hi,
the backplate of the lm is probably connected to one of the pins in the chip.
Check the datasheet to find out which.
If the sink is electrically connected to the chassis or to audio ground than you have shorted that backplate to somewhere it should not.
You must either electrically isolate the chip, but let the heat out, or isolate the heatsink, but accept that some day someone will drop a spanner in the works and blow up the amplifier.
the backplate of the lm is probably connected to one of the pins in the chip.
Check the datasheet to find out which.
If the sink is electrically connected to the chassis or to audio ground than you have shorted that backplate to somewhere it should not.
You must either electrically isolate the chip, but let the heat out, or isolate the heatsink, but accept that some day someone will drop a spanner in the works and blow up the amplifier.
I know that 3rd pin is connected to the backplate, but the heat sink is not connected to GND or chassis ( I haven't made a chassis yet), and it won't; heat sink will just touch the LM.
What do you mean with "drop a spanner"? Literally, drop something heavy in the chip?
I't won't happen, I'll keep it safe,
.
What do you mean with "drop a spanner"? Literally, drop something heavy in the chip?
I't won't happen, I'll keep it safe,
.
Hi,
that confirms that the heatsink is connected to the chip.
I don't understand why the voltage changes when you "plug in".
What are you connecting that changes the voltage?
Try connecting 100k from sink to ground and measure the voltage across the 100k. That will tell us what current is flowing from the chip and what voltage is there.
Measure the supply voltages to the chip when you do this experiment.
that confirms that the heatsink is connected to the chip.
I don't understand why the voltage changes when you "plug in".
What are you connecting that changes the voltage?
Try connecting 100k from sink to ground and measure the voltage across the 100k. That will tell us what current is flowing from the chip and what voltage is there.
Measure the supply voltages to the chip when you do this experiment.
Is it wrong that the heat sink is connected to the chip?
Should I insulate it or not?
The voltage changes when I connect a 4 ohm, 6W speaker.
So, you mean puting a 100k resistor between heast sink and GND and measuring current and voltage?
What is it for?
I think there's something wrong with tracks and soldered joints and I'm tired of it.
Next week I have some final tests at university, so I'm puting the gainclone in santd by.
Anyway, I promise to make a step by step guide of what I did ( when it's working, course!).
Should I insulate it or not?
The voltage changes when I connect a 4 ohm, 6W speaker.
So, you mean puting a 100k resistor between heast sink and GND and measuring current and voltage?
What is it for?
I think there's something wrong with tracks and soldered joints and I'm tired of it.
Next week I have some final tests at university, so I'm puting the gainclone in santd by.
Anyway, I promise to make a step by step guide of what I did ( when it's working, course!).
If heatsink has voltage, must use wooden amplifier enclosure.
Even better to do a wooden enclosure and an insulated heatsink.
Its not a good idea to have both a voltage source (heatsink) and a voltage reference (metal enclosure) within the reach of fingers.
For metal enclosure, insulate the back of the chip--use a size TO220 Mica insulator, White thermal compound and shoulder washers.
Any amplifier enclosure needs air inlet at the bottom and air outlet at the top (or top of back panel).
The surface of MDF is flammable. MDF needs finished, like paint, Lacquer, polyurethane, etc. . . You can use brown spray primer, scribble that with a black sharpie (wood grain looking scribbles), and then paint with "Polyshades" of a dark color like Bombay red or Walnut brown, for a fairly pretty finish on MDF.
P.S.
Also observe a common 2-cell flashlight. This is similar to a split rail power supply. The centrepoint between the two batteries in the 2-cell flashlight is the 0v tap.
Even better to do a wooden enclosure and an insulated heatsink.
Its not a good idea to have both a voltage source (heatsink) and a voltage reference (metal enclosure) within the reach of fingers.
For metal enclosure, insulate the back of the chip--use a size TO220 Mica insulator, White thermal compound and shoulder washers.
Any amplifier enclosure needs air inlet at the bottom and air outlet at the top (or top of back panel).
The surface of MDF is flammable. MDF needs finished, like paint, Lacquer, polyurethane, etc. . . You can use brown spray primer, scribble that with a black sharpie (wood grain looking scribbles), and then paint with "Polyshades" of a dark color like Bombay red or Walnut brown, for a fairly pretty finish on MDF.
P.S.
Also observe a common 2-cell flashlight. This is similar to a split rail power supply. The centrepoint between the two batteries in the 2-cell flashlight is the 0v tap.
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