BeePre2 300B Preamplifier Kit

The quick backstory –  it was decided in 2013 to build a prototype 300B preamp. The result, BeePre, was the best preamp we had made. 

As happens with any product user feedback over the years helped us to prioritize some improvements we felt useful. The basic concept of a super linear 300B Directly Heated Triode (DHT) as a preamp tube was – pardon the pun – sound. However this type of design is very challenging to dial in and we felt we could improve things a bit more. So we have addressed a few issues that we and our users found to be a little bothersome in the original BeePre.

One was to come up with a way to reduce the slight ringing (microphonics) that all DHTs generate. This we did by moving the volume control to the output of the preamp. It’s an unconventional move that requires some mathematical trickery regarding the attenuator values and gain structure. But it works well to reduce the noise floor when the attenuator level is reduced.

The next thing we addressed was the need for a universal power transformer. The massive, well designed PT-9 universal power transformer used in the Kaiju 300B preamp was employed. The PT-9 also allowed us to improve the BeePre’s handling of voltage sag, which in a few cases caused some noise when a user’s AC mains voltage dropped below nominal and affected the original voltage regulators. The new fliament supply regulator adopted from the Kaiju is much more tolerant of those variations.

Other changes were made with an easier build in mind. We found that some of the improvements we had incorporated allowed us to create a more basic and simple overall circuit that still retained the goodness of the original BeePre while making the build far less complex and much easier to debug. The original 12″ x 12″ chassis has also been rescaled to 10″ x 16″ to better match the size and shape of the Kaiju 300B Stereo amp.

The original BeePre preamp came with a quasi-balanced XLR output as well as single ended RCA output. That added some complexity and some limitations to the circuit, and not that many users ended up using the balanced output anyway. So a buffered balanced/single output option will be part of a shunt regulated high voltage supply upgrade that will be released in the near future. Mounting holes for a balanced input transformer will be carried over from the original BeePre as well, for those wishing to perform their own balanced input mod.

What is the bottom line? The improvements to the circuit make the Basic BeePre2 a match to the sonics of the original Beepre. The upgrades will take it past the original BeePre, with a very noticeable improvement in bass punch, lower noise floor, and more natural vocals.  The upgrades will also make the BrePre2 a good match to many solid state and push-pull tube amps. Digital sources and analog sources like the Eros phono preamp and Tube Repro tape head preamp will all work exceptionally well with the BeePre2.

What are the unchanged features from the original BeePre?

Three single ended RCA inputs, with the option for a user modification of one to a balanced XLR input

One stock RCA single ended output with the option of adding a second, balanced XLR output. (with the implementation of a future shunt regulator upgrade package)

Stock volume and balance pots with the option of a new redesign of our 36 step stepped attenuator upgrade in the near future

There’s a lot of nice stuff under the hood including some D style Neutrik jacks that need some extra chassis acreage to fit. And there will be room for your favorite big ol’ boutique capacitor upgrades too. We provide the usual high quality level of American made transformers, an American manufactured chassis panel with our cool new random brushed artisanal finish (a nice thick one at .100″) and lovely Pacific Northwest milled alder wood base. Resistors, capacitors, sockets and other parts are all the same quality level as in the matching Kaiju 300B amplifier. Weight is up from 12.4lbs. to about 17lbs 

Performance? Input impedance is 70K ohms with balance control centered. Output impedance is 3K ohms at maximum (this can be lowered to about 400 ohms with the upcoming shunt reg/buffer upgrade kit). Gain of our prototype at 1kHz measures 6dB. Frequency response -3dB points at 7Hz and 110kHz. Noise level will depend upon the brand of 300B you choose. Our basic BeePre prototype’s S/N measures -70 dB with 2V signal input. THD measures 0.21% at 1kHz at 2Vrms output. Maximum output before the onset of clipping (which presents itself as a very gradual rounding of the sine wave trough) is 32Vrms.

I have been listening to my BeePre already for a couple of months. There’s a thread of my build and some of my system so I won’t bother you with that. I’ve listened to it extensively and carefully. I’ve taken it to other very high resolution systems that I know well. The BeePre is the most amazing piece of audio, period. It will make any system sound better. More body, more resolution, more speed and a better flow to the music. I have friends with good systems and good ears. We often have different opinions on what we like. They are all babbling for the BeePre. I’ve said before that, on paper, it is amazing. In real life it is better yet. BH keeps raising the bar.

—xcortes, on the Bottlehead Forum

Time for some initial listening impressions. First off, I had an interesting start but after a phone call to Dan everything was sorted out. System synergy is different for everyone and I ran into the perfect storm of 100dB sensitive speakers and a very high gain SS power amp (old Quad 303 at the moment) with the BeePre. My system needed a Lpad in front of the power amp to lower the gain.

I’ve only got around 30 hours on the BeePre but from the beginning it sounded great and continues to improve. It must be the DHT magic as I find myself mesmerized by the sound coming from my speakers. The best way I can put it is that the BeePre has added a sense of realism and greater emotion to my listening experience. It images very well, has wonderful tone and a blackness between notes that I appreciate.

The BeePre continues to impress! It’s new and I hate to comment too much on new parts of the system until I’ve grown accustomed to them but it really is an amazing preamp

https://web.archive.org/web/20170207043418/http://www.bottlehead.com/smf/index.php/topic,4045.msg37145.html#msg37145

–johnsonad on the Bottlehead forum

I finished the assembly of my BeePre this evening, completely stock. The manual and packaging were great – assembly was a breeze, with no post-assembly hardware debugging required. I still need to finish the base to match my Eros. I’ll get to that eventually I suppose 🙂

The Bee is replacing an older Denon AVR that I was using as a preamp between my Eros/Squeezebox/TV and a Rotel solid state power amp. New hotness fit in my rack – barely! I actually had to remove the damping o-rings and couldn’t use any damping feet. So far I’ve only listened to it along with the Eros. Spun on a few records, and…

…in a word, brilliant. I was expecting at least some increased detail and clearer soundstage (based on my previous Eros upgrade experience) but am still really surprised by how much my system improved. History seems to repeat itself…just like when I hooked up my Eros I once again feel the need to re-listen to most of my record collection.

Thanks for offering another great kit!

–jaggy, on the Bottlehead Forum

I’m now listening to the BeePre, late at night. It’s very soft, and quite pleasant. The level is 38-70 dB SPL. I’m playing Blue Coast Collection in DSD format through Korg/AudioGate software to emu 404 usb to BeePre to Paramount 2A3 to vintage Klipch LaScalas. The Paramounts have the soft-start upgrade and an L-pad on the inputs. The previous pre-amp was an extended foreplay III.

While I thought the foreplay III was excellent, I think this is a step up. The background noise is completely absent. The voices sound even more alive. The guitar strings sound like I’m listening to my 9 year old son practice. The background instruments sound clear, distinct, and balanced in a way I have not noticed before with this recording. I’ve never enjoyed this music this much at this low a level. I can’t wait to listen at louder levels.

-Dave

–dw on the Bottlehead Forum

Doc I found the problem, you were right I had a wire out of place. Fixed the problem and everything checked out. I am listening right now and all that can say is wow!!!. Clarity and depth to the sound stage, my system always had decent breadth to the sound stage but it was not real deep, it is now. And the clarity is stunning. I am listening to Cowboy Junkies Trinity session on CD and there is more detail than I have ever heard before. Lastly, it is phenomenally musical. With the balance I can dial it into fit the room much better than before.

I bought the sorbathane feet you recommended. I will post the details of what I hear when I get them. While the kit was the most complicated kit I have tried your instructions were fantastic. The pictures really helped in some cases. Good job to you and your crew. To anyone building or wanting to build this kit just take your time and double check your work. No matter how good the instructions are it is amazing how you either misread, misinterpret, or simply make a mistake so take it slow and you will definitely be rewarded.

Thanks again for the wonderful kit and product. You have made my week.

Richard

–rockpassion on the Bottlehead Forum