REVIEW: the Bolder-Rebuilt Singlepower Extreme
Jul 22, 2010 at 12:19 AM Thread Starter Post #1 of 11


500+ Head-Fier
Apr 10, 2006
[size=x-small]I was a happy owner of a Singlepower Extreme until last summer, when I took notice of the threads on Head-Fi regarding the poor design and build quality of Singlepower amps. The general advice in these threads was that Singlepower owners should have their amps evaluated by a "qualified tech". Not knowing any techs, let alone "qualified" ones, I wasn't sure how to follow through.[/size]
[size=x-small]Around that time I read on Audiocircle, another audio forum, that Bolder Cable Company was willing to evaluate and repair Singlepower amps. Bolder is best known for its well-regarded mods of the Squeezebox, a digital music receiver. I got in touch with Bolder, which turns out to be a one man show run by Wayne Waananen. An e-mail exchange, follow-up phone conversation, and his posts on Head-Fi in the Singlepower Extreme repair thread indicated that Wayne meets the criteria of a qualified tech.[/size]
[size=x-small]Off my amp went to Colorado. A few weeks later came a bleak diagnosis: Wayne told me the amp was in its death throes. He didn't use those words, but described the amp's myriad problems, e-mailed me pictures of the board and transformer and also posted them on Head-Fi. On seeing the pictures, Kevin Gilmore wrote a post stating that my amp was the worst Singlepower amp he had seen to date. Wayne's recommendation was to just junk the amp. Although I could afford a new amp, I had "committed" to a substantial inventory of NOS 6SN7s, CV181s, 5998s, and 6080s. Those cost more than the amp. [/size]
[size=x-small]I mentioned this inventory of tubes to Wayne. Wayne hesitantly threw out a second possibility. He could rebuild the amp. He would use the Singlepower Extreme chassis, order all the necessary parts, and use point-to-point wiring to build the amp "properly". When I asked how much the rebuild would cost, he ballparked $1,200 (a figure that proved accurate). When I asked him whether he had ever built a headphone amp before, his response was an honest "no". But he said he had modified stereo amps in the past and that schematics for tube headphone amps are straightforward. [/size]
[size=x-small]At this point, I probably should have hung up the phone and mulled over whether to just cut bait. But it struck me that Wayne's cost estimate wasn't particularly high. I got the sense while talking to him that Wayne saw this as a personal challenge, not an opportunity to make a lot of money. Plenty of Singlepower amps had passed through his shop already, all with build problems of varying severity. If you pull apart enough of these amps, I have to imagine you would learn how it could and should have been done "properly" in the first place. My guess was that Wayne would make sure my amp would turn out right. So I gave him the go-ahead.[/size]
[size=x-small]The one factor I overlooked is that building an amp from scratch takes a substantial amount of time. Wayne indicated the rebuild would take a couple of months, as he had other business to attend to besides my amp. [/size]
[size=x-small]In the interim, other headphone amps became my new "reference" points. I initially used my Hat Peed Thingee (HPT) with Biggie Pipe Power Supply, a solid state amp built by Gilbert Yeung of Blue Circle Audio. That bizarrely named amp is built in a PVC pipe in order to minimize build cost and the retail price ($750). I had purchased the Blue Circle amp to use in my stereo system when listening to speakers is simply not feasible. I moved the HPT out of the stereo rig to use as my main headphone amp while Wayne worked on the rebuild. [/size]
[size=x-small]I also started reading Head-Fi more regularly, and noted glowing reviews of a new tube amp, the DNA Sonett. Thinking I would "rent" the Sonett to bring some glowing red tubes back into my headphone rig, I contacted Donald North and bought one, figuring I could either keep it or sell it, depending on how the Bolder rebuild turned out. [/size]
[size=x-small]In fact the wait time for the Bolder-rebuilt Singlepower was fairly extended, as the rebuild ended up involving two iterations. Wayne first sent the amp back to me in late 2009 and I found that while the amp was completely quiet with high impedance headphones like the HD650s, I could hear a faint background hiss with low impedance headphones, namely the DX1000s. Without making excuses, Wayne told me to send the amp back to him, along with my headphones and the tubes I planned to use with it and he would troubleshoot the amp.[/size]
[size=x-small]Thereafter, Wayne sent me progress reports on what eventually seemed to become a labor of love or obsession for him. He first informed me that a defective replacement transformer was the source of the noise and needed to be replaced. Later, he informed me that he had decided to alter the amp's internal layout further to shorten the signal paths. Finally, he wrote that the amp was finished and exhibited no noise, but that before shipping he wanted to take it to a friend who owns some audio testing equipment. He wanted to compare my rebuilt Extreme to another Singlepower Extreme he had just received from another customer. When those tests were finished, he would ship me the amp. [/size]
[size=x-small]So, for a solid six months or so, the DNA Sonett and the Blue Circle HPT became my new reference amps. In general, I find that it is difficult to assess the attributes of one decent audio component over another during short listening sessions, especially if they are both solid performers. The true sound signature of an amp, its strengths and weaknesses, becomes more apparent over long listening sessions over extended periods. The differences are not as obvious if a favorite set of tracks is played on one amp and then another in quick succession, pen in hand to take notes on each amp's soundstage, extension, treble, mid-range, bass...I had done this sort of listening test when I first received the Blue Circle HPT and found the HPT and the original Extreme -- based on initial impressions -- sounded very similar. [/size]
[size=x-small]Over time, though, I found I could more clearly discern the qualities of the Hat Peed Thingee. As others have attested, the Hat Peed Thingee is a very good solid state amp. It is nicely balanced across the frequency spectrum, does an excellent job at soundstage (with left/right channel separation better than for tube amps), and offers up very good micro-detail. While its mid-range is somewhat warm, it does not offer the same "rounded" mid-range notes and decay provided by a good tube amps. It is transparent, detailed, and neutral. While it is deserving of praise given its price, it is an amp that will cause one to focus a bit more on musicianship, and maybe a little less on music.[/size]
[size=x-small]The DNA Sonett, in contrast, offers some of the stereotypical advantages of tube amps. Its strengths were a warmish mid-range, great treble extension, and excellent imaging. It is almost holographic in its ability to depict where musicians are situated in the recording studio or live venue. And it is excellent at portraying vocals very naturally. It is also extremely quiet, and can be used with very low impedance IEMs. However, one shortcoming of the Sonett in my book was that its sound signature is leaner than I would like. It offers less bass weight and extension than the Blue Circle HPT, which is not regarded as a bass heavy amp. I attempted to improve the bass extension of the Sonett by rolling the stock tubes for a NOS 6H30Pi-DR and a Siemens-labeled Mullard 5AR4 rectifier tube. This moved the amp's "center of gravity" down somewhat on the frequency spectrum toward the mid-range and improved the mid-range liquidity. But I couldn't get the amp to really offer up much satisfying low-end growl. [/size]
[size=x-small]After these amps become my new references, with both receiving equal listening time, the rebuilt Singlepower amp was finally returned to me in March by Wayne. The rebuilt amp looked like a weathered version of the original Extreme, with a much larger transformer on top and some new bolts added to the chassis. It was not as pretty as the original Singlepower Extreme, which like all Singlepower amps, looked like audio jewelry. The amp certainly looked clunky next to the DNA Sonett, with its retro styling and cool aqua-blue chassis. Admittedly, it looked much better than my Hat Peed Thingee, which offers the styling of a pipe bomb.[/size]

[size=x-small]In e-mail exchanges with Wayne, I asked him to describe the process of the rebuild -- what schematic and parts were used. Since I have no experience building amps myself, I will just quote Wayne's response in full:[/size]
[size=x-small]"The schematic came from Dr. Gilmore. The SinglePower Extreme was rather similar to the Morgan-Jones OTL, which was published in his book Valve Amplifiers. Then in 2002, Alex Cavalli submitted revised Morgan Jones circuits with new parts values, based on the White cathode follower optimization techniques developed by John Broskie. [/size]
[size=x-small]I set out to try to correct the 'problems' with the parts selection and layout of the SinglePower Extreme. The circuit, for the most part, was good. The parts selection was not. The first thing needed was a properly sized transformer with the ability to supply the needed current for the filament circuit. Next was the filament circuit itself. The filament circuit in the original Extreme was very simple and allowed too much ripple and noise to come through. I redesigned that section.[/size]
[size=x-small]I built the high voltage power supply section on one 1/8" thick circuit board using turrets. All connections were made with point-to-point wiring techniques with BOLDER Nitro wire. Some of the power supply caps were replaced with low ESR Panasonics. ALL electrolytic caps were bypassed with Sonicap film caps. The filament circuit was assembled on a separate board and received the same treatment.[/size]
[size=x-small]The tube sockets were replaced with gold plated ceramic ones. All wiring, again, was point-to-point using BOLDER Nitro wire. I used a 16 awg for the filament wiring, tightly twisted. All wiring was carefully routed to cross signal wiring at 90 degrees. The resistors in the signal path were replaced with carbon film. The cathode resistors, which were undersized in the stock version, were replaced with aluminum finned 20 watt versions bolted to the chassis, with appropriate amounts of heatsink compound.[/size]
[size=x-small]I re-used the Black Gate 'Power Tank' caps. They were originally in the power supply. Now they are used as the output coupling caps. Again, bypassed with Sonicaps. I used a single point ground and focused on keeping the ground runs as short as possible. The input wiring is a shielded, twisted pair of silver in Teflon insulation. The input circuit from the volume control to the first tube stage was altered to change the gain, slightly."[/size]
[size=x-small]As previously mentioned, Wayne measured the rebuilt amp against another stock Singlepower Extreme he had received. The following two graphs show total harmonic distortion across the frequency spectrum and then across input voltage for the stock Singlepower Extreme.[/size]
[size=x-small] [/size]
[size=x-small]Wayne commented in an e-mail to me that the distortion in the stock Extreme is high enough to be audible (and not in a good way).[/size]
[size=x-small]Next are the same graphs for the rebuilt Extreme.[/size]
[size=x-small]The distortion across the frequency spectrum of the rebuilt amp is much lower than for the stock Extreme.[/size]
[size=x-small]So the important question is how does the Bolder-rebuilt Extreme actually sound? Here's a quick description. I unboxed the rebuilt amp, placed it next to the DNA Sonett and Hat Peed Thingee, loaded "Pink Moon" by Nick Drake into my transport, hit play...and was stunned. Earlier I said that I have a hard time distinguishing the strengths and weaknesses of audio components that are both solid performers...they can sound fairly similar to each other. As I noted earlier, on receiving the HPT, I found it sounded pretty similar to the stock Extreme. And I admired the black background offered by the Sonett and the transparency of the Blue Circle HPT. Both are solid performers.[/size]
[size=x-small]But I have found that some pieces of audio gear are clearly better on first and repeated listening..and the true standouts don't always correlate with prior expectations, reviews, or price. For example, I didn't expect the addition of the PS Audio Perfect Wave DAC & Transport to really transform my speaker rig, but it was evident on first listen that it was not simply a very good digital source, but one that transformed my stereo rig for the better. I found the Bolder-rebuilt Extreme to be just as transformational. I am not talking about subtle improvements over the Sonett or Blue Circle HPT. I am talking about a major improvement over both amps. And admittedly, my memory of the stock Extreme has become clouded. But I don't remember being nearly as wowed by my stock Extreme when it arrived from Singlepower in mid-2007 to dethrone my $400 Original Master headphone amp. Yes, the stock Extreme was an improvement, but it did not knock my socks off.  The rebuilt amp did.[/size]
[size=x-small]The Bolder-rebuilt amp simply offers everything you could want from a headphone amp -- tube or solid state -- without sonic sacrifices. To begin, the amp is extremely quiet. Although the amp is an OTL, I hear no background noise at all when I use the amp with my 18ohm JH16s. It is completely silent when the source is paused and the volume is turned all the way up. Quietness or a "black background" is necessary but not sufficient for good sound quality. [/size]
[size=x-small]What the amp offers in sound quality is an incredibly enveloping immersion in the music itself. Its center of gravity is the mid-range, which offers an enveloping "rounded" full sound associated with really good tube amps. Listening to "To Build A Home" by The Cinematic Orchestra, Patrick Wilson's piano sounds exquisite -- he is clearly playing an older upright, unlike on earlier tracks -- and the decay of piano notes and chords is extended and natural. The amp also demonstrates excellent frequency extension. It offers extraordinarily extended and convincing bass. When the kick drum is struck on Grizzly Bear's "Two Weeks", you hear the resonance of the kick pedal beater striking the skin of the drum. In contrast, the kick drum sounds a little too much like a wet cardboard box with the Sonett. The detail the amp offers is truly astounding. Listening to Broken Social Scene's "Love Sick", I found I could easily hear talking in the background that seemed like a recording mistake. In comparison, I heard some mid-range "hash" on that song through the DNA Sonett and decreased dynamics because the bass extension wasn't nearly as rock solid as with the Bolder-rebuilt amp. The treble is also extended and slightly sweet. Cymbals decay naturally. What the amp offers is a completely coherent window into the music, as it sounds natural across the entire frequency spectrum.[/size]
[size=x-small]Reading these impressions, one might think the amp is colored. It is not. The amp is fast and dynamic. Paired with my source (a second Perfect Wave DAC & Transport) and all three of my "go to" headphones -- the JH16s, the DX1000s, and the HD650s -- the amp in no way sounds syrupy or slow. That said, one nice feature is the ability to roll tubes to significantly alter the sound signature of the amp to one's liking. I personally use either a Chelmer CV181 or a Sylvania 6SN7GTA as the driver tube and a pair of Bendix 6080s as output tubes.[/size]
[size=x-small]One final comment summarizes my impressions of the Bolder-rebuilt Extreme. I often listen to my headphone rig while reading at night before bed. Most of the time, the music being piped through my headphones is supposed to serve as "background", to create an ambience that will allow me to read, get tired, and go to sleep. Maybe the highest compliment I can pay to the Bolder amp is that it has dramatically cut down on the time I spend reading. Many nights, I am listening to a CD I have heard dozens if not hundreds of times before. What is remarkable about the Bolder-rebuilt amp is it just forces me to put down whatever I am reading, close my eyes, and listen with rapt attention to the music. I have heard the track "Dogs" from the Pink Floyd album Animals at least 100 times in the last 30+ years. When listening to the Bolder amp, about 2 minutes into that song, David Gilmour and David Wright reach the instrumental refrain in which Gilmore's guitar line intertwines with Wright's keyboard playing. I find myself completely transfixed by the sheer musicality of that refrain. Not by the musicianship, but by the music itself.[/size]
[size=x-small]Does the amp have any flaws? I can only think of one -- it still has the Singlepower insignia on the faceplate.  It should really have a Bolder insignia. [/size]
[size=x-small]I[/size][size=x-small] highly recommend Bolder Cable as an amp builder. Wayne is an honest and skilled builder. He will turn a shoddy Singlepower Extreme into a state-of-the-art headphone amp. If he ever decides to build an amp from scratch, complete with its own chassis, I would not hesitate to buy it. [/size]
Jul 22, 2010 at 7:57 AM Post #2 of 11


Mar 25, 2010
Minimus, that is a very nice, comprehensive, and balanced write-up. It seems as if Wayne does a good job and I am pleased for you that the investment in time, money and 'concern' have finally paid off.
Good luck with it.
Jul 22, 2010 at 11:34 AM Post #5 of 11


500+ Head-Fier
Apr 10, 2006
My memory fails me slightly, but I think the Extreme's base price was $1,200, but I stupidly paid $1,700 for the "Platinum" version.  In other words, I contributed an extra $500 to Mikhail Rotenberg's Singlepower Ponzi scheme.
Sorry, I don't have any pics of the internals.
Jul 22, 2010 at 3:10 PM Post #6 of 11


Headphoneus Supremus
May 17, 2004
I was just reading an old issue of stereophile and saw one of SP's ad in there; how times have changed.
congrats on the new/improve amp. 
Jul 22, 2010 at 5:00 PM Post #7 of 11


Reviewerus Prolificus
Apr 30, 2005
The Court of the Crimson King
Nice write-up, thanks.  I have also been enjoying my restored/repaired/fixed Extreme, although I almost hate to admit it...
Jul 22, 2010 at 10:45 PM Post #8 of 11


New Head-Fier
Jul 24, 2009

Here is an early picture of the internals of minimus' rebuilt Extreme.
Some of the wiring had to be shortened and rerouted.
Bypass caps were added to the output coupling caps.
The signal wiring was changed a bit.
This should give you an idea of what had to be done to get the graphs in minimus' first post in this thread.
I'm glad the rebuild ended up sounding as good as it did. It just took far too long.
Jul 22, 2010 at 11:01 PM Post #9 of 11


Member of the Trade: Purity Audio
Apr 14, 2005
I decided to look up Mikhail and found him -
He has 3 profiles and is still located in the Denver Area.  That and he has the chutzpa to call himself an electrical/electronics engineer... I hope this isn't old news...
I wonder what his SPA venture is - like to be ahead of the next scam...
Jul 23, 2010 at 8:56 AM Post #10 of 11


Headphoneus Supremus
Aug 31, 2004
There are multiple Mikhail Rotenbergs out there, unless you are absolutely sure that is him I hope you would not disparage/harass a possibly innocent person.
Jul 2, 2017 at 6:08 PM Post #11 of 11


100+ Head-Fier
Nov 2, 2013
I realize this is 7 year old dead thread but I own an extreme which has developed a problem in one channel. It might just be the ceramic tube socket in need of tensioning but I can't figure out how to tension such a socket.
Therefore does anyone know of a person who knows and repairs these amps. I can't even get the miniscule hex bolts to turn. I am not looking for a major modification or expensive upgrade on an amp that is hard to service.
I like the sound so if anyone knows of a reasonably priced alternative tube amp please let me know. (must be tube under $2K)
Thanks in Advance
Thanks in advance

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