feel free to find any other object. I pick this one simply because this is the only thing that I can find at my room (and suitable for this experiment).


Close up shoot. This simple speaker put all the amplifier unit inside the left speaker. Let’s open it!

Aha… there you are. We can see a small PCB contains small amplifier and one potentiometer. Remove and unscrew some screws and pull the PCB outside the chamber.

Now we can see the PCB completely. This speakers are powered with TEA2025B. The next important step is to find datasheet of this TEA2025B. With the help of Internet, I can find it within seconds. Here you can see the datasheet and pin out of the IC. Look below please.
The PCB is single layer only, so very easy to trace! Perhaps because I’ve played with so many dual or even more layers. So now I feel very simple with single layer

I also find useful thing from the datasheet: the stereo application guide. After checking the PCB and trace the layout, I think this speaker uses standard schematic and component value from the datasheet. Ohh… life is so simple

Let’s analyze the schematic (I assume that you have compared between the datasheet and the original layout used on this speaker to confirm – if you haven’t, please do it now, this will simplify your life – trust me!).
From the schematic above and after tracing the real layout on PCB, we can analyze this system.

• Input are at pin 7 and 18
• Output are at pin 2 and 15
• Supply/Vcc at pin 16
• Feedback are at pin 6 and 11
• SVR is at pin 8
• Bootstrap are at pin 3 and 14
• The rest are Ground

What a simple amplifier? Welcome to the world of Integrated Circuit. Everything on single package.
So, I decide some important key components:

• C6/C7 (470uF) as output coupling
• Unnamed (100uF, from pin 16) as main power supply smoothing filter
• C10/C11 (100uF) as feedback capacitors
• C8 (100uF) as ripple rejection
• C1/C2 (0.22uF) as input coupling

You may ask why above components are important? Actually, the first two most important are C6/C7 (output coupling capacitors) and C1/C2 (input coupling capacitors). Then, power supply is a must to get cleaner sound. So we change the 100uF from pin 16 also and C8 as ripple rejection capacitor. Finally, feedback capacitors also play important role, because most likely, the signal will pass this section also. So we change the C10 and C11.
For newbie, you can try to change C6/C7 first. Then C1/C2. Then go with 100uF capacitor at pin 16. After that, you can change C8, then C10/C11. By doing this step one by one, you can learn “which” capacitor makes different and “how” is their contribution in the overall sonic performance.
I dig my shelves to check necessary components. Not many values used, some are 100uF, 470uF, and 1.2uF. I think I have enough stock here (various brand). No need to spend money to buy or order.

Removing all the capacitors is easy. I love simplicity of single layer board.

Here is my mods list:

• C6/C7 (470uF) changed to Nippon Chemicon KME (470uF/50V): I don’t have much option for this section. Nippon Chemicon is not my favorite, but this one is better than the original capacitor.
• Unnamed (100uF, from pin 16) changed to Sanyo (1000uF/50V): I prefer higher capacitance to provide adequate supply and filtering to the main IC. So I upgrade to 1000uF. I think you try to use 1500-2000uF if possible.
  
• C10/C11 (100uF) as feedback capacitors changed to Rubycon ZL (100uF/50V): Low impedance charateristics of this ZL is favorable as Black Gate replacement. The combination with Elna Cerafine as input coupling should produce balance result.
  
• C8 (100uF) as ripple rejection changed to Elna Cerafine non-polar (100uF/25V): Ripple rejection needs good capacitor, so Elna Cerafine or Black Gate are both the best. You can opt to Nichicon Gold for cheaper solution.
  
• C1/C2 (0.22uF) as input coupling changed to Elna Cerafine non-polar (1.2uF/50V): Nippon Chemicon at output coupling, Rubycon ZL in feedback, so Elna Cerafine should be at input stage. Elna Cerafine tends to have good/thick vocal – less detail, Rubycon ZL tends to have mid-hi tonal balance – more detail, while Nippon Chemicon tends to have more mid-low tonal balance. The combination between those three should produce adequate balance in this mod.
  

So, here is the final mods. Not to pretty, ugh? Big capacitor always have problem with small PCB layout. So it’s a matter of how smart you can put the component on the right place (without looked ugly).

Just another shoot. I always use “pin-sleeve” to protect the pins from short-circuit possibilities. And it will looked better on the photo also

This mod also need to “cut” the inside plastic cover. I use my soldering iron to “cut” the plastic. Otherwise, those big capacitors won’t fit inside the chassis. I also cut the LED. LED tends to produce distortion/noise in the supply line and I don’t like the shiny blue light in my dark room.

Here is the final rig after mod. My Asus laptop, connected to my Asus Xonar U1 mod and Simbadda modded speaker. It’s more than enough to fill my daily life.
The result? I’ve owned this Simbadda for over 1 year and it never sounds this good (after mod). The details are definitely better, the staging is wider but more focused, the vocal is thick, warm, and sweet, the high are dynamic, tonality rich, extend, but not bright at all. The low doesn’t improve much – well what do you expect from a small speaker, eh? Overall, with almost “0″ cost (from old components on my shelves) or maybe around $10 cost if you buy the parts – this is a very recommended mods (I can say, this improvement is over twice from the standard version – perhaps around three times better) and also a very good example to learn before you advance into higher level of this audio mods world.
Added May 11th, 2009:
I remove the amplifier from the right chassis and put it on external box. Before, I listen the low frequency is not “equal’ between left and right speaker. This is normal because the right speaker box volume is smaller (some occupied with amplifier), while the left speaker has larger box volume (without any additional parts inside). So I remove the amplifier out of the right box. Now the bass is even more equal. No sign of “not enough volume” as I’ve listened before. Until now, I still just can’t believe how this cheap sound speaker could perform so much better with this mod. Diana Krall’s Love Letters sounds so beautiful, sweet lazy vocal, with superb brass instruments – off course – considering its price, this is excellent!

By : http://jimmyauw.com/2009/05/10/basic-audio-mods-tutorial/