Survey: Describe your perfect remote-control passive preamp?

Discussion in 'Audio Hardware' started by ProfessorC1983, Feb 17, 2019.

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  1. ProfessorC1983

    ProfessorC1983 Forum Resident Thread Starter

    Location:
    Washington, DC
    So, for the past couple months I've been playing around with designing/building my own passive preamp, both simply to satisfy my tinkering hobby and because I just haven't found a product on the market that fulfills all of my needs:

    - Remote control volume and input switching
    - Programmable IR codes (i.e. controllable with any existing remote)
    - 100+ step relay-driven stepped attenuator (no pot)
    - 4 unbalanced stereo RCA inputs and 2 switchable outputs
    - Nothing in the signal path but audio-quality resistors, relays and wire
    - Display indicating currently selected input/output and volume level, clearly visible from listening position
    - Mains relay for turning power amp on/off via IR remote
    - Runs on 5V DC so can be plugged into USB hub rather than needing its own wall wort

    [Yes, I realize the Schiit Saga satisfies some/many of these requirements and has a lot of adoring fans, and justifiably so, but I auditioned and ultimately found it not to be a good match for my system.]

    I've got a prototype unit put together that does all of the above and IMHO it's working pretty well so far. This has me wondering if maybe it's worth taking the next step and designing a custom PCB and perhaps offering it as a DIY kit, if there really is an unmet demand for this kind of product?

    So without further adieu, I'd love to hear more about whether this type of pre would be useful to other folks. In particular I'm wondering:

    1) What features do you consider must-haves when it comes to a passive preamp?

    2) What are your aesthetic/form-factor requirements for a passive pre?

    3) Is there a product currently on the market that satisfies all of your needs?

    4) If not, what's the general price range you'd be willing to spend for your "perfect" pre?

    Appreciate the feedback and looking forward to the conversation.
     
  2. vinylontubes

    vinylontubes Forum Resident

    Location:
    Katy, TX
    Not really interested in this. But I'll provide feedback. You might as well include a mono switch. If it's a kit, you by-pass the feature if it's undesirable to the end user. The feature would only be useful for analog use, either a turntable or a magnetic tape deck.
     
  3. ProfessorC1983

    ProfessorC1983 Forum Resident Thread Starter

    Location:
    Washington, DC
    Nice idea. Thanks!

    One more bump on this to see if anyone else is interested, otherwise I'll assume my needs are unique and take my toy and go home. :winkgrin:
     
  4. Soundsense

    Soundsense Forum Resident

    Location:
    Colorado USA
    Peter Fletcher-Haynes out of Denver, years ago designed one called the 'Diminuendo', which has pretty much all of the features you list. Pretty little thing too. Cute and affordable.
     
  5. Simon A

    Simon A Arrr!

    I would love a good Multichannel passive preamp.
     
    Vinny123 likes this.
  6. BIGGER Dave

    BIGGER Dave Forum Resident

    Found this on the web:

    Diminuendo Passive Stereo Attenuator / Channel Selector, $799

    Specifications
    •Five stereo input channels with approximately 25K constant load impedance (even when input is not selected) minimizing sudden volume changes and noise
    •Computer controlled 26 step attenuation from 0 to - ∞ mute (output grounded)
    •Attenuator steps in -2Db, -4Db and -5Db increments
    •Make-before-break relay attenuator step switching for quiet operation
    •Highly reliable (over 50 million operations) sealed low signal relays
    •Volume up control disabled when muted
    •LED indicators for volume, mute and channel selection
    •When power is turned on, internal computer check cycles through LEDs
    •IR remote control using a standard universal TV remote controller
    •Pre-programmed remote control (brand may vary) uses Philips RC5 protocol, device set to ‘TV’, CH select (+/-), VOL select (+/-), Numeric key pad entry (0-5) and Mute
    •Universal low voltage external power supply 100/240 V 50/60 Hz

    A picture of the Diminuendo was posted August 1, 2011. FletcherHaynes Audio
     
    Last edited: Feb 20, 2019
  7. Larry I

    Larry I Senior Member

    Location:
    Washington, D.C.
    I don't know about perfection, but, a very good passive would involve transformers to convert voltage to current when attenuating. Transformer-based attenuators sound much more dynamic than other passive varieties. However, most transformer-based attenuators don't have enough taps to allow for anything close to 100 steps.

    I agree that having enough steps to allow for something close to 1 db per step change is important. I also agree that the ability to make volume changes by remote control is a must. I would also add a channel balance control to the list of "must have" features.

    The autoformer attenators of Dave Slagle (Emia) do have many steps, allow for channel balance change, and are remotely controllable. I've only heard them at audio shows, so I don't know how they would compare with other passives (including their cousin, the transformer-based controls), but, I think they are promising.

    A friend built a remotely controlled passive linestage using light-dependent resistors. It had many steps for attenuation and sounded decent in a setup that was somewhat passive friendly (short interconnect length, high input impedance on the amp). Light dependent resistors were all the rage then, I don't know where they stand these days. It sounded quite decent, but, he was surprised how much better his system sounded when we tried a decent, tube-based active linestage in its place.

    I would suggest trying different types of resistors before going with a particular type/brand for your passive. There is no such thing as an high end resistor that is a consensus choice. For example, I know a few designers who don't like the sound of the top end Vishay resistors, at least in their particular designs, and prefer old fashion carbon composition resistors. I owned, and liked, the Placette active linestage which did use Vishays, so I don't have anything against them personally (I heard the Placette passive linestage, and in my system, the active linestage ( included a unity gain buffer) sounded much better). I currently own gear that uses very old parts, although the attenuator in my linestage is a remotely controlled pot.
     
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