The New BeePre Pure Speculation Thread

[Deke609]

So Doc B. has chosen the winning prototype?

When will we learn more? I imagine putting together the assembly manual will take a while. Any chance of a brief circuit description in advance, preferably highlighting changes from the previous version?

cheers and thanks, Derek

[Paul Birkeland]

Yeah, all of this started in April 2018 with this prototype.  Ultimately all I was really wanting to do here was to make myself a BeePre that looked more like my Kaiju and to mess with a BeePre  powered with the Kaiju power transformer.  I used the new Kaiju DC filament supply board instead of the specialty BeePre filament regulator which freed me up from being locked into the BeePre operating point and allowed a little extra flexibility.  Being able to adjust the operating point meant that I could move the attenuators to the output and not overdrive the 300B in the process. 

[Paul Birkeland]

After the red prototype, we explored the possibility of different packing and remote control options.  All those extra metal panels drove the cost of the kit way up, and the remote attenuator would have required me sitting down with the boards we ordered and doing surface mount soldering to each one to prep them before shipping, or paying a board house to do assembly.  Stuff like that really messes with lead times, and a $3000 preamp kit wasn't sounding like such a hot idea, so this one didn't make it to the public.

[Raymond P.]

The Bottlehead Instagram has a picture of the underside and showed a stepped attenuator. Is the stepped attenuator an upgrade kit? I hope the basic potentiometers with L/R balance control are still available.

[Paul Birkeland]

So now we arrive at the current design, which from my records is the 5th or 6th prototype (not all of them make it to getting built).  This iteration was inspired by the simplicity of the Moreplay, and in essence what I built could be called a BeePlay. It is a boiled down version of the circuit with the Kaiju DC filament supply but just a CRCRC high voltage supply.  Biasing and plate loading are done with resistors to dramatically decrease the amount of initial debugging, and we just plug/block off the holes for the extra tubes/jacks that come with the upgrades.  This will be the "stock" BeePre 2 offering. 

On Friday, I brought up this basic BeePre preamp and several of the upgrade modules, and we installed them and listened to the various options. 

Ultimately one upgrade will be a BeeQuiet attenuator with completely different values to better work with this new circuit, but this upgrade will also come with active loads for the 300B.  The combination of the lower impedance of the new BeeQuiet and the resistive loading in the stock circuit isn't optimal, hence the combination of the attenuator and C4S board offered together.

The second upgrade module will populate the rear two 9 pin sockets with a dissimilar dual triode that provide individual shunt regulators for both channels as well as adding a cathode follower buffered output that decreases the output impedance of the kit substantially.  This upgrade will also provide balanced outputs similar to the BeePre 1.

The primary benefits of the new design vs. the old are:

• Replacing the two single voltage power transformers with a new universal power transformer.
• Reducing the severity of microphonics and apparent noise in the circuit through relocating the attenuator and using a different 300B operating point.
• Offering a far easier to build stock circuit and modularizing the more difficult components as future (optional) upgrades.
• Providing some additional space with a larger chassis plate that matches the Kaiju.
• Low line voltage regulator dropout is now nearly impossible through the combination of using the Kaiju DC filament regulator, the universal power transformer, and a different circuit design.

[Raymond P.]

My understanding of the upgrades may not be correct, but is sounds like the new attenuator design needs the C4S loads for optimal performance. But is the reverse also true? Meaning, will the preamp work just as well with C4S loads with the basic pots?


I'm hoping the C4S loads (w/o the attenuator) can be a stand alone upgrade.


Thx.

[Paul Birkeland]

My understanding of the upgrades may not be correct, but is sounds like the new attenuator design needs the C4S loads for optimal performance. But is the reverse also true? Meaning, will the preamp work just as well with C4S loads with the basic pots?

Yes, the new attenuator needs the C4S loads for optimal performance. 

I'm hoping the C4S loads (w/o the attenuator) can be a stand alone upgrade.

That is not in the plan as of now.  The new design could, however, allow you to get creative and have both the balance control and the BeeQuiet attenuator.  You'd have to move the balance control to a hole on the wood base, but it's now possible with this design.

[Doc B.]

Everyone wants to know about the upgrades but no one asks about how it sounds?

[Paul Birkeland]

Everyone wants to know about the upgrades but no one asks about how it sounds?

Doc B. didn't want to let me take it home!

[Deke609]

Everyone wants to know about the upgrades but no one asks about how it sounds?

I do, and specifically the stock, stock+C4S/BQ and Stock+C4S/BQ+shunt-reg/cathode-follower as compared to the BP1+BQ. 

Tell us everything Doc!

cheers, Derek

[Thermioniclife]

How about the Microphony?

[Deke609]

See primary benefit #2:

The primary benefits of the new design vs. the old are:

• Replacing the two single voltage power transformers with a new universal power transformer.
• Reducing the severity of microphonics and apparent noise in the circuit through relocating the attenuator and using a different 300B operating point.
• Offering a far easier to build stock circuit and modularizing the more difficult components as future (optional) upgrades.
• Providing some additional space with a larger chassis plate that matches the Kaiju.
• Low line voltage regulator dropout is now nearly impossible through the combination of using the Kaiju DC filament regulator, the universal power transformer, and a different circuit design.

[Thermioniclife]

Yeah I read that but I would like to hear from the designers.

[Raymond P.]

Everyone wants to know about the upgrades but no one asks about how it sounds?

I just assumed whichever becomes the final product will sound great. :-)

[Paul Birkeland]

Microphony is greatly reduced.  The revised design (we'll assume the attenuator upgrade is installed because it makes the math easier) will be at worst only 4dB less microphonic than the BeePre 1.0, but every reduction from -0, -0 on the BeeQuiet attenuators reduces the microphony by that amount of attenuation.

So if you find you listen to -9dB on the coarse switch and -0dB on the fine switch typically, then the new BeePre with the BeeQuiet upgrade would have 13dB less microphony than BeePre 1.0.  For those who happen to use a high gain solid state amplifier with a BeePre or who use a Kaiju with super sensitive speakers will find that they listen with the BeeQuiet attenuators turned way down most of the time, and the new design would be a very dramatic change. 

For reference I don't even bother using my vinyl coated lead rings with the new design.