Better than SET? The radically different 535SE Headphone Amplifier/Preamplifier

Discussion in 'General Vendor Product Announcements' started by liamstrain, Jun 2, 2016.

  1. liamstrain

    liamstrain MOT: The Audio Guild

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    [​IMG]

    Some five years ago, The Audio Guild set out on a mission to see if we could not only capture the magical experience of the classic single-ended triode (SET) vacuum tube amplifier, but to actually improve upon it. And more to the challenge, to do it without the use of a single vacuum tube. This quest led to some very out of the box thinking and resulted in a radically different approach to single-ended amplification; a passive/active hybrid amplifier circuit that retains both the extreme simplicity and single-ended nature of the classic SET amp, but without the inherent limitations that prevent the classic SET amp from advancing the single-ended experience.

    The Audio Guild is pleased to announce that final development of the 535SE is complete and we are currently in the process of funding a couple of pre-production amplifiers for auditioning before moving on to a first production run. Our current estimate for retail pricing is $1,750US.

    • Exclusive passive/active hybrid amplifier circuit
    • Studio-grade input transformers provide ultra quiet, low-distortion signal amplification, ground isolation and high common mode rejection (CMR)
    • Single-ended JFET/bipolar output stage provides low impedance, high current output
    • Zero global feedback
    • Gain: 14dB
    • Maximum output: 14 volts peak/250mA
    • Output Impedance: 1 Ohm
    • THD+N: 0.05%
    • Three inputs, preamplifier output
    • Telecom-grade headphone jack with integral switching of preamplifier output
    • Solid wood case
    • Engraved Traffolyte front panel
    • Bakelite knobs
    • 14" W x 7" H x 7.75" D
    • Made in the USA

    To read the complete story behind the 535's development, please visit www.theaudioguild.com/the-journal/electro-magnetic-amplifier-co-model-535se-headphone-amplifierpreamplifier
     
    Last edited: Aug 6, 2016
    anetode, m.i.c.k.e.y, sfoclt and 7 others like this.

  2. scootermafia

    scootermafia MOIST - Double Helix Cables

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    I'm marked down for one...
     
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  3. bazelio

    bazelio Friend

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    Hmm. Interesting. Could you expand on some of the claims/statements.... Such as:

    without the inherent limitations that prevent the classic SET amp from advancing the single-ended experience.

    I don't know what that means.
     
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  4. dubiousmike

    dubiousmike Friend

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    My interest was piqued when Steve mentioned the development of this amp quite a while ago - congrats to the Audio Guild on bringing it to market! I look forward to hearing it and really enjoyed reading the thoughtful explanation you all provided on your site.
     
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  5. liamstrain

    liamstrain MOT: The Audio Guild

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    Great question @bazelio

    The drawbacks are spoken of in the article, namely asking the active device to provide all of the power (i.e. both voltage and current gain) and the necessity of a steel, air-gapped output transformer. Both the active and passive devices are not being called on to do what it is that they do best. The tube isn't as linear as it would be as only a voltage gain device and the transformer isn't as linear as it would be without an air gap and better laminations.

    So this design makes better use of the respective strengths of the components, offering better performance than the traditional SET configuration resulting in less distortion.

    The fundamental change in the design from a regular SET is that we chose a transformer for the voltage gain because it is less noisy and more linear than a tube (it also provides ground isolation and high common-mode rejection). That leaves the transistors to do what they do best on the output stage.
     
    Last edited: Jun 2, 2016
  6. dllmsch

    dllmsch Friend

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    I can smell confusion between this and SE535.
     
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  7. Serious

    Serious Friend

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    To prevent confusion:
    535SESE535SE535SE.png
    (comic sans and shitty res pics on purpose)
     
  8. chakku

    chakku Friend

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    What happens when you plug the SE 535 SE into the 535 SE?
     
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  9. bazelio

    bazelio Friend

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    That works fine. But absolutely do not try plugging the 535 SE in to the SE 535 SE.
     
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  10. johnjen

    johnjen Friend

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    It's good to see this design concept come to fruition. :thumb

    JJ
     
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  11. bazelio

    bazelio Friend

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    Non-linearity can be corrected for with feedback, though. Feedback isn't always a bad thing, but if any device is run to its edge of saturation, you are going to have issues of course. I guess this design is supposed to divide it up better using the transformer. Fine. But it doesn't seem like a terribly strong argument for the design being a notable improvement over SET. I mean, the principal is sound, I think ... but I don't know why you're dismissing other solutions or claiming this to be better. Darlington pairs are pretty ordinary, as is the fact that JFETs have high input impedance and low input current. If you're trying to achieve a SET-sound without high voltage ... Ok, neat. But why? It does seem convenient to relate this to a much beloved SET design as it'll certainly be eye-catching in audiohpile fora, of course.... But, at least for me, I'm not seeing any real relationship.

    Anyhow, thanks for being open to inquiry here.
     
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  12. liamstrain

    liamstrain MOT: The Audio Guild

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    Thanks all for the kind words and the interesting discussion!

    The 535SE SE535 thing (something we totally overlooked, but I don't think we'll lose sleep over) makes me think of the worst Mad Max Thunderdome followup - the PALINDROME! Two go in...two come out, but their order is reversed. Boring. :/

    @bazelio - I have to admit, I'm out of my depth here - so I shared your post with Steve, who designed the circuit, for his thoughts. So with that brief preamble, here is his response:

    --

    No, feedback isn't always a bad thing, but why use it after the fact as a "corrective" measure when you can achieve far greater inherent linearity using a more appropriate device for the job? It's like the recording engineer's "That's ok, we'll fix it in the mix" instead of getting right in the first place.

    In the case of the classic SET amp you don't really have the luxury of using much feedback. As was mentioned in the article, the price paid for the output transformer is voltage gain which is lost as a function of the transformer's turns ratio. So even before any feedback is applied, the vacuum tube has to muster an excess of voltage gain in order to overcome the loss of voltage gain in the transformer so at the end of the day there's enough gain left at the output to be useful. The application of feedback would require even more excess gain on the part of the vacuum tube in order to achieve the same output level before any feedback was applied.

    And since you will have so little gain to give up in order to apply feedback, you will only be able to apply relatively little feedback which can actually leave you worse off than if you applied none.

    Let's say you have a circuit that is producing a significant amount of distortion, but it is low order. Because of the masking phenomenon it will be somewhat benign. And as you apply feedback, it will lower those low order distortions at the expense of creating higher order distortion, which we are more sensitive to. As Bruno Putzeys put it so succinctly, if you're going to use feedback, use a LOT of it. Because as you use more, you can eventually bring all of the distortion products down to insignificant levels.

    In the classic SET amp, you don't have a LOT of excess gain in order to be able to apply a LOT of feedback.

    But what we can do instead is use a device that has sufficient voltage gain, is quieter than most any specialty low-noise JFET input stage you care to name (even John Curl's), and is extremely linear without the application of after the fact "corrective" feedback.

    Yes, Darlington pairs are pretty ordinary, but I'm not aware of any Darlington pairs that use JFETs as the driving device. At least not in any commercial amplifier circuit that I am aware of, where they are all bipolar Darlington pairs. And it was this unique pairing that allowed us to have the input transformer directly drive the output stage without either having any bipolar transistor base current flowing in the transformer's secondary or resorting to capacitively coupling the two.

    We wanted to create an extremely simple, single-ended amplifier that was "right" from the start, without the need for applying any "corrective" measures after the fact.

    Those who designed the original SET amplifiers were limited to what they had to work with, which was triode vacuum tubes and transformers. But today we have modern transistors to work with as well. So why not use them where they can work best? I don't think those who designed the first SET amplifiers would be content to use only the tools they had to work with at the time if new tools became available and I'd to think this amplifier in its own small way pays tribute to those who came before us.
     
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  13. Armaegis

    Armaegis Friend

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    Haven't a few of the ECP designs been a transformer gain stage with current buffer afterwards?
     
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  14. liamstrain

    liamstrain MOT: The Audio Guild

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    Hey there @Armaegis, another forum name I recognize...I love the ECP amps. I know more about the L-2 and Torpedo Parafeed amps. But yes, as far as I can tell, Doug has similar goals for his amps - and his DSHA-1 solid state is a parallel idea to our 535SE. I'll see if Steve has any insight into salient differences.
     
    Last edited: Jun 2, 2016
  15. liamstrain

    liamstrain MOT: The Audio Guild

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    From Steve:

    Yes, Doug and I have trod parallel paths regarding the same basic concept of passive voltage gain and active current gain but have chosen different implementations. Doug's designs have been push/pull with much more complicated circuit implementations. The DSHA-1 uses an input transformer, a differential push/pull MOSFET active buffer and an output transformer. The Black Diamond sandwiches the transformer between two complementary push/pull diamond buffers. I have stuck to refining the simplest single-ended circuit.

    --

    I hope that answers the question @Armaegis. Thanks for bringing it up.
     
  16. bazelio

    bazelio Friend

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    There's a beauty in the simplicity of the design for sure. And I guess that's where you're "paying tribute" because the classic SET design itself is pretty minimalist. But the "better than SET" mantra can arguably be applied to push pull designs as well as simplistic approaches that will fit inside an Altoids tin. And yet SET amps maintain a cult following ... for a different reason. I'm very curious where this design will fit in subjectively.

    By the way, who is "Steve"? I know of a Steve from SAS, a Steve from Decware... Sorry, I am not sure who this particular Steve is?
     
    Last edited: Jun 3, 2016
  17. liamstrain

    liamstrain MOT: The Audio Guild

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    We did put a question mark at the end of the statement. :)

    We think it is better than SET - while still very much harkening to it (in sound and philosophy), but ultimately, it is the listener who will have to make that call for themselves. We can't wait to get production units out there.

    We are working on the mechanical drawings to get the chassis built, and faceplate engraved today. Moving forward on schedule!

    He is just zis guy, you know?... (eh, ok, he's not Zaphod Beeblebrox) - He is Steve Eddy
     
    Last edited: Jun 3, 2016
  18. zerodeefex

    zerodeefex Unpaid LH Labs volunteer - Admin

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    This looks super interesting!

    I'm glad someone asked the ECP Doug question since I thought the DHSA1 was doing something similar but it's good to get a real explanation :)

    Do you guys have measurements on the step up transformers you're using at different voltage levels like cinemag or jensen put out? Super curious about how you avoid distortion when using step up transformers.
     
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  19. Armaegis

    Armaegis Friend

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    So Doug's stuff is sort-of-not-really balanced versions of this topology. I'm curious what else is on the drawing board :cool:
     
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  20. liamstrain

    liamstrain MOT: The Audio Guild

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    Thanks, @zerodeefex - Steve and Doug are no strangers. It was Steve who did the mechanical drawings for the DSHA-1's metal chassis.

    As for the transformer measurements, you can find them here: http://cinemag.biz/mic_input/PDF/CMMI-5C.pdf
     

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