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  1. Old Comment

    Chinese class D amp modules.

    You might start a thread about this in the Class-D forum. That is likely to get more responses than a blog post...
    permalink
    Posted Today at 04:50 PM by CharlieLaub CharlieLaub is online now
  2. Old Comment
    davym's Avatar

    Exploring laptop sound

    Was a cure for this ever found?
    permalink
    Posted 13th August 2016 at 04:12 PM by davym davym is offline
  3. Old Comment
    rjm's Avatar

    RJM Audio discrete op amp (circuit schematic)

    Thanks. Nice diagram, I appreciate having all the voltages written on there. Yes, I expect if I put the current sources back in to my circuit I will end up with something very similar. The main difference in the topology is just that my version has a follower/buffer before the VAS.
    permalink
    Posted 8th August 2016 at 05:35 AM by rjm rjm is offline
  4. Old Comment
    permalink
    Posted 8th August 2016 at 05:15 AM by FritzS FritzS is offline
    Updated 8th August 2016 at 05:31 AM by FritzS
  5. Old Comment
    Tea-Bag's Avatar

    Salas Board Minikits and Full Kits

    Quote:
    Originally Posted by Liliya
    Hello Teabag

    I intend to build a a positiv shunt regulator for my miniDSP 4x10. I have not had time to readt he hole thread, but as far as I can see, there have been some changes from the first version. As I have both 2SK170BL(and PF 5102), IRF240 and IRF 9240, I do hope that all this component can be usedand do the changres according to you first version?
    The transformer I have is 11.8V AC and 108VA. MiniDSP 4x10 work properly from 6V DC to 15V DC. I want to go for the max version that can handle 3A. Can all my "wishes" be realized. I need your advice before starting up this prosject and ordering the PCB.

    Eivind Stillingen
    I think using the DCB1 board, gives you a lot more flexibility here.
    permalink
    Posted 31st July 2016 at 01:48 PM by Tea-Bag Tea-Bag is offline
  6. Old Comment
    alexcp's Avatar

    First Watt B1 clone

    Hi Marc, sorry I was away from diyAudio for a few months. Thank you for the positive comment. To your question, I did not source the relay selector but designed and built it myself - there is not much to design there, so it was mostly soldering.
    permalink
    Posted 30th July 2016 at 02:43 AM by alexcp alexcp is offline
  7. Old Comment

    Salas Board Minikits and Full Kits

    Hello Teabag

    I intend to build a a positiv shunt regulator for my miniDSP 4x10. I have not had time to readt he hole thread, but as far as I can see, there have been some changes from the first version. As I have both 2SK170BL(and PF 5102), IRF240 and IRF 9240, I do hope that all this component can be usedand do the changres according to you first version?
    The transformer I have is 11.8V AC and 108VA. MiniDSP 4x10 work properly from 6V DC to 15V DC. I want to go for the max version that can handle 3A. Can all my "wishes" be realized. I need your advice before starting up this prosject and ordering the PCB.

    Eivind Stillingen
    permalink
    Posted 28th July 2016 at 08:33 AM by Liliya Liliya is offline
  8. Old Comment
    rjm's Avatar

    A Rant on Why Passive Preamps are Totally Stupid

    The high impedance section is susceptible to noise pickup, so the longer and more exposed it is, the more likely it is to inject significant noise into the signal.

    An amplifier input also has a noise current which will induce noise in proportion to the impedance seen by its inputs. This noise will not depend on the length of cable between the volume potentiometer and the amplifier.

    Putting a lowZ buffer after the volume control eliminates both issues.

    Yes, the buffer input now faces the volume control output. So if the current noise of the buffer is higher than the current noise of the amplifier it's true you are worse off in that respect even if the noise pickup from the cable is eliminated.

    So obviously you design your buffer to have low current noise, which is not a difficult task given the low signal voltages involved.
    permalink
    Posted 26th July 2016 at 11:39 PM by rjm rjm is offline
  9. Old Comment
    bear's Avatar

    A Rant on Why Passive Preamps are Totally Stupid

    ok, so moving the buffer next to the "pot" eliminates the cable and then drives the cable with a very low Z, removing the impedance that is generating the noise? But is the cable the offending element, or would it still generate noise if the "pot" were inside the amp, AT the input stage??

    And, also, isn't the input to the buffer the same (in essence) high Z input??

    Seems confusing to me.
    permalink
    Posted 26th July 2016 at 01:07 PM by bear bear is offline
  10. Old Comment
    rjm's Avatar

    A Rant on Why Passive Preamps are Totally Stupid

    Absolutely. Worst case is when the wiper perfectly divides the resistance in half. This is usually around the 2-3 o'clock position, so it is rarely encountered in practice... but above 11-12 o'clock the impact can often be heard.
    permalink
    Posted 26th July 2016 at 07:50 AM by rjm rjm is offline
  11. Old Comment
    bear's Avatar

    A Rant on Why Passive Preamps are Totally Stupid

    so ur saying midrange of the theoretical pot is the most problematic for this noise issue...?
    permalink
    Posted 26th July 2016 at 03:40 AM by bear bear is offline
  12. Old Comment
    rjm's Avatar

    A Rant on Why Passive Preamps are Totally Stupid

    A 47k volume potentiometer at maximum is just a 47k resistance to ground. There is no series element, so the output impedance is defined by what the stage before it consists of (in parallel with 47k). It is essentially removed from the circuit - no negative influence - but at the same time it's function (adjusting the volume) is also defeated.
    permalink
    Posted 26th July 2016 at 02:48 AM by rjm rjm is offline
  13. Old Comment
    bear's Avatar

    A Rant on Why Passive Preamps are Totally Stupid

    If you turn the volume all the way up...?
    It looks like another resistor in parallel with the input resistor on the "amp", no? This would have what sort of negative effect... and I'm a bit unclear how the input to a buffer looks much different than the input of a power amp, unless you are saying the interconnect is going to generate that noise, is that what's being said?

    The problem with a "TVC" is that it is a transformer, and with that comes all the issues of using transformers... having looked at the waveforms coming off some of the highly regarded ones, I've not opted to go that way.
    permalink
    Posted 25th July 2016 at 11:37 PM by bear bear is offline
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