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Old 23rd April 2010, 05:37 PM   #21
trzn is offline trzn  Lithuania
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Quote:
Originally Posted by pacificblue View Post
If you have more capacitance on the 7806's output than on the input, you should add a flyback diode.
How exactly should I do it?

Quote:
Originally Posted by pacificblue View Post
Shouldn't there be an input resistor to ground?
Are you talking about 5kOhm one? If so, I was explained that it tells me that my source needs to drive a 5k load and that I don't need 5kOhm resistor.

Quote:
Originally Posted by pacificblue View Post
The symbol you used for the input is the ground symbol.
I know, but there is no such a symbol in Eagle as input. And I don't know how to draw my own symbols.
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Old 23rd April 2010, 09:17 PM   #22
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Quote:
Originally Posted by trzn View Post
How exactly should I do it?
There is a drawing in the datasheet. You connect a diode in parallel to the regulator in the opposite direction of the current through the regulator.


Quote:
Originally Posted by trzn View Post
Are you talking about 5kOhm one? If so, I was explained that it tells me that my source needs to drive a 5k load and that I don't need 5kOhm resistor.
Why would the datasheet recommend an unnecessary component? All sources will be able to drive a 5 k load, but not all sources will be happy to drive a capacitive load. Without that resistor they will see a capacitive load below the corner frequency of the input filter. With the resistor they will see a nearly resistive load.


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Originally Posted by trzn View Post
I know, but there is no such a symbol in Eagle as input. And I don't know how to draw my own symbols.
In supply2.lbr there is the symbol 'V-->' which you can name any way you like. If you don't have that library, you can get it from the Eagle donload site.
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Old 24th April 2010, 02:05 AM   #23
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I might be just drinking the coolaid, but i think its just a badly drawn schematic on the data sheet. During testing they use an "Rs" of zero to 5kohm. In the schematic they show an "Rs" and an "Rl". They also tell you the input impedance is 20k. It also doesnt use a normal volume control. I honestly think Rs just represents the source, and Rl represents the load.
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Old 24th April 2010, 05:59 AM   #24
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A source with 5k?
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Old 24th April 2010, 12:02 PM   #25
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No no thats the max they want, and the number they used for max distortion. hell a 5k source couldnt drive a 10ft cable. But on the other hand when was the last time you had a 5k input impedance? and on a sub 10 watt amp.
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Old 24th April 2010, 07:00 PM   #26
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Originally Posted by nightanole View Post
No no thats the max they want, and the number they used for max distortion.
The drawing is quite clear. There is a 5k resistor and there are two wires coming in from the left. One is ground, the other is labeled 'positive input'.


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Originally Posted by nightanole View Post
when was the last time you had a 5k input impedance?
LM4780 datasheet, page 7, figure 4 comes pretty near. At max volume it is ~5k1. There are also some inverting designs with low input impedance.

I am confident that the engineers who wrote the TDA7052A datasheet had their reasons to specify that value.
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Old 24th April 2010, 07:51 PM   #27
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Well he is air wiring it so its real easy to add the resistor.

Still a 5k in, my poor bantam and gamma1 with pio .33uf caps are shaking in their boots. That puts the -3db in the 100hz range. id need 10x more capacitance to get it back down to 10hz
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Old 24th April 2010, 10:52 PM   #28
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Do you mean you have sources with 330 nF output capacitors?

The inner resistance of the TDA7052A is 20k. The recommended 470nF Cin leads to -3dB at ~17 Hz.

Pretty academic anyhow, because 1 W is not enough to produce anything audible or notable at that frequency with any speaker except maybe a headphone.
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Old 24th April 2010, 11:16 PM   #29
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ya most of my sources just have 1uf-.2 uf caps. Right now they are just paper in oil .33uf ones. So if i hooked it up to his new amp with the 5k resistor installed, it would filter out the sub 100hz. Vs the 20k internal resistance only.

I have no idea what source he is using, or even what its for. All ive come up with is thats its 12v battery powered, the load on the bat is only 40ma, and it will be ran 24/7/365.
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Old 25th April 2010, 06:45 AM   #30
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Your sources are unique then. Usual output caps are so big, they have to be electrolytics even in "high end" gear. For all standard sources the 5k//20k=4k should not be an issue. Frequencies below 100 Hz are normaly not much of an issue for 1 W amplifiers anyhow, because they simply have not enough power. And the speakers that match 1 W amplifiers are rarely able to reproduce much deep bass either.
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