Opinion on OBiie voice card cap voltage

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Opinion on OBiie voice card cap voltage

Post by Skiroy » Thu Jan 31, 2013 2:49 am

Okay so Im down to getting my caps for the voice cards. Here is the service manual.

http://www.lazyblueoctopus.com/oberheim ... nual_3.pdf

Now everyone says to go with higher Voltage caps. I did throughout the PSU and motherboard. I really want to stay as close to the original caps as possible in the audio path. Im wanting the Elna Cerafines as they are known to be more aggresive and thats what the OBXa is all about. The issue is the 35V versions of today are to large and I would have to go with 25V for them to fit. The originals are 35V.



Now scotrod is a very knowledgable guy and said that the audio path does go above 11V and the power rails do not go above 15V, 25V would be fine. But most of what I read says to get higher voltage caps than originals and if the originals are 35V Im weary about getting 25V. But I have the utmost respect for scotrod and I know nothing ,but I would like to get some of your opinions after looking at the schemo of the voice cards on page 56.

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Re: Opinion on OBiie voice card cap voltage

Post by Ashe37 » Thu Jan 31, 2013 7:48 am

I'd be very wary of using different voltages. Caps are rated for their capacitance at a specific voltage. If you use a cap too far over or under the original value you may end up with a capacitor that is not performing to the needed spec.

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Re: Opinion on OBiie voice card cap voltage

Post by Skiroy » Fri Feb 01, 2013 8:04 am

I guess that leaves the Nichicons,just for the voice card caps.

I have the choice between "audio grade" which have 62ma ripple current,lower temp rating and 1000hrs life.

http://www.mouser.com/Search/ProductDet ... FG1V220MEM


Or the "general purpose" UPW caps that have 180ma,higher temp rating and 2000hrs lif.
http://www.mouser.com/ProductDetail/Nic ... uy95tMw%3d


Seems like the UPW would be a no brainer but are the other, "audio grade" caps better for the cards?

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Re: Opinion on OBiie voice card cap voltage

Post by Don T » Fri Feb 01, 2013 12:05 pm

.....
Last edited by Don T on Sun Feb 03, 2013 12:38 am, edited 1 time in total.
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Re: Opinion on OBiie voice card cap voltage

Post by Skiroy » Sat Feb 02, 2013 1:32 am

Your not discouraging me at all. I greatly respect and appreciate everyone on this forum. Everyone is very knowledgable,helpfull and respectfull. Thank You for your advice.

I have considered size. Thats why I have narrowed it down to the two I posted a link to. I know both have been used in the OBXA. The "audio grade" version is slightly larger diameter at 6.3mm but two of my voice cards currently have 6.3 Elna caps so they will be fine.

In regards to the ESR consideration I have looked at the data sheets linked on the mouser website for each and due to my inexperience I am not seeing any data. Thought the audio grade FG series caps doeas say it "Rich sound in the bass register and clearer high end" which sounds pretty cool to me.

But if someone could look at the data sheet and tell me what the ESR ratings are I would be very greatfull so I can take the plunge and be done with it. I understand that it may be a slight differencein sound but with how much I have invested in time,money and thought in this things I dontwant to skimp. plus they are the same cost, $.28 each.

Cheers

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Re: Opinion on OBiie voice card cap voltage

Post by Skiroy » Wed Feb 13, 2013 4:09 am

Can anyone tell me about the ESR ratings for each capacitor I posted the links to. Thw ebsite will take to to the product page where they have a link to the ducumentation. Im not seeing and info on the ESR.
Can you help?

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Re: Opinion on OBiie voice card cap voltage

Post by adhmzaiusz » Wed Feb 13, 2013 5:32 am

Ashe37 wrote:I'd be very wary of using different voltages. Caps are rated for their capacitance at a specific voltage. If you use a cap too far over or under the original value you may end up with a capacitor that is not performing to the needed spec.
Capacitance isn't affected by the voltage rating, the voltage rating is the maximum volts the capacitor can handle. A capacitor rated at 650v will store a charge the same as a 25v capacitor with a 5v signal input and perform the same. The rule of selecting capacitors is to choose a voltage rating that is at least double the rating of the power supply for headroom. If you go under the voltage rating, you will damage or blow it up.

In synths most of the signals going through the voice boards are typically 15v analog and 5v digital, so even a 25v capacitor in these areas would be fine.
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Re: Opinion on OBiie voice card cap voltage

Post by synthroom » Wed Feb 13, 2013 10:42 pm

Skiroy wrote:Or the "general purpose" UPW caps that have 180ma,higher temp rating and 2000hrs lif.
2000 hours is only 83 days...
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Re: Opinion on OBiie voice card cap voltage

Post by Skiroy » Thu Feb 14, 2013 1:28 am

synthroom wrote:
Skiroy wrote:Or the "general purpose" UPW caps that have 180ma,higher temp rating and 2000hrs lif.
2000 hours is only 83 days...
? I dont know what that value means but thats the specs.

What about the ESR question comparing the two?

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Re: Opinion on OBiie voice card cap voltage

Post by Ashe37 » Thu Feb 14, 2013 1:45 am

adhmzaiusz wrote:
Ashe37 wrote:I'd be very wary of using different voltages. Caps are rated for their capacitance at a specific voltage. If you use a cap too far over or under the original value you may end up with a capacitor that is not performing to the needed spec.
Capacitance isn't affected by the voltage rating, the voltage rating is the maximum volts the capacitor can handle. A capacitor rated at 650v will store a charge the same as a 25v capacitor with a 5v signal input and perform the same. The rule of selecting capacitors is to choose a voltage rating that is at least double the rating of the power supply for headroom. If you go under the voltage rating, you will damage or blow it up.

In synths most of the signals going through the voice boards are typically 15v analog and 5v digital, so even a 25v capacitor in these areas would be fine.
Ok, not the capacitance at that voltage, but the ESR can be a problem,especially if you are using drastically higher voltage caps.

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Re: Opinion on OBiie voice card cap voltage

Post by synthroom » Thu Feb 14, 2013 3:10 am

Skiroy wrote:I have the choice between "audio grade" which have 62ma ripple current,lower temp rating and 1000hrs life.

http://www.mouser.com/Search/ProductDet ... FG1V220MEM
I'm no expert in electronics, but I think you're confusing ESR (Equivalent Series Resistance) with "Endurance" for that 1000 hrs figure. Looking at that spec sheet, the endurance test is performed as:

"The specifications listed at right shall be met when the capacitors are restored to 20°C after the rated voltage is applied for 1000 hours at 85°C."

I read that as they take a capacitor and subject it to it's maximum rated voltage for 1000 hrs. The capacitor is then tested to verify that it still meets its stated capacitance. It's not saying that the life of the capacitor is 1000 hours, they are saying that it will survive for 1000 hours at that max voltage.

Is ESR an actual issue here when working with audio frequencies like you will have on a voice card? It's not going to be subjected to gigahertz freqencies like being hooked to a modern CPU. Read the last paragraph in this paper:
http://www.low-esr.com/QT_LowESR.pdf
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Re: Opinion on OBiie voice card cap voltage

Post by Ashe37 » Thu Feb 14, 2013 3:20 am

Point being, a higher voltage resistor can have a higher resistance, whether actual resistance or ESR, than a lower voltage resistor.

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Re: Opinion on OBiie voice card cap voltage

Post by adhmzaiusz » Thu Feb 14, 2013 3:32 am

Higher voltage in resistors are operational tolerances to volts the same as with capacitors, its how much it can handle. What determines how close a resistor is to its rated value is measured in % like 5% resistors are a value within 5% of its rating... for example a 15k 5% resistor can actually be be as low as 14.25k or as high as 15.75k. If you hook a volt meter to any resistor no matter the voltage rating you will get its value... the signal coming from a volt meter is very small...
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Re: Opinion on OBiie voice card cap voltage

Post by Ashe37 » Thu Feb 14, 2013 3:49 am

the discussion is capacitors, not resistors.

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Re: Opinion on OBiie voice card cap voltage

Post by Skiroy » Fri Feb 15, 2013 2:00 am

I was really just looking for an easy answer as to which is better. Im just going to pick the "audio grade" one that is gold and shinny!

I cant keep up with the engineering.

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