Quote:
This is the board.
please don't hesitate to put signs in the parts that you suggest, I can change.
Overall the caps, beacuse for the others components I understand.
My doubts are on the quality of ST and National ( now installed in my LC ) vs. Fairchild and On Semi.
Will be an important upgrade?
The most important parts are transistors and capacitors. If you do not have matched transistors, changing those with another (unmatched) is not worth. Big influence in sound picture have high pass (DC blocking - in this case) and low pass capacitors. Second are opamp coupling capacitors and third are supply capacitors near transistors.
1. Low pass filter (blue capacitors from the left side of OPAMP / close to ALPS pot) should be MKP/FKP or polystyrene. MKT/MKS does job but not enough. MKT/MKS is good for power supply - not in the signal path.
2. Try to replace coupling (yellow capacitors) near OPAMP with Polystyrene (Styroflex) 20nF or 10nF. Here is excellent place for them.
3. Signal caps on input (DC blocking) have good voltage but bigger capacitance would be better (3,3 uF is good, more is better). If you are able, try to find MKT (10uF) and couple them with MKP. Or you can make good combination with big MKC 63V (4,7 uF) and fast MKP 250V (33 nF) in a parallel connection.
4. Blue elcos near transistors are Philips BC?I changed them with Panasonic FC (NOT FM) and there is more depth and bass. But BC seems to have faster response (more bright). Cerafine and Silmic are too big and demand lower temperature environment (85C). You should go with capacitors that are ranked within 105C.
5. Blue elcos near opamp. They are energy tanks and with resistor (47R) they make RC filter. You can change them as elcos near BD transistors. I put here Panasonic FC. Others put here Cerafine, Silmic, etc... Be aware that Cerafine won't fit if it is bigger than 470 uF / 25V, and Silmic won't fit (at all) if it is bigger than 220 uF / 25V. Quality matters a lot (dielectric isolation or rated voltage). If it is rated as 50V it will have better characteristic than something rated as 25V. But, there is not enough place for 50V...
6. This is trimmer pot. With it you can tune ONLY POSITIVE VOLTAGE (LM 317) and lower your DC offset.
All this depends on other parts in your amplifier. The best would be if you change one part (for example input DC caps and opamp coupling) and listen to music. If your demands are satisfied - your tuning stops there. If you are not satisfied you might continue with upgrades. You can't be sure that other people choices will be the best bet because we all have different DAC, headphones, type of music, media (CD/MP3/DAT/WAV), different music tastes, etc, etc...