Thank you NareshBrd for your reply..... Using a common heatsink on a common supply split rail or not I wasn't too sure about any earthing issues reagrding hum etc.
I should have known really since the tabs are at the same potential, no hardship I guess to slip isolation kits on should there be any problem.
What it is, I built a LM1875 stereo amp. and used a common heatsink, along with a 8 amp bridge and two 10,000uF, now I'm down to mounting the chips and heatsink. I was hoping to take the supply up to something like 25-0-25V DC since I have a suitable transformer.
Dave
I should have known really since the tabs are at the same potential, no hardship I guess to slip isolation kits on should there be any problem.
What it is, I built a LM1875 stereo amp. and used a common heatsink, along with a 8 amp bridge and two 10,000uF, now I'm down to mounting the chips and heatsink. I was hoping to take the supply up to something like 25-0-25V DC since I have a suitable transformer.
Dave
I always use mica-grease-nylon nipples even if single supply, simply so >>I<< choose the Ground path.
Mucho mystery oscillation and instability can be avoided that way.
Remember in this case amp ground return carries high current audio frequency current, what the Doctor ordered to contaminate ground.
Mucho mystery oscillation and instability can be avoided that way.
Remember in this case amp ground return carries high current audio frequency current, what the Doctor ordered to contaminate ground.
Now I am confused, I can see the heatsink being 'live' or above ground potential at least, I do think I'm better using micas and better isolating them now.... at least they can be grounded without any flash n' bangs and melting the silcon slabs, they can be grounded which must aid stability of kind.
Obvious to me if we are building them for power then I ought to consider using higher power devices. Thanks for the input, I'll isolate now, Dave.
Obvious to me if we are building them for power then I ought to consider using higher power devices. Thanks for the input, I'll isolate now, Dave.
Silicon pads do work, compared to mica it is a matter of taste.
Heat sink size please see it can take the heat.
And at +/- 25 volts you will be at about 25 watts output, quite high for a little chip, but NS says it can take it.
It is simpler than the 3886 to make, and there are many variations to that basic circuit.
Enjoy.
Heat sink size please see it can take the heat.
And at +/- 25 volts you will be at about 25 watts output, quite high for a little chip, but NS says it can take it.
It is simpler than the 3886 to make, and there are many variations to that basic circuit.
Enjoy.
hi
I prefer to isolated the chip as adason and JMFahey wrote
hint from Mr.X (XRK971) use ceramic plates like this:
10pcs aluminium nitride ceramic substrate thermal conductive insulating ceramic TO 220/247/264/3P/3 aluminium nitride|Air Conditioner Parts| - AliExpress
chris
I prefer to isolated the chip as adason and JMFahey wrote
hint from Mr.X (XRK971) use ceramic plates like this:
10pcs aluminium nitride ceramic substrate thermal conductive insulating ceramic TO 220/247/264/3P/3 aluminium nitride|Air Conditioner Parts| - AliExpress
chris
Yes, I've inserted the micas and grounded the heatsink. I've come across ceramic plate insulators in TV's and switch-mode power supplies, thanks for the link, I just might get some, always seem on the thickish side to me as I have non myself, I would think ceramic is a better conductor than mica, just never give it a thought, had no reason to do be honest.
Dave
Dave
He has already got answer of his question. Do you think that it should be repeated again and again? I don't think so. Anyway my advice was for him not for you so chill
I can understand variations in thoughts.... I wasn't too sure myself should there be any 'gotcha' being the reason I asked, no hardship trying both way's I guess.
I reckon it's pointless building a amp. and then having it run 'flat out' in general usage, that's OK for trying, testing and seeing it's capability, we'll see how it goes.
Dave
I reckon it's pointless building a amp. and then having it run 'flat out' in general usage, that's OK for trying, testing and seeing it's capability, we'll see how it goes.
Dave
It's also a matter of how much of a mess you're willing to deal with. The silicone pads are now good enough that there's really no compelling reason to use mica+goop. If you happen to have the mica washers, there's nothing wrong with using them, but I would buy a good thermal pad like Keratherm Red for new builds.
Even if the tab of the IC is grounded, as it would be in a single-supply amp, I would still add an insulating washer. I like to have control over where the chassis ground connection is made and through the back of the IC is usually not the preferred option.
Tom
Here the heat sinks in kits are the grin and bear it quality.
Silicon pads not easy to get.
The need is also for the air gap to be closed and better heat conduction.
And a firm mechanical connection is needed.
I have had to level out uneven heat sinks, partly because I can.
Silicon pads I see in Chinese origin computer supplies.
All these affect your choice of parts.
The mica washers can break, goop can be messy... though I find rubbing alcohol great for smoothing out and cleaning dried up heat sink compound.
Also, the temperature at which you intend to run, though pure silicon rubber can go above most chips' thermal shut down temperature.
Mica won't go stiff with years of use, silicon rubber might do that.
Choices, choices....
Silicon pads not easy to get.
The need is also for the air gap to be closed and better heat conduction.
And a firm mechanical connection is needed.
I have had to level out uneven heat sinks, partly because I can.
Silicon pads I see in Chinese origin computer supplies.
All these affect your choice of parts.
The mica washers can break, goop can be messy... though I find rubbing alcohol great for smoothing out and cleaning dried up heat sink compound.
Also, the temperature at which you intend to run, though pure silicon rubber can go above most chips' thermal shut down temperature.
Mica won't go stiff with years of use, silicon rubber might do that.
Choices, choices....
I agree with NareshBrd... "Mica won't go stiff with years of use, silicon rubber might do that....."
Yes I've seen that when removing heat sinks from TV's, they don 't always come off clean leaving parts of the fabric on the heatsink and leaving their impressions, they kinda dry out.
The amp. worked flawlessly on a rough test using only a 12-0-12V ac supply, I do have a 300VA 18-0-18 tranny. but that was far too big and wanted that for something else, no noise no hum, I added a UPC1237 chip speaker n' thump protection I saw elsewhere.
I reckon once you've seen a TDA/LM circuit you've seen em' all, the only thing different may be the values or the the two gain setting resistors on the feedback, some may have a 220pf cap across the input for RF protection.
I built a Radio 4 AM/FM radio for the bench using a NE602 mixer and a two transistor IF amp pre-tuned on Radio 4 and for FM I used a TDA7000 chip. The noise on LW was horrendous masking Radio 4..... I was gobsmacked when I added a 470nF across the 15V secondary on the mains tranny - what a difference that made! LW was every bit as quiet as FM.... except for thunderstorms.... so I did the same with the amp. build.
It's quite surprising what trash comes down the mains, RF, re-radiation, arcs n' sparks from everywhere, industrial sites with their arc welders, arcing power lines. The capacitor need be one rated for AC use and marked as such, making no different if on the primary or secondary side.
The racket finds it's way via inductive and capacitive coupling through the tranny and rectifiers into any hi-gain circuit, plus it protects the rectifiers against any voltage spikes.
Dave
Yes I've seen that when removing heat sinks from TV's, they don 't always come off clean leaving parts of the fabric on the heatsink and leaving their impressions, they kinda dry out.
The amp. worked flawlessly on a rough test using only a 12-0-12V ac supply, I do have a 300VA 18-0-18 tranny. but that was far too big and wanted that for something else, no noise no hum, I added a UPC1237 chip speaker n' thump protection I saw elsewhere.
I reckon once you've seen a TDA/LM circuit you've seen em' all, the only thing different may be the values or the the two gain setting resistors on the feedback, some may have a 220pf cap across the input for RF protection.
I built a Radio 4 AM/FM radio for the bench using a NE602 mixer and a two transistor IF amp pre-tuned on Radio 4 and for FM I used a TDA7000 chip. The noise on LW was horrendous masking Radio 4..... I was gobsmacked when I added a 470nF across the 15V secondary on the mains tranny - what a difference that made! LW was every bit as quiet as FM.... except for thunderstorms.... so I did the same with the amp. build.
It's quite surprising what trash comes down the mains, RF, re-radiation, arcs n' sparks from everywhere, industrial sites with their arc welders, arcing power lines. The capacitor need be one rated for AC use and marked as such, making no different if on the primary or secondary side.
The racket finds it's way via inductive and capacitive coupling through the tranny and rectifiers into any hi-gain circuit, plus it protects the rectifiers against any voltage spikes.
Dave