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Dennis Had Inspire Fire-Bottle SET amp review

Hello to all,
I have been a tube amp lover for years and foolishly parted with a HK-CII and CV a couple of years ago. I have a Don Sachs 6SN7-based tube preamp that is even better than the HK-CI I had, with all the HK gear upgraded by Don with Jim McShane mods. I recently got a pair of Spatial Audio Hologram M4 open-baffle speakers and wanted to make the foray back to a tube amp. I auditioned a Musical Paradise MP-310 with an unfavorable impression of its sound so I casted about for an affordable ~12 wpc tube amp and ran across a Dennis Had Inspire Bottle-Fire amp. It came with new JJ EL34 tubes which, after a few hours on them, sounded quite good at low SPL, but at maybe 85 db, just sounded awful, with the bass distorted as hell. Well, a buddy laid a pair of KT120's on me to swap for the EL34's, and holy hell, the sound is just fantastic! OMG, I can drive them very nicely to 90db with negligible distortion.

 Here is my take on the amp.   With the KT120's, and a 274B rectifier, this is a quintessential "tube" sounding amp. It gives up a degree of accuracy and control compared to my CJ MF80 SS amp, but ah, Dennis's amp creates such a luxurious warm and euphonic sound, like a "warm wet wall of sound", with and enormous soundstage, far beyond the speakers.  Honestly, I have been in search of exactly this sort of sound for decades and the pairing of Dennis's amp with my OB speakers, which are very conductive to a low-powered SET amp, is just a supreme match. The vast array of power tubes and rectifiers available to roll through this little gem very well might tailor the sound to benefit of many listeners.  My best advice is that if you have compatible speakers, you would be smart to acquire a Dennis Had amp. I feel fortunate that all the knowledge and skills he applied to his Cary Audio line of tube gear is still available to us tube-amp lovers in his current line of tube equipment.  There are lot of fine SET amps available on the market these days, but the price of most of them is quite expensive, out of my budget for sure, but the cost of Dennis's gear is affordable to all music lovers. 
Cheers, Whitestix
whitestix
coltrane1's avatar
coltrane1
813 posts
 
Did anyone see the Inspire Fire Bottle KT88 driving a pair of Martin Logan Theos on youtube? It's a small 12x12 room but still impressive.

https://www.youtube.com/watch?v=jlR9B22kOiM
coltrane1's avatar
coltrane1
813 posts
 
Re the previous post suggesting the Inspire KT88 isn't a true SET amp, and more simply a Pentode amp, here are a few words from the designer Dennis Had, speaking to an Inspire amp owner from the Audio Aficionado forum:

"The Inspire single-ended pentode amplifiers are operating beam power pentode output tubes in a fashion that the tube designers intended. These pentodes were never meant to run in what is called Ultra-Linear mode. The pentode is a higher gain vacuum tube with an additional grid called a screen grid. In order for the screen grid to act in a reinforcement mode of directing the electron flow the potential should be less positive than the plate (anode). If full voltage or more is applied to this screen/beam grid vs the plate it will start to act as the plate. This is what ultra-linear causes. Keep this very important fact in mind about ultra-linear ... UL is a form of degenerative feedback. In simple words UL is a feedback method. The ac audio signal in the primary winding of the output transformer appears on the screen grid in a reverse polarity equating to a lower gain feedback high impedance signal impressed on the screen grid. ... <snip> ... In the Inspire SE pentode design I go a step further toward the original pentode design factor with a low impedance regulated screen-grid B+ power supply. Without a fully regulated screen supply the distortion becomes very high when the tube is pushed. In fact in my design one can run the livin' you know what and still have a listenable experience. Run in UL or without a regulated screen supply at a lower voltage potential than the plate you have all the reasons for discounting pentodes. Pentodes operated in a fashion that the designer of the tubes intended will yield a magnificent sound closer to the recording studio original than a triode in my opinion.. I can go on and on .... I find it so difficult to read the crap that is spewed about triode vs pentode. Either tube will yield a magnificent presentation in pure class A if designed properly. Oh, I definitely use a modest amount of global negative feedback to lower the output impedance of the amplifier. The lower output impedance will allow the low power amp control the loudspeaker drivers. Feed back implemented in a proper fashion is desirable. Speaking of feed-back ... <snip> ... another bunch of marketing hype when I read amps claiming no feedback. When in reality most amps do have feedback in the form of current feedback, degenerative feedback, ultra-linear feedback and local and global feedback.

I better stop before I blow a gasket ... LOL Triode directly heated single-ended class A audio amps offer a bloom in the midrange. Pentode single-ended class A amplifiers offer a full bandwidth with loudspeaker control. I might add the Inspire single-ended class A amps have bass slam and a huge sound stage."
whitestix OP
729 posts
 
DH is a gem of a guy and a genius with tube amps.  I am using his EL84-based tube amp in my system and the sound is outstanding.  And the price of his gear is very reasonable compared to Ayon, etc.  

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