I have designed a audio spectrum analyzer circuit with THAT4315 and a drivers for IN-13 bar graph nixie tube to visualize the signal level.

To supply +-12V to the opamps, the Meanwell NSD15 module is used. At the moment, no additional input/output voltage filtering (other than the caps on the module) is used.

Here's the schematic for one frequency band. THAT4315 + IN-13 schematic

The problem is that the electrolytic capacitors are getting too hot. I measured around 55 deg.C using an infrared thermometer. It's hard to pinpoint the exact caps, which are getting hottest, but it looks like the ones encircled in the schematic are slightly hotter than others.

These are the caps I used: EEE-FK1H220SR, EEE-1HA100WR, EEE-1HA4R7SR

Any ideas about what might be causing the caps to get hot in this circuit?

  • 2
    \$\begingroup\$ Generally a hot capacitor would suggest excess ripple current, or being installed backwards. \$\endgroup\$
    – Colin
    Dec 4, 2018 at 14:56
  • 4
    \$\begingroup\$ hey, you don't happen to have a higher-resolution image of your schematic? \$\endgroup\$ Dec 4, 2018 at 14:56
  • 3
    \$\begingroup\$ Are those tantalum caps? Because the polarity markings on tantalum caps are generally opposite of those on aluminum electrolytics.. \$\endgroup\$ Dec 4, 2018 at 15:11
  • 3
    \$\begingroup\$ Don't know about the other, but C17 has no reason to be getting warm. It has 10kohm between it and the only current source, and its only load is an opamp input that shouldn't draw any current. \$\endgroup\$
    – JRE
    Dec 4, 2018 at 15:40
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    \$\begingroup\$ Given the odd way IC4 is powered (you have a split rail, may as well use it), C14,15 are probably the wrong way around, and (not this particular problem) I think IC6 inputs are also backwards. \$\endgroup\$
    – Dan Mills
    Dec 4, 2018 at 19:47

1 Answer 1


Looks to me like the caps would see reverse polarity on the negative signal excursions. Ground is probably at 0 V between +12 V and -12 V. Use (or make) non polarized caps.


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