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Old 27-07-2020, 01:59 PM   #13
Master Member
Join Date: Apr 2019
Posts: 3,266
S-300i Amp teardown

Yeah, need to repair it. But it sounds very good. Maybe it can be better after recap. I like the chassis most... ITs really solid compared to the 300IL/400XI. That one the top cover is flimsy. The problem with this amp is that you feel there is so much to

The pre-amp board looks good. Other than crappy capacitors which needs to be replaced. The op-amp is OP177G. Pple say it sucks but it seems to sound ok to me. I am not sure if I should replace the opamp with a newer model..OP177G is a 3rd gen opam and we are not in 6th gen with the 4077....

The power section. Interesting to note that this is designed like a dual mono amp with 2 mono modules. And the burnt marks at the right side. The SMD resistors gets very hot. Some were fried and needs to be replaced. ITs worse on the S-300i because they are smaller and so closed together. Unfortunately, there isn't enough space to put better ones.

Seriously, I don't understand what they have to cramp the parts together on such a tiny circuit board when the chassis has so much space. I really felt tempted to redo the whole thing from scratch but afraid I might just give up

The while blocks are MPR ballast resistors from a korean company....Hmm.... I really feel like replacing it with discrete resistors.

This amp is rated 150W and we can see why. There are only 4 pairs of sanken bjt compared to 6 pairs for 300il. Interesting to note is that the output of the leftmost sanken pair is goes back into the input of the other 3 (believe is current feedback loop).

Several diodes near the power. They are not rectifiers. Got a feeling they are DC blocking filter but can't confirm.

Last edited by Clearnfc; 27-07-2020 at 02:04 PM..
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