Rolls / Bellari Tube Preamp PA555

Discussion in 'Preamps' started by Je La, Oct 3, 2021.

  1. Je La

    Je La Rando

    Apr 28, 2021
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    Dallas, TX, USA
    Hi friends,

    I spent some time evaluating this budget preamp. I would like to share my impressions with you.

    Claimed Specs
    • Input Impedance: 10K ohms
    • Max Output Gain: 11.1 dB
    • THD: 0.1%
    • S/N Ratio: 103 db, unweighted
    • Frequency Response: 5 Hz – 198 KHz +/- 3 db
    • Crosstalk: -75 dB
    • Output impedance: 100 Ohms
    • Power source type: DC power supply included
    • The PA555 uses a 12AX7 tube running at 150 volts
    • The input signal is connected directly to the grid of the tube
    • All of the gain of the PA555 is from the 12AX7 tube
    • No feedback circuit or integrated circuits in the audio path, it is all analog
    • Made in USA

    My primary use case is a tube line stage. Their marketing team splattered `the PA555 sounds “good for any money" ' everywhere. I'm sorry to say I cannot agree. I didn't have terribly high expectation given the budget nature of the device.

    On the positive side, overall - the sound is enjoyable. There was no hum. The unit responded well to tube rolling - different tubes impacted the sound in modest but noticeable ways. My favorite tube out of several tested was the Vintage Telefunken. The stock tube is a respectable sounding Ruby Chinese grey plate.

    You can hear the differences here:

    In the end, I was less than satisfied with the background noise. In my opinion, this did not seem to achieve the claimed spec (although I only compared recordings by listening - with & without it in the chain. No measurements. I also didn't like ultrasonic noise introduced @ 35k, 52k, 66k, 69k & 87k in the left channel. Although inaudible to my ears, seeing it only in the left channel makes me think a bit more QC could deliver 2 clean channels. (I did reverse the cables and capture without it in the chain to ensure that was not coming from any of my other equipment). In addition, without it in the chain, I am able to capture more high frequency ultrasonics - the bandwidth does seem to be less than advertised.

    To sum it up, the best I could say is - it is pretty decent for the money, but I'm willing to spend a little more to find good for the money. I am returning it. So, I'm still searching for the ~$1000 wide bandwidth tube sound with solid but not flabby bass.
    Last edited: Oct 3, 2021

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