ATC SCM20 upgrade

Discussion in 'DIY Discussion' started by Polarity, May 5, 2008.

  1. Polarity

    Tenson Moderator

    Nov 12, 2003
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    Kent, UK
    The images have been removed by the host, so I've uploaded the xover schematic again here. (7 years later! How time flys)


    Please bare in mind that this was simulated using the D27TG-35-06 as a reference instead of the original 27TG-46-06 becasue there was no data for that. It is said to be a drop in replacement. I then adjusted the crossover parts until the Scan-Speak 9800 matched as close as possible without massive changes to the crossover.
    Tenson, Jan 10, 2015
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  2. Polarity


    Feb 21, 2018
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    Thank you very much for this valuable post, and for keeping it alive for others to benefit years later. I am in the same exact position as Bruno. I have a vintage pair of SCM 20 SL that still have the original Vifa D26TG off which you modeled for the Scan D2905 that Bruno used. I am finalizing the switch to the Scan D2905 / 7800 and I was able to get a copy of your modeled schematic off Photobucket, thank you.

    However I am a bit perplexed as my stock crossover does not have the same T Pad values as given by Bruno. Mine have a 4U7 and 6U8 cap tied to a 300 inductor as in his schematic. The T Pad resistors however are more in line with what is published, with the R1 values both 3R3 and the R2 value a 6R8. Thus my crossover has greater T pad attenuation than Bruno's it would appear given his series 4R7's and the 10R at the R2 position in his T pad.

    Would my current T pad values affect changes in the cap values and the inductor value that you calculated for Bruno based on the values given for his T pad resistors? And if so, is it possible to run those values for me? Hard to explain the difference between Bruno and my crossover unless the explanation is that mine has the upgraded SL main driver and his did not. The LF portion of my crossover is identical to the original schematic listed in the prior post, and thus identical to Bruno's.

    Much appreciate your help, would like to get these values correct for the HF filter the first time around if possible.

    best Paul
    petland, Feb 21, 2018
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  3. Polarity


    Jun 10, 2018
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    Hi all

    I had just found this thread. I have a pair of SCM20T which one of the crossover is acting up.
    It’s a very early version of the series. The crossover have ‘issue02’ printed on the board. All the components does not have any printed value, which make parts replacement much more challenging. I’ve tried contacting ATC but yet to have any response.

    I wonder if any kind soul could help me with any information on the circuit or have schematic that you can share.

    Thanks guys.

    Best regards

    Attached Files:

    Last edited by a moderator: Jun 11, 2018
    7of9, Jun 10, 2018
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