1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Posting a two page schematic

Discussion in 'General Electronics Chat' started by MrDEB, Jun 19, 2012.

  1. MrDEB

    MrDEB Active Member

    Joined:
    Apr 16, 2007
    Messages:
    4,364
    Likes:
    22
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,437
    Likes:
    933
    Location:
    Canada, of course!
    The voltage from a "9V' Ni-MH battery varies with load current so the voltage might bounce all the time. Also 9V is too high because a high output level will blast your head off. So a 5V low-dropout regulator is a good idea.

    You have the coupling capacitors wrongly connected on the IC side of the volume controls instead of at the inputs to the volume controls. The volume controls are connected to 0V and make the inputs of the TDA2822M ICs at 0V DC as is needed.
     
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,437
    Likes:
    933
    Location:
    Canada, of course!
    The datasheet for the LM2931 says the output capacitor must be at least 100uF to maintain stability. With a lower value then the regulator will probably oscillate. You want a stable voltage regulator so use 100uF on its output.
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. chemelec

    chemelec Well-Known Member

    Joined:
    Apr 4, 2004
    Messages:
    2,116
    Likes:
    77
    Location:
    Hedley, B.C. Canada

    The 5 Volt Regulator is Not really Needed, IF you put a 100 OHM resistor in Series with each headphone Output.
    This will significally Reduce Noise in the headphone and also Prevent Excessive POWER/VOLUME from Damaging your EARS.
     
  6. MrDEB

    MrDEB Active Member

    Joined:
    Apr 16, 2007
    Messages:
    4,364
    Likes:
    22
  7. MrDEB

    MrDEB Active Member

    Joined:
    Apr 16, 2007
    Messages:
    4,364
    Likes:
    22
    Am kinda lost about Audios post about "You have the coupling capacitors wrongly connected on the IC side of the volume controls instead of at the inputs to the volume controls. The volume controls are connected to 0V and make the inputs of the TDA2822M ICs at 0V DC as is needed. "
    If I remove C2 and C5 the schematic is exactly? like the link to the Altoids amp I posted??

    http://www.electro-tech-online.com/attachments/
     
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,437
    Likes:
    933
    Location:
    Canada, of course!
    No, it does not have an input coupling capacitor feeding the input to the volume control.

    It should be like this:
     
  9. MrDEB

    MrDEB Active Member

    Joined:
    Apr 16, 2007
    Messages:
    4,364
    Likes:
    22
    Made changes.
    THANKS again
    hopefully I can order boards today. Itead = 10 boards for about $29
    Dorkboards 3 boards = $32.50 ($5 sq inch) but can get quicker like 1 week plus they I believe are in Portland Oregon
     
  10. MrDEB

    MrDEB Active Member

    Joined:
    Apr 16, 2007
    Messages:
    4,364
    Likes:
    22
    Made changes on vol caps etc.

    Here is hopefully the final revision. The board design looks good but still contemplating using a To-92 case voltage regulator vers the Dpack but using the Dpack it has some heat sinking ability but that shouldn't be an issue anyway.
    Still contemplating mic mounting methods. Using 4 mics (two front and two back)U1.1 turns the back ones off and on.. I guess I am spoiled with being able to turn off the back mics (my $5K aids have this feature)
    Going to order 3 boards and if you want one PM me with mailing address.
    The board has a ground plane on the top as well as the bottom layers. Not real tight but not far apart. Total length of traces = 77.01 inches w/ 38 vias. 3.319 x 1.969 inches (84mm x 50mm)
     
  11. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,437
    Likes:
    933
    Location:
    Canada, of course!
    C5 is 1000uF instead of 100uF.
    How will you connect front mics and rear mics? In parallel?
    I connected about 10 electret mics in parallel for a boardroom conference sound system and they worked fine.

    Thanks, but I don't need one of your pcb's. I never built anything with surface mount parts.
     
  12. MrDEB

    MrDEB Active Member

    Joined:
    Apr 16, 2007
    Messages:
    4,364
    Likes:
    22
    The mics are connected in parallel (one front, one rear mic for left channel and same for right channel. The slide switch disconects the rear mics for noisy environments.
     
  13. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,437
    Likes:
    933
    Location:
    Canada, of course!
    I think mics in parallel affect each other. With two mics in parallel then the sensitivity is less than with one mic but the difference is small (about -6dB).
     

Share This Page