ppl
Building amps and assuring water resistance.
- Joined
- Jun 21, 2001
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the 20 Volt OS-Con capacitors are in fact connected to the Primary rail and they indeed are presented with 24 Volts and this Voltage has proven not only to be safe but sonicaly preferable to the same Amp operated at 20 Volts Furthermore this sonic change did not happen with a similar rated Muse Bi-Polar capacitor (A Very nice alternative to the OS-Cons) I might add, so i attribute the sonic change with voltage as a quality unique to the OS-CON's. Alot of people suggest using a capacitor rated for a higher voltage than its rated WKV so as to add a margin of safety. I do not subscribe to this view as a more in depth study showers that Electrolytic type capacitors are designed to operate at there Rated WKV that stands for the capacitor's Working Volts. The OS-Con type of capacitors are similar to Electrolytic in this regard in that they are intended to operate at there WKV and in this instant the 20 volt OS-Con Capacitors are designed to operate at 20 volts. My investigations showed that the Leakage currents in these capacitors do not start to rise until 26-27 volts indicating the capacitor has the same linear operating parameters at voltage higher than its rated WKV indicates the capacitor is deliberately underrated and considering the Enviorment OS-Cons are intended to operate in like High speed high current Microprocessor Rail capacitors. It was noting the use of 6.3 volt OS-Con capacitors at 10 volts in Some microprocessor applications that started my investigations into this. Out of the Sprague and Sanyo OS-Con capacitors i found the Sprague/Vishay to have the lowest leakage and to tolerate more over voltage than the Sanyo. The Sanyo were about 2 volts lower at the point that the Leakage currents started to rise. this resulted in the 20 volt os-con Vishay capacitors to be tried in the Prototypes of the LISA and as expected things worked just as i expected and operating these capacitors at 24 to 25 volts in this application is perfectly safe and has in addition proven reliable in the field with one notable exception that i am addressing hear. I have personally tested these os-Cons at up to 30 volts before leakage currents become non linear and capacitor failure is imminent however unlike conventional electrolytic capacitors that get hot and vent under these failure modes they result in an electrical open circuit. OS-Cons on the other hand do not get hot as the failure point is reached in over voltage applications they behave like a semiconductor and simply short circuit and thus your DMM will read 0 Ohms of placed across the terminals and thus shorting the output of the power supply and or batteries. if these three capacitors are replaced the amp in question will most lickly work as no other components generally fail as a result of over voltages less than 40 volts at which point all the semiconductor IC's are taxed.
Once again i am sorry for the inconvenience this issue has caused you Oh the Previous link provided my n-maher may not work however this link will get you acess to the complete LISA III Folder with unplublished photos schematics parts list and related Documentation. http://www.esnips.com/web/lisa-iii
| Originally Posted by n_maher /img/forum/go_quote.gif Do you have access to a multi meter? The reason that I ask is that if you do I would suggest the following: carefully measure the output voltage of the wallwart when setup with what you think will produce the "center pin positive" condition. From the pictures it looks like you can change this setting for the wallwart, which is something I haven't seen before and looks like it would be easy to get backwards. There are two reasons to take this measurement, one to check the polarity and make sure that you're doing it correctly, two to check the unloaded output of the wallwart. Given that the wallwart is rated for 800mA on the 24V output (at least that's how I read the label) you may very well find that at the lower settings it is still outputting well over 24VDC. The reason for this higher output is that the LISA is probably drawing less than 250mA at idle so there's pretty large excess of capacity that translates into more voltage. If the rail-to-rail capacitors are only rated for 20V it would seem very unwise to me to use anything higher than say a 12VDC supply. I've seen 12V supplies output well over 15V when lightly loaded and I always like to have a little headroom left over. I found a couple of pictures on Phil's site in which it's pretty clear that the caps are 20V rated and that's what they are spec'd at in the schematic that I found as well. I am a bit surprised that Phil and the builder would do this since even if the amp was configured to run off of 9V batteries you could still easily see over 20V across C4. A fair number of 9V rechargables run over 10V on a full charge and unless I'm reading the schematic wrong (definitely a possibility) C4 sits across both rails and would see the full power supply voltage. Someone please confirm this as I'm operating at the bleeding edge of my capabilities here. Link to LISAIII schematic as posted by the manufacturer, so I'm assuming it's safe to share. |
the 20 Volt OS-Con capacitors are in fact connected to the Primary rail and they indeed are presented with 24 Volts and this Voltage has proven not only to be safe but sonicaly preferable to the same Amp operated at 20 Volts Furthermore this sonic change did not happen with a similar rated Muse Bi-Polar capacitor (A Very nice alternative to the OS-Cons) I might add, so i attribute the sonic change with voltage as a quality unique to the OS-CON's. Alot of people suggest using a capacitor rated for a higher voltage than its rated WKV so as to add a margin of safety. I do not subscribe to this view as a more in depth study showers that Electrolytic type capacitors are designed to operate at there Rated WKV that stands for the capacitor's Working Volts. The OS-Con type of capacitors are similar to Electrolytic in this regard in that they are intended to operate at there WKV and in this instant the 20 volt OS-Con Capacitors are designed to operate at 20 volts. My investigations showed that the Leakage currents in these capacitors do not start to rise until 26-27 volts indicating the capacitor has the same linear operating parameters at voltage higher than its rated WKV indicates the capacitor is deliberately underrated and considering the Enviorment OS-Cons are intended to operate in like High speed high current Microprocessor Rail capacitors. It was noting the use of 6.3 volt OS-Con capacitors at 10 volts in Some microprocessor applications that started my investigations into this. Out of the Sprague and Sanyo OS-Con capacitors i found the Sprague/Vishay to have the lowest leakage and to tolerate more over voltage than the Sanyo. The Sanyo were about 2 volts lower at the point that the Leakage currents started to rise. this resulted in the 20 volt os-con Vishay capacitors to be tried in the Prototypes of the LISA and as expected things worked just as i expected and operating these capacitors at 24 to 25 volts in this application is perfectly safe and has in addition proven reliable in the field with one notable exception that i am addressing hear. I have personally tested these os-Cons at up to 30 volts before leakage currents become non linear and capacitor failure is imminent however unlike conventional electrolytic capacitors that get hot and vent under these failure modes they result in an electrical open circuit. OS-Cons on the other hand do not get hot as the failure point is reached in over voltage applications they behave like a semiconductor and simply short circuit and thus your DMM will read 0 Ohms of placed across the terminals and thus shorting the output of the power supply and or batteries. if these three capacitors are replaced the amp in question will most lickly work as no other components generally fail as a result of over voltages less than 40 volts at which point all the semiconductor IC's are taxed.
Once again i am sorry for the inconvenience this issue has caused you Oh the Previous link provided my n-maher may not work however this link will get you acess to the complete LISA III Folder with unplublished photos schematics parts list and related Documentation. http://www.esnips.com/web/lisa-iii
