This is my new project, although I have the PCB for a long time. Maybe this is not too interesting project but there is something special with the chassis. The chassis are build by 2 big heat sink and L aluminum that usually used for panel or cable rail in IT industries . This is some pictures about what I’ve planned.
Two identical PCB for stereo amplifier. My friend give it to me for free. He bought it at HR Electronics Kramat Jati - East Jakarta
Solder side View
View inside the chassis
This is the chassis I've planned, but that's not a final design, because there's no place for a transformer, I need to enlarge the chassis for placing all parts.
Well I’m still working on it, soon I’ll update this post.
May 30th Update
Metal work is the most killing time and absolutely make you sweat fall hard, except you have a proportional tools for the job. But maybe I’m not the lucky one to have that tools, so I do it with manually and of course that’s a challenge for me. I use a hand electric drill, handsaw, grinder, pliers and standard tool I’ve got. Well I hope the result makes me happy.
Basic of the chassis
For better performance, metal film resistors, MKP/MKM/MKL/NP/NPO caps are used for this project. Some people use teflon at the input caps but the price is quite expensive. In this amp I'm using 4x470nF MKM + 680nF MKL for input caps.
Some improvement for several components, I hope it make a good result. I also adding 2x 2200uF + 2x 100nF at PCB supply rail for reducing hum.
Planned PCB placing
14 pieces of KME elco 2200uf/63Volt + 2 pieces of MKP 100nF as power reservoir
Standard PCB mounting and gold platted terminal for connecting all elco's.
June 22th Update
I finished some wiring job and put a speaker protector which is have DC protection and start up delay. I put it above the capacitors bank with PCB mounting and fiber glass. I’m using cable terminal for supply rail and speaker for easy maintenance.
July 23th Update
After I finished wiring job, I run the amp for testing. When I turn on the amp, the speaker protector (which is has DC protection) detect some failure. The Led is flashing indicating DC voltage at amp output. After some checking, I found failure at left channel amp. There is unexpected problem with the driver transistor that I actually found this error for the first time and took lots of time to find that fault. The MJE340 transistor is a PNP transistor?? I don’t know how it could be, but I’m happy because it is not damaging the output transistor. After I replace the MJE34o(incorect label) with another MJE340 NPN transistor, the amp is working. Now is time for setting the questcent qurrent.
When I set the quescent qurrent there is another failure. The right channel is getting hot so fast and almost burn my fingger when I touch the driver transistor heatsink. Turning left/right VR1 doesn’t make changes. I check all diodes and transistor bias and I can’t find fault of that parts. That condition is confusing me for some time. After that I decide to replace all bias diodes (IN4148) with the new tested diodes and it’s surprisingly clear the failure.
Next I continue test the amp. I put my onkyo speaker at the output and IBM R52 Thinkpad with 12MB “the dreamer Ozzy Osbourne” mp3 file song for source. Like I wrote before I didn’t matched all the transistors and diodes for this project. I only matched the output transistors pair 2SC2922 and 2SA1216, but the amp sound greats. I didn’t hear any noise at all even with open line in. I think this is enough for the purpose and I’m happy for the result.
Improvement Recomendations
-The matched transistor for input stage, buffer and driver will increase the sound quality.
-High quality multiturn variabel resistor for VR1 is important for setup the quescent qurrent more save and easy.
-Bigger transformer for power supply can make this amp more reliable especially when operate the amp at full power.
-Vertical fin heatsink (it is quite hard to find at my local store and more expensive) is highly recomended for the chasis because it can releases heat more efective.
August 8th Update
I test the spider with audiophile female voice CD and the result quite surprising. The amp deliver good sound qualities and enough power for all day purpose. The amp has deep sound stage, good stereo imaging and natural sound. Overall I recomended this amp for your hi-fi system. For daily use it never let me down… 🙂
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