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Help with amp

Discussion in 'General Electronics Discussion' started by shorteddiode, Aug 12, 2013.

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  1. shorteddiode

    shorteddiode

    41
    0
    Mar 23, 2011
    I want to add a reverb tank to this circuit but not sure where to tie it in. I want it adjustable and my first thought is to put it before the input, is that right?

    The schematic calls for an 8 ohm speaker, mine is 4 ohm. Can I just add a resistor to the out put going to the speaker?

    Thanks in advance
     

    Attached Files:

  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Yes. That circuit is a power amplifier. It accepts an input signal at "line level". This is also the signal level that a spring-line reverb or other reverb circuit will operate.

    You will probably also need a preamplifier, to provide variable gain, tone control, impedance matching, and amplification, to drive that power amplifier. Typically, the reverb section would be connected around the output of the preamplifier.

    You should have posted a link to the project page for that amplifier. It is at http://www.circuitstoday.com/150-watt-amplifier-circuit. The accompanying text states that the amplifier can deliver 150W into a 4 ohm load. So it seems that your 4 ohm speaker can be connected to it.

    I have several concerns about that design though. My first clue to the nature of the design is that it is extremely badly drawn. So I redrew it.

    [​IMG]

    The biasing of the output transistors is wrong and will cause nasty crossover distortion at low output signal levels. The transistors are probably not adequately rated to deliver 150W into any load, and a 4 ohm load is more likely to exceed their SOA (safe operating area) and destroy them. In any case they will need a large heatsink. Also the long tailed pair transistors are only rated for 30V and should be replaced with BC557s at least.

    In general I think the circuit is an amateur design and I do not recommend it. Go to a professional site with properly designed circuits. An IC amplifier is probably a much better option, because the device is designed by experienced, educated people and there is much less for a designer to get wrong.
     

    Attached Files:

  3. shorteddiode

    shorteddiode

    41
    0
    Mar 23, 2011
    Thanks KrisBlueNZ, a lot of good information. I'll do more digging before I settle on a guitar amp. Thanks again
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Also, Q3 should be specified as a TIP41C. The TIP41 (no suffix) is only rated for 40V Vce!
     
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