Hi all,
(Inexperienced first timer here)
I am playing with a 3886 that I bought second hand, and I noticed each channel has a jumper marked In-Out-Gnd. I have been unable to locate any instructions or info by googling similar boards - can anyone hazard a guess as to what it is for? I'm guessing its got something to do with the audio input, given it is near the preamp chip.
I also did a quick 5 second power on test (18-0-18 160VA + 60W 4 ohm full range speaker + audio signal from phone on 10% volume) and it was shockingly loud! (music quality was otherwise OK). Should I be careful with running it as single channel and leaving the other channel with no audio in or speaker out?
My long term goal is to put passive tone controls (given there is already a 5532 there) and use both channels.
thanks,
Chris.
(Inexperienced first timer here)
I am playing with a 3886 that I bought second hand, and I noticed each channel has a jumper marked In-Out-Gnd. I have been unable to locate any instructions or info by googling similar boards - can anyone hazard a guess as to what it is for? I'm guessing its got something to do with the audio input, given it is near the preamp chip.
I also did a quick 5 second power on test (18-0-18 160VA + 60W 4 ohm full range speaker + audio signal from phone on 10% volume) and it was shockingly loud! (music quality was otherwise OK). Should I be careful with running it as single channel and leaving the other channel with no audio in or speaker out?
My long term goal is to put passive tone controls (given there is already a 5532 there) and use both channels.
thanks,
Chris.
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You would have to trace it out to be sure, but I expect it is a way to insert a tone board or similar into the audio path. I'm assuming the jumper goes from "out" to "in".
Maybe a connection for a volume pot? It looks like it's jumpered from IN to OUT at the moment, so volume pot would make sense.
Tom
Tom
Dudes, you're way over thinkin' this, just take a look!
On the left you got the PS comin' in, thru the rect. and big caps then off to the right to the regs for the opamps.
Bottom left is input, bottom right is output and you can see the holes for the 3886 on the right.
So why would a crazy asian, cut-and-paste--from other designs and the datasheet--PCB 'designer' put IN//GND/OPUT right beside an input opamp ...
Well it's probably a 'tap' after the isolating input opamp; you can tap the signal for a ... volume pot, filter or both and it's a desert topping as well! 😉
So the jumper is bridging input to output [or more precisely the OUT of the opamp to the IN of the 3886; i know, i know, sigh, ...], , , ,and you could make a cable that runs off to a pot [not toooo far] and back.
You can also do good testing processes like make a few simple cables and then you could plug the output of the right opamp into the input of the left 3886, or from one opamp to the other and then to both 3886s, or ...
{... some weird distortion or something tester where you send the signal through one opamp to both 3886s then ... ~ subtract them through some driver or passive component and then back to the second opamp for filtering and analysis ...} 😱
..or it might be a tap before the opamp itself. That would actually be a better design:
input connector to basic input circuit w AC coupling cap [keep DC from delicate pot wiper]; off to pot; back from pot; off to opamp (isolate the 3886); on to the 3886. That's how Tom would do it.
Good luck
PS Doh, what Tom said. 😱
PPS If it was LOUD at 9 oclock, it may be a linear pot (or not audio taper enough--easy enough to replace) 😀
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