G'day,
Working in progress, slowly
Working in progress, slowly
An externally hosted image should be here but it was not working when we last tested it.
On second look I'm a little worried about your "micas".
In some pictures they look dark orange.
*If* they are transparent , dark orange and "hard" (can be bent but flipping an edge with the nail makes a "click" sound) then they are probably a sheet of Kapton (or tinted Mylar) and *need* grease.
Now if they are like a sheet of thin rubber, which are opaque (the rubber is loaded with zinc oxide dust or some other thermal transmission enhancer) and "soft" , similar to a rectangle cut from a Kid's Party balloon, yes, they are Silpads and don't need grease.
Some kind of "paste" or elasticity is needed because neither the transistor back nor the heat sink are *perfectly* flat and "something" must fill those almost invisible air pockets.
Please confirm.
If you need to add some grease, no big deal.
Even if mounted, you just unbolt them and spread a little grease with a toothpick; later pressure will spread it where it's needed.
In some pictures they look dark orange.
*If* they are transparent , dark orange and "hard" (can be bent but flipping an edge with the nail makes a "click" sound) then they are probably a sheet of Kapton (or tinted Mylar) and *need* grease.
Now if they are like a sheet of thin rubber, which are opaque (the rubber is loaded with zinc oxide dust or some other thermal transmission enhancer) and "soft" , similar to a rectangle cut from a Kid's Party balloon, yes, they are Silpads and don't need grease.
Some kind of "paste" or elasticity is needed because neither the transistor back nor the heat sink are *perfectly* flat and "something" must fill those almost invisible air pockets.
Please confirm.
If you need to add some grease, no big deal.
Even if mounted, you just unbolt them and spread a little grease with a toothpick; later pressure will spread it where it's needed.
Hi JM,
Mica's is like this :
TO-220 Silicone Heatsink Kit
Thank's for you comment.
Hi Mooly,
Thank's, but sorry, I don't understand very well
You mean : connect a 40 w bulb on loudspeaker output ?
What voltage ?
Mica's is like this :
TO-220 Silicone Heatsink Kit
Thank's for you comment.
Hi Mooly,
Thank's, but sorry, I don't understand very well
You mean : connect a 40 w bulb on loudspeaker output ?
What voltage ?
Mmmmhhh, they don't *really* say what it's made of.
Although "silicone" hints more towards a "rubbery" material, than to a rigid one.
Let your nails test it
As of the "40W bulb", wooly refers to some version of this:
Light Bulb Limiter
Although "silicone" hints more towards a "rubbery" material, than to a rigid one.
Let your nails test it
As of the "40W bulb", wooly refers to some version of this:
Light Bulb Limiter
Oh, I forgot about "single rail".
Yes, *in this case* you can avoid the micas ..... but not the grease.
Or leave the silicone pads and consider them "grease".
Genarally I always use insulators, even on single rail jobs, so I can ground wherever I like using a piece of wire, instead of where the chip is bolted to.
But in this *very very* particular case, there's not much chassis to speak of , so, be my guest.
Yes, *in this case* you can avoid the micas ..... but not the grease.
Or leave the silicone pads and consider them "grease".
Genarally I always use insulators, even on single rail jobs, so I can ground wherever I like using a piece of wire, instead of where the chip is bolted to.
But in this *very very* particular case, there's not much chassis to speak of
, so, be my guest.Hi,
Yes it's single rail. So it's better without heatsink ? Why, (except shielding) ?
Pin 3 is connect with TO220 and ground, no.
For loop and big inductances, it's true, but it's my first diy amp.
When I saw the components arrive, I thought "problems"
No, you NEED the heatsink! you do not need the insulators between the IC and heatsink for single rail use as the tab on the IC is circuit ground potential. Use heatsink paste between the IC and heatsink for good thermal conductivity.
The reason why I don't care for those insulators (when not necessary) is because they add quite a bit of thermal resistance, something like 1 c/w. If your dissipating several watts as heat, the IC will be several degrees hotter. Heat is the enemy of electronics.
Even on my dual supply amps, I let the heatsink have the negative rail on it and insulate it from the chassis.
Well, there's a difference in concept here.
The TDA may be fed only <200Hz signals, because it's meant to drive a subwoofer.
Fine.
*BUT* the chip amp itself *still* has wide frequency response, way into the 10's of KHz and above, and still can be unstable, oscillate, etc.
That's why you must still be careful with grounding, wiring layout, etc.
On another thread, somebody commented that he did not use the Zobel network, because "when he connected it the resistor smoked".
Proof of *strong* HF oscillation !!!!
Yes, I think you are right
1 : test and try like this
2 : how to prevent or reduce oscillations in my case ?
You won't like the answer to number 2. It involves tearing down what you already built and reassembly on a board with short lead lengths, star ground and RF input filter... However, since you are far along, just complete this amp and test it. If it sounds good to your ears, that all that matters.
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