Question about Audio & Video Receivers
I dont know what all modifications you have done but here are some tweaks that would be good:
IMO the tweak steps that should be made and order I suggest is good would be following
1) eliminate the output electrolytic caps from analog output (C656, C658, C655, C657)
I have replaced them with wire jumpers. It would be wise to check the DC component at output connector with multimeter. In my experience it's never more than abou +/- 20mV, which is mostly of no concern. Only if you have a true direct coupled amp where there are no caps in signal line it might happen that the DC component will also be amplified and sent to speakers. I think there is no commercial amp built this way, but some DIY projects might be.
2) Change the opamps. National LM6172 seems to be the most popular candidate and is the one I'm using.
Here the most important is to make sure you will place the additional decoupling caps to the supplies of opamp as close to pins as possible. I have 0.1uF polyprop caps from pins 4 and 8 to ground. When choosing the caps go for the ones that have as small dimensions as possible and as short legs as possible. Also place a cap on top of the opamp between +/- pins (pins 4 and 8). The value of this cap is not critical. Here you should pick some sort of SMD cap with as big capacitance as possible. I used some that were soldered off of some scrapped Intel PC motherboards. It is (at least I think so) non polar cap and the DMM measured it 20uF !!! I don't know if its right but it fits well on top of SMD opamps (I didn't get DIP cases from RS for some reason, even though the part nr. was right). A good place to look for ideas about opamps and decoupling is audioasylum forum.
3)Modify the clock. Install a sepparate one or use the description on acoutica.org site. I did my clock mod very sililar to that independently and as it turns out the techical solutions were similar and also our findings about changes in sound...
4)Better decoupling to supply lines. Use your imagination here.... One warning though, I once decided to change almost all the el. caps in the player for better ones (Nichicon xx, I don't remember the series at the moment). So, I replaced them and to some places I just put bigger values than stock. Well as it turned out I managed to overtweak a bit and now it takes about 30 sec before the display lights up :) I have studied it a bit, also with scope but can't fiqure out what causes the delay. Player starts normally and other than that there is no problem... so I have accepted it as just one more little thing that makes my player special.
Posted on Mar 12, 2008
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