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Old 5th December 2003, 11:48 AM   #1
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Default For active bass only - 1000 or 10000 uF?

Hi!

So far I have built all my GCs with just 2 * 1000 uF directly at the IC, and 2*220 uF in the (distant) supply.

But now that I am building my own "boombox", I wonder if using a "normal" supply with somewhat like 2*10.000 uF or 2*20.000 uF would be more appropriate, in order to get more control over the bass?

I am using two OPA541 for the bass, attached to 2 16.5 cm bass drivers, 4 ohms, supply voltage will be +- 35 V (25 - 0 - 25 toroid). The XO is set to 90 Hz.

So, just 1000 uF caps at the IC, or more capacitance directly at the supply, with bypassed 220 uF (or additionally 1000 uF) caps at the IC?

Just need an answer prior to ordering some missing parts...

Thanks,

Arndt

BTW: The Mid / High section will be powered by a OPA548, with two 13 cm coax, 4 ohms drivers. Enclosure sizes were not calculated, but found by experiment, since I had no TS parameter...
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Old 5th December 2003, 12:01 PM   #2
UrSv is offline UrSv  Sweden
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Since, AFAIK, the 1000 uF recommendation (or 2200 uF depending on supply voltage and religious conviction) only applies to the LM38XX series of chips I think that a more common suggestion of 10.000 uF would not be out of place.
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Old 5th December 2003, 12:21 PM   #3
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I got up to 5000uf quite happily on my 549s before the mids started getting a little congested, with a slight improvement in bass, so if you were just going to use them for bass, then I would start at 5000, and just add extra until you get no perceptable difference. I was using 1000uf by the chip, and the extra capacitance in the power supply section, so it was quite easy to change.
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Old 5th December 2003, 01:17 PM   #4
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I would also expect improvement in bass with more caps. As you won't be using mids, it doesn't hurt
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Old 5th December 2003, 02:16 PM   #5
Mad_K is offline Mad_K  Norway
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Quote:
Originally posted by UrSv
Since, AFAIK, the 1000 uF recommendation (or 2200 uF depending on supply voltage and religious conviction) only applies to the LM38XX series of chips I think that a more common suggestion of 10.000 uF would not be out of place.

I like 2200uF with the opa's (fullrange). 10000-22000uF seems a good choice for subwoofer-use
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Old 5th December 2003, 02:29 PM   #6
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Hi!

Thanks for the input.

I will go for this kind of setup:

1 toroid (300 VA, 25 - 0 - 25)
2 bridge rectifier
2 * 10.000 uF at the supply for bass
2 * 220 uF at the supply for mid/high
2 * 1000 uF per channel, bypassed with 100 nF for each bass and mid/high
2 * OPA 541 for bass
2 * OPA548 for mid/high

Of course there is lot of room for improvements, but I have one simple goal:

Make a ghetto-blaster like setup, with better performance than the JVC boomblaster series (albeit with more weight, since I use MDF), for less than 100 € (including parts which I already have or which didn't cost me anything). I only had to buy some small stuff, the speakers (60 €), the wood (10 €), the big caps (13 €), using surplus toroid, bridges, cables, heatsinking, active XO, bass processor (Thommessen), and samples from TI...

I also have to finish this until the 20th of december, since from then on I intend using it while doing work / holidays in Saas Fee (skiing and cooking ). So time and costs are my priorities. Not looks and outstanding performance

That comes in January / February...


Bye,

Arndt
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Old 7th December 2003, 10:24 AM   #7
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what do you mean by bass processor? what is it
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Old 7th December 2003, 10:49 AM   #8
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Hi!

I am pretty sure that the origina JVC boombox uses some active equalization in order to produce that kind of "fat" bass out of its comparatively small enclosure.

I could use a linkwitz-transform-circuit, but don't have the time, so I settled for an old Thommessen module I have lying around.

Take a look at

Thommessen Bass Extremer

Nothing fancy, but I really need something like it, since I do not have the thiele-small parameters for the speakers I use, and bass without EQ is too thin for my taste...

Bye,

Arndt
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