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new opamp

Discussion in 'Electronic Repair Modifications DIY' started by goodguys, Feb 23, 2011.

  1. goodguys

    goodguys Active Member

    Hi and thanks for taking the time to read this post.

    I have purchased a nice dac which uses an Burr Brown opa2604 opamp.

    Can anyone suggest a good upgrade. I was thinking of the ever popular BB opa627ap but have been told this is quite old and should really consider a modern one.

    Can anyone please advise, something which works well in the opa2604's current environment (voltage, current, etc)

    Many thanks in advance. John.
     
  2. Boswell

    Boswell Moderator Distinguished Member

    You are not going to get a lot better than an OPA2604 in this audio application for a dual FET-input amplifier. You could possibly fudge a solution using a pair of OPA627s, but it's doubtful whether the result would sound any better than the OPA2604. If your DAC unit used single OPA604s it might have been worth trying the OPA627 or even an AD825, but it's a lot of work shoe-horning two op amps into the pads of a single one. What make and model of DAC is it?

    By the way, this thread should really be in the DIY Pro Audio forum.
     
  3. goodguys

    goodguys Active Member

    Hi. Thanks for the response.

    The dac i picked up is the firestone fubar 2
     
  4. Link555

    Link555 Well-Known Member

    I use the OPA 627 a lot. It does well for my apps. I also like the AD825's they are not as lively.
    more subjective info....
    Notes on Audio Op-Amps
     
  5. goodguys

    goodguys Active Member

    Hi. So is it possible to remove the OPA2604 and simply slot in a higher spec chip or will i need to perform modifications to the board.

    Next to the opa2604 is another opamp chip labelled tl072cp, is this worth changing.

    Many thanks in advance. John.
     
  6. Boswell

    Boswell Moderator Distinguished Member

    I'm sorry that in my earlier post I may have mis-judged your experience in doing this sort of thing. You could put in another chip that was pin-compatible and sufficiently similar in specification with the OPA2604, but the point is that there is little concensus that there is any in this category that is sonically better.

    With a lot of care and probably a fair amount of practical experience behind you, it is possible to build arial constructions of two single amplifiers that can plug into the socket of a dual amplifier chip like the OPA2604. However, this is not something for the faint-hearted as it's easy to make a disastrous mistake, and you have to be very sure that it is worth the risk.

    Do you have a schematic for this dual DAC unit?
     
  7. TheJackAttack

    TheJackAttack Distinguished Member

    When people come to me wanting to modify their french horns, my first question to them is what is the horn doing that you don't like? Many times they don't know. They just think they need to change something because horn player "X" has a particular setup. The horn itself in reality performs perfectly adequately for their needs and abilities. Additionally, they lack understanding about what function the mouthpipe plays as opposed to the bell flare for playing characteristics.

    I guess I'm wondering what about the current DAC you don't like and more importantly what you think will change for the better by changing anything? You started asking about a particular opamp and now ask what would happen if you change the adjacent opamp. If all this is for shits and giggles then have at it. If you are trying to accomplish something you ought to have a reason and an idea what it is you want to alter and why, and what your end goal becomes.
     
  8. Link555

    Link555 Well-Known Member

    The OPA2604 is a jelli bean footprint, what are the power rails? its does up to +/-24VDC a lot of chips don't do this.
    You have this correct?
    http://focus.ti.com/lit/ds/sbos006/sbos006.pdf

    Now the 627 is single op-amp and is not pin for pin compatible:
    this

    So you will need to make a surf board or do a dead beetle construction with two chips as Boswell pointed out.

    You do a search at digikey.com for more options. But there is very little selection at +/-24 volt rails.
     
  9. goodguys

    goodguys Active Member

    Hi. Many thanks for the reply.

    Is there a simple drop in replacement for the opa2604 and the tl072cp.

    Other forum users report the lme49720 and opa2134 were good drop in replacements for the tlo72cp, and the opa2227 substituted well for the opa2604.

    Does anyoone have any experience of drop in replacements for these two opamps as upgrdades.

    Many thanks.
     
  10. MrEase

    MrEase Active Member

    While I appreciate there are many, like yourself, who love to mess around with substitute chips, I can personally see little point to it. JMHO though. What I will say that any suggestions are of little value without detailed circuit specifics. Without these we have little idea of the impedances and voltage levels in use.

    What I will say is that whoever suggested the LME49720 as a replacement for the TL072 is on dangerous ground. The TL072 is a FET input op-amp and the LME49720 is NOT. In circuits that require the high impedance input of FET's the LME49720 is not going to perform adequately. That's all I have to say!

    Good look in your quest. I hope you get some better advice on replacements.
     
  11. Link555

    Link555 Well-Known Member

    The OPA2227 does not have +/-24volt rails, this will cook it you do have 24 rails.
     
  12. Boswell

    Boswell Moderator Distinguished Member

    The TL072 is likely to be in the d.c. servo loop and not in the audio chain. Don't change it.

    If you don't have a schematic, you will have to measure the power rails in the unit before anyone here can give examples of chip replacements that are safe, let alone might sound better.

    Once you have ascertained that the rails are +/-16V or less, you could get a pair of OPA627s (or a selection of other devices) already mounted on a single 8-pin DIP adaptor from Brown Dog.
     
  13. goodguys

    goodguys Active Member

    Hi. Many thanks for the reply.

    Is it possible to bypass the opa2604 all together, my thinking is the best type of opamp is no opamp at all. At the moment the dac is running into a 300 watts rms amplifier, i am hoping that with all that power the music should still be loud enough.

    Many thanks. John.
     
  14. Boswell

    Boswell Moderator Distinguished Member

    Find a schematic for the DAC unit and we may be able to answer your question.

    Don't confuse power output with voltage gain on your hi-fi amp.
     

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