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  • Budget (cheap) DIY Amp Stupid Questions

    Hello,

    Was thinking of building a dual mono amp based on (2) of the ICE 50ASX2BTL modules. I realize that these need a balanced input signal to function.

    The first question I had was "how do I control the volume"? I thought that was an easy one - I just need my phono preamp to have an output level knob, right? I'm not sure if it's that simple, but that was my first assumption. I have read a few things about these modules needing a low output impedance, and that's where I'm starting to get lost. Sounds like maybe just turning down the preamp might lead to some really unsatisfactory high frequency performance from the amp, but like I said, I start to get a little lost there. FYI, I was thinking of using a Rolls/Bellari PA550 for the preamp.

    I was thinking of using a case kit from Ghent, and I saw that they offer what they call the "RTX Module". This would help create the balanced inputs from the SE outputs from the preamp. Would this also act as an input buffer and address the impedance issues?

    Alternatively, I would be open to a little less power, but greater simplicity, by using a 125ASX2 stereo module with SE inputs. Same question about volume though - output level on the preamp sufficient? If I were to go the 125 route, how can I tell genuine from fake? For the 50ASX2BTL I can source them right here at PE, but for the 125 it seems like they would have to come from the bay, which is unnerving.

    In summary, will this work? Turntable -> PA550 -> power amp (either dual 50BTL or 125) -> loudspeakers

    Thanks in advance for any help,

    Mike

  • #2
    Buy this: https://www.parts-express.com/art-cl...erter--245-868 or this https://www.youtube.com/watch?v=gD3ypntBF8c. Watch this video: https://www.youtube.com/watch?v=gD3ypntBF8c. Instead of those boards buy one IcePower 200ASC and one 200AC. The first will power itself and the 200AC. If you want mono-blocks then buy two 200ASC. This will give you a volume control and single ended to balanced conversion, and you can feed that into the amplifier via XLR

    Comment


    • #3
      Thanks for taking the time to respond. I've seen that video, I know about the ASC and AC modules. However, the 200ASC is out of stock until basically June, and I've read/heard good things about the ASX series being nicer, utilizing the newer, updated ICE topology. Hence the questions, restated more simply below.

      1. Will a preamp with an output level control, into an RTX module provide satisfactory input to a 50ASX2BTL module?

      2. Should I be concerned about counterfeit 125ATX2 modules? Anything to look for to verify genuine product?

      Thanks again,

      Mike

      Comment


      • #4
        Looking at the data sheet for the 50ASX2BTL I don't see balanced inputs. Gain is specified as 20.5dB. It will take 1.84V peak to hit peak output voltage. You just need to check if your pre amp has that output.

        In bridge mode, the amp does need an inverted signal for one of the channels, so a balanced input would do the trick or a separate inverter circuit.
        Electronics engineer, woofer enthusiast, and musician.
        Wogg Music
        Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

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        • #5
          Thanks very much for the reply wogg. The preamp I was looking at has 57db of gain on the phono section, so with a 2.5mV cartridge, that calculates to 1.7V...good enough for 92% of peak and output. I think that should be ok, right?

          Do I need to be concerned with the issues mentioned in the linked thread below? I'm thinking the RTX modules I would use to create the balanced signal may make this a non-issue, but I'm not sure.

          ​​​​​ Thanks,

          Mike
          I've purchased several of the B&O ICEPower 125ASX2's. The bass is astoundingly granite solid, but the rest of the range wasn't as good as my Hypex

          Comment


          • #6
            So, what is this RTX module? You need an active buffer that outputs balanced to drive that amp board without that treble issue mentioned on DIY audio. That ART cleanbox would do it.
            Electronics engineer, woofer enthusiast, and musician.
            Wogg Music
            Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

            Comment


            • #7
              Sorry, I should have included more info on what I was referencing. Link attached for Ghent RTX module.

              Thanks again,

              Mike

              Comment


              • #8
                That's an active buffer, should be fine. Plus that 6dB of gain module gives you another factor of 2 on the input voltage.
                Electronics engineer, woofer enthusiast, and musician.
                Wogg Music
                Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

                Comment

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