Hallo Besucher, der Thread wurde 1,6k mal aufgerufen und enthält 6 Antworten

letzter Beitrag von dukestah am

End-Amp of the Audio-output of Sid2

    While designing the Pcd for my Sid-Synth, ArSid, I came to the next bump. And that is (as the title say) the next.


    When studying the FpgaSid, I read about a Raw Audio signal, which is a thru-hole soldering island on the Fpga-Pcd.
    In the image, in the upper-right corner, it is the gold-coloured circle, which I named "Audio 2 Raw".
    fpgasids_05-updown.jpg


    But there is also an End-amp on the PCB. That End-amp is directly used in the replacements in all Cbm-computers.


    1) How is the sound-quality of the audio from the Sid2 (so thru the End-Amp), compared to the Sid 1 (the Trans-Amp on the Computer-Pcb)?


    2) The End-amp on the FpgaSid, is it the same as used in the schematics of the Cbm64?
    Sid_End-Amp_Schematics.jpg


    Or is there a new amp designed?


    3) The sound of this Audio 2 Raw, has it (about) the same specs as the Audio Out of the Sid 1 (which is on pin 27)?

    Zitat von Arsid Builder

    1) How is the sound-quality of the audio from the Sid2 (so thru the End-Amp), compared to the Sid 1 (the Trans-Amp on the Computer-Pcb)?

    The sound quality is a bit better, less noise compared to the on-board C64 amp.

    Zitat von Arsid Builder

    3) The sound of this Audio 2 Raw, has it (about) the same specs as the Audio Out of the Sid 1 (which is on pin 27)?

    I think so. I'm using the raw-outs only (most of the time) and I haven't spot any difference so far.

    @dukestah has written almost everything that is to be said. Just some more details on the SID2 output amp:


    The schematic of the output buffer stage is exactly the same as in a C64. The difference lies in the components which are modern SMD components rather than wired components as in the C64. Esp the output capacitor of 10uF is no longer an electrolytic capacitor but a High-C ceramic capacitor with potentially better specs than the electrolytic cap. Most audible difference however is the reduced noise level against the original circuit on the C64 board caused by better decoupling of the supply voltage, better PCB layout with 4 ground and Vcc planes and traces routed in a way that the interference with the digital circuit is minimized. All this has not been done on the original C64 PCB, resulting in a higher audible noise level of the original C64 output against the FPGASID Sid2 output.

    Zitat von dukestah

    The sound quality is a bit better, less noise compared to the on-board C64 amp.
    I think so. I'm using the raw-outs only (most of the time) and I haven't spot any difference so far.

    Thanks for your answer. The second part I find the most interesting. As I see the FpgaSid still more as a normal component, than as a "special one on a Pcb", I'm not fond of soldering a wire to it. But if it is needed, than it must be done. :)


    Zitat von andi6510

    The schematic of the output buffer stage is exactly the same as in a C64.



    All this has not been done on the original C64 PCB, resulting in a higher audible noise level of the original C64 output against the FPGASID Sid2 output.


    And the Transistor, it is still the PN2222?


    I'm still doubing to use the RAW-outputs from the FpgaSid and process all audio into my Amp-board (using OpAmps), or to use the End-signals from Sid2 (and building an extra Trans Amp for Sid1 on my Sid-board) ... In the last case I prefer to use the same component(number)(s) as you used in the FpgaSid.


    My Project stopped last year abruptly when I was developing the Amp-part (still on bread-board), so I still have some choice on the Amp-part.

    Zitat von Arsid Builder

    Thanks for your answer. The second part I find the most interesting. As I see the FpgaSid still more as a normal component, than as a "special one on a Pcb", I'm not fond of soldering a wire to it. But if it is needed, than it must be done.

    It's not necessary to solder a wire to it. I have created an adapter to get access to the two signals. You can use the three pin connector to connect whatever cable you want :)
    IMG_20190225_095635.jpg