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OPA134 in Tina

Other Parts Discussed in Thread: OPA134, OPA1641, OPA827

I want to use an OPA134 connected as a unity gain follower with a fixed load of 1kohms.

Then I want to take the signal out of the supply rails via cascodes and mirrors so that I can get an output of 60V P-P.

However there is no signal on the op-amp rails, any way round this apart from building a discrete op-amp?

Clive Read.

  • Clive,

     You are right. The signal is not on the power supply rail. It only exists at the output of theOPA134. From there you will need another amplifier with power suppiles that exceed +/- 60 volts so you can get your 60V p-p output. Is there a reason that you are not starting with a power amplifier with the gain that you need, bypasing the OPA134?


  • Bonnie,

    Thanks for the input.

    My project is to design an audio power amplifier. The output stage is done (unity gain), I have to come up with a front end.

    Given that matched pairs of bipolars or j-fets are expensive & becoming hard to get I want to use an OPA134 or similar for low offset & drift & bias current.

    The problem lies in getting the output swing of 60V p-p. The method I suggested works although I cannot simulate it with the OPA134 but it works fine with a discrete op-amp.

    There is another problem with IC op-amps not showing signal current in their supplies. If, when designing the power supply, you want to check the amount of signal appearing on the power supply rails it will be wrong! OK, it can be fixed but not everyone will be aware of this.

    C'est la vie...


  • Clive,

    The OPA134 model is a Boyle model and and doesn’t model supply current correctly. Since the OPA134 is specified for high performance audio, we tested two models that we thought would be suitable; the OPA1641 which is available for TINA Spice, and the OPA827 component-level model available for TINA or PSpice. Both models are very modern and simulate the load current supplied through the supply rails.

    Hope that maybe one of these will work for you -

  • Rick,

    Many thanks for that. However, my golden eared colleagues did a blind test on audio op-amps. They were unaware of the part number and cost. They picked the OPA134 as the best, it certainly is a very fine product.

    So it would have been useful to run a simulation to see if there are crossover issues once the signal currents on the rails are summed. My feeling is that may be although when you remember current in = current out maybe there won't be. Seems a little risky & I don't want to compromise the performance of the OPA134.

     Therefore I am considering hanging a single ended class A output stage on the OPA134 output using a high voltage NPN bipolar & including it in the loop. Then with a 1kohm load I can use the  signal current riding on the collector current.

    There is an additional benefit in going this route, the OPA134 output will not now be loaded so its THD should be even better !

    Shouldn't be any problems simulating that !

    Thanks again,


  • Clive,


    thanks for bringing this issue to our attention. if you have any other quesiton, please let us know.