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Old 5th June 2003, 12:30 AM   #1
elizard is offline elizard  Canada
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Default Gainclone Help

Well,
I received the chips from Peter today (thanks again!) and I finished one gainclone
i've decided i'll do one at a time .. get one working first, then the other

The power supply I've completely finished, and its putting the right voltage at the right output. So I'm sure of that at least!

The gainclone I've finished, but I'm afraid to power it up. I won't touch it until tomorrow at least. Get rest, then check everything

One thing I would like to know. Is there ANY measurements/tests I can do with a multimeter (that's all of my "testing" equipment I have) to check the gaiclone? The only thing I could think of is resistance, but not sure where to measure and what to expect?
Or is it mostly power up and duck? (I don't sadly have a variac or a variable power supply! one of these days i tell ya)

Thank You
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Old 5th June 2003, 12:37 AM   #2
elizard is offline elizard  Canada
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oh yeah, and one thing i haven't paid mind to yet is heatsinking
my "heatsinks" are 2" wide, 2" long, 1" high .. will that be enough (1 of these per chip). Also, unfortonately its mounted upside down (i.e. the chip is facing up, fins facing down) and is enclosed in a box that's about 5.5"x3.5"x2" (and has holes on bottom).

Should this combo of a small heatsink and a small case cause a problem???
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Old 5th June 2003, 12:39 AM   #3
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You can't go wrong here. Feedback resistor goes between pin 3 and 8 (assuming it's inverted GC), pin 7 to ground, pin 1 is positive PS and pin 4 is negative PS. I use voltmeter to check the amp. If the DC offset is around 28mV (at pin 3), there is a good chance I have a working amp
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Old 5th June 2003, 12:40 AM   #4
elizard is offline elizard  Canada
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sure i can go wrong peter .. why i already DID go wrong .. that's why i want to double check
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Old 5th June 2003, 12:41 AM   #5
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Don't worry about heat sink. Check it from time to time and if it's too hot, you will have to make it bigger. But nothing will happen if you don't push it too much
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Old 5th June 2003, 12:41 AM   #6
elizard is offline elizard  Canada
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btw, i just did a quick look-over of the amp, and everything looks in order ..
also all of my stuff is looking a LOT neater than the last time i made it (second time around, take it slower, do a better job)
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Old 5th June 2003, 02:40 AM   #7
elizard is offline elizard  Canada
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well i got enough guts to turn it on

no turn-on explosion - check
no overheating - check
dc offset - 28mV
rails - 33V

so far so good

put on a speaker - nothing, no turn on thump .. no sound
put another speaker - nothing, no turn on thump/no sound
a third speaker (that i KNOW works) - NOTHING!!!

so .. now i've a gainclone but no sound
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Old 5th June 2003, 02:44 AM   #8
elizard is offline elizard  Canada
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also as far as i can tell, and i've checked it a billion times .. everything is wired correctly for the inverted:

pin 1 - +V
pin 3 - 220k resistor to pin 8, to one speaker out
pin 4 - -V
pin 7 - to star ground
pin 8 - 220k resistor to pin 3, 10k resistor to 4.7uF cap to input

the other speaker out comes from star ground

anything amiss in here?

edit: also there is no resistor/pot between input and ground (i.e. no connection between the 2)
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Old 5th June 2003, 03:04 AM   #9
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Elizard,

If you do not get things going ok by the weekend, I would be willing to come over and help you out the best I could.

Let me know.

Thanks

Kevin
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Old 5th June 2003, 03:13 AM   #10
elizard is offline elizard  Canada
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thanks kev .. help always appreciated, but i work saturday/sunday
maybe if i get a day off and i don't get it workin i'll take you up on your offer

as an aside:
i know for sure that the 1000uF caps are working fine and both the resistors are working fine ..
peter sent me the lm3875's, so i'm pretty sure those are fine as well
the 4.7uF cap is MOST LIKELY fine .. don't know how it would have gotten damaged
orientation of the 2 polar caps looks fine to me
the one soldered to pin #1 is +, the - of that goes to star ground
the one soldered to pin #4 is -, the + goes to star ground as well

i've 6 things going to star ground
the ground from power supply (or 0 V), the negative speaker out, the input ground, pin #7, and the 2 caps (+ from one and - from the other)
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