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Chip Amps Amplifiers based on integrated circuits

why no dc protection
why no dc protection
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Old 11th September 2018, 05:40 AM   #41
goodguys is offline goodguys  United Kingdom
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Hi. Thanks for the replies, much appreciated.


For the 0.1uf caps across the power supply caps is there any advantage to using ceramics with lower esr. In signal pathways they are bad, but what about power supplies.
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Old 11th September 2018, 06:34 AM   #42
FauxFrench is offline FauxFrench  France
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The idea with the 0.1uF capacitors is that they have a low ESR and can decouple higher frequencies. I use ceramic capacitors or foil capacitors. Depending on the layout and use, they may cause some ringing at higher frequencies which can then be damped with low-impedance resistors in series. I do not use such resistors unless I notice a ringing problem.
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Old 14th September 2018, 07:08 AM   #43
goodguys is offline goodguys  United Kingdom
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Hi!


On the front of the amp boards there are two capacitors on the middle left and right 100uf 35 volts for local power supply decoupling, i have swopped these for my favourite panasonic fm's and noticed an improvement in sound quality.


There is another capacitor at the very bottom of the board and a few smd's on the back, are any of these worth swapping out. If could please tell me the function of each that would be very mcuh appreciated.
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Old 14th September 2018, 11:01 AM   #44
FauxFrench is offline FauxFrench  France
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100uF/35V is not enough voltage rating. Should be 100uF/50V as the supply voltage range is until +/-40V. What are your Panasonic capacitors?

The third black electrolytic capacitor appears to be a decoupling capacitor as well. Change that to the same as the two other.

C1 must be the input signal coupling capacitor. Replace that with a foil capacitor if possible.

I have not managed to find more detailed photos of front and rear side of the board. It is very difficult to follow the design from small photos.

Last edited by FauxFrench; 14th September 2018 at 11:04 AM.
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Old 15th September 2018, 05:20 AM   #45
goodguys is offline goodguys  United Kingdom
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Hi!


I am using panasonic fm as replacments. I will put up photos of the boards to clarify.


In an earlier post you mentioned capacitors and decoupling frequencies. If i were to use a 0.1 uf capacitor in the power supply, would it decouple higher frequencies than a 1 uf capacitor. Does the frequency rise with decreasing the size of the capacitor.

Also, ( If the above is true ) purely by way of example, if a 0.1 uf capacitor decouples at 20khz and a 1 uf decouples at 15khz, then paralleing together 10 x 0.1 uf, would that mean the 20khz is decoupled 10 times over. ie, everytime the dc goes through one of the 0.1 uf capacitors the same frequencies are decoupled, or does the 10 parallel capacitors act as a 1uf capacitor and decouple down to 15khz.


Thanks
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Old 15th September 2018, 06:17 AM   #46
FauxFrench is offline FauxFrench  France
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Capacitors decouple according to their capacitance value and their ESR. The smaller the capacitance value, the higher in frequency they have to be used to have an efficiently low impedance to decouple the signal. The ESR depends on the type of the capacitor and, as a rough guide, on the actual outline of the capacitor chip and the leads - the smaller the capacitance value, the lower ESR.

Therefore, capacitors are chosen according to which frequencies you want to decouple. The higher the frequencies, the smaller the capacitors. But, as small capacitors are of little use at lower frequencies, you end up using more capacitors of different value and type in parallel such that some are efficient against lower frequencies and some efficient against higher frequencies.

Ten 0.1uF capacitors in parallel will result in 1uF capacitance. But, as the ESR of each 0.1uF capacitor is put in parallel, the resulting ESR of the ten capacitors in parallel will be much lower as if you took only one 1uF.

As an example of decoupling of a wide range of frequencies, you may use the parallel coupling of a 1000uF electrolytic capacitor (low frequencies), a 10uF/low ESR electrolytic capacitor (mid-range frequencies) and finally a 0.1uF foil/ceramic capacitor (high frequencies).

In theory, using a lot of smaller foil capacitors in parallel leaves a resulting capacitance that is efficient against a range of frequencies. The problem will be cost and the space they take up.

Last edited by FauxFrench; 15th September 2018 at 06:23 AM.
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Old 16th September 2018, 12:12 AM   #47
goodguys is offline goodguys  United Kingdom
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Hi!
I have managed to find some 10uf polyester film capacitors and am going to parallel connect ten of them together. The esr of each one is 1 milliohm, for all ten this should be 0.1 milliohm in total.
Low esr is generally considered to be useful, but is it possible to take it too far. Is there a chance that very low 0.1 milliohm esr may be seen as a dead short and cause damage.
For the 1uf capacitors mentioned in the last post, this is only decoupling the high frequencies and there is no real power at such frequencies.
The 10uf polyesters will be decoupling mids, where there is more power, and possibly bass, where there is even more power.
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Old 16th September 2018, 12:23 AM   #48
PRR is online now PRR  United States
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> this should be 0.1 milliohm in total

What is the resistance of the wire/PCB connecting these caps?
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Old 16th September 2018, 06:45 AM   #49
goodguys is offline goodguys  United Kingdom
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I do not know what the cable resistance is, it is 12 awg thick cable so should be good. When the power supply is complete i will measure the total esr of all the caps with my esr meter, but at this point it is just a theoretical point of view. I am trying to address possible oscillation problems or potential damage
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