Fun with op amps!

Discussion in 'Audio Hardware' started by felix.scerri, Apr 22, 2014.

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  1. felix.scerri

    felix.scerri Forum Resident Thread Starter

    G'day all, I've entered a new phase in my design work with my DIY gear in the area of op amps. Most of this has been 'inspired' by noise/hiss issues with my DIY ESP P06/P99 phono stages and despite the general sonic excellence of the OPA2134 dual op amp, it is 'slightly' noisy/hissy when used with the relatively high inductance Shure M97xE.

    As it stands presently, I am using the old venerable NE5532AP in the first stage of my P06's (closest to the input from the cartridge, and an OPA2134 in the second gain stage. Overall it is considerably quieter than using an OPA2134 in the first stage.

    I've been doing a lot of reading on op amp performance aspects of late and the FET input op amps like the OPA2134 are inherently at least 3 db noisier than the NE5532! Speaking of the NE5532, it may have been around since the mid 1980's but it is still an excellent dual op amp in every way.

    However I have ordered ten LM4562's which 'may' be better than the NE5532 in some respects. I am chasing lower noise, but in practice it may or may not be apparent. I'll see. I use high quality sockets, so op amp changeover should be straight forward as long as Mr. Murphy stays away!

    I am actually happy with the performance of the NE5532 but it will be an interesting exercise to see if the LM4562 is much better. Stay tuned! Regards, Felix.
     
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  2. tim185

    tim185 Forum Resident

    Location:
    Australia
    Interesting Felix. I am about to start building a P06. Have you given up on the AD823 op amp, I think it was. I seem to recall a thread elsewhere where someone was quite adamant that this was the best choice for this amp. Was also running it off batteries if my memory serves. I'm yet to purchase the op amps and can't decide which way to go. I'm going with a power supply from rods site , but am also interested in trying the AD823/battery combo. I'll keep your tip in mind when trying the other combinations. Thanks.
     
  3. felix.scerri

    felix.scerri Forum Resident Thread Starter

    G'day mate, AD823's work ok (I've tried them), but they are not really designed for audio applications. They are more of an instrumentation amplifier.

    For the P06, I think the OPA2134, NE5532, LM4562 and LM833 are probably best. The noise figure is more important in the first op amp position, which is why I'm using an NE5532AP. I recommend building the P99 sub bass filter too, especially if your loudspeakers are ported. Regards, Felix.
     
  4. tim185

    tim185 Forum Resident

    Location:
    Australia
    Thanks Felix. They are ported and I will be adding the bass sub filter. You might have saved me some cash re the AD823's. Might just stick with a OP in the output and one of your suggestions for the input stage. That may well give lower noise , but did you notice any change for better or worse in tonality compared to a dual OP setup as it's designed?
     
  5. RonW

    RonW Forum Resident

    Location:
    New York
    And as such are very sensitive and quiet. They will work fine with audio if biased correctly and decoupled from oscillation using .1uf Polypropylence caps. Again, not "cheap" but correct.
     
  6. tim185

    tim185 Forum Resident

    Location:
    Australia
    Hi Ron,

    Polypropylene v polyester for this application. Any difference? Was planning on polyester as that's what's easily available here...thanks.
     
  7. tim185

    tim185 Forum Resident

    Location:
    Australia
    Also Felix,

    You have extensive experience I see with this phono pre. Did you build them with stock components? It seems easy just to go to jaycar for example and get everything there. I have seen one guy using elna electrolytics and oversized film caps etc for this thing. I actually contacted Rod about this and he dosent seem to be a fan of exotic components. Thinks that most of them are no better than stock components and is bit of a waste really. Was wondering what your experience is.
     
  8. dividebytube

    dividebytube Forum Resident

    Location:
    Grand Rapids, MI
  9. RonW

    RonW Forum Resident

    Location:
    New York
    You could get away with them but the metalized pp are a higher quality part with better filtering ability.
     
  10. felix.scerri

    felix.scerri Forum Resident Thread Starter

    G'day all, I used all passive components sourced from Jaycar (metal film resistors) and MKT and bipolar electrolytic capacitors, although I used WIMA polypropylene capacitors for input loading (if needed), and also the high frequency RIAA capacitors.

    It is also important to 'match' all passive components in value between channels if at all possible. This does make an audible difference. I did end up trying oversize polypropylene capacitors at one stage and ended up cracking the circuit board tracks. Never again. Use capacitors with the correct lead spacing (MKT or WIMA). regards, Felix.
     
    Last edited: Apr 22, 2014
  11. Burt

    Burt Forum Resident

    Location:
    Kirkwood, MO
    If you have a low output moving coil, you either need a transformer at the preamp end or use a discrete bipolar stage as a front end. These carts are a very low impedance source.
     
  12. dividebytube

    dividebytube Forum Resident

    Location:
    Grand Rapids, MI
  13. felix.scerri

    felix.scerri Forum Resident Thread Starter

    G'day all, well the LM4562 op amps I had ordered arrived by courier a little earlier and frankly I am a little disappointed with it compared to the NE5532 it replaced.

    It may be ever so slightly quieter than the NE5532 but not by much, in all honesty. I almost expected that. The 'ole NE5532 is very, very, very nearly as good. Regards, Felix.

    EDIT: I've now replaced both dual op amps in my P06 with LM4562's and it is now significantly quieter. Further observations will follow.
     
    Last edited: Apr 24, 2014
  14. tim185

    tim185 Forum Resident

    Location:
    Australia
    I'll be waiting Felix. Surely this must have effected it sonically compare to the original OP's?
     
  15. felix.scerri

    felix.scerri Forum Resident Thread Starter

    G'day mate, with my relatively limited listening so far, I'd say not at all! The sonics sound totally unchanged except for the marked reduction in hiss level.

    I know that the OPA2134 is a very nice sounding dual op amp, as I remember being rather impressed when I retro-fitted them into a stereo line amp stage using LM833's, however in something like a high quality phono stage where noise levels are important the OPA2134 fails somewhat sadly. Regards, Felix.
     
  16. tim185

    tim185 Forum Resident

    Location:
    Australia
    I'm yet to buy op amps for the P06 so I'm eagerly awaiting your thoughts as you go along. Thanks Felix.
     
  17. felix.scerri

    felix.scerri Forum Resident Thread Starter

    G'day mate, for the ESP P06 based on what I know now, I'd recommend either the NE5532 or the (more expensive) LM4562. Regards, Felix.
     
  18. missan

    missan Forum Resident

    Location:
    Stockholm
    Felix here is another way to build a phonoamp.:)
     

    Attached Files:

  19. felix.scerri

    felix.scerri Forum Resident Thread Starter

    G'day mate, I did build a simplified version of something like that once. It worked ok and sounded quite good too. Regards, Felix.
     
  20. missan

    missan Forum Resident

    Location:
    Stockholm
    You wouldn´t have to worry about any hiss with this design, maybe nothing else either.
     
  21. Love those schematics with no component values ;)
     
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