AC vs DC Heaters & The Tonal Affect

Discussion in 'The Workbench' started by NewReligion, Mar 4, 2021.

  1. NewReligion

    NewReligion Well-Known Member Double Platinum Supporting Member VIP Member

    Joined:
    Nov 17, 2009
    Messages:
    11,498
    Likes Received:
    8,714
    Location:
    Paradise
    I am very interested in your opinions as both tech’s and guitarists.

    I clearly hear and feel a huge difference in the substitution/installation of DC heaters on preamp tubes vs AC heaters.

    I run a separate $10 6VAC or 12VAC transformer mounted inside the chassis. Rectify the VAC to VDC while raising the output DC voltage a couple bolts into the appropriate 7806/7812 voltage regulator (as the DC input should be a couple bolts higher than the voltage to be regulated) which is bolted down to the chassis as a heatsink.

    I experimented with several ways to skin this cat when a customer requests DC heaters.

    Personally I dislike DC heaters. It took two of my 4 stage high gain amps that I modded(Pandora’s). Both were very close in characteristic.

    After adding DC voltage to 5 stages (VX one side of added gain stage) original V1 a & b, V2 a & b cathode follower, it was clear that in my analog all tube builds DC heaters neutered the tone.

    It added some sizzle but lost low end. It made the amp sterile to the point the chords no longer bloomed and the lead lines became uncharacteristic of a great growling singing high gain amp. I brought about a feeling of playing through a toy to me.

    That is not to say it may not have its place in pre tone stack Fortin or Gower Kali ++ or Gainmonster type Jose clipper builds but for a dynamic crying singing blooming analog signal it is disappointing to my audiophile ears.

    I repeated this experiment multiple times with the same audio results IMO.

    Best Regards, David Hopkins

    EDIT: Video Comparison Demo AC vs DC Heaters on Identical circuits at 90db.

     
    Last edited: Mar 4, 2021
  2. JP2036

    JP2036 Well-Known Member

    Joined:
    Aug 7, 2020
    Messages:
    456
    Likes Received:
    476
    [​IMG]

    Personally don't think it matters or amps 50+ years ago would have had it.
    Lets say it did matter how would you measure the difference other than a human ear ?
    A heater meter ?
    Purely subjective preference like hair color & the car we drive.
    If there is tangible scientific data other than "sound" or "feel" im all ears.
     
  3. NewReligion

    NewReligion Well-Known Member Double Platinum Supporting Member VIP Member

    Joined:
    Nov 17, 2009
    Messages:
    11,498
    Likes Received:
    8,714
    Location:
    Paradise
    I absolutely agree that it is subjective as a guitarist, personal feelings, tastes, & ones opinion is what I asked for.

    I still have not replaced my oscilloscope though I suspect the waves would be similar to respond to your “all ears” scientific aspect.

    Building well tuned circuits is a craft beyond a set of mathematical equations.

    But then again it is the “all ears” part that sets builders apart as I have seen/heard work from some guys in which the amp functions properly but just sounds lifeless to me & other builders in the room.

    On the clean signals I prefer (subjectively) a Fender 6G3 Deluxe every time over a 1970’s Twin Reverb.

    When getting into high gain amps the circuit signal will certainly benefit or suffer “subjectively” by the component type & brand depending on where & how used.

    This is where the human ear becomes Primary & the scope becomes Secondary as it is this ability to choose and apply the subjective component types though equal in value can make a good amp sound better to the player.

    An example is SoZo caps vs Mallory 150’s as couplers & in the tone stack.

    I will use the Mallory 150’s or Sprague 715/716 every time before I use a Sozo.

    Which brings us back to subjective opinions again as this entire thread is subjective.

    I certainly “hear” the difference between DC vs AC heaters. When I converted one of my BE 100’s over to all AC heaters it now sounds much better. Then removing the 220k from the wiper of the treble pot to lug 3 of the master volume then the 1 Meg from lug 3 master volume to ground really opens up the amp but that is a modification in components and lay out.

    In summary, DC vs AC is subjective. I wanted to know who possessed the ability to hear and feel the difference both as a guitarist and technician between the two, then give their opinions.

    I thank you for your time & assessment.

    David
     
    Last edited: Mar 4, 2021
    JP2036 and Guitar-Rocker like this.
  4. JP2036

    JP2036 Well-Known Member

    Joined:
    Aug 7, 2020
    Messages:
    456
    Likes Received:
    476
    You make a good case.
    If DC heaters had a lower noise threshold & contributed to better tube tone overall it would be worth that alone IMO.
    And its true ears matter.
     
    NewReligion likes this.
  5. XTRXTR

    XTRXTR Active Member

    Joined:
    Feb 14, 2021
    Messages:
    133
    Likes Received:
    82
    I don't have any DC heater amps but was thinking of doing a mod.
    You are making the case that DC is less hum and noise. If that is true then SNR is better which means clean and distortion tones are better represented at the OT. That should be able to be heard easily. However you are also stating that it sounds bland which indicates to me that the amp, while SNR could be better, that it could also be THD worse aka more amplified odd harmonics or less amplified even harmonics. That can be measured by a scope and some calculations.

    So if none of those parameters are different then you might be interpreting the silence between notes or chords as sounding different and that is very real. If it really is that quiet. You could test that by recording some high quality files on various DC rectified amps versus VAC heater amps then blind test what you are hearing on the recording. Decibel meter the room in silence and then measure output of each amp to make sure Db levels are the same. Setup same mic without changing input levels on the recording device. Keeps all the lighting etc the same for all recordings. Do a close mic and a far mic, amp placement at same point in the room same direction of speakers etc. Your ear should flush out any differences easily enough listening to the recordings. Literally blindfold yourself and have someone playing the files in random order and taking down whether you think its DC or AC and see how you do.
     
    sloan_amps and NewReligion like this.
  6. NewReligion

    NewReligion Well-Known Member Double Platinum Supporting Member VIP Member

    Joined:
    Nov 17, 2009
    Messages:
    11,498
    Likes Received:
    8,714
    Location:
    Paradise
    Exactly. I have done this by & large just to ensure I am hearing what I believed to be. I am correct as I was gifted with great defined hearing.

    I plug into the DC heater amp and am totally uninspired & underwhelmed.

    Thanks for your input.

    I have seen no other thread anywhere on this point of view concerning this topic.

    David
     
  7. KraftyBob

    KraftyBob Well-Known Member Gold Supporting Member

    Joined:
    Sep 5, 2017
    Messages:
    1,883
    Likes Received:
    2,420
    Location:
    Chicago Suburbs - USA
    I'm not really understanding how the heaters are wired makes a difference in the tone? Aside from the noise that you can get from AC heaters, your just heating up the cathode. Or are you saying AC vs DC voltage heats the cathode differently, which could then affect the transfer of electrons to the plate?

    I'm currently working on a Peavey Valveking that has all DC heaters wired in series. It's certainly not a high level of amp compared to others out there, however, I would not describe the tone as sterile. In fact, I think it sounds pretty good for a $500 all tube amp.

    Having said all that, my DSL40C has DC heaters in V1, and the rest are AC. I suspect Marshall did this to minimize the noise at V1 since that's the critical preamp tube, but then why did they not just stick with DC for the rest of the tubes? There must be a reason they went with AC for the rest?
     
    NewReligion likes this.
  8. NewReligion

    NewReligion Well-Known Member Double Platinum Supporting Member VIP Member

    Joined:
    Nov 17, 2009
    Messages:
    11,498
    Likes Received:
    8,714
    Location:
    Paradise
    All very good points. With DC the signal appears to get a little more sizzle with less note definition. It is not in my head (forgive the pun). I noticed this a few years ago and just got around to doing a head to head comparison.

    DC heaters must be affecting the electrons passing through the grids somehow.

    I have to and will figure out this puzzling audio mystery.

    Neither amp was noisy to start with. I will go as fas as to say we know that less bass or more treble can be perceived as gain. This anomaly is occurring as well. The amp loses the punch in the low end it had and clarity in the signal but picks up more sizzle on the top side. Easier to play but uninspiring for me.

    No I am not having a Ken Fischer (Train Wreck) purple wire delusion lol.

    I came here searching for answers. It appears I will need to resolve it on my own.

    I know Cameron does not care for DC heaters. The only time I really see them used is as Friedman stated in mass production to assist in not having to worry about signal to noise ratio’s.

    My ears have never failed me.

    Thanks to all. I will find the reason to the quite discernible difference now that I know it exists.

    For those who say the difference is negligible, I reply tone is the some of all circuit assemblies & the hands of the player.

    Any opinions please keep them coming.

    In fact if any one is able to do the same experiment with two identical high gain amps that do not sound fizzy but smooth like Wizard, Friedman, Soldano etc... I would be very interested in your findings.

    In fact I would bet even with a single amp most would experience what I am calling attention to.

    My friend Shea (Monomyth Amplification) is coming over Saturday to run through our new discoveries & developments. We will to try this on his ears.

    Best to all. Never stop the creative process.

    David
     
    Last edited: Mar 4, 2021
    KraftyBob likes this.
  9. KraftyBob

    KraftyBob Well-Known Member Gold Supporting Member

    Joined:
    Sep 5, 2017
    Messages:
    1,883
    Likes Received:
    2,420
    Location:
    Chicago Suburbs - USA
    I'm looking forward to your results!
     
  10. thetragichero

    thetragichero Well-Known Member

    Joined:
    Jun 6, 2010
    Messages:
    3,202
    Likes Received:
    1,149
    Location:
    flo rida
    the thing between the ears influences hearing considerably more than how you're heating up the tubes. that's why there's a whole audiophool industry with expensive low oxygen copper power cables. guitarists often "hear" with their eyes, that's why yellow rolled film caps with fancy printing on them "sound" better than equivalent ones with just the pertinent values printed on em (there's also very little "ear memory" when switching things in amps)

    why do some amps only have the input tube with dc heaters or no tubes with dc heaters? cost. need about twice as much current per tube on the 6.3v winding (converting ac to dc has losses) so that requires a bigger winding on the transformer plus big filter capacitance (4700-10000uf or more). they only use when it's necessary
     
    sloan_amps, KraftyBob and NewReligion like this.
  11. NewReligion

    NewReligion Well-Known Member Double Platinum Supporting Member VIP Member

    Joined:
    Nov 17, 2009
    Messages:
    11,498
    Likes Received:
    8,714
    Location:
    Paradise
    Had you read the entire thread you would notice that I add an extra required transformer to rectify from AC to DC just for this purpose.

    This thread was not created as a platform for insult or debate. Either your ears can assist a tech to go beyond what the scopes display or not.

    I qualify that with the sets of ears like Peter Diezel, Mark Cameron, Jose Arredondo etc...

    Jose would add an extra transformer to the PT circuit on the early JCM 800 models due to the lower stock voltage. Jose liked the voltages closer to 500VDC to make his work satisfy expectations before release to the customers. Smart man with Golden Ears by and large).

    I do not hear with my eyes. My eyes never influence my hearing, that is absolutely out of the question as it would pertain to me. That is for inexperienced kids. I have been playing 50 years and building 12 years. I have qualified ears.

    I use both, sets of 4700uf and or a single 10,000uf to smooth the ripple depending on the type of DC set up.

    In fact I can notice how adding a relay switching/DC rectification board operating off of the AC heaters affects the amp.

    I was aware when I posted this there would be at least two camps of strong opinions some backed by science and others by refined ears, some by both. I fall in the later.

    Some can hear everything and others are less fortunate.

    I must admit I have not seen anyone post noticing a difference but then again it is a controlled experiment. As I said before my ears have always served me well. There is a distinct difference when used in the high gain capacity.

    Some deviations are subtle, others not. But in the end having a great ear can make all the difference between good results & great results.

    David
     
    Last edited: Mar 4, 2021
  12. _Steve

    _Steve Well-Known Member

    Joined:
    Apr 29, 2020
    Messages:
    391
    Likes Received:
    326
    Location:
    Los Angeles
    My theory here is you unloading the main PT's primary when you are running the DC heaters from the separate PT. This maybe changing the main PTs response. However I need to learn a bit more about the effect of DCR on PT primaries to be sure. I doubt the difference between AC and DC is changing anything. Heat is heat.
     
    sloan_amps and NewReligion like this.
  13. geddy

    geddy Active Member

    Joined:
    Nov 11, 2013
    Messages:
    176
    Likes Received:
    184
    The only way to evaluate differences objectively is to use suitable test equipment...such as a scope and spectrum analyzer. Subjective evaluation is well.... subjective. Test equipment will inform you why you think there's a difference and allow you to optimise your designs.
     
    sloan_amps likes this.
  14. thetragichero

    thetragichero Well-Known Member

    Joined:
    Jun 6, 2010
    Messages:
    3,202
    Likes Received:
    1,149
    Location:
    flo rida
    those who are convinced they harbor no unconscious biases are generally the ones most effected by them. most of hearing goes on in between the ears. there's nothing wrong with that, but understanding it is important. there's a reason why any reputable study is done double blind, so that they are not influenced by the subjects or observer. that's why i will often use my non-musician wife as a control group for things like op amp swaps in solid state devices because "this" or "that" is based off sound alone and not "mojo 4558d" vs "cheap tl062"
     
    sloan_amps, T wilcox and NewReligion like this.
  15. NewReligion

    NewReligion Well-Known Member Double Platinum Supporting Member VIP Member

    Joined:
    Nov 17, 2009
    Messages:
    11,498
    Likes Received:
    8,714
    Location:
    Paradise
    Great point. The character of the amp most certainly changes.

    I am surprised this has never came to attention before.

    Don't get me wrong the amp still sounds good but different. In fact some players may prefer it.

    My BE 100 dual Horizontal input #170 of 200 was all AC heaters. I preferred it over the 2014 I kept. I gave the other to my son for getting his Masters at Rose Hulman in Electrical Engineering Management.

    David
     
    Last edited: Mar 7, 2021
    Sustainium likes this.
  16. NewReligion

    NewReligion Well-Known Member Double Platinum Supporting Member VIP Member

    Joined:
    Nov 17, 2009
    Messages:
    11,498
    Likes Received:
    8,714
    Location:
    Paradise
    Agreed. My Fiancée has developed an ear over the last 8 years in my studio, live and is one of the final tests before I send an amp out. She was particularly amazed at the overhaul I did to the first Friedman Pink Taco 20. She she “No way all of that tone and volume is coming out of that little amp. So we had the wattage discussion. LOL, she loves this stuff.

    She hears the difference clearly.

    I am not blinded by science lol. I use a oscilloscope, decade boxes for resistors and capacitors in addition to signal generators, load boxes and specialized test equipment fabricated for me to trouble shoot where the signal is lost etc...

    In the end it is my my ears that make the final adjustments to tweak the amp to where it sits in the Goldilocks zone.

    It is the Customer however who has final approval.

    To each their own.

    David
     
    Last edited: Mar 4, 2021
  17. NewReligion

    NewReligion Well-Known Member Double Platinum Supporting Member VIP Member

    Joined:
    Nov 17, 2009
    Messages:
    11,498
    Likes Received:
    8,714
    Location:
    Paradise
    At this point it appears we are beating a dead horse.

    There are guys with formal training, guys with some training and guys with no training.

    Equipment is important but my ears are the most important tools I use.

    I will not throw names but I was surprised to find how many famous builders have no formal training and how little they use scopes etc...

    It all is important and leads us to where we want to be.

    I will discover why there is a character change when switching to an isolated transformer & rectification to DC heaters.

    Thank you all for the suggestions & places/ways to search.

    David
     
    Last edited: Mar 4, 2021
  18. Guitar-Rocker

    Guitar-Rocker Well-Known Member

    Joined:
    Mar 5, 2012
    Messages:
    2,917
    Likes Received:
    2,584
    Location:
    Estero, Florida formerly from Indianapolis
    While measuring devices have their place, I can attest that David has a great set of ears (hearing).

    And as Dylan said, “ you don’t need a weatherman to know which way the wind blows”,
     
    NewReligion likes this.
  19. NewReligion

    NewReligion Well-Known Member Double Platinum Supporting Member VIP Member

    Joined:
    Nov 17, 2009
    Messages:
    11,498
    Likes Received:
    8,714
    Location:
    Paradise
    Thank you Terry. Your opinion means more to me than any other. And thank you for all of the lessons & support over the last decade.

    Speaking of decade, the decade box you gave me is so important that I bought a second for resistance & one for capacitance.

    David
     
  20. XTRXTR

    XTRXTR Active Member

    Joined:
    Feb 14, 2021
    Messages:
    133
    Likes Received:
    82
    There are a lot of electrical differences to heat. The question is whether that transfers to SNR or THD and Freq Response. But imagine 60 cycles of 6.3VAC on electrons. The electrons respond at near light speeds even though the cycle or wave is hard to hear, the electron popped instantly anywhere between 0.1 to 3.15VAC and then may be attracted as soon as -0.1 to -3.15VAC. A perfect sine wave looks different than a 60 Hz ripple, 120Hz ripple, or a flat perfect DC. Each of those have some effect to the cathode - electrically. Can you hear it is the question.
     
    sloan_amps and NewReligion like this.

Share This Page