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Thread: Solid state preamp grain compared to valves

  1. #221
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    This article explains a lot about the input/output impedance thing in plain English https://www.lifewire.com/output-impedance-3134904
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  2. #222
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    Quote Originally Posted by Stratmangler View Post
    This article explains a lot about the input/output impedance thing in plain English https://www.lifewire.com/output-impedance-3134904
    That was indeed a very helpful article ... and easier to follow than many.

    I found this paragraph very interesting but am curious what exactly the 'substantial effect on the frequency response' would be (i.e. how it would sound) Don't know if any tube amp designers would care to clarify/comment.

    "to simulate the sound of a tube amp in his Sunfire solid-state (transistor) amplifiers, famed designer Bob Carver added a “current mode” switch that placed a 1-ohm resistor in series with the output devices. Of course, this violated the 1-to-10 minimum ratio of output impedance to expected input impedance that we discussed above, and thus had a substantial effect on the frequency response of the connected speaker, but that’s what you get with many tube amps and it’s exactly what Carver wanted to simulate."

  3. #223
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    The wiper of the pot usualy goes to the input of the amplifier, Agreed ? thus varying the pot, also varies the resistance of the ampliers front end or input, taking it nearer, or further away from Ground!
    Quote Originally Posted by RothwellAudio View Post
    A passive attenuator doesn't present a "low and varying" input impedance to the first stage of a power amp - it presents its source impedance to the amplifier.
    However, this could be an explanation to what people hear. Some power amps' distortion goes up when fed from higher source impedances.
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  4. #224
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    Therefore; by varying the pot, you're varying the resistance, or impedance that the source has to drive, and thus at low volumes, where the wiper of the pot is nearest to ground, your're literally making the front end of the amplifier harder to drive! I hope that makes sense.

    Quote Originally Posted by RothwellAudio View Post
    Correct. That's the source impedance (or output impedance) of the pot, not its input impedance. Actually, the output impedance is the resistance above the wiper in parallel with the resistance below the wiper. A 10k pot's output impedance is 2.5k at its maximum, but drops towards zero at both ends of its travel (more accurately, zero plus the source impedance of whatever is driving it).
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  5. #225
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    With an AVC does the impedance seen by the source increase as the higher turns are used? I recall they differ from pots.
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  6. #226
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    Quote Originally Posted by mikmas View Post
    That was indeed a very helpful article ... and easier to follow than many.

    I found this paragraph very interesting but am curious what exactly the 'substantial effect on the frequency response' would be (i.e. how it would sound) Don't know if any tube amp designers would care to clarify/comment.

    "to simulate the sound of a tube amp in his Sunfire solid-state (transistor) amplifiers, famed designer Bob Carver added a “current mode” switch that placed a 1-ohm resistor in series with the output devices. Of course, this violated the 1-to-10 minimum ratio of output impedance to expected input impedance that we discussed above, and thus had a substantial effect on the frequency response of the connected speaker, but that’s what you get with many tube amps and it’s exactly what Carver wanted to simulate."
    I think that because they use output transformers a valve amps frequency output will vary with the load it sees from the speaker.
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  7. #227
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    First of all; the speaker load is a constant variant, due to the varying signal frequency it has to deal with in musical content,, so both types of amplifiers will put out diffrent amounts of power into the load throughout the frequency bandwidth, due to this ever changing load impedance of the speaker, ofcourse, the affect will vary depending on how good the speaker is, but dont be fooled into thinking one topolgy is perfect at driving a speaker over the other, I have gone into this in some detail in various other posts over the years here.Yes, you can introduce some form of crude impedance, by inserting a resistor in the output of a solid state amp in an effort to similate what a valve amp's output does when connected to a speaker, but its not an accurate way of describing the diffrences between how a solid state amp deals with a speaker versus a valve amp, I just see it as an attempt to bias non technical folk into thinking that solid state amps are automaticaly better than valve amps, which is far from the case in many situations.
    Quote Originally Posted by Macca View Post
    I think that because they use output transformers a valve amps frequency output will vary with the load it sees from the speaker.
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  8. #228
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    https://forum.audiogon.com/discussio...eed-attenuator
    Quote Originally Posted by Clive View Post
    With an AVC does the impedance seen by the source increase as the higher turns are used? I recall they differ from pots.
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
    Nikola Tesla



    Its now a conspiracy theory to believe that the Immune system is capable of doing the job it was designed to do.
    A fish is only as healthy as the water its swimming in ! [Dr Robert Young]


    www.tubedistinctions.co.uk

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  9. #229
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    In the Carver challenge he used null testing to tweak his SS amp so it sounded like the valve amp. He succeeded but I don't think the resulting SS amp was unconditionally stable as a result.
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  10. #230
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    The input resistance/impedance of the pot, ie; the part that the source see's [usualy the full resistance of the pot] as you and I both seem to agree on" is not the problem, where the issue some describe as some passives sounding lifeless, IMHO, its all to do with the lowering of the amplifiers input resistance, or impedance, by the wiper of the Attenuator being nearer to ground at low, to medium volumes!
    Quote Originally Posted by RothwellAudio View Post
    No; changing the position of the pot's wiper has very little effect on the impedance seen by the source, eg CD player. Yes, the power amp's input impedance is in parallel with the lower half of the pot, but as long as the power's amp's input impedance is considerably higher than the pot's resistance there won't be much impact.
    Take for example a 10k pot and a power amp with an input impedance of 100k. With the pot turned fully down the CD player sees a load of 10k. With the pot turned to half it's resistance value (which is more than half way round for a log pot) the CD player sees a load of 5k plus 5k in parallel with 100k. That works out at 9.8k, ie very nearly 10k.
    With the pot turned up full the CD player sees a load of 10k in parallel with 100k. That works out at 9.1k, ie still very nearly 10k, so the load impedance seen by the source (the CD player, for example) doesn't change very much at all.
    When I referred to "the source impedance" earlier I was referring to the source impedance, aka the output impedance, of the pot.
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
    Nikola Tesla



    Its now a conspiracy theory to believe that the Immune system is capable of doing the job it was designed to do.
    A fish is only as healthy as the water its swimming in ! [Dr Robert Young]


    www.tubedistinctions.co.uk

    Matthew 5:10

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