Single-ended amps vs. push-pull amps

Discussion in 'Amps and Cabs' started by LHakim, May 24, 2005.


  1. LHakim

    LHakim Member

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    With all the quality single-ended single output tube amps available now (Cornford, Univalve, Mini-Z, Victoria Regal, etc. etc.) I was wondering if these newer single-ended designs give up anything to a push-pull circuit (using identical output tubes) in terms of richness, fullness, complexity and "feel".

    My own experiences with S.E. amps are limited to BF Champs/Vibrochamps, and the Crate VC508, and IMHO those amps are thin sounding and not that smooth or rich compared to dual el-84/6V6 circuits although I'm sure the smaller cabs and speakers play a big role in that.

    Anyways I'm once again thinking of getting an S.E. amp (for lower volume reasons) and would welcome everyone's opinions, observations and experiences on this topic.

    Thanks,
    Larry
     
  2. tedwoods

    tedwoods Member

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    I've had a few single ended amps in my life and I can tell you that a good single ended amp in a proper cab has all the richness in the world and superb midrange detail and response to boot.
    Single ended amps may actually fall short on only two areas:
    1.Noise levels can be higher(but that's not a rule...)

    2.Because most designs that are around are usually of the low power variety,there may be a sense of lack of punch and presence which is ofcourse balanced by their sheer detail retrieval.

    Since there are many models floating around( apart from those mentioned there's also Siegmund,Auble,BadCat,Star,Savage...to name but a few)try to see which one is closer to the tone you crave.

    Ted
     
  3. John Phillips

    John Phillips Member

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    IMO there is a quite a big difference in the way they sound and respond, and I find it odd that there are no (or very, very few - none that I know of anyway) low-wattage Class AB push-pull amps - especially with fixed bias.

    Personally, I find fixed-bias Class AB amps have a bigger, tighter, more controlled but also more open tone. Single-endeds can get quite soft and saturated. Cathode-biased Class ABs have a characteristic compression and 'bloom' which is distinct from either type - and from cathode-biased Class A, for that matter.

    Yes, I know we're supposed to think that Class A is better :rolleyes:... but if you think about it, since almost every single classic guitar amp used on the great recordings of the past is a Class AB push-pull (no matter that it may be wrongly called Class A), and many if not most are fixed-bias, it puzzles me why no-one has followed this through to its logical conclusion...
     
  4. tedwoods

    tedwoods Member

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    Propably, because there are no suitable current production tubes(pentodes) to use in a lower powered class A/B amp...
    Maybe the ECL82 but it's abit uncommon.
    Come to think of it,not even small output triodes were used like the ECC99(a E182CC,5687 variant)...
    Designers are afraid to experiment or what?

    Ted
     
  5. The Whiz

    The Whiz Member

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    I believe the zvex nano is push pull. It's power tube is a dual pentode or dual triode, I think. Cathode bias I assume. I may be wrong.

    taco
     
  6. riffmeister

    riffmeister Gold Supporting Member

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    Aside from power, nothing is given up in terms of richness etc.



    Carr Merc
    Siegmund Midnight Special

    are two particularly nice sounding examples.
     
  7. erksin

    erksin Member

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    Cathode-biased ABs are my favorite amps for just that reason - I think you nailed the description, John...

    For low volume playing, I think they're the perfect solution.
     
  8. TRIODEROB

    TRIODEROB Senior Member

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    the single ended screamers are very nice and
    i HAVE PLAYED A TON OF THEM.

    but-

    GIVE ME A TWEED DELUXE PUSH PULL 6V6 CLONE ANY DAY!
     
  9. LHakim

    LHakim Member

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    Thanks for the responses so far. It seems that most of the SE circuits are cathode-biased. Some amp builder (maybe Marc Auble?) has an SE design with single output tube thats fixed bias. I wonder how much of a difference that would make in the tone and response of an SE amp?

    My own experience with vintage 6V6 cathode-biased AB push-pull amps is that they are alot of fun to play alone but in a band situation become "all midrange" and just don't cut through that well on stage, and its not a volume issue either.

    One benefit that makers of SE amps claim is the ability to cut through the mix more effectively. I found that to be true of my old Vibrochamp, but it still (to my ears at least) came at the expense of "girth", even when played through 2X10 speakers.
     
  10. John Phillips

    John Phillips Member

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    No reason you can't just use EL84s, you don't have to use all the available power capacity of a tube.

    Or, you could use a "preamp" tube as a power tube - either two of them (each tube in parallel) or one using both halves in push-pull - that would be a good application for a matched dual triode ;).
    No, it's single-ended. I'm not sure if the tube (it's a dual triode) is used in parallel, or whether only one half of it is the power stage and the other is the driver. I talked to Zachary about it a while ago, but I forgot which...
     
  11. loverocker

    loverocker Member

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    I'd have to agree with John - there's something about push-pull.

    It's normally hard to tell, because when you compare this PP amp to that SE amp, there are just too many other variables. But if you get to spend some time playing an amp with a SE-PP dial (e.g. Kevin O'Connor's London Power Studio), the difference is night and day. IMHO it's far more obvious than switching from cathode to fixed bias or pentode/triode mode (both of which KOC's Studio amp also has).

    To my ears, PP sounds significantly thicker than SE.
     
  12. riverastoasters

    riverastoasters Member

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    Isn't part of the problem that it's more complex to make an AB circuit than a simple single ended stage? And then how do you justify the cost when people are used to paying more for bigger amps. I think the recent trend in guitar player thinking might create a market for a low power AB amp though.

    Here's a thought, why not just make a little class AB output stage. Almost everyone has amps and/or preamps already. Then people could take the preamp out of their amp and get a lot powered output stage for when that mood strikes.

    There is the question of whether an AB output stage can be low power with the usual sort of tubes operating in the usual range. If you run EL34s hot enough to get some nonlinearity then aren't you developing a good deal of power? In which case what do you do with the power you need to get rid of?

    If you change to little bitty tubes then do they end up with desirable distortion characteristics?

    This might be one place where the Pritchard type idea has a lot of advantages.
     
  13. drbob1

    drbob1 Silver Supporting Member

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    Two comments:

    1. No question SE sounds different than PP. It's hard to characterize, but more compression, less "thump" leap to mind. That said, my Emery is one of my favorite amps.

    2. There are at least two companies currently making low output, class AB, push-pull designs. I've promised never to mention them in the same post again, so I'll talk about the other one today. London Power has a fairly low tech way of separating the voltage used for bias and heaters from the B+, which results in the ability to run the power of the amp down to almost nothing. Of course, Fletcher Munson means that it sounds pretty anemic there, but at 1-5w range it's a rocking amp. He also has reconfigurable power amp topology (individual tube bias, SE-PP continuously variable knob to allow wildy asymmetric waveforms, class A/AB, impedance match/mismatch) so you can go from super clean and punchy to spongy and compressed with a few flips and twists. There's a lot more technology in there than the Emery, so the character of the tubes isn't quite as naked, but they're great sounding amps and not super expensive if you ever find one use (or new for that matter).
     
  14. Scumback Speakers

    Scumback Speakers Gold Supporting Member

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    Not sure what the best low wattage (under 20 watts) push/pull (PP) amp there is, but in side by side tests against a Blockhead 18 watt amp, the entry level Scumbag has a bigger bottom end, more gain, and slightly more volume when dimed. If I remember right, the 18 watt is a cathode biased push pull design, correct me if I'm wrong on that.

    I realize that some single ended amps may be designed differently however, and my amp uses a preamp section with more lows/low mids than a stock single ended Class A Gibson Gibsonette GA-8 amp (which mine evolved from). Also, I favor the JJ 6V6, which several folks say is a mini 6L6 tube, and it does seem to produce about 25% more power than older NOS 6V6 tubes, too.

    Typically, as you turn a single ended amp up to over 1/2 power, it's tone signature gets fatter, or at least that's been my experience with them. I usually run mine around 6 for cleans and 9 for crunch (out of 11) on the volume dial for clean to crunch tones (this assumes a dual channel amp with an ABY box). I also use two speakers, a 55 and 75 combination, to achieve the widest tone response.
     
  15. hasserl

    hasserl Member

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    Well, there is the Carvin Vintage 16 which uses 2 EL84's in puch-pull arrangement & class AB, and also with fixed bias.

    Here's some clips of one after I did some minor modifications to it: http://www.geocities.com/rlhasse04/V16soundclips.html?1098587481692

    I just finished up another one of these the other day and I am just amazed at how good they sound. They definately get that 18 watt Marshall vibe going, but with a bit more gain.

    Besides that, don't know if you consider a Deluxe Reverb low pwer or not, but there's another one. The old Princeton Reverb was another.
     
  16. loverocker

    loverocker Member

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    I suspect the reason that there aren't many PP amps in the 1-5W bracket is that the extra complexity of a PP circuit makes their price seem unattractive to most guitarists. By the time you've done a 5W one you might as well have done an 18-20W one.

    Doug Hammond's Firefly project (over at www.ax84.com) is about as simple as PP gets. Real simple - there's no PI!

    One other thing - SE seems quite popular with the hi-fi crowd. Which may be why guitarists like it so much :)
     
  17. hasserl

    hasserl Member

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    Well the Carvin does have a Triode mode for which Carvin claims 5 watts, but that's still pretty loud to me.

    I have several SE amps in the 1.3 to 2.5 watt range, they are actually pretty loud too. You can crank them up, but you drive everyone else out of the room. And they are loud enough to bother the neighbors if you tried to use them in an apartment.

    And actually, I have an old Symphonic with two 50C5's in push-pull, that would be about 5 watts, but with cathode bias. That is another project that I've not had time to work on yet (planning on a self split design for that one). I think mfg's go with cathode bias because of the simplicity, no bias winding or circuit to deal with. Makes it easier and less expensive to produce.
     
  18. Phloored

    Phloored Member

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    London Power has a fairly low tech way of separating the voltage used for bias and heaters from the B+, which results in the ability to run the power of the amp down to almost nothing. Of course, Fletcher Munson means that it sounds pretty anemic there, but at 1-5w range it's a rocking amp. He also has reconfigurable power amp topology (individual tube bias, SE-PP continuously variable knob to allow wildy asymmetric waveforms, class A/AB, impedance match/mismatch) so you can go from super clean and punchy to spongy and compressed with a few flips and twists.

    Amen to that, and with a detuned cab, you can rock out at even lower levels and it sounds really good! PP is definatly punchier and fuller sounding.
     
  19. John Phillips

    John Phillips Member

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    Definitely! I had to make an attenuator for my Tweed Champ when I lived in the city :). The actual power you need for bedroom volume is around 100 milliwatts through a normal guitar speaker :eek:.

    Also definitely. I wonder if the market is changing a bit though - 'low wattage' amps aren't just cheap practice amps any more, for a lot of players they may be becoming more of a quest to get great tone at apartment volume regardless of cost... the cheap-practice-amp market has probably disappeared, for tube amps anyway. A fixed-bias circuit isn't a lot of work, if you do it like a Marshall 50 (drop resistor from the main HT secondary) - half a dozen parts, a couple of $ worth, maybe 10 minutes to assemble it.
     
  20. hasserl

    hasserl Member

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    I think you are right, there's no reason why low power has to mean cheap design and production. And I think there is a market for a well designed and built low power amp; though it may not be huge, it is certainly there.
     

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