Gonna "bust a cap" in my LM3875.. What size cap?

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Hey guys..
I am working with a Audiosector LM3875 KIT and recently added 2 x Panasonic 10,000uf caps to the PSU and I quite like the ummph in the bass end.

So, I was thinking "lets add some BIGGER caps".. is that a sane idea? If so, what is the max anyone has ever added? What difference did it make?
 
I use an input filter of ~90ms for my Power Amps.
That suits a +-20mF of smoothing feeding an 8ohms amplifier channel.
If I were using 4ohms speaker I would have to increase the smoothing to +-40mF per channel.

If you high pass filter your power amplifier at a lot less than 90ms, then you can manage with a lot less capacitance.
 
There are usually two input filters for any audio gear.
A Low Pass filter, it attenuates the very high frequencies. This is used to reduce the effects of VHF interference from motors and lighting control and relays switching and wireless telephones and mobile phones and wireless alarm systems and WiFi and etc......
This a resistor in series with the signal followed by a capacitor to Signal Return. It is seen as an RC and is a single pole when just two components are used.

A High Pass filter, it attenuates very low frequencies. This is used to reduce the effects of VLF interference and blocks DC from faulty equipment, or from poorly designed equipment (with inadequate instruction manual).
This is a capacitor in series with the signal followed by a resistor to Signal Return. Again this is a single pole filter when just two components are used.

These two input filters should always be used on every piece of audio equipment until you understand why they are there and in what circumstances you can design out their need at the inputs.
Together they cost just 4 cheap components.

Finally, you should, in my opinion, not be modifying audio equipment designs by guesswork.
In the very early stages you can COPY existing good designs and as your skills accumulate you can apply science to what effects your proposed modifications may have on performance.

I never recommend guesswork modifications. It can lead to gross errors in performance.
 
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If so, what is the max anyone has ever added? What difference did it make?

The max I've added to a chipamp has been around 200,000uF per channel. Definitely it improved the bass 'snappiness' over 100,000uF. I plan to go higher with my latest build, at least 400,000uF. Note this is being fed from a SMPSU, not a trafo plus bridge rectifier. If you went the latter route I'd recommend CLCLC filtering before the final wallop of capacitance.
 
There are usually two input filters for any audio gear....

Hi Andrew,
Thank you again for taking the time to reply. It is much clearer now :) I assumed it was only the speaker crossover that had hi and low frequency filters.

The CAP I was reffering to was following on from your suggestion regarding adding Smoothing caps to the PSU. So, I had added 2 x 10,000uf caps as per this pic posted by 6L6:

DSCF0353.jpg


So, my question is, should I up the caps to bigger ones? Would it make a noticeable difference?
 
Well I don't know yet in regards to my chipamps. For my DAC it really makes a difference to the low frequency ambience retrieval. I hear further into a recording's acoustic space. As my DAC runs from a lower voltage I've been using more caps than I've shown here - I'm currently between 1 and 2F, using 6.3V caps.
 
Impedance to anything other than DC is very high with so much capacitance.
Other possibilities include:
PSU > K-Multiplier > Regulator > DAC
or
PSU > Tracking Pre-Regulator (simple "nested regs") > Amplifier
The "tracking pre-regulator" is the secret on how to get the high current regs to sound good.
These active alternatives aren't nearly as bulky as giant cap banks; however, there is some heat output from the regulators.
 
There's a simpler unregulated option in the attachment below.

Here are some notes for Audiosector.com and Chipamp.com amplifiers when used with the power supply attached.
Amp hookup: The power supply 0v hooks to amplifier board common ground, "CG" via (the PG vias are Not used at all).
Speaker negative hookup: From speaker jack, the speaker negative attaches to the power supply 0v, not the amplifier board (amplifier board speaker negative is not used).
Power supply cap options: The pair of 6800u can be swapped for either a pair of 10000u or 5x3300u (per rail).
Board options: This can be fabricated easily with 14ga solid copper wire for the rails and some copperless phenolic perfboard.
 

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