Essential Reverb: Cathode vs Fixed Bias

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  • Опубліковано 23 гру 2024

КОМЕНТАРІ • 40

  • @joshboncoeur6985
    @joshboncoeur6985 3 дні тому +1

    I like the fixed bias for clean and the cathode bias for overdrive. Nice comparison.

  • @krauz111
    @krauz111 10 місяців тому +3

    Really liked the fixed bias

    • @beareamps
      @beareamps  10 місяців тому

      Yeah my preferred too!

  • @harrypalmer3481
    @harrypalmer3481 Рік тому +4

    For slight growl/overdrive/distortion cathode bias is my preference. For clean they both sound great. For louder clean, the fixed bias would be preferable. They both sound great!

    • @beareamps
      @beareamps  Рік тому +2

      Cheers Harry! Its hard to choose a favourite - they both have advantages. For greater headroom the fixed-bias is the go!

  • @cameronlesley2428
    @cameronlesley2428 Рік тому +1

    Hey atvyhe 3:15mark on the amp you can hear natural harmonica that sound killer. Well done

  • @carlcarrasco102
    @carlcarrasco102 16 днів тому +1

    Cool video! It might be helpful to know what plate dissipation of the cathode biased amp was? Was it set similarly to the fixed bias or was biased hot like a traditional cathode bias stage? In addition, the cathode bypass cap's value (if one was used) would have an effect too. How was implemented? The dissipation set to a similar level and larger cathode bypass cap would likely sound more similar. In addition, the loss of the plate voltage on the cathode would slightly reduce headroom so an amp made specifically for cathode bypass might use a higher Va voltage to compensate.

    • @beareamps
      @beareamps  22 години тому +1

      @@carlcarrasco102 You make interesting points Carl! The cathode-biased amp is biased hot with a large cap. Your point about the voltage difference would be a significant factor.

    • @carlcarrasco102
      @carlcarrasco102 18 годин тому

      @@beareamps I've experimented with different bias levels and cap value for cathode bias in my amp line up (Carl's Custom Amps) but haven't done a head to head comparison like this. Generally, I've found a larger cap and cooler bias to be firmer sounding. I really should make one with switchable bias.... That's fine sounding amp you've got there. Keep up the good work!

  • @DMSProduktions
    @DMSProduktions 6 місяців тому +2

    BOTH sounded good, I thought the fixed bias amp had better attack, the cathode biased was a bit softer in the attack!
    (Assuming you put the SAME Lorantz speakers in both! )
    \m/

  • @Jonathan_Doe_
    @Jonathan_Doe_ Рік тому +1

    Now try a chain of LEDs for cathode bias, instead of the usual resistor/caps method. Be interesting to see if the claims of it being quieter/more like fixed bias due to LED’s having low resistance is actually audible or not.

    • @beareamps
      @beareamps  Рік тому

      Interesting! Can LEDs pass enough current for this application though?

  • @jimamsden
    @jimamsden Рік тому +1

    I thought the fix bias was a bit cleaner for longer, had slightly less sag, and a bit more overall punch, possibly because of slightly more power output from the same set of tubes. Do they both have the same negative feedback?

    • @beareamps
      @beareamps  Рік тому

      Completely agree. Yes - same negative feedback circuit on both.

  • @artysanmobile
    @artysanmobile 7 місяців тому

    Cathode bias is also fixed bias, implemented differently but accomplishing the same thing, and set-able just like grid bias. Each method can be designed to overload asymmetrically if desired. These amps sound great, by the way.

    • @hanswurst9120
      @hanswurst9120 7 місяців тому +1

      No, cathode bias is different in that the voltage at the cathode swings with the signal going through the power tube, meaning it varies by a lot under load. Fixed bias is called fixed because the bias voltage at the control grid is stable and independent from any signal through the tube. Of cource it is overlapped with the signal at the grid but here we are talking up to 40 volts DC and negligible AC as the signal.
      Sound-wise i am not too sure myself, even from own expierence. But with a power amp clipping, there is an audible difference between its bias types. Contrary to popular belief though, power amp clipping is rare or at least rarely the (single) source of overdrive in a non-master-volume tube amp.

    • @artysanmobile
      @artysanmobile 7 місяців тому

      @@hanswurst9120 You are correct. I completely misstated. I was referring to the load following the cathode. Brain fart! Sorry about that.
      Power stage nonlinearity has a big sonic effect and is usually the result of the power supply being swamped by tube dissipation. It is a different sound to anything the preamp tubes cause.

  • @noel3422
    @noel3422 10 місяців тому

    Actualy i think both have a good tone but the cathode bias topology has a different gain structure, so my next question would be are both amps biased at the same dissipation for the wattage expected from both amps, if not, the lower volume of the cathode biased would be expected.

    • @beareamps
      @beareamps  10 місяців тому

      Yes true! The fixed bias is 20 watts and cathode bias is 15 watts output power (not plate dissipation) which is about as much as you can get from a pair of cathode-biased 6V6.

    • @noel3422
      @noel3422 10 місяців тому

      @@beareamps you stuck on the 70% bias thing, I'm not, but nothing you said was wrong just not too many people have built, tested and rebuilt too many amps, sometimes you just have to sacrifice a few tubes to get where you want to go instead of worrying about replacing tubes.

    • @beareamps
      @beareamps  10 місяців тому

      @@noel3422 the cathode-biased amp is biased to 100% plate dissipation and the fixed-bias to around 70%. I haven't found biasing hotter than 70% (fixed-bias) to yield sonic benefit whereas reliability and longevity are of utmost importance to me.

  • @delatronics3257
    @delatronics3257 Рік тому +1

    Not sure what you mean; cathode fixed to earth or cathode adjustable?

    • @beareamps
      @beareamps  Рік тому +2

      The terminology used in biasing schemes is super confusing.
      Cathode-bias is also known as “self-biasing” and involves the bias being created by a voltage drop across a cathode resistor.
      Fixed-bias (which is the one where you actually need to adjust it!) has the cathode grounded and a bias voltage is applied to the grid.
      The name “fixed-bias” comes from the bias voltage being constant regardless how much current is flowing through the tube. In cathode-biasing the bias voltage varies depending on the amount of current flowing through the cathode resistor.

  • @Zac.J
    @Zac.J 7 місяців тому

    Sounds great! What speakers are in that amp?

    • @beareamps
      @beareamps  7 місяців тому +1

      Cheers! Lorantz 50W “P” model ceramic. Great Australian speaker company!

    • @Zac.J
      @Zac.J 7 місяців тому

      @@beareamps Yeah right! Didn't know us Aussies could make such a good speaker!

    • @beareamps
      @beareamps  7 місяців тому +1

      @@Zac.J My fav speaker!! They do bass and PA models also.

    • @Zac.J
      @Zac.J 7 місяців тому

      Yeah right! Might have to check them out. What would you compare them to, tone wise?

    • @Zac.J
      @Zac.J 7 місяців тому +1

      I only have experience with celestions and a WGS G12c

  • @cameronlesley2428
    @cameronlesley2428 Рік тому

    Strait out of the gate the cathode bias sounds hotter then the fixed.
    Does this mean the benefit of fixed bias is you can just put
    New tubes without the need to bias your amp each time? And can you make a cathode bias fixed?

    • @beareamps
      @beareamps  Рік тому

      Other way around - cathode biasing is “self-biasing”. With fixed bias the bias needs to be adjusted each time the tubes are changed - very confusing.

    • @beareamps
      @beareamps  Рік тому

      A cathode-biased amp can be converted to fixed bias and vice versa.

  • @oficinadomarcheto
    @oficinadomarcheto 6 місяців тому

    Cathode bias pulse jumping punch with faster low end decay, only all tube cathode bias can be this magic, im sorrow covert my tiny terror to estabilized cathode bias like as fixed ( fixed tension cathode)

  • @richardnacamuli7498
    @richardnacamuli7498 Рік тому

    Couldn't tell much difference. I think the cathode bias broke up a little earlier than the fixed bias.

    • @beareamps
      @beareamps  Рік тому

      Yes the differences are subtle! You're right about the breakup 👍

  • @jupitermoongauge4055
    @jupitermoongauge4055 Рік тому

    Fixed bias is way more punchy