Output Transformers

Discussion in 'DIY' started by MoatsArt, Oct 10, 2015.

  1. purr1n

    purr1n Desire for betterer is endless.

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    Just consider my observations that driving the HD800 or HD6x0 via transformers where the secondaries are floating (aren't tied to ground) as better sounding (particularly in staging, separation, localization) than when the secondaries have a common ground as pure BS audiophoolery on my part. You can choose to believe it, not believe it, submit yourself to blind test, or not. There are lots of things in audio where I don't see it making a difference (e.g., Wyrd, Regen, etc.), but they do.
     
    Last edited: Oct 13, 2015
  2. dsavitsk

    dsavitsk Friend

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    I am not sure I follow the logic. Can you explain?


    I think you'd need to blind test this to convince me as I see no theoretical argument in favor of it.


    Fair enough.


    Yes and no. Yes if the parafeed OPT has the same inductance. But the practicalities of making a parafeed transformer are that the inductance is a lot higher. The T3 nickel OPTs are rated at 10K, but they actually have a primary inductance of about 120H which works out to more like 15K at 20Hz. That will allow them to be used with 50 Ohm phones on the 32 Ohm tap without penalty. And we have driven them with a 10K impedance and performance was basically as good as with a 0R source.

    With choke loaded parafeed, there are lots of variables here and it is probably too hard to generalize. But I'll do so anyway :) the Z driving the OPT is the load and the plate in parallel. If you run your OPT at a high impedance than it is capable of, you will lose bass. The big variable here is that parafeed creates bass resonances which may counteract this in odd ways, particularly with a choke involved.
     
    Last edited: Oct 13, 2015
  3. purr1n

    purr1n Desire for betterer is endless.

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    Well, let's consider an extremely unlikely hypothetical transformer failure (keep in mind the risk of this scenario is 108x lower than someone shoving his hand through a tube) where the primary winding breaks and part of that winding near B+ inexplicably ends up fusing with one of the wires of the secondary and the other leg of the secondary is grounded and my cat licked the exposed leads from the cable that was dislodged from the HD650. In this case, you could argue that if the secondaries were floating, the cat has less of a chance of death.

    BTW, it's my understanding all this stuff on grounding or floating the secondaries resulted in a medium rare tenderized horse steak many years ago on some other forum.
     
    Last edited: Oct 13, 2015
  4. OJneg

    OJneg The Most Insufferable

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    I think that floating the load could have some theoretical benefits. Along the same lines as any other balanced transmission, the ground path is completely removed from the equation
     
  5. zerodeefex

    zerodeefex SBAF's Imelda Marcos

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    Did you join to troll?

    Let's assume you didn't, why does the BA balanced sound better than the SE out?
     
    Last edited: Oct 14, 2015
  6. 2359Glenn

    2359Glenn MOT: 2359glenn | studio

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    No troll
    Just my opinion
    And technically no benefit
    Maybe it is something in the output of the BA
     
  7. purr1n

    purr1n Desire for betterer is endless.

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    2359Glenn: we are a fairly tight community where members know each other well, oftentimes in real life. What zerodeefex is getting at is that it's customary for new members to read the guidelines, introduce themselves, and first get a sense of the community before blessing us with their truths in their very first posts.
     
    Last edited: Oct 14, 2015
  8. ultrabike

    ultrabike Measurbator - Admin

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    I'm trying to get my head around this.

    I guess w electrostats the bias could be considered a ground and therefore you have +/- drive there where the + and the - carry signal only and have the benefits of common mode rejection.

    But even w/o the ground, for the planar and dynamic cases, wouldn't driving the headphone with signal carrying +/- give you common mode rejection? Isn't this differential drive w the benefits of balanced drive?
     
    Last edited: Oct 14, 2015
  9. purr1n

    purr1n Desire for betterer is endless.

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    The standard thinking is that common mode rejection a la balanced lines is of no use in home environments and more suited to studio environments to reduce noise and hum. However, the world is different today with cell phones, computers, WiFi, dimmers, LED and CFL ballasts, switching power supplies, Ethernet through AC, and all sorts of crap inside the home. Heck, I've found that gear measurements using the differential probes to the QA400 (even from SE sources) yielded much less spurious signals (many in the audio band) compared to the SE probes.
     
  10. ultrabike

    ultrabike Measurbator - Admin

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    Tell me about it. My Focusrite 2i2 kicks some ass differential over short runs. Not so SE.

    This may not be due to just external noise (which may be a concern), but from internal noise of the driving unit were some compromises may have to be made for this or that reason.

    Many driving units for dynamic cans are USB powered, w/o all the benefits of a super clean power supply, like in the case of some stat amps.
     
    Last edited: Oct 14, 2015
  11. 2359Glenn

    2359Glenn MOT: 2359glenn | studio

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    I didn't realize there were guidelines
    Didn't bash any person or product.
    As a amp builder I am a technical type person and like to know the reason behind what sounds better.
    To say something and get attacked by 2 staff members is a bit much.
    I think I am done here
     
    Last edited: Oct 14, 2015
  12. ultrabike

    ultrabike Measurbator - Admin

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    Well. What are u waiting for. Introduce yourself in the Intro thread :)

    (Then please express your thoughts about this stuff, cuz I still don't see how differential drive w/o the ground fails at common mode rejection. And no, I dunno everything and my question is honest)
     
  13. peef

    peef Friend

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    I haven't had the opportunity to finish reading it yet, but Bruno Putzeys recently (?) published an article on grounding that goes in depth about balanced/differential signal transmission that seems pretty relevant to the discussion. Here's a link.
     
  14. purr1n

    purr1n Desire for betterer is endless.

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    Well, I guess it's too late for me to apologize.

    A huge difficulty with electronic communication is being able to effectively convey and understand tone or body language. In this regard, we interpreted your posts as dismissive rather than inquisitive, particularly since your very first posts were voiced as a disagreements. In our experience of running the predecessor forum for a number of years, we've had poor experiences with new members who immediately started to post disagreements right off the bat. I am not saying that you are one of those kinds of people, but rather that we may have jumped the gun. Exacerbating the situation was that your posting style wasn't conversational, but in the form of concise sentences, sometimes without punctuation, and without paragraph development. This is not a attack against you, but it rather highlights our own difficulties in being to able understand what you may have been trying to convey. The members here all have their idiosyncrasies in how they communicate; and over time, we have learned to be able to understand each other in terms of tone.

    These are the reasons we have people first introduce themselves: to allow us to learn each other's our mannerisms and posting styles over time - and to avoid this very situation. This familiarity among the members is what allows the people here to have differences of opinion (sometimes very major differences) and still get along. One thing that I did not realize (in our haste to get this new site up and running) is that we did not make explicit the usual disclaimers from the predecessor site about first reading the guidelines, making a proper self introduction, and understanding its core beliefs. This was definitely our fault and I apologize for this.
     
    Last edited: Oct 15, 2015
  15. Cspirou

    Cspirou They call me Sparky

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    Decided to resurrect this thread because I was rereading my old post and I have another question about this. Although maybe this is more appropriate in the Torpedo III thread but I felt like I'd be hijacking the thread.

    The argument that you are throwing away a lot of signal and then reamplifying makes a lot of sense to me. However I was just reading the specs to the Torpedo III, which has a high and low gain switch, and the 32 ohm tap has an output of 1.3W. This translates to 6.45Vrms on a 32 ohm load which is greater then the 5.7Vrms that you mentioned is a problem with Grados. Which leads me to believe that you would have the same problems with gain in the Torpedo III as you would with the hypothetical amp configuration I was talking about.

    I haven't heard the Torpedo III but it was my assumption that it's fine with Grados. Is Torpedo III not meant to drive sensitive low impedance headphones? If Grados are in fact fine, then how does the Torpedo III get around the problem of added gain causing noise and distortion?
     
  16. dsavitsk

    dsavitsk Friend

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    The T3 has a low and high impedance switch, not a gain switch. It is designed based on the somewhat old fashioned notion that Grado and Sennheiser phones are both about the same efficiency, but that they have different impedances. Since transformers preserve power, they will output the same power (e.g., 100mW) on the high setting into a 300R impedance, and on the low setting into a 32R impedance, and the volume will remain the same. What will change is the voltage and current draw, but they will change proportionally to be the same power.

    In the earlier discussion, there was an interest in using the same circuit for speakers and phones. In that case, comparing the output necessary for the hugely less efficient speakers made sense. Here. there is no sense that a T3 can power speakers. I am not sure where the 1.3W figure comes from (I don't think you are going to get that much power from the amp for a variety of reasons), but it is a bit of a red herring.

    What matters here is likely the distinction between gain and output power, two distinct notions that are often conflated. For instance, one can conceive of an amplifier that can output many watts of power, but which has no gain. Similarly, one can conceive of an amp that has lots of gain, but very little power. Even if the output stage was up to the task of putting out 1.3W and the OPTs could handle that, the amp is gain limited. The gain is set at 6dB (~2x) for low impedance phones. The consumer audio line level is supposed to be -10dBV (0.316Vrms) so you should, with a reasonable source, never be able to get to such a high volume. I recognize that almost no sources adhere to this standard, but even so, very few of them output 3.2Vrms either.

    I might note that this is (at least part of) the reason people think the T3 can't dive some of the other Low Z phones out there. It is not necessarily the limited power output, but rather the limited gain. For those for whom this is an issue, you can actually do some rewiring of the OPT to run the primary from a center tap which provides a lower stepdown. It requires some trace cutting on the PCB, so I don't recommend it unless you really know what you are doing, but it can be done. You can also use a preamp before it for a little bit of extra gain.
     
  17. Cspirou

    Cspirou They call me Sparky

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    You are correct that it is an impedance switch. I am used to other amps having a gain switch to change the amount of feedback for SS amps to power high impedance headphones, so I said it was a gain switch for the T3. The figure comes straight from the beezar.com page for the Torpedo III,

    http://www.beezar.com/catalog/product_info.php?products_id=166

    It says that 300r has an output up to 1.4w and 32r is 1.3w. If this is wrong then I think you should tell them to correct it.
     
  18. dsavitsk

    dsavitsk Friend

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    I am not sure where those numbers came from - I'll get them changed. The output power of the circuit is actually more like 200 - 250mW. The output stage can swing considerably more voltage than that, but it is current limited to swinging a little over 50Vrms into the transformers and would thus clip if pushed. And the OPTs would distort much past that anyway.
     
  19. Besnia

    Besnia Facebook Friend

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    I second that. Don't have any Grados, but I it's certainly not a headphone dependent phenomenon. I've tried it on my speakers amps and the speakers shift towards Low Fi performance, if the secondary is grounded.
     
    Last edited: Sep 8, 2016
  20. TomB

    TomB MOT: Beezar

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    Ugh. I just found this thread. Doug told me a while back I had made a mistake and got me to change it. So yeah - it was my fault. He had told me the current and voltage the circuit would swing, but I went ahead and multiplied to get a product (power) without realizing he was giving me peak-to-peak, not RMS. :(
     

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