After months of deliberation, misguided attention, unrelated delays, etc., I was finally able to install the BT2250 prototype that Biketronics recently built for me. The team at Biketronics and myself had been kicking this idea around for quite some time after the overwhelming success I've had with the BT4180 amp powering my front stage. I needed either a medium-power two channel or a big mono amp to drive one or two of my Stereo Integrity BM MKIV 12" subs and thus the idea for this amp was born.
For anyone unfamiliar with Biketronics, they are a small family owned and operated electronics company based in Moscow, Idaho. They specialize in making aftermarket electronics for Harley Davidsons, including high-end audio equipment. You can view their website here: Biketronics Inc
Biketronics builds their amplifiers using Hypex Class-D amp modules, a design many of you know I absolutely love thanks to their tiny size, big power, class-leading efficiency, and Class-A frontend. Biketronics builds their own DSP controlled preamp boards as well as the specialized power supply which converts 12v to the necessary high voltage required by the Hypex modules. They also build their own metal enclosures which are a cool understated black box with silver logo on front and employee signatures in silver on the back. Very cool that, aside from the Hypex modules, everything in these amps is soldered and assembled in their small Idaho location, meaning they are truly “Made in the USA”.
The standard BT2180 and BT4180 amps use two and four Hypex UcD180OEM amp modules each, respectively, which provides a very substantial amount of power in such a tiny package. However, the team at BT mentioned to me that a more powerful UcD250LPOEM module is nearly identical in size to the UcD180OEM so two could easily be installed in a BT2180 chassis. We had also kicked around ideas for a single UcD400OEM or UcD700OEM module in the BT2180 or BT4180 chassis but the stereo UcD250LPOEM design would require the least amount of modification to the power supply and enclosure.
Another reason why I love Hypex amps is how linear they perform with varying impedances. Though existing documentation from Hypex does not report 2 ohm performance, reading up on the UcD250LPOEM modules and using various testing sources, we concluded these amps should make ~400w RMS per channel at 2 ohms which is a great match for the SI BM MKIV. Furthermore, analysis of the max current these amps are capable of yields max output at 2ohms with some losses at 1ohm, though fully stable. Though 20% less RMS power than my Vibe Litebox Bass 1 mono Class D amp which is rated for 500w RMS at 2 ohms, I was gaining a second channel at roughly 1/3 the size. This smaller footprint meant I could stuff the modded BT amp next to the BT4180 in the factory amp location and then I could reinstall the plastic cover for the rear interior of my truck's cab which also doubles as sound dampening. It's a win-win, assuming the 2250 can perform well. For reference, here is Hypex’s datasheet for the UcD250LPOEM: http://www.hypex.nl/docs/UcD250LPOEM_datasheet.pdf
A regular BT2180 on the outside:
Picture of the internals, including the UcD250LPOEM modules:
It’s also interesting to note other companies that use Hypex modules which includes some Genesis home amps, 10+ boutique high end makers including Channel Islands, and specific to this application, Rythmik Audio and GR Research for their wide array of subwoofer amps. This is especially interesting because Hypex amps typically have flat output/response down to 0hz, making them a great option for driving subs. My Rythmik FV15HP in my home theater is a BEAST with one 15” GR Research driver powered by a 550w Hypex amp and the FV15HP is routinely tested with substantial output to nearly 10hz, driver limited. Insane!
Fast forward to last night, I was locked and loaded to take my new Nikon D500 camera out kayaking for some wildlife photos; there are at least six Bald Eagles taking spring refuge in the local wetland and on my bucket list this year is to photograph one from water level catching a fish. However, I had been laboring over yard work all weekend and I knew if I spent 2-3 hours on the water, I would be anything but physically functional for my day job on Monday. So, instead, I decided to go kayaking after work on Monday and use the pleasantly warm 75 degree Sunday evening to install the BT2250 amp that had been sitting in my office for the past few weeks.
Now installing these amps can be a little tedious because they are meant to be installed in a Harley motorcycle. Normally these amps have a ~45hz high pass filter to keep bike owners from blowing their speakers when cranking Def Leppard at 80mph on a Harley Ultra Classic which means their power draw on a bike is going to be much less than an amp used for sub duty. The BT2180 is usually shipped with ~12-14ga. power/ground wires but I wanted to make sure I’d have enough wire gauge for subwoofer power demand. I went to the BCAE system power wire calculator which I highly recommend you save to your favorites: http://www.bcae1.com/images/swfs/sys...assistant2.swf
16oz. Aquafina for scale:
A quick calculation showed that I needed at least 10 ga. power wire between my distribution block and the BT2250 amp to avoid melting any wire, assuming 400wrms output at 90% efficiency. When I add the second SI sub I will need to upgrade from 10ga. to at least 6ga. according to this calculator. Stuffing 10ga. into the factory BT2250 terminal was not an easy task so I’ll need to research some options when the sub expansion happens.
Together at last, BT4180 and BT2250 squeeze 1520wrms into the factory Hummer amp footprint:
So, about 9:45pm last night everything was ready for initial testing. I fired up my P99 and with my iPhone plugged in, I navigated to Spotify which is now my music source for 95% of my listening. I’d been rocking out to Flo Rida most of the day on my headphones while mowing the lawn and weed whacking so I immediately pressed play for “My House”. It has a nice subtle drum kick in the intro verse before transitioning to a deep bass line during the chorus. This bass line gets pretty intense when you crank it up and the BT2250 was certainly putting the BM MKIV through its paces. Next, I played Jane XØ’s “Hard To Forget” which has some intense deep bass typical of current EDM fare. Holy smokes this thing is FULL. What’s more interesting is that I’m noticing control of the sub that was never present with the Vibe amp. What?! I must be delirious from the heat and exhaustion. Plus, it is now 10pm and I probably shouldn’t be cranking my system in my driveway, time for bed.
Monday mornings are always a gamble because my biggest client has 90% of their IT staff located overseas and by the time I’m logging in, they’re already done with the work day. So when I open my email inbox at 8am, it can be anywhere from “nothing-went-wrong-over-the-weekend” and I’m off to other projects or, more likely, things went sideways during a Saturday change window and I’m about to spend most of my week organizing resources to get things back on track. To my pleasant surprise, zero issues had happened and so it was business as usual. Which meant a lunch hour listening session!
After a very restful 8 hours of deep sleep and a very productive morning of work, my wits about me; I was ready to attack the perception I’d developed the night before. No way was the sub sounding “more controlled”. To me, a sub amp either works or it doesn’t; there isn’t much in-between. I was expecting some trade-off in output which would hopefully be made up by adding the second BM MKIV powered by the extra channel from the BT2250. I always enjoyed the sound of my system using the Vibe Litebox Bass 1 but I also always felt I was missing out on some output. I must admit that now I do not feel this way and the single BM MKIV may be all that I will ever need.
Another thing to note, with the Vibe amp I always felt like I was reaching the maximum excursion of the BM MKIV at the P99’s 45 volume level using some of my bass heavier tracks. However, using these same songs I was getting MORE output at lower levels and with less cone movement. Now I know this is pretty hard to claim without specific measurements but the difference seemed exceptional; otherwise I would not include this observation. So with that, I played the following demos for further investigation:
Vic Mensa w/Skrillex – “No Chill” – I have NEVER heard the BM MKIV fill the cab of my truck this much and because of this song I will be measuring SPL when I get the chance this week. I was cranking the P99 to volume level 50 and still not quite reaching maximum excursion of the BM MKIV. I am suddenly realizing I may not need the second BM MKIV that’s been sitting in my garage since inception…WOW!
Skrillex w/Zhu and They – “Working for It” – Similar experience as “No Chill”, whether or not you like Skrillex and his “trendy” haircuts, his bass lines are legendary and no contest for rigorous subwoofer duty. Once again, the BM MKIV was articulating everything well below maximum excursion. Could this be a damping factor issue?
Vibe does not publish a damping factor for the Litebox Bass 1 nor does Hypex for the UcD250LPOEM. I did find documentation that listed the UcD180HG with a damping factor of 400 which is probably close to the 250, given the very similar design and components. However, this is a stretch without clear specs for the Litebox Bass 1. Time to send the Vibe amp to Biketronics for a go on the Audio Precision Analyzer and also testing for the 250 modules so that we can determine actual output at 2ohms as well as with both channels driven to really put the modified PSU through its paces. We’re headed back to Idaho for a wedding in about a month so I’ll bring the Vibe with me for bench testing, can’t wait!
Back to the subjective listening test, I wanted to switch things up from bass-head tracks to some rock to see how well this new combo handles more sensitive source material.
Foo Fighters – “The Pretender” – A very laid back kick drum and full realism without overpowering. Just perfect.
The White Stripes – “Seven Nation Army” – If Foo Fighter’s kick drum in “The Pretender” is understated, “Seven Nation Army” has a bass guitar and kick drum that are about as in your face as it gets. Huge and enveloping, on my dash and in my chest. I freaking love this song and the new combo make it all that much better.
Alt-J – “Hunger of the Pines”, “Bloodflood pt. II”, and “The Gospel of John Hurt” – Alt-J has a way with instruments that I haven’t quite experienced before with any other artist, except for possibly Audioslave. Their usage of unorthodox time signatures is risky yet rewarding but easily muddied with a poorly setup subwoofer. No issues here, the offset beats are clear and articulate, just as they were meant to be heard.
Okay, time to get back to work (and to write this review between work emails). Plus, the moms dropping their kids off at the home daycare across the street are starting to look at me funny. I’ll be adding more thoughts to this review as the week progresses as I’m able to get more listening time in during driving. And stay tuned for technical testing details in a little over a month when we put one of these and one of my Vibe amps on the AP tester. Until then, thanks for reading!