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Inspire IHA-1 tube headphone amp

Discussion in 'Headphone Amps (full-size)' started by burn1, Oct 18, 2014.
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  1. bazelio
    I guess X said it politely, but induced hum is a design flaw.  Nevertheless, what's the sensitivity of the phones you folks are using when you say it's nearly inaudible?
  2. BlakeT
    It is not a design flaw, it is a conscious design choice.
    From Dennis Had: 
    "The other slight back ground hum in the right channel is down over 78 dB from music playing.  It is more pronounced in the right channel because of the proximity of the right channel output transformer closeness to the power transformer.  A bit of old transformer theory at work ... a slight electrical field picked up from the power transformer.  I might mention on most tube headphone amplifiers without exception, at least the ones I am very familiar with use a resistor divider network in series with the output of the headphones.  Yes this is effective in bringing the noise level down but and here is the catch and advantage of the Inspire ... the signal does receive corruption in these divider resistors."
    Dennis views his design choice as the lesser of two evils.
  3. bazelio
    Shielding or additional spacing comes to mind.
    Bottom line: In my case, I'm very interested in this amp, but $1500 for some right channel hum is a bit hard to swallow and thus without first listening it's quite difficult to pull the trigger.  I doubt I'm alone.
  4. atubbs
    I'm totally sold on the theory that adding resistor dividers to clear out noise is a hack in this regard. I think that's bait and switch from Mr. Had, however. I disagree strongly that there is no design flaw.
    The signal to noise issue is orthogonal to the fact that the close proximity of the right channel output transformer and power transformer leads to noise being induced from one to the other and that there's "no way to fix it." Had seems to gloss over this with "wow you sure can hear well!!!!" A little transformer theory indeed.
    Whole situation still feels like BS to me. I haven't heard a convincing argument about why a different layout or chassis wouldn't fix it. When I emailed him about the noise in the right channel he fed me the same line, but when I asked him if it was in any way a product of the layout or if a different physical layout would change this, he did not respond. Maybe that's insulting from a heathen that hasn't spent decades designing circuits, but c'mon? I'm not complaining about the SNR, I'm complaining that the right channel in specific picks up hum from the power transformer and that there's a bug in the design. Had's defense against this seems to be "look at all my happy eBay customers, they can't be wrong!"
    I say all this as a relatively happy owner of the amplifier. It's a good value and sounds good. I like it. It has hum in the right channel. It's easy to ignore it when there's a lot of signal but it's obviously there in quiet passages or when there's no signal, at least with e.g. Audeze LCD cans plugged into it (which seems to me, still, like a great synergistic pairing). Maybe in another few decades I too will have lost enough hearing that I don't notice it, but for now it's obvious and it's insulting to a purchaser of a four-figure headphone amplifier to suggest that everything's hunky-dory and the quirks are just an inescapable trade-off ... when they aren't.
    If I run across another similarly-priced transformer-coupled single-ended design that sounds great and doesn't hum in the right channel, I don't know that I would keep the IHA-1. I'm not aware, yet, of a great alternative ... so I've stuck with it. But I think it's disingenuous to gloss over the fact that the product is imperfect just because Dennis is a nice guy or a legendary audio equipment designer.
  5. jelt2359 Contributor
    Anyone tried transformer rolling on these? Would be interesting to get a cinemag in there... Or one of those hand made tribute transformers :)
  6. Rotijon
    Thats a whole new level of rolling roflmao
  7. Alexander N
    I completely agree!
  8. Xcalibur255
    Not a design flaw.  An inescapable part of tube amplifiers that employ output transformers.  The reason Woo amps and their like don't (normally) exhibit this hum is because their designers add lots of negative feedback into the circuit along with other trickery to eliminate it.  They do this to protect themselves from getting customer complaints mostly and to meet the expectations of people who are used to a silent noise floor coming from solid state designs.
    But here is the dirty little secret of this:  it does tremendous damage to the music.  All these design tricks that make the amps silent result in a tonally dead amp with no sense of spatial depth in its imaging and no sense of dynamic "pop" to it.  I have a custom made OTL amp that dumps a VERY noticeable amount of hum and static into the headphones, all background noise being picked up by its big hulking 10 amp power transformer.  But when there is actual music playing it is simply not a problem, the amp sounds wonderful and outperforms stuff costing 3x the price what it cost to make it.  It's a real shame that background noise is such a witchhunt in tube gear, because its honestly not a big deal and bending over backwards to get rid of it does more harm than good.  Dennis is one of the most knowledgeable and experienced designers on this whole planet and he knows this.  He made a conscious choice to go the purist route and give the amp the best transparency and musical resolution possible rather than cater to the needs of the least common denominator (I know that sounds nasty and uppity, but I can't think of a nicer way to put it).
    Honestly I'm impressed at how quiet the amp is given the design and the small size.  If the background hum were 4x worse I would still not be bothered by it at all.
  9. Xcalibur255

    If you're actually hearing hum in musical passages then you might just be a statistical anomaly.  Meaning perhaps your power tranny is wound a bit off and has more magnetic field than normal, or perhaps some internal wiring is just a tiny bit off where it normally is and is picking up interference that normally isn't in the design.  I have never heard hum from my amp while actually listening to music, in fact I don't hear hum at all most of the time even when there is no signal.  My primary headphones are all fairly low sensitivity (hence all my issues with not being able to get a lot of volume out of the amp), so this benefits the hum situation in my case.
    I would push Moon or Dennis to take a look at your amp and see if they can add some shielding in your case.  I've seen this happen with Woo amps too, some people have gotten WA22's with hum issues and initially Jack would tell them "oh it's normal" until a bunch of owners with the same setup would make clear it was not.  Then he'd take it back and rearrange whatever wire was too close to a transformers and wrap a few things in some shielding material and the problem would be solved for that owner.
    Unfortunate but this kind of variability does sort of come with the tube amp territory, at least the ones that target this kind of old school purity of design.  The upside is how natural and transparent they sound, there is just nothing else like them.
  10. Bellasperson
    I had Dennis  build mine with both XLR and RCA inputs. When I use the XLR input and the 6BX7s there is no hum and I do mean no hum. I have spent a lot of time listen to the IHA-1 and comparing it to the EC Balancing Act and the DNA Stratus. I own all three.  I prefer the IHA-1 to the Balancing Act. I prefer the Stratus to everything I have ever heard including the IHA-1. That said the IHA-1 is the best bang for buck that I have found. My most used phones are Audeze LCD-3f with a set off Oppo 2s as the phones I use most with the IHA-1. The detail and price point of the IHA-1 is hard to beat. I hope one day Dennis builds a big form factor or two box version that addresses the hum for the 6sn7. If he does I will buy it. In the mean time the IHA-1 is for me a keeper and a piece of equipment that I would recommend to anyone with Audeze headphones and a love of detail.
    Alexander N likes this.
  11. Xcalibur255
    6BX7s only have about half the gain of a 6SN7 so this will drop the noise floor.  They're also really good sounding tubes, as good as the most expensive NOS 6SN7.  The only catch is the low gain is actually too low if you have low sensitivity headphones.  With my LCD-2r2 plugged in there is only one volume setting I listen at:  maximum.  It's usually just right unless the level of the recording is low but knowing there is nothing left if you want to go a little louder is a bit of an issue.  The small benefit that comes with the problem is being able to take the volume control completely out of the signal (step 24 on the attenuator has no resistance value and is a straight pass through of the signal) adds another degree of transparency to the sound.
    I think the ultimate expression of this amp design would be to take a pair of EML 30A direct heated triodes and do a larger chassis to better isolate components and control hum.  The 30A has a gain of 32, more power and voltage swing than the 6SN7, and is basically a modern interpretation of the 45/2A3 type tubes.  A single gain stage design with all those advantages may well be the top rung of the tube amp ladder if top shelf transformers were used.  It would probably cost at least double what the IHA-1 goes for but IMO it would be worth it.
    Alexander N likes this.
  12. jelt2359 Contributor

    About the volume, when did you buy yours? I messaged Dennis on eBay and he said he made a change a few months ago and now they'll drive every headphone on the planet. The title of my message was "HE6" :)
  13. Alexander N
    In trying to reach perfection we often spoil what is or might be good enough...
  14. Xcalibur255
    I hope that change wasn't to wire each section of the 6sn7 in series instead of paralleling them. That would certainly fix the gain situation but the amp wouldn't sound as good since there are now 2 gain stages.
  15. Rossliew
    Can one use the 422A or 596 tube with the IHA-1?
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