Dennis Had Inspire Fire-Bottle SET amp review

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.  

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."

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

I am a bit bi-polar about amps.  I prefer certain aspects of the performance of SS amps, just as I do with tube amps.  Neither completely satisfy me, but overall my preference these days for the Spatial Audio speakers is Don's tube preamp and a McCormack DNA .05 Deluxe SS amp.  

@whitestix After all that, you went with a SS?

I ended up with a newer SS amp so I didn't take delivery of Don's new amp.  

Whitestix,

How do you like the Don Sachs kt88 Amp?

Thanks

Hi , I received a little package from Grant Fidelity today . After only 6 days a pair of Psvane Tii's arrived . I put them in the amp with a NOS Mullard GZ34 and a Tesla Red Tip driver . I just turned it on and let it play at moderate volume . Soundstage is huge ! Sounded a little bright and forward . But hey this was at 5 minutes . At about 30 minutes they were already smooth . Left the house to run errands , be home in a few hours . I left the system playing and I'm really excited to get home . I've never had a power tube sound that good right out of the box . The only caveat so far is that the internal coating is so thin on one tube , that you can see through it . I have OCD , and God has a sense of humor ! And I'm probably the only gear head that obsesses ! 😮 Anyway , Happy Thanksgiving and I'll report back upon completion of my mission . Happy Listening , Mike.

Great post, Mike, happy listening!

Hi to all , just touching bases. I recently picked up a pair of 1970 NOS Tung-Sol 6550's . They now have some time on them . I'm using a NOS Mullard 4 notch GZ-34 and a NOS Telefunken E88CC. The sound is fantastic . Great clarity and a 3-D image that rivals good headphones . I just finish listening to Simon and Garfunkels first recordings and it was outstanding . I played some Chris Issac due to the quality of his studio crew and it was sublime . Diana Krall sounded like she was in my living room ( sorry Elvis C. ). However, at $358 for the pair , they would not be my first choice. I don't own a signal generator and an oscilloscope but the output is lower than the KT-88's and definitely the KT-120's. At 12 watts , dropping a few make a big difference in " THE WALL OF SOUND ". The 6550's lack bass and even with a good sub it's noticeable with certain music. But the mids are open and the treble is SWEET ! They make the Gold Lion Reissue sound dry , but that's a great tube . Giving up a little tonal quality ,  but with a huge soundstage and fantastic bass are the Tung Sol 120's. I still going to try the Psvane II''s . I have found a huge difference in my system using NOS driver tubes . And lesser tonal change with the rectifier as mentioned by you , but still worth the effort . What I have learned so far is how good the NEW PRODUCTION power tubes are . In closing I'm thankful for everything posted as it is spot on . I hope that I've contributed something worthwhile too. Happy Holidays and Happy Listening , Mike .

Hi there,
I have the Tube Store 2748 rectifier in the amp, pretty inexpensive.   In my experience, rectifier don't have much of a sonic signature.   Don's KT88 power tube of choice, after his long-time love affair with Gold Lion's (which are still very very good), is the Psvane T-II.  You can get them in China directly shipped at a better price than from the other well-know Northern American supplier.  BTW, I am running KT150's in the amp at the moment, which are affordable and sonically pleasing, and perhaps a bit more impactful than the KT120's.   Still, I'd love to hear a pair of the Psvane T-II's in the Had amp.  Cheers, Mark

Hi , thank you for the suggestion on the KT 88 tubes . However I'm confused as to the Psvane Treasure ? I find Psvane Ti 11's and Shuguang Treasures . Could you clarify this for me please ? Also your input on the 274B rectifier would be appreciated. I've yet to try one . Also I found Grant Fidelity on the internet , but it looks like they " Drop Ship" from China upon payment . Any purchase input on the recommended tubes would also be appreciated . Regards , Mike.

Buellrider97,
You have auditioned the holy grail of tubes for the amp so you have heard most all variations that the amp can produce.  Dennis's amp would be a match made in heaven for your efficient Zu's.  Don Sachs and Jim McShane, and humbly, myself, are all devotees of the Gold Lion KT88's.  However, the Psvane Treasures are much better and definitely worth a listen.  Don Sachs spec's them in his KT88 power transformer.  They are pricier than the Gold Lion's but Don thinks they are well worth the money.
Cheers,  Whitestix

Hi , I too have a Dennis Had Inspire. I've been enjoying it for about 10 months . Mine came with the Gold Lion reissue KT88's and a Gold Lion rectifier . I am using Zu Omens and a single 10" sub. I have a Rogue RP-1 pre with Tecktronix Telefunken ECC82's. I have upgraded cables , interconnects and a power conditioner . The tube combos I've tried so far are JJ KT-77's with a NOS RCA 5UG4 and a NOS TESLA E88CC, the Gold Lion KT88's with a NOS Phillips 5R4GYS and a NOS Telefunken E88CC , New production TS KT120's with a NOS Mullard GZ34 and the Telefunken E88CC. I also have tried a NOS Mullard E88CC, Phillips Herleen PQ E88CC, JAN ECG , and a Russian Rocket . In the pre I've also tried NOS Mullard and NOS JAN RCA. Overall I like the Gold Lion KT 88's the best. I've switched around all the driver tubes and rectifier tubes ( the amp is extremely forgiving) . The Phillips rectifier is the most detailed and the Mullard takes away the harshness of the KT120's that took forever to break in . I would like to try the Gold Lion reissue KT77's . I will eventually buy a metal base rectifier and some nos power tubes like GEC KT 88's and Tung Sol 6550's. All of the tube combos have been enjoyable ! A BIG HAND TO DENNIS FOR THIS ! I'm running FLAC files with a Schiit dac. I will eventually get a new turntable . I appreciate all of your input, as it has been very helpful. Regards and Happy Listening , Mike .

Nope, I haven't.

Whitestix, have you compared Dennis' LP27A with the Don Sachs preamp?

Audioman,
It was a big jump in performance from the EL34 to the KT120's, night and day.  However, I plugged in a pair of new KT150's this week and after a dozen hours on them, I'd be hard press to notice the improvements you refer to above.  I will swap the KT120's back in after 100 hours for a useful comparison.  BTW, I have never been much of a fan of JJ tubes, but the Gold Lions KT 88's and the big Tung Sols have been an excellent value/performance proposition.  

I just ordered a KT88-based amp from Don Sachs in which he spec's the Shuguang  KT88 Treasure tubes.  It will put out 60-70wpc and Don feels it is a significant improvement on the upgraded HK-CII amp that has been near and dear to his heart for many years and which I had for a couple of years.  I am running the Shuguang CV181-Z (=6SN7) Treasure tubes in Don's preamp and they are simply stunning and in Don's view, better than nearly any pricey NOS tube around.  They are faultless to my ears and fairly affordable.  Happy listening!

As good as the kt120 may be the KT 150 may have better mid,low bass and has a  nice open top  end. Well worth checking out !!

Right on, Rob.  I have been through a dozen speakers in the past maybe ten years and enjoyed all of them a lot, except for the KEF LS50s.  Before the Holograms, I had pair of Linkwitz LXmini's, which in many respects were simply amazing -- very holographic -- but they lacked a strong sense of presence and sonic impact.  The Holograms fulfill that need very well.  And again, I personally think they sound their best with tube amplification, but it is of course a trade off.  

Finding the Inspire amp was serendipity.  The less expensive Musical Paradise MP301 amp was not at all to my tastes and the Decware SE amp are a fair bit more expensive so picking up Dennis's amp was a boon.  With my Don Sachs 6SN7-based tube preamp and the Inspire amp, running the volume pot at 12:00 yields about an average SPL of 87db with peaks to 100db, which I only listen to for short periods of time.  Yet at that volume, there is no perceivable distortion and great control of the bass.  However, the amp did not perform well at all to my ears with new JJ EL 34's, breaking up like hell in the bass on loud passages.   However, with the KT120's, the amp is "large and in charge" all the way around.  I am gonna roll some Gold Lion KT88's through the amp and I have no doubt they will be splendid.  However, the Tung Sol KT 120 are just remarkable and not expensive.  I have few NOS rectifiers on the way to see how they sound in the amp, including the laudable NOS Phillips 5R4GYS tube, which Dennis advises is fine to use.    

I have responded to several folks about the amp so sorry if I am repeating myself here.  I have never had the pleasure of hearing Cary Audio gear, but don't doubt its legendary status and Dennis's contribution to the nascent interest  ~20 years ago to the sonic wonders of tube amplification.  The path of many audio designers is towards increasingly more complex, sophisticated, and uber-priced gear, but Dennis has taken a road less traveled, but not less rewarding for his customers.  I desire more of his amps for my other systems.  Cheers, Whitest 

Thanks whitestix, I'll look for the review. I'll catch the Spacial at the next audio show I attend. Best, Rob

Mikirob,
I have posted a review on Audiogon of the M4 Turbo's.  As much as I like them with a SS amp, they are even more euphonic with the SE amp.  I paired a REL T7 sub and they are very full ranged.  If I had the room, I would have opted for the M3's.  I hope you get a chance to hear them sometime. Whitestix

Thank you Whitestix for a nice compact review Dennis Had's Inspire amp. As a Cary fan when Dennis was running the show (I own the V12 and SLP98) as well as previous designs I am always interested in what this stellar designer/person is up too. Could you also say a few more words about your experience with Spacial. I'm feeling like l'd like to try the M3 with my SET stuff. As always, Best, Rob

JM, thanks for the correction, not that I can fathom the difference between triode and pentode.  David, thanks for the fuse suggestion, but I have tried the SR Red fuse, and came to the same conclusion that Dennis has --  there is no sonic difference compared to a standard AC fuse.  I am gonna save my money.  

Day by day, this amp continues to impress me more and more, with a warm mid-range, good control on the LF, and a sparkling high end. To repeat, the JJ EL34's did not please me, but the KT120's are just marvelous.   I will be rolling a pair of  Gold Lion KT88's soon for the heck of it as they are top-notch new tube.   

I suggested to Clayton at Spatial Audio that he might alert folks to pairing of his speakers with SE amps, as the Inspire amp drives them with ease.  The speakers are somewhat better controlled with my CJ solid-state amp and completely enjoyable, but clearly the heart and soul of the music emerges with the Inspire amp.  The difference is amazing. 

 I don't know if the forum rules will permit me to post his very recent link to an interview with Dennis that reveals a great deal of information about the man and his products.  If there is a nicer, more self-effacing, fellow in the audio industry, I have never met him.  I think his gear is in the class of heirloom gear that some day might not be available so give it a listen while you can.  Whitestix
https://www.youtube.com/watch?v=xLQsEeBKg1E

Actually Dennis Had’s Fire Bottle line are SEP amps not SET amps. Single Ended Pentode design, as opposed to Single Ended Triodes.

That said, I am very happy to hear that the Fire Bottle lit your fire. It’s always nice to find that *magic* combination or amp/speaker.
Dennis is a great guy to deal with, and very passionate about this hobby.
I enjoyed working with him very much.

However, his KT-88 Fire Bottle SEP amp did not work well at all in my system. He was very helpful sending me all sorts of power tubes and rectifier tubes to try out, but none of them could open the sound up in my room. Eventually I sent the amp back and received a full refund.

I have no qualms, as dealing with Dennis was a pleasure.
I was a bit disappointed though, as I really wanted that little Fire Bottle amp to work *magic* for me. Alas, it was not to be.
FWIW, my speakers sensitivity were 90 dB and a 8 ohm nominal load. Maybe not an optimal match.

Congrats though, and if I recall correctly, there was a long thread about the Dennis’ Inspire amps and preamps on Audio Aficionado.

whitestix:

Congratulations on discovering the  speaker - amplifier pairing that stirs your soul. Your are correct that there a lot of tube combinations you could try.

I would suggest trying a Synergistic Research Black fuse in the amp. I have found them to be a wonderful upgrade in the SET tube amps I use.

You are listening to the efforts of two very talented designers.

David Pritchard