Delta 1010 Clock Mod

[mtl777]

I'd like to revisit my original question that started this thread...

Someone did a clock mod on my Delta 1010 PCI card by replacing the clock with his own improved design that uses a PI filter. The improved clock is on a small board that is attached with wires to the original card:

http://home.ca.rr.com/mtl777/Files1/Delta 1010 PCI Card BLA Mod.jpg

It uses a United Chemi-Con MVH series 2200uF 16V 125 deg.C aluminum electrolytic surface mount capacitor (see the big cap in the picture) which has been retrofitted with leads in order to attach to the board. My question is, why was a 125 dec.C cap used? Does it really get that hot in that area of the board? If not, what could have been the specific reason for this choice of cap when there are many other 2200uF 16V caps with lower impedance and higher ripple current rating that might be better.

In the case of the capacitor there could be all sorts of reasons why that capacitor was chosen, none having anything to do with the temperature rating. ESR does not tell the whole story particularly in high frequency applications, ESL plays a large role, and the cap ESR may play a role in regulator stability not to mention damping high q resonances in the capacitor itself. I doubt ripple rating is an issue in this application - it does not appear to be a filter capacitor following a rectifier.

In this circuit, is a cap with lower ESL better? Looking more closely at the board, I see that the supply (top red wire) goes through a resistor, then through an inductor in series with the MVH cap in question. So it looks more like a LC filter than a Pi filter.

An externally hosted image should be here but it was not working when we last tested it.

If ESL is the important factor here, I'd like to know how can I determine a cap's ESL when it's not given in the datasheet?

Does the ESL increase as the cap's lead length increases? Look in the picture how long the MVH cap's lead is, due to the way it's installed. I guess this is a bad thing, right?

I hope someone would kindly answer my questions. I apologize if my questions are so newbie, as I'm really just starting to learn. Thanks.

 

[mtl777]

I hope someone would be so kind to answer my last question. Anyone, please?

Thanks!

 

[kevinkr]

Yes, I would assume that is an LC filter, and is intended to decouple the supply to the oscillator at high frequencies.

I think what you really want here is an os-con, but in my searches I have not been able to find a ready source. These have extremely low esl and esr and are designed for low impedance decoupling of high frequency circuits.

Another good choice would be the rubycon za/zl series of electrolytics, again you will have to search around for a stocking vendor.

I use Rubycon Black Gate FK types for these sorts of applications, but the supply is drying up. Check with Michael Percy (audio consultant) for availability here:

http://www.percyaudio.com/

 

[mtl777]

Thank you so much, Kevin! The Rubycon ZA is discontinued, but I happen to have the ZLG which is a substitute for the ZA. The one I have is 10V, though. The MVH cap that's currently installed is 16V. But I read that PCI card voltages are 3.3V or 5V, so I guess the 10V ZLG would be fine, don't you think so?

BTW, am I right in thinking that ESL increases if the terminal lead is too long? If so, this is one reason I would prefer a smaller 10V cap as it would fit on the cramped space in upright position and I would not have to install it lying down with long leads like the way the MVH cap is installed.

 

[kevinkr]

Yes, longer lead lengths do effectively increase ESL so I would keep the leads as short as possible. Measure the voltage across the existing cap first to make sure that it is no more than 80% of the 10V cap's voltage rating. (Also check the manufacturer's guidelines for derating lest it conflict with what I told you above.) In any event make sure it is less than 10V!

 

[kevinkr]

Where have all the good caps gone, long, long ago?

Now the ZA too eh... Bummer..

 

[mtl777]

Yes, longer lead lengths do effectively increase ESL so I would keep the leads as short as possible. Measure the voltage across the existing cap first to make sure that it is no more than 80% of the 10V cap's voltage rating. (Also check the manufacturer's guidelines for derating lest it conflict with what I told you above.) In any event make sure it is less than 10V!

Thanks! Now, how do I measure the voltage across the cap? Please confirm if this is correct: "With the PCI card installed and running inside the PC (the power is on), set the DMM to about 20V DC range, connect the red probe to the (+) terminal of the cap and the black probe to the (-) terminal of the cap. Make a note of the highest DC voltage reading on the DMM. This voltage must not exceed 8V in order for a 10V cap to be usable as substitute."

Embarassingly I must admit that I have only been reading about electronics on the web and have had no formal training. So please pardon this newbie question.

Where have all the good caps gone, long, long ago?

Now the ZA too eh... Bummer..

Yeah, too bad. But the ZLG is pretty good and still being made. It's the smaller, longer life substitute for the ZA. It sits between the ZA and ZL as far as low ESR is concerned. Then there's the ZLH, which is the smaller, longer life substitute for the ZL and comes next after the ZL in terms of low ESR.

 

[kevinkr]

Yep, what you describe is fine, as insurance insulate the meter probes to within a 1/4" or less of the tips with some heat shrink tubing, this will make the inevitable slip of the probe less likely to cause a catastrophic short.

 

[mtl777]

Now that I think about it, it's gonna be hard to probe that cap with the PCI card inside the PC. So I will solder a wire to the (+) terminal of the cap and another wire to the (-) terminal, with the wires long enough so that they're accessible from outside the PC case. Then I will stick my probes on the wires. That way it will be safer.

I just remembered something that makes me wonder. A capacitor is supposed to pass AC and reject DC. So, is it really correct to set the DMM on DC measurement mode when doing this test? I wonder why capacitor voltage ratings are in DC if capacitors accept only the AC component and not the DC.

Thanks!

 

[kevinkr]

I think you are having a mis-apprehension about the way capacitors actually work. Yes you do want to measure the dc across the cap - there should be no ac present that your meter can measure.

Capacitors perform a variety of functions including in this power supply case storing energy (dc) local to the load and providing a very low impedance to ground for any ac noise component riding on the dc if present.

Best place to look up capacitor characteristics is probably here:

http://en.wikipedia.org/wiki/Capacitor

It's all explained much better than I have the energy or time to do so..

 

[mtl777]

I understand now. Thanks for the heads up and for clearing my misconceptions about how capacitors work!

 

[mtl777]

Sorry, I have one more cautious question that I want to be sure about. If I try to measure the DC voltage across that MVH cap, isn't there a danger that doing so might cause the cap to not perform its filtering function, and because of this, some component down the line might get damaged? If so, would it be safer to check the voltage across the resistor instead, and whatever voltage that would be, to make the assumption that the capacitor will not be subjected to a voltage higher than that?

 

[kevinkr]

NO, just measure the voltage across the cap. Your meter is a high impedance device and takes just the tiniest amount of current from the nodes it's measuring, this is perfectly safe to do using the technique you previously described. Modern digital meters have high input impedance and don't draw significant current from the device they are measuring - there are some instances in very high impedance circuits where this can cause measurement errors, but no damage will occur.

ESD is a much bigger issue, I assume you are using a grounded wrist strap when you are working on this card, and have no pile of loose papers or styrofoam plastic cups nearby. (Both generate large amounts of tribo-electricity when disturbed and this can zap static sensitive devices.)

Obviously the other big issue is shorts..

Just be careful, you're doing fine so far.

 

[mtl777]

I'm glad it's safe to do. Thanks very much for this great info! Your help is so very appreciated.

 

[mtl777]

I have measured the voltage across the MVH cap. It is 8.8V DC! I researched the pinout of the PCI card. It is getting 12V supply from pin A2. The voltage must have reduced after going through the resistor. All along I thought PCI cards use only 3.3V or 5V supply. What the 3.3V or 5V actually meant was the "signaling level" (though I don't really know what that means ).

I'm glad I did this test to be sure about the voltage! Thanks, Kevin, for guiding me on this! Now the next question: Is a 10V cap sufficient for replacing that large MVH cap?

 

[kevinkr]

No, you need to use a 16V cap for this application. I assume there are additional regulators on the card to provide the application circuit voltages.

 

[mtl777]

Thanks, that's what I thought too. 10V seems too close for comfort to the measured 8.8V operating voltage. I will go for Nichicon HN 2200uF 16V which is even lower impedance and higher ripple current rating than Rubycon ZLG. And yet the HN is smaller than the ZLG for the same 16V rated voltage.

The HN datasheet doesn't show ESL specs, though. I'm hoping it is also low ESL and will work great for this application. Are low impedance caps usually low ESL or not necessarily?

 

[mtl777]

Let's go back to the PSU now. I have decided on the following capacitors to replace the stock M-Audio ones:

For "Booster" caps C14 and C17 - United Chemi-Con KZE 560uF 63V (0.024 Ohm impedance at 20 deg.C, 2500 mA ripple current, 0.01CV leakage current).

For pre-regulator caps C18 and C12 - NIC Components NRSY 2200uF 50V (0.045 Ohm impedance at 20 deg.C, 1750 mA ripple current, 0.01CV leakage current. Not too good impedance and ripple, but physical size was the limitation for this choice due to the cramped space.)

For pre-regulator caps C60 and C22 - United Chemi-Con KZH 2200uF 25V (0.013 Ohm impedance at 20 deg.C, 3450 mA ripple current, 0.01CV leakage current).

For post-regulator caps C61, C23, C19, C13 - Either (a) Rubycon ZL 560uF 35V (0.022 Ohm impedance at 20 deg.C, 2150 mA ripple current, 0.01CV leakage current); or (b) Rubycon ZLH 560uF 35V (0.020 Ohm impedance, 1960 mA ripple current, 0.01CV leakage current).

Two things:

First, I'd like to know if you see anything wrong with any of these choices before I buy them. Like, if the impedance or ESR is too low (which I read could be an issue with LDO regulators, but I'm not using LDO anyway), or if the leakage current is too high, and things like that. What do you think?

Second, I'm torn between Rubycon ZL and ZLH for the post-regulator caps. The impedance of these two is practically the same, but the ZL has higher ripple current rating (190 mA more) than the ZLH. However, the ZLH has longer life of 6000 ~ 10000 hours at 105 deg.C compared to only 1000 ~ 5000 hours for the ZL. So the ZL is better in ripple current, but is 190 mA difference a lot and do I really need that higher ripple current rating, considering that this is already after the regulator so the ripple is probably pretty much "tamed" at this stage? Is longer life more important than ripple current rating in this case because of the caps being close to the heat-dissipating regulators? Please help me decide between ZL and ZLH -- which of these two do you think is the better choice here?

Thanks!

 

[kevinkr]

You won't need the higher ripple rating post regulators so that becomes a non issue, just choose the more economical choice I guess.
Otherwise the choices look reasonable enough..

 

[mtl777]

Thank you so much, Kevin! With the higher ripple rating being a non-issue for post-regulator, I'll get the longer-life ZLH then.

So my booster and pre-regulator cap choices are fine? I'm just being careful of any gotchas or what-not, as the PSU is a delicate part and a mistake here could be disastrous. My traumatic experience with that noise problem which happened after I first messed with the PSU has taught me to be really careful.