Opa 637bp problem

Discussion in 'General Electronics Chat' started by Nichloas123, Apr 12, 2013.

  1. Nichloas123

    Thread Starter New Member

    Apr 12, 2013
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    Hello there

    I just purchased the opa637 for my cmoy tin amp but they don't seem to
    Work properly , there is a lot of static when I turn it on but the sound becomes
    Stable in just over a quarter turn on the volume , do you think that it might
    Be the gain , I'm new to all this I'm a big fan of great sound quality would
    Not call myself an audio file , I would love to be but can't get my head around
    All the technical stuff please help.

    Thank you
     
  2. #12

    Expert

    Nov 30, 2010
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    Post a schematic of the circuit.
     
  3. YokoTsuno

    Member

    Jan 1, 2013
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    Does this mean that it worked before with another Opamp?
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    The mccoy amp is an internet gimick "pocket amplifier" many beginners seem to find but is a terrible design. A standard audio amplifier will sound much better because the bass will be loud enough to be heard. Just because a high quality op amp is recommended and some audio can be heard doesn't mean it is high fidelity in any way.

    The floating ground will fluctuate as the load varies (V= I x R) especially since the resistance is relatively high.

    The maximum power into the headphones is 3.5 mA which is mostly limited by the 4700 ohm resistance from the floating ground to a "power" rail.

    http://tangentsoft.net/audio/cmoy-tutorial/misc/cmoy-tangent-sch.pdf
     
  5. Ron H

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    Apr 14, 2005
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    Aren't you ignoring the 2x220uF caps on the virtual ground?
     
  6. Nichloas123

    Thread Starter New Member

    Apr 12, 2013
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    Like I said I am a beginner to all this technical stuff and answer your
    Question regarding the cmoy pocket amp
    I do know the difference between good sound reproduction and bad sound
    And the cmoy is far from a gimmick in my eyes
    I think that it has great sound when paired with good quality headphones
    I admit yes it's not the greatest design in the world but its a budget amp
    Of course it's not the best I know that .
    I just want to learn what is the best for audio and I do want the absolute
    Best when it comes to sound quality .
    Back to the opa637 in the cmoy .
    All my other duals work perfectly and I have 2 opa627aps on a brown dog
    Adapter biased into class A and it works fine .
    The 637s I assume the gain is an issue ,I read that the 637 is not stable
    Below 5 gain , I don't know about gain or even how to get a schematic
    To show you guys , so I guess I will do some more research
    About the technical stuff , but if you guys have the time and the patients
    To point me in the right direction to achieve the best possible sound quality
    From a portable device that would be truly appreciated .

    Thanks people :)
     
  7. Nichloas123

    Thread Starter New Member

    Apr 12, 2013
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    diy.com/schematics/797/CMOY_SCHEMATIC.png"][/URL

    A link for cmoy pocket amp

    Thanks people
     
  8. patricktoday

    Member

    Feb 12, 2013
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    I think this is the correct link:
    http://electronics-diy.com/schematics/797/CMOY_SCHEMATIC.png

    The way you describe the problem makes it sound like the gain is the issue, but the gain is actually fixed at 10X by the 1k and 10k resistors, R3 and R4, so that shouldn't be the problem. The op amp itself is always operating at a gain of 10 and the volume control attenuates the signal before it ever gets there.

    As GopherT said, the power supply circuit could be a problem. Here's a probably overly-technical writeup about it with a mod at the bottom that mainly adds a few extra capacitors:
    http://tangentsoft.net/audio/hs-opamp.html

    As a minimum, I'd try connecting 1 100nF cap directly across each op amp's power supply pins with as short of leads as possible, one end to the positive, one to the negative.
     
  9. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I suspect the problem is with the volume control. Is it new? Pots wear and/or get dirty with use, which can cause them to get scratchy-sounding.
     
  10. Nichloas123

    Thread Starter New Member

    Apr 12, 2013
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    Wow that is technical bloody Nora I'm sorry I just can't get my head around
    That its to me major complicated , i think I will just invest a bit more money on
    A better circuit and let the professionals do the work , me and maths and
    Equations are not the best of friends and as a music and audio lover it is
    Majorly depressing , could you guys just point me in the right direction of
    A portable amp which can deliver the best performance and which can accept
    Different opamps with no complication I was recommended the 02 from jds labs does anyone have an opinion on this amp , it's not very portable in any regard
    But I don't think I would get better sound or equivalent from a portable device?
    Just thought i would mention ' I tried the LM4562 in my cmoy pocket amp and to
    Me the sound presentation , soundstage , clarity was much better than the opa627s on the brown dog adapter , am I going mad , or could it be that my circuit is not designed for them chips and the true potential of these chips have
    Not been let loose in any way , the soundstage of the LM4562 was huge.


    I'm using an iPod classic which has been rockboxed
    Shure se 535 I.E.M.S
    Cmoy headphone amp by biosciencegeek.

    Thanks for your time people otherwise how else are we going to learn :)

    Nice one :):)
     
  11. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Nicholas, no disrespect intended, but I would like see you to run a blind "taste test" of an amp circuit, with LM4562 vs OPA627. Your "soundstage" comment smacks to me of things like oxygen-free copper wire. You will find a lot of skepticism of things like this from people like me, who understand electronics and physics.

    Did you solve the noisy volume control problem?
     
  12. patricktoday

    Member

    Feb 12, 2013
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    Technical bloody Nora, huh? :D So it sounds to me like the circuit works fine with some op amps but not with others? To quote Henny Youngman:

    To really understand a circuit and to know how to improve it there are many basics you must learn. If you desire to learn them it is very doable and there are many resources out there.

    If you want to do plug and play with various op amps that's perfectly fine too. Just so you understand that each individual op amp has complex circuitry inside of it and while they're supposed to amplify your signal with no concerns, in fact, the ideal op amp is an abstraction that a real life op amp is merely trying to mimic. Plugging in one for another will not always work as expected because they all have different properties.
     
  13. #12

    Expert

    Nov 30, 2010
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    Why hasn't anyone said, "Just connect a wire from between the batteries to ground."?
    The problem isn't the amp, it's in how the circuit is arranged.
     
  14. patricktoday

    Member

    Feb 12, 2013
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    True genius. I guess it is kind of floating...
     
  15. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    I said that from the start "floating".

    I thing the original version posted on the web about 5 or 7 years ago was wired with the ground between the two batteries but the beginner audience was having trouble wiring the switch that turns off the whole thing (including the voltage divider).

    The originator of the circuit does admit there are limitations and shows the ground between the batteries as the solution (he no longer shows any wiring to a switch, just how to connect the ground between the batteries.

    http://tangentsoft.net/audio/cmoy-tutorial/tweaks.html#vground
     
  16. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Maybe reading a little bit?
     
  17. patricktoday

    Member

    Feb 12, 2013
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    You did but you posted a different version of the circuit than OP did. It was somewhat of an apples and oranges analogy at the time.
     
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