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  • #61
    saureign, I currently use an RME dac/pre. The RME seemed to work fine with my former SCM100asl speakers. I hope I'll get 'usable' sound quality when my 150's arrive.

    AlasairH - were you in the older ATC Forums? I seem to recollect your user name. A minimal box count is my goal. My xlr cable length is 7 metres - not too short. I also have a larger room 6.5m x 5.5m. I wonder what room size thebadcat has and what choice of xlr cables he has made.

    Larry, Thanks for the tips about level adjustment. I don't recall having that facility on my former 100asl speakers. But then again I didn't really look. Regarding the relative pricing points of the CDA2 compared with the SCA2, I guess you get what you pay for. I did a little more reading on the SCA2; this option looks a better match for the thebadcat's 100asl speakers and my new 150asl speakers.

    If thebadcat is still there, what are your thoughts?

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    • AlastairH
      AlastairH commented
      Editing a comment
      Yes, I was also on the old forum!

  • #62
    Originally posted by Bulldog View Post
    I was considering a CDA2 to match with my SCM150asl classic speakers when they arrive in Australia from the UK. The comments above about a possible mismatch with the active speakers concerns me. I understood that the CDA2 was specifically designed to match all of ATC's active speakers. Surely there shouldn't be a volume control level disparity(?) ATC have very competent engineers. There must be something else going on...
    From a good engineering PoV, there always must be enough overall system gain from pre-amp and 'speaker for the worst case installation. I think that worst case is a large studio (listening far away) with treated walls (no SPL reinforcement from sidewall reflections) and at studio-standard SPL (higher than normal domestically).

    ATC certainly are very competent engineers, but it's a tricky compromise to design for all possible end-user installations. The available total gain must cope with the worst case studio but will almost certainly be more than you need in most homes.

    That's only a problem if your volume control potentiometer ends up too low at home. That's where even the best potentiometers struggle with increasing rotational sensitivity and sometimes worsening L/R channel balance.

    If there is a mis-match from too much pre-amp gain for your installation then the 6 dB trim potentiometers on more modern amp. packs can help; and identifying which aperture is for the gain trimmer (not the bass trimmer) has already been covered. One thing I will add is that these trim pots are not intended to be adjusted too often. I think Bourns specify them for 200 operations. That may seem a lot and indeed should be. But do remember they are "adjust and forget" controls, best adjusted very carefully with a screwdriver blade that nearly matches the full length of the white slot seen through the aperture, and then left alone.

    As an alternative or if you need an even higher setting on the volume pot., XLR attenuators in the cable between pre-amp and active 'speaker work perfectly too. People seem to worry about sound degradation but attenuators are very simple devices and the drivers in ATC amplifiers are more than capable of driving them. I use 10 dB Rothwell attenuators between my CDA2 and SCM50ASL. I also use the amp pack trimmers but more to adjust for L/R imbalance in my room (and maybe my ears too). The result sounds magnificent to me. I can comment more on the selection and use of attenuators from practical and electronics theory points of view if anyone is interested but this post is already getting long.

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    • #63
      I also used Rothwell attenuators when I had the ATC pre amps in the system. I don’t need to now as I use the calibration settings in my 861 to adjust to 75dBs at the listening seat for 5.1. I might run my sub a little hot though ;-)

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      • #64
        It's good to know Rothwell attenuators.are an option. If I had to resort to using the amp pack trimmers, I would do so using a digital spl meter. My RME dac/pre is provides sufficient gain at 90% to drive my SCM100's to around 90 db in room @ 3 metres. Plenty for me.
        Last edited by Bulldog; 01-07-2022, 08:05 AM.

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        • #65
          Originally posted by AlastairH View Post
          I also used Rothwell attenuators when I had the ATC pre amps in the system. I don’t need to now as I use the calibration settings in my 861 to adjust to 75dBs at the listening seat for 5.1. I might run my sub a little hot though ;-)
          One of the thoughtful design decisions from ATC with the SCA2 preamp is that I believe it has a setting for gain. When engaged (according to this HiFi News review (pdf)) it inserts 13 dB of attenuation for situations such as typical homes where you don't need the loudness you may want in the studio and want the volume control set a bit higher instead.

          IMHO, generally speaking, an ideal preamp for ATC's active loudspeakers, for a fairly usual home environment, has about 0 dB gain (x1 - no gain at all in fact). That's my experience with the CDA2 Mk2. This has 10 dB gain which I think is right for studio use but as I wrote earlier I insert a 10 dB Rothwell attenuator (which actually attenuates 12 dB driving the 10 kOhm per leg input impedance of the SCM50ASL).

          That seems to make a versatile DAC with a standard 4V balanced maximum output (I assume this for your 861) an ideal source without any preamp.

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          • #66
            jophill, thanks for the info. It's easy to forget ATC's pro-audio slant. I checked out the SCA2 preamp on ATC's website - it looks a better match with SCM150asl speakers than the CDA2 Mk2. I need to be patient until some $$$ come my way.

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