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Bass preamp schematic help needed

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Skywalker83, Dec 8, 2008.

  1. Skywalker83

    Skywalker83 New Member

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    I think i'll go with the LM4562. would i use these for all four of my op amps?
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The opamps in the circuit, the LM833 and the LM4562 are dual opamps with two opamps in each package. Each package has 8 pins.
     
  3. Skywalker83

    Skywalker83 New Member

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    Ok, i'll go and re-draw my circuit so its laid out better!! Thanks for all your help. I shall return.
     
  4. dave

    Dave New Member

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  5. Skywalker83

    Skywalker83 New Member

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    I realise a mistake i've made in the circuit. If im using 2 dual op amps to give my four op amps (1 dual chip for the input, Bass and treble section. And the other chip for the Mid and output), then i've made a mistake with the 3rd and 4th op amps . If you look, they are both set up with pins 5, 6, and 7. If i now correct that and put the the op amp with pins 1, 2, 3, 4 & 8 at the Mid section , how does that effect the set up??
     
    Last edited: Dec 9, 2008
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    You can use either of the twp opamps with pins 1, 2, 3, 4 & 8.
     
  7. Skywalker83

    Skywalker83 New Member

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    Ok , here the new version of the active, a bit cleaner and different layout. i haven't added the values and part ID's yet. If you need reference just look at my last diagram

    I've taken a connection from the input path of V+ to the first set of op amps along to the pin 8 on the second set (it runs across the top og the scematic). Would this work?

    [​IMG]
     
    Last edited: Dec 10, 2008
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The power supply is feeding both opamps on their pin 8 and is fine.
     
  9. Skywalker83

    Skywalker83 New Member

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    Great ,Thanks!!
     
  10. Skywalker83

    Skywalker83 New Member

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    I have a question about the circuit. Someone on another forum said the following

    Why does The MID and FREQ come straight from the input and not from the output of the first op amp like the BASS and TREB??

    I'm just wondering.
     
    Last edited: Dec 10, 2008
  11. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Where?
    Mid and Freq are fed from the output of IC1b which is the Bass and Treble opamp.
    R16 connects to "half the supply voltage" (C1) which is DC and biases IC2a.
     
  12. Skywalker83

    Skywalker83 New Member

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    I kind of thought the same thing, but i just wanted to check! Thanks again guru!
     
  13. Skywalker83

    Skywalker83 New Member

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    Ok, a couple of questions about the construction of the board now as far as parts go.

    I'm going to go for parts rated at 25v + (incase i want to try the circuit at 18 volts at some point)

    The trim pot will be 100K varaible resistor trimmer.

    Resistors will be 0.25W carbon film 5% tolerence

    Capacitors will be ceramic

    There are currently 2 tant capacitors in the circuit, and the other polarised capacitors would just be electrolytic capacitors. As party of my circuit was more or less copied from an already existing circuit, should i just keep the 2 tant caps as they are , or switch them to electrolytic,or switch all the polarised caps to tant ones OR keep the whole circuit as it is?

    Also, the polarised caps that go from IC1 and IC2 pin 8 to ground. Are they the correct way round. i though i read somewhere at somepoint that the plus side should be towards ground. Is this correct or are they fine the way they are?


    I may change tha value of some of the pots that i have in the diagram.

    the bass and treble and goin to be a 100K stacked concentric pot

    the Mid frequency sweep will be a 50K log pot.

    The Mid pot on original circuit was a 5K linear pot, but im not sure if this may be to low, and should be increased to 25K??

    And the volume pot will be a 10K linear pot.
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Ceramic and tantalum capacitors produce distortion when they are used for audio coupling. Use metalized plastic film capacitors with a 5% tolerance instead.
    The power supply polarized capacitors should have their positive wire connected to a positive voltage and the negative wire connected to a less positive voltage.

    Dual concentric pots are a special order. Single pots are common. The tone control pots should be linear and the volume control should be an audio-taper.
     
  15. Skywalker83

    Skywalker83 New Member

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    How do electrolytics go as far as this kind of circuit is concerend. I have see high quality preamps that use them. If i was to use a mixture of Met.plastic film and non-polar electrolytics would that work? I'm just concerned about board size. I'm trying to keep it as small as possible.
     
  16. audioguru

    audioguru Well-Known Member Most Helpful Member

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    My cheap clock radios and telephone answering machines use cheap small non-polar electrolytic coupling capacitors. The same for cheap PA amplifiers.

    High quality amplifiers (and audio things that I design) use inexpensive, small, accurate, extremely low distortion metalized plastic film coupling capacitors. One of my projects uses two 1uF 5% 63V metalized plastic film capacitors that are small but cost about $1.00 each. I try to keep the impedance of a circuit high enough so that a 0.33uF capacitor produces enough bass frequencies.
     
  17. Skywalker83

    Skywalker83 New Member

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    What suppliers and or makes of parts do you recommend? I know that ALPS come recommended but i can only see the option of bulk buying from them (qnty of 100+). RS certainly have all thae parts i would need, but i have heard numerous stories about product poor quality.
     
  18. audioguru

    audioguru Well-Known Member Most Helpful Member

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    RS might be RadioCrap. They sell "seconds" parts from China. They are gone from Canada.
    Digikey and Newark sell good quality electronic parts.
     
  19. anextday

    anextday New Member

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    bass preamp schematic

    Hey just joined this forum and saw a guy asking about bass preamps and i was wondering if i can get the full, correct schematic diagram for it. thanks very much.
     
  20. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I don't know what instrument you want to preamp. Is it an electric bass guitar? Is it a bassoon? Is it a string bass? Is it a tuba?
     
  21. anextday

    anextday New Member

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    bass preamp schematic

    Hey sorry for not being specific...I'll like to build a preamp for my electric bass guitar, however i also want to have the option of choosing active or passive like the guy you helped out named skywalker83. Its just an experiment i'd like to do just like skywalker83. Thank you...
     

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