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Looking for a good tube amp for my Massdrop x Fostex Thx00 purplehearts

DKT88

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SIY

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I think Amir may have reviewed that one? Of course, if it's a hybrid, the important parts may be solid state with the tube not really acting any differently than a solid state device.
 

DKT88

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I think Amir may have reviewed that one? Of course, if it's a hybrid, the important parts may be solid state with the tube not really acting any differently than a solid state device.
the output stage is solid state
Oh but it's single tube, half-buried on a flat black surface, with no big giant transformers, looks so lonely and sad....
1553489179105.png

I agree, I don't like the burried single tube look.
 

SIY

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That looks like a version of the 6J5 headphone amp.

If money weren't tight, I'd have some transformers wound and design a proper tube headphone amp. I'm amazed at the lameness of the commercial stuff I've seen so far.
 
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Nobunaga

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Well I have one of those here in my office that I tried a few years ago. I've never seen any measurements of its performance other than manufacturers specs. I wasn't impressed with the sound, but it seems a lot of people are as I must have had some reason to buy it. Its a low power OTL amp and so paring with the right headphones is important. I just used it with what I had, Hifiman HE400i and Sennheiser HD650 headphones. I tried some NOS Mullard tubes also.

Well, it's the Mark III that gets hyped so much, the IV seems less popular.
 
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Nobunaga

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Nobunaga,

The Purplehearts are quite low impedance headphones (25 ohms), so theoretically they will not provide an accurate sound, particularly in the bass, with headphone amps that have high output impedance. To match the Purplehearts you would want an amp with 3 ohms or less output impedance.

The Technics amp has an extremely high output impedance, which as Solderdude points out, means its output into your headphones should not be at all accurate. That does not mean you or others would not find it pleasant.

The Asus Xonar has a headphone output impedance of 10 ohms, so also too high to be accurate with your Purplehearts. Not a good choice for accurate reproduction.

The great majority of tube headphone amplifiers also have high output impedances, so will not match well with the Purplehearts for accurate reproduction. There are quite a few that will work well. The Woo WA6 is one example. Most are either Transformer Coupled (like the WA6) or are hybrid, with a tube preamp section and a solid state amp section.

So, neither the Asus or Technics are technically good choices...but, you like the Technics better. I think you need to compare to a better suited amp. Perhaps you should try or borrow a low impedance amp 1st (almost all of Amir's recent headphone amp reviews include a chart of measured output. See if you like an accurate amp low impedance amp 1st. If you do, then look for good matches like the WA6. If not, then you will probably have to listen to a bunch to see which ones best match your tastes. Nothing wrong with that

How do you know the ideal output impedance for a specific pair of headphones? Is there a mathematical formula for that?

But a tube amp with 3 or less OHM would work then, right? I've seen a few.
 

RayDunzl

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How do you know the ideal output impedance for a specific pair of headphones? Is there a mathematical formula for that?


Ideal?

Wouldn't that be 0Ω ?
 

GGroch

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How do you know the ideal output impedance for a specific pair of headphones? Is there a mathematical formula for that?.....But a tube amp with 3 or less OHM would work then, right? I've seen a few.

Yes, there is a rule, the 1/8th rule. See This for a technical explanation. If you google headphone amplifier impedance and 1/8th rule you will find various more or less technical explanations but most all of which agree. So 1/8th of the Purpleheart's 26 Ohm rating = 3.25 or lower, so 3 Ohms or less should be OK if accurate.

To Ray's point, Zero Ohms would be ideal in that it would work with any headphones but 3 Ohms or less should be fine for the X00s.
 
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solderdude

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In this case you can forget about the 1/10th rule or 1/8th rule...
For planar headphones the 'rule' doesn't even exist.
Some headphones are even designed to be driven by a higher output Resistance.

The impedance rise is very small so even with a 10 Ohm output resistance there is only a 0.5dB bass boost.
A lot of headphones are mechanically that well damped that the electrical damping does virtually nothing.

As your headphone sounded great to you from 330 Ohm you have already proven that the output resistance of an amplifier is NOT a negative factor (for you) with this particular headphone. Don't try it with certain other headphones though.

OTL amps are not really suited for driving low imp. headphones.
You need to look for either a hybrid or one with an output transformer.
In your specific case you could even use an OTL amplifier and use a series resistor of say 220 Ohm (these exist in adapter form)
 
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Nobunaga

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In this case you can forget about the 1/10th rule or 1/8th rule...
For planar headphones the 'rule' doesn't even exist.
Some headphones are even designed to be driven by a higher output Resistance.

The impedance rise is very small so even with a 10 Ohm output resistance there is only a 0.5dB bass boost.
A lot of headphones are mechanically that well damped that the electrical damping does virtually nothing.

As your headphone sounded great to you from 330 Ohm you have already proven that the output resistance of an amplifier is NOT a negative factor (for you) with this particular headphone. Don't try it with certain other headphones though.

OTL amps are not really suited for driving low imp. headphones.
You need to look for either a hybrid or one with an output transformer.
In your specific case you could even use an OTL amplifier and use a series resistor of say 220 Ohm (these exist in adapter form)

Some amps have a variable gain, isn't that the same? Then i could just cycle through the impedance of the output and see what suits me
 

solderdude

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There aren't many amps with a variable output resistance.

There are tube amps with different output tabs (via a selector) but it would be best to choose the tab closest to the range the headphone falls in.
That could be seen as different voltage gain settings ....

The variable of switchable gain settings on headphone amps is to create a suitable 'volpot range' for different impedance / efficiency headphones.
IEM's and very sensitive headphones need less gain, high impedance and very insensitive headphones need more gain.
 

GGroch

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We are at the limits of my knowledge when discussing planars and output impedance issues. Tyll measured the Fostex TH family last year and produced this PDF.
There are 2 measurements of the TH-X00, one shows what looks like a 5dB bass boost using a 600 ohm output impedance. Am I reading this correctly? If so, the 330 Ohm Technics could well be audible, but lower modern amps should be ok.

The problem then is OTL tube amps, rather than transformer coupled or hybrid. What exactly is the issue here?
 
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Nobunaga

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We are at the limits of my knowledge when discussing planars and output impedance issues. Tyll measured the Fostex TH family last year and produced this PDF.
There are 2 measurements of the TH-X00, one shows what looks like a 5dB bass boost using a 600 ohm output impedance. Am I reading this correctly? If so, the 330 Ohm Technics could well be audible, but lower modern amps should be ok.

The problem then is OTL tube amps, rather than transformer coupled or hybrid. What exactly is the issue here?

i just wanted to clarifiy again:

it's not about a bass boost from the Technics. Actually, more the contrary, when plugged in to the Asus, the bass was very boomy, it had almost like an echo, you could hear the bass playing but also a sort of rumble, the bass would take up much more space.

With the technics the bass is much more contained, still very dominant, but it's tight, the bass doesn't bury other frequencies, in other words, there is not a bass boost but overall the sound is more balanced. Other than that, i can hear much more detail, things that with the soundcard weren't audible, the overall tone is more pleasant, smoother, mellow, warmer. The seperation between the instruments is also better.

There aren't many amps with a variable output resistance.

There are tube amps with different output tabs (via a selector) but it would be best to choose the tab closest to the range the headphone falls in.
That could be seen as different voltage gain settings ....

The variable of switchable gain settings on headphone amps is to create a suitable 'volpot range' for different impedance / efficiency headphones.
IEM's and very sensitive headphones need less gain, high impedance and very insensitive headphones need more gain.

Stupid question, the switchable gain settings on headphone amps isn*t the same as variable output resistance?
 

solderdude

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We are at the limits of my knowledge when discussing planars and output impedance issues. Tyll measured the Fostex TH family last year and produced this PDF.
There are 2 measurements of the TH-X00, one shows what looks like a 5dB bass boost using a 600 ohm output impedance. Am I reading this correctly? If so, the 330 Ohm Technics could well be audible, but lower modern amps should be ok.

The problem then is OTL tube amps, rather than transformer coupled or hybrid. What exactly is the issue here?

It shows a 5 Ohm increase at around 40Hz. How much bass boost that gives is a question of calculations.

At 330 Ohm the (sub)bass boost is 2 dB, at 10 Ohm about 0.5dB. A matter a calculating dB differences between extremes due to voltage division.

It is measured at 600 Ohm so that the output of the test amplifier becomes more of a current source instead of a voltage source.

The issue with OTL amps is that these usually have very low current capabilities but have a high voltage swing (talking about the cheaper ones)
These perform well at higher impedances but have a low output voltage for low impedance headphones, also the distortion increases substantially in these amps.

In this particular case one could use such an amp when some extra resistance is added.
 

solderdude

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Stupid question, the switchable gain settings on headphone amps isn*t the same as variable output resistance?

Indeed. 2 separate things BUT in the case of tube amplifiers with output transformers the various output impedance range settings do have a similar effect as a gain switch.
 

GGroch

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i just wanted to clarifiy again:
it's not about a bass boost from the Technics. Actually, more the contrary, when plugged in to the Asus, the bass was very boomy, it had almost like an echo, you could hear the bass playing but also a sort of rumble, the bass would take up much more space...

This surprises me. The Xonar STX appears to be a pretty serious stereo sound card with a decent headphone amp. Audiophile focused, not surround/gamer focused. Specs are quite good.

I have never used an Asus sound card, but I know that when I used Creative cards and heard things like you describe it was because it had defaulted to one or more of its dozens of built in effects. In some cases I had to go several menus deep to turn them all off. While stereo audio focused, I understand the Essence has quite a few built in effects as well.
 
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Nobunaga

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This surprises me. The Xonar STX appears to be a pretty serious stereo sound card with a decent headphone amp. Audiophile focused, not surround/gamer focused. Specs are quite good.

I have never used an Asus sound card, but I know that when I used Creative cards and heard things like you describe it was because it had defaulted to one or more of its dozens of built in effects. In some cases I had to go several menus deep to turn them all off. While stereo audio focused, I understand the Essence has quite a few built in effects as well.

I deactivated every effect, equalized it and set the sampling rate to maximum, which i always do on any device.

Anyways, sure it does give an improvement over onboard audio (better than my Asus Maximums IX hero at least). But i bought the Schiit Fulla (the older one) for my laptop (audio jack broke) and oh boy the improvement was massive compared to the Asus, like really massive. Punchier sound, way more clarity, way more details.

The Asus is totally not worth it considering that it costs twice as much as the Fulla.
 

solderdude

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But i bought the Schiit Fulla (the older one) for my laptop (audio jack broke) and oh boy the improvement was massive compared to the Asus, like really massive. Punchier sound, way more clarity, way more details.

The Asus is totally not worth it considering that it costs twice as much as the Fulla.

Laptop headphone output in a low impedance headphone usually is around 30mW or so.
The Fulla reaches 300mW which is about 2x as loud.
Perhaps that could be a clue ?
 
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