It is not for bias because it is before the decoupling cap, and furthermore 1M would be too large a resistance to provide this bias current; this is where the 22K after the decoupling cap is for.
This is not to say I can tell you where the 1M is for and how it does prevent oscillations. But, by applying some logic, it is clear that the 1M becomes relevant only at very low frequencies. So the 1M might have to do with creating a path to ground for the signal wire in case the preceding stage is also cap decoupled. I will have a good night's rest over the question how the absence of this resistor could lead to oscillations before venturing any more guesses.
This is not to say I can tell you where the 1M is for and how it does prevent oscillations. But, by applying some logic, it is clear that the 1M becomes relevant only at very low frequencies. So the 1M might have to do with creating a path to ground for the signal wire in case the preceding stage is also cap decoupled. I will have a good night's rest over the question how the absence of this resistor could lead to oscillations before venturing any more guesses.
I promise that it will be more entertaining than the datasheet sample, but I cannot promise that it will be more suitable. Anyway, I prefer it.
Its my 2007 design, when I had even less idea of what I was doing; however, after a technology update for 2013, she finally images like a champ, has even more headroom, and the blockbuster dynamics are now sheer overkill. In my opinion that thing sounds like music. It is surprising.
Don't be confused--Although diodes are shown, they are actually filters (a sort of shield); therefore, the power is expected to be DC from a real power supply board. It is compatible with the prefabricated K50 boards.
Its my 2007 design, when I had even less idea of what I was doing; however, after a technology update for 2013, she finally images like a champ, has even more headroom, and the blockbuster dynamics are now sheer overkill. In my opinion that thing sounds like music. It is surprising.
Don't be confused--Although diodes are shown, they are actually filters (a sort of shield); therefore, the power is expected to be DC from a real power supply board. It is compatible with the prefabricated K50 boards.
I haven't any explanation for this phenomenom. The same circuit (without de 1M resistor) works OK when using a TDA2040, but it becomes oscilating with the LM1875 on-board
Anyway, as the datasheet recommends the 1M resistor... just put it.
These high value resistors (1 Mohm in this case) are sometimes used on the input or output to allow the the coupling cap to charge up. If you have the amp on and grounded the input or connected something and the coupling cap was not charged you get a nice loud thud as 1/2 the supply voltage would dump through the cap. Of course, it is not needed if a volume control or signal source is permanently connected to the input.
I do like to see a small value cap across the input to keep the amplifier from receiving its own output and oscillating at (usually) a high frequency.
I do like to see a small value cap across the input to keep the amplifier from receiving its own output and oscillating at (usually) a high frequency.
With regards to post #7 and post #8:AndrewT said:
The paralleled 220u caps (instead of solo 220u or solo 470u caps)
The diodes for series element (works better than creativity with cables)
The plausible sized 100u nfb-shunt cap (instead of a wrong size 22u or 47u)
The 100k feedback resistor for 38X (instead of 114k for 43X)
And the input coupling cap value set at 2u2 (instead of 1u)
There's only DC on an audio amplifier power circuit when there is no audio; so, I probably wasn't talking about filtering DC.
A voltage drop followed by a stiffening cap can serve as a filter.
It is more typical to see it at a discrete amplifier's small signal area; however, for the little LM1875, we can assume that the entire amplifier board is a small signal area.
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Sorry, I don't have that layout.
Getting a second set of 220u onto the K50 board takes some effort; however, the rest is almost plug and play. It could use a layout that looks very much like this: http://www.electronics123.com/kits-and-modules/CPS50-K50-PCB-only.html
Getting a second set of 220u onto the K50 board takes some effort; however, the rest is almost plug and play. It could use a layout that looks very much like this: http://www.electronics123.com/kits-and-modules/CPS50-K50-PCB-only.html
No.
You have been told this before !
Why do you insist on inventing your own version of non science?
Stated correctly it should say:
A series impedance followed by a shunting capacitor can serve as a low pass filter.
The voltage drop has nothing to do with the filtering action.
The dynamic impedance of the diode to the applied frequency is what creates the impedance that is one half of that low pass filter.
Hey Daniel,
Did you ever try taking the positive rail's decoupling caps to the negative rail instead of to ground (with the negative rail's decoupling still going to ground)? For many chip amps, that makes more sense. For the reasons why, see Klaus's post, at:
http://www.diyaudio.com/forums/powe...evoir-capacitors-chip-amps-5.html#post3631062
Edit: And you can see the effect on the rail voltage ripple in simulations, in my post at:
http://www.diyaudio.com/forums/powe...evoir-capacitors-chip-amps-5.html#post3632628
Cheers,
Tom
Did you ever try taking the positive rail's decoupling caps to the negative rail instead of to ground (with the negative rail's decoupling still going to ground)? For many chip amps, that makes more sense. For the reasons why, see Klaus's post, at:
http://www.diyaudio.com/forums/powe...evoir-capacitors-chip-amps-5.html#post3631062
Edit: And you can see the effect on the rail voltage ripple in simulations, in my post at:
http://www.diyaudio.com/forums/powe...evoir-capacitors-chip-amps-5.html#post3632628
Cheers,
Tom
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