META42 voltage and power cap questions
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finleyville

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Hello all,

I am making out a parts list for my amp and have a couple questions that are not covered in Tangent's well written documention.

There is room for 4 main power caps in the design not counting the high speed reservoir caps. What is the benefit of using all 4 caps instead of 2 larger caps? Obviously, all of the caps should be above the maximum voltage that they might see. Also, do all 4 caps have to be the same farad rating? Would it be benefitial to have say C2L/R be 1000mF and C3L/R be 470mF? Would the circuit see any difference? Would it sound different?

I'm also stumped in picking a power supply for my home only amp. Even though I only own a Sony V6 right now, I will buy a better can in the future. Not knowing the impedence of my next choice would it behoove me to choose a larger input voltage? Say around 24V? Is that too much for my V6's? Am I right in thinking cans like the Senn's need that extra voltage to sound better? Any recomendations on clean sounding power supplies would be greatly appreciated.

Also, I am interested in the AD8620 opamp. I know the max voltage it can take is 12V. Is this enough for the Senn's?


Thanks for the replys!
 
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Nezer

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More voltage helps...

One thing to consider about the power caps is the *speed* of the caps over the values.

I would rather have 4*470uf Cerafines over 4*2200uf generics. I highly recommend the Cerafines. They will cost a bit more but it does wonders for the bass response and overall 'tightness' of the amp.

No, all the caps don't need to be the same rating.

With the Meta42 I'm considering builindg an off-board power supply with some monster 5000uf Cerafines (at $50 each!). I'm also going to regulate the voltage rails to +/- 15v and stabalize them with 3 or 4 EL2001 buffers in parallel. Then I'm gonna filter the crap out of the power both inside the power supply chasis and again at the Meta's input.
 
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tangent

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Quote:

What is the benefit of using all 4 caps instead of 2 larger caps?


Using four caps instead of two helps you to stuff more capacitance into a fixed case height.

Let's say you're using a relatively small case like the Serpac H-67. (About 1" high inside.) That means you're pretty much limited to about 20mm high caps, after accounting for the board, and air gaps above and below. Since that case uses a 9V battery, you would want to use 10V power caps. Let's then say you wanted to use the Panasonic FC series because they're readily available at DigiKey. The largest 10V/10mm diameter part in that series is 1200uF. If 1200uF on a side is enough for your purposes, then use two -- if you want to try 2400uF on a side, then the board allows it.

Quote:

More voltage helps...


...and doesn't hurt, up to a point.

More power supply voltage won't hurt your headphones. It just affects the op-amp's ability to "swing". High-impedance headphones need more swing, as a rule, than low-impedance headphones.

Obviously you can't use a higher supply voltage than your op-amp can handle. Read the datasheet, and stay below the maximum recommended value. (As opposed to the absolute maximum, which is generally significantly higher.)

Also, more power supply voltage means your power caps need to be rated for the higher voltage. If you used an 18V power supply, you would have to use 25V caps. Let's say you're still using the Serpac H-67 line; perhaps you've fitted it with a DC power jack instead of using the version with a 9V battery compartment. The biggest 10mm/25V cap in the Panasonic FC line is 680uF. Going with higher supply voltages may be necessary, but realize that you're making a tradeoff in other areas. If the tradeoff is worth it, then by all means, go for it.

All of this applies to other cases and other lines of capacitors. I used the Serpac H-series and the Panasonic FC lines just for examples.
 
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finleyville

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Tangent

If I understand your comments correctly, you say that if I use two 470uF caps instead of one for each side, than my total capacitance is actually 940uF. It's been awhile since I knew the formulas and I don't have a reference book right now. Going from memory, the power caps are in parallel so one just adds the values up to get a total number. Is that right?

Also, since I will be casing this amp in a wooden cigar box, space is not an issue. Can bigger caps be used and set down beside the board with just the leads to the board? Is this a bad idea?
 
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I believe the META42 that eric made for me uses quad 220uf Elna Cerafine caps. I will probably be upgrading the amp even further later on, in which the case will be twice as wide (original case is around 3"x2"x5"). I don't think I'll be needing to use the dual 9v batteries internally anymore, external psu and battery pack will be fine. What effect would using larger caps have on the sound? Say quad 440uf cerafines? Also, what would using two EL2001 in parallel do for the sound? I am using the amp with Sennheiser HD600.
 
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The thing about 4 470uF 25V Cerafines is that they don't easily fit on the META42 board. However, what I'll be doing is putting 470uF Cerafines on the ends, and 220uF Cerafines in the middle of the power supply section - I found these will fit the board just fine.
 
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tangent

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Quote:

if I use two 470uF caps instead of one for each side, than my total capacitance is actually 940uF.


Right.

Quote:

Can bigger caps be used and set down beside the board with just the leads to the board? Is this a bad idea?


What I would do is mount them on a separate piece of protoboard, and then run wires from the protoboard to the META42 board. You don't want the power caps flopping around loose in the case. If their leads touched across something they shouldn't, you could fry your board.
 
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Quote:

Can bigger caps be used and set down beside the board with just the leads to the board? Is this a bad idea?


You may want to keep the leads short to minimize wiring impedances. Of course, using the largest gauge wire, that is reasonable, would also help.
 
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