Audio Refit (obs. STK IC)

I am refitting a unit with an output amp that used to use the SI-1125-HD ch ip. I have enough experience that I know not to trust people who are sellin g these chips now, if they are bad the seller can claim something else on t he board fried it, although in many cases that is dmanear impossible.

Another thing is that I don't ever want to take it apart again. this means I need it to just work the forst time. It is a Mitsubishi X-11. You can loo k it up. It is a cool unit having the vertical turntable. I know that is a bad idea because it is more likely to cause feedback but, it is a cool ass little unit. Plus I will get paid. the guy is all for the mod to a newer ou tput chip rather than trying what might be fakes or defects out there.

The unit is like 25 watts per channel, meant to work into its own 8 ohm spe akers but does have outputs for remote speakers though I do not know if it wires them in eries or parallel. I would bet series but it doesn't really m atter.

I did not consider them before, but after looking at the data sheet, I have decided to use a pair of LM3886s.

The unit has the tone controls in the global power amp feedback, a thing wh ich I and aother audiophiles really disapprove. (if they now wha tit is) th e LM3886 has about 100 dB gain so this will work fine. Datasheet :

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Originally, guitar amps introduced me to that chip so I thought it was goin g to have high distortion or have some stupid low current shit to emulat tu bes but it appears not to, in fact its THD+N is almost all under 0.05 % unt il it hits clipping. Someting like that, and really probably lower than the original.

The manual does give a THD spec but not frequency response. I found out why - it does not have flat frequncy response. Apparently they couldn''t care less. It has loudness comp but no way to switch it off. The component value s in the bass and treble circuit just look off, and no I do not feel like d oing the math. I also see atttachment points for speakers on the sides.

Nonetheless I am sure it is a good solid 25 watts a channel.

So anyway, on these LM3886 chips, this unit already has a relay with a dela y for the turnon transient, can I just directly connect the mute pin to Vee ? their drawings seem to indicate putting a resistor in there, maybe with a bypass cap. Can I kjust dispense with all that and connect it directly to save wiring ?

It is likely these chips will never ever need to be replaced. they are quit e overrrated for the job. It has +/- like 332 volts, and the transformer is not all that big. But I intend to just find wires of enough colors to come up out the board where the original was, up to the chips. Like say green a nd red for power, black for ground. Maybe blue and white for the + and - in puts and whatever for the output, yellow ? One set of wires per channel, wi th the chips mounted side by side under the clamp mount on the (what I cons oder by today's standards) ample heatsink.

The guy's olady loves the thing I guess. Unfortunately it is not one of tho se that play both sides of the record without flipping it over. But it is s till unusual, and I bet it really dosn't sound bad. It is not audiophile bu t for example, neither is your car stereo, and you can dig that, y'know ?

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jurb6006
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