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OPA134: Capacitor Replacement Question

6574347
Prodigy 10 points
Part Number: OPA134

Hi there,

I have an older high performance DAC and I'm looking to replace some of the older capacitors on the circuit board.

I'm a amateur electronics kit builder so I don't have knowledge of circuit design.

If you look at caps: (see attached circuit diagrams)

256, 257, 260, 261 on the left DAC channel

356, 357, 360, 361 on the right DAC channel

Both of these are shown as analogue grounding circuits I believe?

Someone has installed old Black Gate caps which are lower value (100uf 16V instead of the 220uf 25V shown in the circuit diagram)

What I'd like to know is what would be the best capacitors to replace these with? Are they in the signal path? Should they be low ESR? Low Impedance? What parameters should I use

when searching Mouser or Digikey for replacement capacitors in this application?

Any suggestions as to what would work well would be appreciated.

Thanks,

Jason

Jason

  • 0
    TI__Guru* 93105 points

    Hi Jason,

    It is very difficult to see on the schematic images just where the capacitors you mention are placed in the circuits. If I am correct, viewing the schematics these capacitors are located at each supply pins of the PCM DACS. If that is correct, then these are the low frequency power supply bypass capacitors. They are placed and connected in parallel with some much smaller value, higher frequency bypass capacitors.

    The fact that the circuit functions okay with the 100 uF capacitors, which were used as replacements for the original 220 uF capacitors tells us that they aren't especially critical in value. However, it is best to use the manufacturer's assigned values. It may not make a big difference in the unit's overall performances, but when the unit was spec'd it was done with the intended components.

    Capacitors produced today by the major capacitor suppliers are only better in terms of their technology and performances compared to decades ago. Indeed, look for quality electrolytic capacitors from the major manufacturers that have low ESR, sufficient breakdown voltage and a size that fits the PC board space provided. My experience with products supplied by Digikey and Mouser has been very good. We use components supplied by these and other reputable suppliers to supply components for our TI evaluation modules (EVMs) and other circuit needs.

    Regards, Thomas

    Precision Amplifiers Applications Engineering 

  • 0 in reply to Thomas Kuehl
    Prodigy 10 points

    Hi Thomas,

    Thanks very much for your quick reply and information. I appreciate you taking the time to answer.

    Just to follow up on your feedback...

    Both Panasonic and Nichicon have aluminum electrolytic caps - including OS-CON Aluminum Organic Polymer Capacitors (which indicate specific lower ESR values, higher ripple current values, and longer hour lifespans)

    Nichicon has an 'audio' series of standard aluminum electrolytic caps (eg. Muse Fine Gold or KZ) and Panasonic has FC and FR series.

    My follow up question is not for an endorsement of either or any manufacturer (as numerous companies have similar sized products that would fit) - my question is would standard or 'audio' series caps be more appropriate in this position on the circuit board? Or OS-CON caps offer better performance due to their lower ESR, and higher ripple current specifications? Or is it any capacitor with 220uf 25V that has the correct dimensions good enough?

    The fact that the user installed Black Gates made me think it was a somewhat important capacitor in the signal path. Hence the boutique pricier cap.

    Any quick follow up thoughts you might have.

    Best Regards,

    Jason

  • 0 in reply to 6574347
    TI__Guru* 93105 points

    Hi Jason,

    If you have a look at the DIY Audio forums you will find many ideas opinions about supply bypass capacitors. I think the most important characteristic as that it appears as low of impedance as possible over the frequency range of interest. Therefore, the capacitor used as the bypass should have very low equivalent series resistance (ESR) and very low equivalent series inductance (ESL) to be most effective. At some frequency, out in the several kilohertz range the ESL in conjunction with the capacitor's capacitance exhibit series resonance Once that frequency is exceeded then the ESL inductive reactance increases making the bypass less effective as the frequency is increased. That is why it has become common practice to bypass the low-frequency electrolytic with another capacitor such as the common 100 nF. That capacitor value is popular and seems to be based on popular practice.

    I don't think I would sweat this too much. It sounds like the OS-CON capacitors are very nice and will certainly do the job, but I suspect the lower cost, low ESR capacitors would do the job just about as well. I doubt that anyone is going to hear anything different from the audio systems based on the bypass capacitors although some might argue they can!

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • +1 in reply to Thomas Kuehl
    Prodigy 10 points

    Brilliant. Thanks for the info!