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LM4702 + SAP15 amplifier - new design

Wawrzo. 2607 14
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  • LM4702 + SAP15 amplifier - new design
    I just thought that if anyone was interested, maybe they would benefit. The test project was created in EASYEDA and it even looks quite good, after Christmas I will start it.
    https://easyeda.com/wawrzo1970_7526/lm4702_darlington_mt200
    The project itself is available in four versions:
    with transistors: sap15, std03, darlingtons in MT 200 and TO3 housings, the last two versions are in the process of being finished, because they require slightly larger PCBs. I encourage you to modify it yourself.

    Cool? Ranking DIY
    Can you write similar article? Send message to me and you will get SD card 64GB.
    About Author
    Wawrzo.
    Automation specialist
    Offline 
    Wawrzo. wrote 260 posts with rating 17, helped 16 times. Live in city Radom, i inne..... Been with us since 2001 year.
  • #2
    simw
    Level 26  
    Not bad. If I remember correctly, the LM4702 can be found in the Arcam AVR500 and AVR600 series receivers. These receivers were great both for home theater and stereo. I think I have 2 chips and SAP15 left after the damaged CambridgeAudio. Maybe I'll be tempted with the next pcb order. Thanks for sharing.
  • #3
    spec220
    Level 24  
    Since we have 2 rectifier bridges, was it not possible to build two independent power supply systems on a common transformer? Or at least if there is common filtration, then separate fuses for the right and left channel?
  • #4
    Wawrzo.
    Automation specialist
    The LM4702 does not have a separate power supply for both channels and the division of the transistors themselves seems pointless in this case, it will only cause an unnecessary expansion of the system. Two bridges are supposed to give the effect of faster charging of the capacitors, especially when loaded with bass. A proven solution in a few other amplifiers.
  • #5
    spec220
    Level 24  
    Wawrzo. wrote:
    The LM4702 does not have a separate power supply for both channels

    The US power supply is not a problem here, but what if one of the channels is defective? E.g. power level? We immediately lose the second channel (there is not even a division into fuses).
    Wawrzo. wrote:
    Two bridges are supposed to give the effect of faster charging of the capacitors, especially when loaded with bass.

    A diode is not a resistor. Parallel connection of the same diodes gives a replacement diode with greater power, but still with a forward voltage similar to one diode. This way you simply break the heat down into two bridges, but does that noticeably improve efficiency as well as efficiency? A shottky bridge would be better.

    Wawrzo. wrote:
    A proven solution in a few other amplifiers.

    I do not doubt. Proven because it works, but is it the best?

    Wawrzo. wrote:
    it will only cause unnecessary expansion of the system

    This is probably the only argument that explains the way in which you realized the power supply to your circuit.
  • #6
    Nepto
    Level 11  
    Interesting. It is a pity that both the LM4702 and SAP15P / N transistors are no longer produced and the chance of getting the originals at a reasonable price is probably negligible.
  • #7
    Wawrzo.
    Automation specialist
    As for the parallel connection of the bridges, in this case the assumption was to reduce the dynamic resistance of such a tandem, which causes when the bridges connected in such a way are loaded with a short current pulse - of course below the maximum forward current - much faster recharging of the filter capacitors. But you can solder a single one.
    As for the separation of the power supply - that was my concept, maybe after testing - if the sound is satisfactory, I will add something to it.
    I also have a prepared board on the LME49830 chip and ECX10N20 / ECX10P20 (EXICON) lateral transistors and there are other solutions there - the circuit is monoblock.
  • #8
    spec220
    Level 24  
    Wawrzo. wrote:
    As for the parallel connection of the bridges, in this case the assumption was to reduce the dynamic resistance of such a tandem, which causes when the bridges connected in such a way are loaded with a short current pulse - of course below the maximum forward current - much faster recharging of the filter capacitors. But you can solder a single one.

    I still do not understand how this dynamic should look like for two parallel loading bridges for a total filtration of 40 mF in relation to two independent loading bridges for independent filtrations of 20 mF? A very slight difference may be noticeable on the oscilloscope only with relatively unbalanced load on the outputs, the only question is will you hear it?
    As long as you're clinging to such details, a better solution is to use a suitable shottky bridge, on which you will get a better effect than on two parallel conventional bridges.

    Wawrzo. wrote:
    and there are already other solutions - the circuit is monoblock type.

    And it's good that they are different. And since they are different, you may be tempted to also work in the exit bridge, although for a typical set I do not know if such a solution is needed.
  • #9
    Wawrzo.
    Automation specialist
    To me personally and subjectively, the bass on the two bridges seems warmer, but this is my subjective opinion resulting from listening to the STX Quant 300 speakers and the DIORA WS600 amplifier (with minor modifications). The design is generally available and nothing prevents you from modifying it to your own needs and preferences.
  • #10
    spec220
    Level 24  
    Wawrzo. wrote:
    To me personally and subjectively, the bass on the two bridges seems warmer

    My colleague knows, sometimes it is an auto-suggestion effect (this topic was once discussed on the forum as a constructor's impression or something). Only specific measurements can indicate something, especially since the difference resulting from one larger or two smaller parallel bridges is so minimal that it can be compared to the fluctuation of the mains voltage supplying the device, which is not always ideally 230 VAC.
  • #11
    dktr
    Level 22  
    Quote:
    To me personally and subjectively, the bass on the two bridges seems warmer

    How is the "temperature" of the bass measured?
  • #12
    spec220
    Level 24  
    You're getting into really difficult terminology.
  • #13
    Wawrzo.
    Automation specialist
    A subjective feeling, if a colleague had doubts, and besides, he does not measure, but feels. We can only measure physical values according to the laws of physics. An example would be temperature. Ehh ...
  • #14
    Jawi_P
    Level 35  
    dktr wrote:
    How is the "temperature" of the bass measured?

    Are you clinging? You may have asked what the author thinks that term means. Unfortunately, when describing sound impressions, similar expressions cannot be avoided, either someone understands them intuitively or not. There are no audio-woodo tours in this thread.