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Integrated with seperate pre/power

Discussion in 'AV Receivers & Amplifiers' started by eviljohn2, Jun 23, 2004.

  1. eviljohn2

    eviljohn2
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    A lot of the new integrated amps seperate their pre/power sections with external terminals. Nad and Marantz spring to mind.

    Would it be sensible to connect both the preouts of the stereo preamp and the preouts from an AV integrated into the power section using either a 2>1 interconnect or a splitter/combiner?

    I can't see how this would cause a problem but presumably there's a reason it hasn't been suggested before? :confused:

    It would provide a lot more options than the current Arcam/Musical Fidelity choices for fixed gain input.
     
  2. John Dawson

    John Dawson
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    It won't work without a switching box to select either the stereo amp or the AV amplifier, becuse otherwise the outputs of the stereo preamp and AV preamp will be trying to drive into eachother resulting in major audible distortion.

    The fixed gain option on the Arcam amps (and no doubt others now) is designed to save you from going down this flawed route when integrating an AV amp into a stereo system.

    HTH.

    John Dawson (Arcam)
     
  3. eviljohn2

    eviljohn2
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    Thanks John

    I gathered it could be done with a switchbox, but surely it wouldn't be a problem with only one of the preamps being used at a time? I'd have thought the preamp outputs would be protected against a line input being connected to it.

    It's not that I don't want an Arcam, I just can't afford one ;)
     
  4. John Dawson

    John Dawson
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    John - this is a technical issue. Modern audio electronics generally have low preamp output impedances (around 50 to 200 ohms) for driving long cables but expect to look into a high impedance (say 10 k ohms) at the input of the power amplifier. If one preamp finds itself also looking into the 50 - 200 ohms output impedance of another preamp output circuit then it is unlikely there will be enough current available to drive this and heavy distortion will ensue on high level signals. It is unlikely anything would break, as the maximum output current will be deliberately limited to say 20mA, but simple sums show this will cause the kind of distortion to which I have referred at high levels. This is not a design fault - you are trying to use your units in ways they were not designed to support.

    Apologies for the technical stuff but there is no other way to explain this!

    John Dawson (Arcam)
     
  5. eviljohn2

    eviljohn2
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    Thanks John

    That was actually the conclusion I'd reached on my own but wasn't sure if I was barking up the wrong tree because it seemed so obviously simple. Don't worry about the technical stuff, as a physics student with a particular interest in electronics it doesn't bother me. :)

    I think perhaps the switchbox idea should be more well publicised though - QED would make a killing with theirs if people knew what potential they had! Obviously not by you though ;)

    Still can't get a relevant job anywhere though :mad:
     
  6. nikyzf

    nikyzf
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    Sorry if I'm missing what you want to do, but why not connect the preamp's tape output to the AV amp's Aux input? Or vice versa of course.
     
  7. eviljohn2

    eviljohn2
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    I had that brainwave a few weeks ago only to be quickly discounted. The tape output does indeed circumvent any gain controls, but set up like that it just means that you don't have any way of controlling the volume so is the exact opposite of what we're trying to achieve!
     
  8. nikyzf

    nikyzf
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    ? You control the volume on the preamp whose Aux input you are using.

    IF the "source" preamp has 2 pairs of variable outputs, you can feed the second pair to the Aux input as before and this gives you 2 gain controls in the chain.
     
  9. eviljohn2

    eviljohn2
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    That's what a number of people do. The overall idea is to use a stereo amp for stereo use. This means connecting just this to your speakers which means the AV amp can't also be connected to them, to get round this we use an input on the stereo amp from the preouts on the AV amp.

    The problem here is that to set the system up properly we need a fixed gain on the stereo amp when it's used for AV purposes. This can be done by setting it to a constant point (usually vertical) but I'd like to avoid this. The Arcam/Musical Fidelity amps have a dedicated input which bypasses the volume control.
     
  10. nikyzf

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    Ah, I'm with you. My Linn preamps (Kairn and Kolektor) both have the option to make one input unity gain. In addition, they each have 3 pairs of line-outs, so I have a few options to play with! (I only play stereo, even with DVDs).
     
  11. eviljohn2

    eviljohn2
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    Not to worry, it confused me for a while but there's quite a big difference between a fixed input and a fixed output! I almost found a way round it too if it hadn't been for those meddling electrical engineers not impedence matching their inputs and outputs :laugh:
     

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