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  • More than 30W per chanel Class A transistor amps

    From Howard Stone@21:1/5 to All on Mon May 6 13:37:38 2019
    This may be of interest

    https://www.pinkfishmedia.net/forum/threads/rebuild-of-classic-krell-ksa50-fan-heater.227491/

    (Still not heard it yet -- the latest info is slightly worrying in fact, I got an email saying:

    "There is a slight hum from the transformers which is pretty quiet most of the time but at peak TV time last night with some DC on the mains it did hum quite badly so you may want to use it with a DC blocker. To be clear, this is from the amp chassis
    itself and mechanical hum from the transformers and not hum through the speakers. It is silent from the speakers in background noise." )

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  • From Peter Wieck@21:1/5 to All on Mon May 6 17:52:30 2019
    50 hz current has that awful effect in some cases - and will (very slightly) de-rate the amp. Given that those appear to be toroidal transformers, there is no easy cure other than an isolation transformer at the head-end. And that will be a pretty
    massive item, 20 A (@ 120 VAC) anyway.

    As it happens, if that amp is still set to US voltage (120 VAC), there are some very good 240:120 isos out there that will do nicely.

    http://www.farnell.com/datasheets/2279306.pdf?_ga=2.187485032.1926575215.1557160509-1096436046.1551096751&_gac=1.184557019.1556715333.Cj0KCQjwh6XmBRDRARIsAKNInDFhpeJKNAxViDjwsTsi2VzMrHglXPmgALeX25Ld31b6Fo3bVrcTomoaAlPcEALw_wcB

    Nor is there anything wrong with an iso on the system for general noise reduction.

    On the other hand, I suggest that you not panic, but see how it goes in your environment.

    Peter Wieck
    Melrose Park, PA

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  • From Trevor Wilson@21:1/5 to Howard Stone on Mon May 6 22:37:06 2019
    On 6/05/2019 11:37 pm, Howard Stone wrote:
    This may be of interest

    https://www.pinkfishmedia.net/forum/threads/rebuild-of-classic-krell-ksa50-fan-heater.227491/

    (Still not heard it yet -- the latest info is slightly worrying in fact, I got an email saying:

    "There is a slight hum from the transformers which is pretty quiet most of the time but at peak TV time last night with some DC on the mains it did hum quite badly so you may want to use it with a DC blocker. To be clear, this is from the amp chassis
    itself and mechanical hum from the transformers and not hum through the speakers. It is silent from the speakers in background noise." )


    **Pretty normal with many toroidal transformers. They can become noisy
    when subjected to excessive DC on the mains supply. It is location
    dependent. You may not have a problem in your location. As suggested, a
    DC blocker is a simple, inexpensive possible solution.

    A few comments on the repair:

    * Your tech appears to have done an excellent and thoroughly
    professional job.
    * See if you can arrange to have the fan suck air UP, rather than
    blowing it down. Those idiots at Krell made a huge mistake with early
    KSA50 amps, by forcing air down, rather than up. (Hot air rises, after
    all). This insanity was rectified in later variants.

    --
    Trevor Wilson
    www.rageaudio.com.au

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  • From Howard Stone@21:1/5 to All on Tue May 7 09:47:24 2019
    Oh the other thing Jez said to me which maybe he of interest was this

    “There are speaker fuses at the output which are supposed to be 4A, 5A was found to be fitted. Such high values are unlikely to offer any real protection (2A is more common as a speaker fuse... and does sound bad!) to the speakers but could cause a
    slight reduction in sound quality. I will be opening it up again to check bias and offset after a couple of days use so if you wish I can bypass them altogether. let me know.”

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  • From Trevor Wilson@21:1/5 to Howard Stone on Tue May 7 21:44:51 2019
    On 7/05/2019 7:47 pm, Howard Stone wrote:
    Oh the other thing Jez said to me which maybe he of interest was this

    “There are speaker fuses at the output which are supposed to be 4A, 5A was found to be fitted. Such high values are unlikely to offer any real protection (2A is more common as a speaker fuse... and does sound bad!) to the speakers but could cause a
    slight reduction in sound quality. I will be opening it up again to check bias and offset after a couple of days use so if you wish I can bypass them altogether. let me know.”


    **Fuses are a really bad idea on speaker lines, as a fuse is, in
    reality, a non-linear resistor. Therefore, a fuse (any fuse) will
    introduce distortion. The lower the value of the fuse, the higher the distortion.

    --
    Trevor Wilson
    www.rageaudio.com.au

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  • From Howard Stone@21:1/5 to All on Wed May 8 07:33:56 2019
    Brilliant, thanks for your advice.

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  • From Trevor Wilson@21:1/5 to Howard Stone on Wed May 8 09:00:19 2019
    On 8/05/2019 5:33 pm, Howard Stone wrote:
    Brilliant, thanks for your advice.


    **I should add, that, if the fuses are bypassed, then another means of
    speaker protection should be considered.

    --
    Trevor Wilson
    www.rageaudio.com.au

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  • From Peter Wieck@21:1/5 to Trevor Wilson on Wed May 8 11:30:50 2019
    On Tuesday, May 7, 2019 at 5:44:53 PM UTC-4, Trevor Wilson wrote:

    **Fuses are a really bad idea on speaker lines, as a fuse is, in
    reality, a non-linear resistor. Therefore, a fuse (any fuse) will
    introduce distortion. The lower the value of the fuse, the higher the distortion.

    Source: Bob Cordell "Designing Audio Power Amplifies"

    Section '13.11 Fuse, Relay and Connector Distortion' page 268.

    Conclusion:

    "At 20 Hz, amplifier distortion due to the fuse is calculated to be 0.0033 %."

    Me: And, of course no harmonics are affected or altered.

    How much are your speakers worth that you would put them at risk over the silliness of fuse adding distortion at audible levels?

    Peter Wieck
    Melrose Park, PA

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  • From Peter Wieck@21:1/5 to All on Wed May 8 12:13:40 2019
    RANT WARNING!

    Guys and gals, there is common sense (which isn't), and then, there is received wisdom (AKA: Religion) when it comes to audio. Typically, but not always, they are mutually exclusive. Also commonly practiced in this hobby/religion are several common
    fallacies, the most prominent of which are:

    1. Leaping to conclusions: My cat is grey, therefore all cats are grey.
    2. Begging the question: Given that all cats are grey, therefore my cat must be grey.
    3. False premises: My cat is wet, therefore it rained last night.

    What brought this on was Trevor's post on fuses, which more-or-less encompasses two 1 & 3 of the above, with a glancing blow to 2.

    Some Math:

    If Output Watts = V^2/Speaker Impedance
    Then V = Square Root of output watts x Impedance

    OR: If watts =30
    Impedance = 8
    Voltage = 15.5
    Amps = watts/volts
    OR: 2 A in this model

    Which, of course, will vary as the actual impedance differs from the nominal impedance.

    A 4 amp fuse will not even warm up under normal operating conditions - and well-designed speakers will be able to handle a 30-watt input all day and all night as long as there are no/limited DC components. Sources of DC components could be from clipping
    in an amp with limited protection circuits, or catastrophic failure in one-or-more internal components. At which point the fuse comes into play. Aren't >you< glad that it was?

    Other problematic speaker-damage sources: A user chooses to send a pure sine wave into a speaker at full volume. The fuse WILL NOT protect the speaker in this case, and 30 watts is 30 watts = heat. Even the very best voice coils will not withstand a
    constant 30 watts at a single frequency. Similar damage may be caused by a feedback loop.

    Point being that a fuse is a line of defense that when deployed protects >your< speakers better than _ANY_OTHER_OPTION_.

    That fuses can add distortion at audible frequencies does not mean that they do add distortion.
    That a fuse once added distortion does not mean that all fuses add distortion. That the speaker is distorting does not mean that the fuse is the cause.

    And, of course, I could get started on the many types of fuses out there - including an entire cohort based on audiophoolery.

    Peter Wieck
    Melrose Park, PA

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  • From Howard Stone@21:1/5 to All on Mon Aug 26 22:38:03 2019
    In fact, the Krell did develop a slight problem. The fan would become noisy, a sort of rattle noise. If you turned it on and off then it would stop, but still I thought it was best to get it changed. The new one is almost silent and, as Trevor
    recommended, it sucks up. Jez says that the amp runs slightly cooler as a result.

    The amp is wonderful!

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  • From Trevor Wilson@21:1/5 to Howard Stone on Tue Aug 27 09:48:07 2019
    On 27/08/2019 8:38 am, Howard Stone wrote:
    In fact, the Krell did develop a slight problem. The fan would become noisy, a sort of rattle noise. If you turned it on and off then it would stop, but still I thought it was best to get it changed. The new one is almost silent and, as Trevor
    recommended, it sucks up. Jez says that the amp runs slightly cooler as a result.

    The amp is wonderful!


    **Good to hear. Literally.

    --
    Trevor Wilson
    www.rageaudio.com.au

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