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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. jelt2359 Contributor
    Yes. Sounds good. The he1000 is not particularly difficult to drive.
     
  2. Rossliew

    Thanks for the clarification. Will keep that in mind. I think Glenn is swamped with amp builds so I'd rather not bother him as yet.
     
  3. Xcalibur255
    The Inspire and Glenn's OTL share a lot of character actually.  Both my Glenn amps and the Inspire bring a lot of musical satisfaction.
     
  4. Compassionator

    Not for me.  I also tried the HE560 and no go either.  Before 12:00 on the volume level it sounds pretty good, but after just doesn't get louder/dynamic.  And no, I'm not a "basshead."  The IHA can't even drive the HP1000 to satisfying levels, but utterly fantastic with other Grados and AKG.  The IHA is super clear, grainless and natural, but only with certain headphones.  
     
  5. Xcalibur255
    I primarily use a non-Fazor LCD-2 on m IHA-1.  I'm on record with the volume issues, I can often max the control out, but the amp has never felt like it was struggling to power the headphone.  It's a very full, open sound with satisfying bass punch when needed.  Where I found the amp to struggle a bit was with high impedance headphones, despite the maker's claim that it is capable in that regard.  My 600 ohm DT880s not only couldn't achieve any useful listening volume, but it also sounded soft.  I think the amp prefers low impedance loads, particularly given the output impedance on the transformers being only 3 ohms.
     
    Alexander N likes this.
  6. cakebreaker
    In order to drive my HD800 I have use my volume knob at ~3-4 o'clock. Is this normal?
     
  7. Alexander N
    This is normal.
     
  8. cakebreaker
    So, why would this be normal? It is because no caps and resistors design?
     
  9. Alexander N
    What tubes do you use in the amplifier?    Inspire.jpg
     
  10. Xcalibur255
     
    It's because there is only one amplification stage in the amp.  Nearly all tube amplifiers have two (some have three or more).  Let's take the Icon Audio HP-8 for example, a fairly similar amp in feature and price.  It has a 12AX7 first stage and 6SN7 second stage.  That's a gain factor of 120 multiplied by 20 for a total gain of 2,400.  This gets reduced by a certain factor in the transformers but it's still a lot, and the reason why you can't really turn the volume in that amp past 9 o'clock without it blaring.
     
    Contrast that with the IHA-1 which ONLY has a 6SN7 stage for amplification.  Further more each section of the tube is in parallel to increase current drive so the total gain is that of a single section, which is 20.  You can see the effect of changing output gain by using 6BX7 tubes in the amp (whose gain is only 10), as you need to go a couple of clicks higher to get the same volume.  In the case of high impedance phones or ones with low sensitivity, you end up running out of clicks.
     
    The reason the designer did this was to maximize sound quality.  A single stage amp has very low distortion and is very transparent sounding, but the drawback that comes with it is this inflexibility.  The amp only really likes high sensitivity headphones, and planars whose sensitivity is high enough to get the volume you need.  It's a major reason why the amp isn't more popular I'm guessing.  I think at some point we'll see Dennis do a V2 of this amp and he'll go with another tube choice with higher gain to get around this problem.  The 6SN7 is not a very high gain tube and is normally used as a driver stage, here it's both driver and output.
     
    An easy solution would be to make each section of the 6SN7 a separate gain stage, then you have a gain of 20 x 20 = 400.  But the highly transparent nature of the amp would suffer and there would be less ability to drive low impedance high current loads.  So either design choice is a trade-off.  The designer went with performance over flexibility.
     
  11. cakebreaker
    Sooo... You are telling me high imedance phone like the HD800s is not a good match for this amp, correct?
     
  12. Rossliew

    Very well said :thumbsup:
     
  13. Xcalibur255
     
    Not at all, I'm just answering your question as to why you feel you have to turn the volume up so high.  FWIW I often listen to my Inspire with the volume wide open at max with my LCD-2s.  It sounds fantastic, there just isn't any extra volume leftover for music that was recorded at a low level such as some classical pieces.
     
  14. cakebreaker
    Okay, thanks for the confirmation. I've had this amp for only a couple of days. I guess I was just a bit surprised. Especially, considering how much money I paid for it )) 
    Now, here is the response from Dennis on the same question regarding volume knob position:
     

    New message from: radioman731 (828[​IMG])

     

    Hey Paul:

    So nice to hear from you. Yes, this is normal. You have the purest version of the IHA-1 without a pre-gain stage. All is well ... enjoy and welcome to the Inspire family of crazed audiophiles.

    Take care and may God Bless you and the family

    Dennis


     
     
    I hope it is helpful for those like me )))
     
  15. Alexander N
    I also once received a response from Mr. Dennis Had:
    "Alexander:
    With the 6BX7 installed the gain will be slightly less than the 6SN7 but to my ears the presentation has more weight in the upper bass and lower midrange with the 6BX7's. A fuller sound to my ears. Running at 3:00 O'clock is just fine no problem.
    Dennis"
     
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