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Output impedance of tube HP amps


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Like what? Bottle head crack, little dot, etc? I’m sure it’s all on headfi. Curious what you’re seeking to know?  OI generally isn’t an issue if it’s 1/8th your headphone’s impedance or less. Some tube amps have pretty high OI and are really only suitable for 300ohm cans. 

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On 4/7/2018 at 10:50 PM, buonassi said:

Like what? Bottle head crack, little dot, etc? I’m sure it’s all on headfi. Curious what you’re seeking to know?  OI generally isn’t an issue if it’s 1/8th your headphone’s impedance or less. Some tube amps have pretty high OI and are really only suitable for 300ohm cans. 

 

Sorry for the late reply Buonassi.  Yep, I was thinking of those but also the Woo Audio amps, Inspire, etc.

 

As you say, "some tube amps of pretty high OI" but which ones?  I just don't see any actual OI ever from the manufacturers and of course most "sounds like" reviewers have neither the knowledge or the will to actually measure - so my question is if anyone knows of anyone (reviewer, users, etc.) that are actually measuring these amps?

Hey MQA, if it is not all $voodoo$, show us the math!

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I don’t know of anyone who maintains a measurement database or runs a similar blog. But I’d have assumed manufacturers would publish OI for their gear.  Interesting that this doesn’t seem to be the case with the few you’ve mentioned. I haven’t yet gotten into the tube game but I imagine I will pretty soon. 

 

Even solid  state manufacturers publish this. Perhaps the OI is part of the magic sauce in that tube sound and they prefer not to divulge? 

 

If you have two or three that you’re interested in, I can hunt around my usual sources on the web to see what’s out there, ie help get you an answer.  

 

Keep in in mind that OTL amps will have higher OI as a result of their topography but hybrid tube amps generally have 2 ohms or less OI. This is about as far as my knowledge extends!

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5 hours ago, buonassi said:

 

Even solid  state manufacturers publish this. Perhaps the OI is part of the magic sauce in that tube sound and they prefer not to divulge? 

 

 

That is certainly plausible.  I have assumed that because most (all, really to an extant) tube circuits have OI of double digits at least, they don't want to limit their market to 300 + ohm HP's.  With the advent of TOTL planer and dynamic HP's, most of which are below 300 (many in the 75>150 range) an OI of 20+ starts to have an impact.  

 

BUT, I don't really know why the OI is not a usual part of the spec with tube designe, though I note it is often exlcuded from SS designs as well.

 

Yep, OTL circuits OI is even more of an issue, and not an usually an issue with a "hybrid" tube/SS - but I really only want to see OI on the more usual designs.

 

Thanks for your reply!

Hey MQA, if it is not all $voodoo$, show us the math!

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