$3,500 PER PAIR



The Fletcher-Haynes Kokopele amplifier is designed and built in the Santa Fe arts district of Denver, Colorado; this seems a very appropriate location for the creation of music electronics. The person behind Fletcher-Haynes Audio is Peter Fletcher-Haynes, an Englishman who now resides in Colorado and displays a contagious passion for his work. Arriving at Peter's shop to take delivery of the amplifiers both he and his wife are very genuine, down to earth folks. They have two businesses, the other being the sale of vacuum tubes, so for me this was a treat, tube heaven.


I was presented with an attractive but not flashy pair of mono block amplifiers and given a verbal tutorial on their basic design and operation. The pair of amps I received for review was the shop pair, perfectly functional but not cosmetically perfect.


These amplifiers are in some ways conventional tube amplifiers; a 12AU7 DC coupled to a second 12AU7 configured as a cathodyne phase splitter which feeds a 12AU7 driver and finally into a pair of KT88 output tubes operating in Ultra-Linear mode. The output stage bias is adjustable and front panel meters are provided to read the current directly. The adjustment range is sufficient that most any pentode can be used. I did not try any other tubes but I've no doubt they would have worked fine.


What is a little unusual about these amps, is the availability of user adjustable feedback, varying from no feedback to ~9dB in roughly 1.5dB steps. Front panel level control is also provided using linear potentiometers in place of the standard log style audio pot. High quality linear pots are more common than an audio taper pot and they are designed to set the level, not be used as a volume control, so the lack of a logarithmic audio taper should not pose a problem. A hum balance control is also provided.


Per my usual practice of testing unknown equipment, I chose one at random and put it on the test bench. I have adopted this practice after having several speakers destroyed by renegade power amplifiers. The amplifiers have a main switch located on the rear panel which places them in standby mode; this provides about 85% of normal voltage to the heaters and keeps the tubes somewhat warm and will lessen the shock of power up, a nice feature which should provide long tube life. A second, momentary style switch on the front panel engages a micro processor controlled circuit which first applies full power to the filaments and then about 10 seconds later, engages the high voltage and places the amplifier in operational mode, this worked as designed with no problems.


Putting the amp in standby mode and connecting up the analyzer I observed 1.9mV of 60Hz noise. I disconnected the amp from the analyzer to verify I was not picking up something else in the room, this was not the case. The amp was reconnected to the analyzer and fully powering the amplifier up changed the noise very little, a small increase to about 2.1mV with the display moving between five and six hundred Hertz. I tried adjusting the hum balance pot but it was already at optimal adjustment. With six possible feedback settings, the decision was made to measure at zero feedback and at maximum. 


With the feedback set to zero and after allowing it to become warm I took a few measurements. Driving 1 Watt into an 8 ohm load at 1kHz, .104% THD was recorded; signal to noise ratio at this power level was 60dB unweighted, improving to 69dB A weighted. Fletcher-Haynes rates the amplifier for 35 Watts, at a power level of 37.4W no visible clipping was observed on the oscilloscope, THD was 2.83% and the signal to noise ratio was 87dB. Frequency response at 1W:  -3.4dB @ 20Hz, -1.75dB @ 30Hz, -.72dB @ 50Hz, -.2db @ 100Hz, -.42dB @ 10kHz, -1.5dB at 20kHz, -2.9dB @ 30kHz. Gain was very high at 44.7dB with the level control fully clockwise.


Setting the feedback to maximum returned the following results:


Output noise dropped to .9mV unweighted and to .33mV weighted, this equates to 66.6dB unweighted ref 1W, 78.6dB weighted. Gain with input level at maximum was 35.62dB, so feedback is ~9.14dB. THD @ 1W = .046%, THD 39.14W = 1.05% with no visible clipping on oscilloscope. Unweighted signal to noise ratio ref full power was 82.8dB. Frequency response at 1W was -.55dB @ 20Hz, -.27dB @ 30Hz, -.1dB @ 50Hz, -.025dB @ 100Hz, -.09dB @ 10kHz, -.38dB @ 20kHz, -.96dB @ 30kHz.


As expected, even the moderate amount of feedback present greatly improved measured performance.


Finally, it was time to put them into the system and see how they sounded.


After connecting  them up to my GedLee Abbey 12 speakers which are 95db sensitive (pictured), and engaging the standby switches I noticed a very slight hum from both speakers. Disconnecting the preamp did not change this. Recalling the results on the test bench brought to mind the fact of a low level 60Hz signal in standby mode. With 95dB sensitive speakers, this is enough signal to hear in a quiet room, which my listening room is. Setting the amps to operate mode dropped the hum by about 6dB, nearly inaudible from the listening position and not at all objectionable. The input level controls were set at about the 11 o'clock position, this equates to about 26dB of gain, an average for most amplifiers and also the gain the subwoofer amplifiers were configured for. No hum or buzz problems when connecting the preamp, indicating proper attention to grounding in the amplifiers.


One amplifier had a very small amount of mechanical noise and both were plugged into the same receptacle. I expect this is related to them being the shop amplifiers and not something customer ready. It was inaudible from the listening chair.


From my notes while listening; Once the system was warm I queued a 96kHz/24bit copy of Stanley Clarke's first album taken from vinyl. This is still playing as I type these words and I am completely enjoying both the music and the presentation, a very live sound, very concert like and making it difficult to concentrate on writing. In fact I think I'll stop and just listen.


As time passed I added; No lack of dynamics, things can get really loud without apparent strain. Nice.


A bit more; Just queued up Ben Webster - Soulville Verve master edition, upsampled to 176.4kHz/24bit. Ben's sax is just as rich and full as can be, superbly dynamic. No problems with noise once they are powered on, at least with the current feedback settings. They are quieter on than in standby and I don't notice them while sitting in the comfy chair.


On the next evening I did some more listening, all vinyl. As before I found them very live sounding and enjoyable. Towards end of my listening session I decided to try them with the feedback set to the lowest option, which should be none. My friend and neighbor was over and while not an audiophile, he is very familiar with the sound of my system and very good at describing changes. We both noted that the front to back sound stage collapsed and the highs were almost missing in action, cymbals were much less defined. This correlates with the measured performance with the feedback at minimum, the response at 10kHz was down .42dB and -1.5dB at 20kHz.


I then chose a middle setting for the feedback and most of the high frequency information returned and the image expanded. The end result was something akin to a singled ended amp but not quite as rich harmonically. Overall I preferred the maximum feedback setting, it sounded the most like real music. Of course this will vary with the speaker connected, experimentation is key and having the ability to dial in the  sound to ones liking is a very nice feature.


A couple of weeks later I toted the amplifiers over to Brian Boehler's house to allow him some time with them so he could provide a second viewpoint. Our systems are quite different, while I have fairly sensitive speakers and powered sub woofers, Brian has Vienna Acoustics Mahler speakers normally driven by a Krell FPB-600, a giant class A behemoth. They handled the Mahler's better than I expected but I don't really think they were a good match for the Kokopele amplifiers, the big Vienna Acoustics really seem to like an amp with a high damping factor to rein in all those woofers. Brian has weighed in with his thoughts on the Fletcher-Haynes amplifiers but in fairness I have not read them yet. A week went by and Brian returned the amps and I of course put them back in my system for further enjoyment, and enjoy them I did.


For whatever reason these babies really like to rock, playing Cruise Control on the Dixie Dregs “Unsung Heroes” album (vinyl) really brought out Steve Morse's guitar and I just wanted to crank it up and jam, a beautiful thing when the system just sucks you in like that.


As you have likely discerned, I very much enjoyed my time with the Kokopele amplifiers, they simply made music that was fun to listen to. I do have some quibbles but they are minor. The noise in standby mode is a little off putting though not really a problem since I'm not listening to them that way, when fully powered on they were almost but not quite silent in my room with fairly high sensitivity speakers. The build quality is very good and the looks are sort of retro industrial in my mind. Given the solid construction and standby/soft start treatment of the tubes, they will likely last for a long long time and be easy on tubes as well. I would prefer they had a fixed input level but for those using a passive preamp, such as the Diminuendo offered by Fletcher-Haynes, having the ability to dial in additional gain is very valuable. Perhaps Peter Fletcher-Haynes could offer that as an option in the future.


I had the pleasure of a long conversation with Peter when returning the amps and he was extremely open about the design, describing the circuit in detail and opening the amp to show how everything was laid out and fitted together. We discussed the slight hum in standby mode and he is aware of this and has some ideas on addressing it. Peter designed all of the transformers and has them custom made to his specifications, amazing at this price point and excellent at any level. I did ask Peter if the Kokopele design was influenced by his musical instrument amplifiers (he also builds guitar amps). He said not directly but the circuit was designed to be adaptable. Given the delightful way they serve up high energy music, I think he may have subconsciously been influenced, just a little bit pehaps.


So how do they compare to the Atma-Sphere M-60 ($7,000/pr), which has been my benchmark for the last couple of years? Quite well but there are some important differences. The M-60's are not very “tube like” in the sense that they are not particularly warm but they are very fast with the ability to make notes just float in air. Both amplifiers had no problem playing as loud as I needed, the Kokopele had a fuller, richer tone. I found this enjoyable as the M-60 can be a bit lean sounding on some music. The Kokopele had the ability to just make you want to jam, whereas the M-60's tend to be cerebral in presentation. Hmm, that sounds odd but it somehow fits.




Brian Boehler


The Fletcher-Haynes Kokopele mono-block tube amplifiers spent a week in my system and I wanted to share my perspective on the sound.  In simple terms the Kokopele is an ultra linear push pull AB1 amplifier that outputs between 35 and 40 watts depending on the tube compliment (KT88, KT66, 6L6, EL34 and more).  The feature I found fascinating to play with was the adjustable feedback control.  This feature allows you to adjust the damping control over the woofer.  Trust me it works but I found both a positive and negative side to this feature. 

After a week of listening to music I came to some conclusions.  Tube equipment can really sing beautifully if paired with the right speakers.  It is a matter of complimentary pairing and playing to the components strengths.  On the flip side of this equation, we have a pairing that challenges the amplifier and speakers and produces a sub-optimal result.  My current speakers are the Vienna Acoustics Mahler loudspeaker.  While I know there are some issues with its measured performance, this speaker has a truth in timbre that just works for me.  I don’t get lost in the audiophile hyperbole but instead disappear into the music better than the vast majority of speakers I have auditioned.  The speakers are 87db sensitive and run right around 3 ohms in the bass range.  It has a -3db low end of 22 hertz and is specified as an overall 6ohm load.  In simple terms, this was not a complimentary pairing that allowed the Fletcher-Haynes Kokopele to strut its stuff. From a pure power perspective, this was like asking a really good lawn mower engine to push along two-ton Dodge Ram truck. Being so unfair, the goal here is to appraise the amp as best as possible under the circumstances.

The use of the adjustable feedback control provided some needed relief in the bass.  I could dial up the setting to max and get reasonable bass control and tightness.  The highest setting produced better than expected results in bass tightness but at a price.  As I applied more feedback to control the bass wooliness I found the soundstage/soundscape shrunk.   Almost zero feedback produced that incredible soundstage that tubes excel at.  The obvious trick was to find the best balance of bass tightness and expansive soundstage.   The unfortunate situation was that I never found an acceptable setting that balanced the bass and soundstage.  I always felt like I had hampered both and never optimized either.  I want to stress that I don’t consider this the fault of the Fletcher-Haynes Kokopele amplifier but the result of a less than optimal pairing of components. 


I found the overall build, fit and finish, and look of the amplifiers to be fine, if a bit utilitarian in nature.  No big deal but definitely not audio jewelry like, say, MBL. But a lot of people find such audio finery ostentateous with a low bang-for-the-buck quotient. There are also a lot of people who absolutely love the styling from the 1960's and early 70's; the vintage look. What we have here is a modern amp in vintage clothing.

I believe the price is very reasonable and represents good value in today’s escalating prices.  The professional market ethos is apparent and I’m sure that helps keep the cost of the overall product down to reasonable levels. 

The key point I want you to take away is what we at Stereomojo have been emphasizing from day ONE, and that is that you have to compliment the strengths and weaknesses of your components.  An absurd example to highlight this point would be to pair a 2 – 3 watt 2A3 amplifier with an Apogee Scintilla.  Disaster awaits!  While my example is not as extreme, it still highlights that you want to pair products that complement the strengths of each component and minimize the weaknesses. 

Publisher's note: What many audiophiles do is read a review of an amplifier and think to themselves, "Yeah! That's what I want"! Then they read a review or even hear a pair of speakers, decide they like them and buy 'em. Often, little if attention is paid to the sensitivity of speakers (low or high) versus the rated output of the amp. That's just for starters! you can still buy low sensitiveity speakers and pair them with a high wattage amp and still have a terrible mismatch! The key word is impedance. Know how your amp matches up with your speakers - at least. Publisher's note: If you don't have the knowledge to read the specs and make an educated decision yourself, here's my advice; do not post your question on some audio internet site first. While there are certainly so knowledgeable, helpful people there, there are also a lot of people who want to portray themselves as knowledgeable and really are not. So what to do?

Call up the speaker company (or the guy who makes them) and aks for his advice. Tell him you're thinking about buying his speakers and you'd like to make sure to have a great amp matchup. Have a selection of 1-3 amps (or the amp you already own) in which you are interested and their specs when you call. I can tell you that the vast majority of speaker makers would LOVE for their customers to do this!

Next step: If possible, do the inverse and call or write the maker of the amp you have or are considering and and tell him about the speakers. Have the specs. Ask if it's a good match. Again, most amp guys like Peter Fletcher-Haynes would be happy to let you know. Now you have two highly creditable answers and your chances for audio heaven are greatly enhanced.

If all else fails, write us! Send us the amp name and model WITH its specs and the speaker name and model with its specs. We're not going to look it all up for you. If there is any question (if it's a close call) we will often be able to reach a person who made the produce that you might not - we have friends in high places. We've done this hundreds of times. We want our readers to make good, informed choices.


You are looking for synergy where the combined effect is greater than the individual parts.  I’m guessing that Mike Galusha with the GedLee Abbey 12 Loudspeaker would make a better match for the Kokopele amplifiers.  I hope my perspective helps you carefully consider if you have the right ancillary equipment to support these tube mono-block amplifiers.  In the right situation, I’m sure that the Fletcher-Haynes Kokopele amplifier can sing and make beautiful music. 



The Fletcher Haynes Kokopele Monoblock power amplifiers are, we believe, that a lot of people will love but just as many will not love. First, there is their decidedly vintage look. These will appeal to a lot of people who like the retro/vintage look but want up-to-date sound that real vintage amps just can't deliver without some modding or at least updating. That's often expensive.

At $3,500 per PAIR, you're getting separate power amps for the price of many stereo, single chasis amps.

Fletcher Haynes is made in Colorado, USA. Judging from the email we get, Americans at least seem to be growing more inclined toward domestic products.

Whether via the designer's biases or not, we think these amps work better with music that leans more toward rock and jazz than classical string quartets, guitars rather than harpsichords. They do love to boogie!

If the Atma-Sphere is an audiophile's amp, then the Fletcher-Haynes is a musician's amp, it wants to play and wants you to play along.

With a 45 or so wpc power output, speakers of reasonable sensitivity and with fairly well-damped woofers are likely the best match. While it will drive multiple large woofers, some control is sacrificed and of course the ultimate level will be limited by the power demands of the speaker vs the power available from the amps. See what our publisher noted, but we would say at least 89dB sensitivity would be desirable.



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