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Old 6th August 2009, 01:07 PM   #1
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Default complete noob question

Been reading up alot lately and i looked at alot of various gainclone builds. one thing i noticed was the massive difference in size of various caps in different builds and kits. Peter Daniels gainclone kits are small and compact using small sized caps, but then theres something (this is a big difference tho) like the BPA300 where some use 4 huge RIFA 47000uF caps in the power supply.

Im just wondering, where do these big RIFA caps fit in in the PS schematic, because i havent really found one to look at and see. What is the purpose? to provide larger current which 6 lm3886 might need? What about on the smaller kits like Peter Daniels LM3875 kit, what would increasing cap values (and which caps) do? Forgive me for being a complete noob at this, faily new to it all

Also, does anyone know good places to get solid core copper/silver and silver coated copper wire in melbourne (various gauges)?

cheers
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Old 6th August 2009, 01:51 PM   #2
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Yes, the large caps are to provide current for the amp. Also known as reservoir caps. Larger current demands (eg BPA300) usually result in larger capacitance values. Higher voltages result in larger capacitor sizes as well. Capacitance values can be considered to form a high-pass RC filter with the speaker load, resulting in loss of bass if too small a value is used. That said, smaller capacitances seem to improve mid and high range. As always, it's a trade-off.
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Old 7th August 2009, 06:14 AM   #3
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ah ok cool, im starting to get better at all this stuff. Where are the reservoir caps usually placed in a circuit, such as a basic gainclone design? Straight after the rectifier bridges?
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Old 7th August 2009, 11:25 AM   #4
AndrewT is offline AndrewT  Scotland
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I believe it is better to have the rectifier close to the transformer and the smoothing capacitors close to the rectifier.
Once this is done and the amplifier is working you can check for hum and may find that rotating the transformer, even quite small angular adjustments may show a benefit, you can finally shorten and twist all the transformer to smoothing capacitor wiring to minimise the radiated fields from these wires. They carry very high current pulses and can cause interference in any of the low level circuitry.
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Old 8th August 2009, 08:43 PM   #5
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ah ok cool thanks for that. What about cap values? The caps on the rectifier boards on, say, audiosector permium kits. What is the effect when changing these capacitor values etc?
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Old 9th August 2009, 07:04 AM   #6
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Quote:
Originally posted by AndrewT
you can check for hum and may find that rotating the transformer, even quite small angular adjustments may show a benefit,
..if you do not have a toroid transformer.
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Old 9th August 2009, 07:32 AM   #7
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thats good but my question still stands
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Old 9th August 2009, 08:18 AM   #8
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The size of the smoothing caps?

Well the classic theory is, bigger is better. The bigger they are the smoother is the DC rail and the less does it sag under load. Drawbacks of bigger is better are bigger is more expensive, bigger takes up more space, there will be a point, where the theoretical advantage does not bring any further sonic advantage.

Where that point is, depends on your taste, your speakers, the volume at which you listen, etc. In a classical electric or electronic formation you learn that 1000 F / 1 A load current is an economically reasonable compromise for most power supplies. Any increase or decrease has its pros and cons. E. g. bigger capacitors draw more charge current and may need bigger rectifiers.

Usually an increase of capacitance improves the bass performance. An improvement there may appear as a decline in the other regions, so it is a matter of taste, what you prefer.

To my taste bigger is better up to a certain limit. 1500 f is still well below that limit.
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Old 9th August 2009, 08:35 AM   #9
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ah ok, so in your opinion what would you use on audiosector premium 3875 kit? I cant remember what caps it comes with for the rectifier board. Would your opinion change for a lm4780 kit instead? I like listening to a wide range of music but i do like some alive bass response. I guess the best way is trial and error. But im still interested to know what you would do/have done
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Old 9th August 2009, 02:01 PM   #10
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My opinion about the LM4780 is the same as for two LM3875.

My personal experience is that the bass with less capacitance is weaker, less punchy, but more alive. With more capacitance it is stronger, with more punch, and seems to be more laid back when it delivers, more authoritative.

I use to find my personal favorite somewhere in the middle between the extremes. With 1000 or 1500 F I find it lacking, while values in the range of many tens of thousands of F make it too languid for my taste. That is all with 8 Ohm speakers. The absolute size depends on the supply voltage and the speaker of course. The higher the voltage, the higher would I choose the capacitance, because higher voltage means higher current. With a four Ohm speaker, you need more capacitance, because it also means more current. The louder you listen, the more capacitance should be there. And you can play with the capacitance to level out certain speaker flaws in the lower regions a bit.

In the long run however, any change you make to your speakers will have a much bigger impact than the amount of capacitance, as long as the capacitance is in a reasonable range. Listen to the kit without any additional capacitance, then add 4700-10000 F per rail and channel and listen again. If you like it, work upwards from there until you cannot perceive any further improvement or until you don't want to pay any more for capacitors.
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