bazelio
500+ Head-Fier
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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?
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?
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.
Anyone tried transformer rolling on these? Would be interesting to get a cinemag in there... Or one of those hand made tribute transformers
I'm surprised and a little sad that this thread is so dead, and that this amp gets so little attention on Head-fi. I am utterly in love with my IHA-1, it's hard to imagine the music sounding much better than this. With good tubes in it this thing is a giant slayer in the tube amp world.
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?
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.
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.
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"
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.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"