Bottlehead Forum
Bottlehead Kits => BeePre => Topic started by: Ivan303 on January 04, 2022, 05:47:38 AM
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Maybe?
But a few questions and a preface.
I am currently running newly constructed MonAmours into a pair of 106 dB EdgarHorns. After much work, such as lifting the ground on the preamp AC input and running it to a separate 'GFCI' outlet due to ground loop issues and... Constructing a small 'L' pad using AudioNote non-magnetic 'tants' on the input to the MonAmours to get rid of the latent 'tube rush' present at all volume settings from the 6SN7 pre I am currently running.... I can now pretty much stick my head into the mid-bass bins and salad bowels of the EdgarHorns and hardly tell if the the system is on.
The MonAmour replaced a near 20 year old pair of DIY HIFI Supply 300b monoblocks which I was running with real WE 300Bs that are still quite OK(and maybe the least microphonic 300B one can get their hands on), so what do do with them? PreBee 2 maybe?
So my questions would be...
Quiet? Guessing quieter that the toob PS 6SN7 pre I am currently using? Horns being more directional so microphonics no as big of a problem when using horns set in front of the toob gear?
Does the stepped pot upgrade (BeeQuiet? Also referred to 'first upgrade' in posts below?) have the same top plate to use to set levels/inputs as that upgrade on the original PreBee did? Wife uses the system and the volume control is her only tool so she uses it. Two volume controls (left and right) might be an issue if not easy to see that the levels are matched. Also, how may steps?
About when (and how much) for the 'second' upgrade (shunt regulator?) which includes more tubes? (More 'toobs' is good!). Know that's a hard question and maybe too far future to know?
Need a winter project so PreBee2 might be it.
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Quite a bit of the impetus for making the changes to the BeePre circuit had to do with noise and very sensitive systems. It's completely possible that you may still need some inline attenuators at the input of the Moreplay, but then again maybe not! With the BeePre volume pot turned all the way down, the output of the preamp is shorted to ground, so you don't The BeePre is very, very gently on 300Bs so using your WE tubes in it isn't such a bad idea.
The stepped attenuator upgrade does use the same top plate label overlay, and it's a pair of stereo switches, with one having a large step in volume and the other having a small step.
I have a little work left to do on the second BeePre upgrade, which keeps getting pushed back since we are getting a pretty heavy volume of custom build orders at the moment.
-PB
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Thanks, valuable information as I thought the two volume controls were 'left-right' not course-fine.
So does the stock PreBee 2 have a balance control as the third knob?
Maybe happy with just that?
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The third knob is the input selector. No balance control on the upgrade. It's a very precise stepped attenuator and doesn't really need it.
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Saw a reply somewhere here that recommends doing the 'whispers' stepped attenuatior mod BEFORE the shunt mod (if and when it is available).
Is that a hard rule and if so why? One of the appealing features to me is that the BeePre2 has a balance control.
If the shunt regulator mod is an improvement, why does it require the stepped attenuator mod to be effective or is it something to do with the way the volume control is on the output that makes a balance control not work with the shunt regulator?
Thanks
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The attenuator modification comes with the active loads for the 300B plates. Since we remove the resistive plate loads and replace them with something that is a higher AC impedance, this provides more freedom in terms of what's optimal for the stepped attenuator.
There is a way to retain the balance control with the BeePre 2 and its upgrades, but you'd need to install the balance control in a hole on the wood base or somewhere else on the chassis plate.
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Ah yes...
Gotta read the fine print below the 'related products' section.
"This manual is divided into two sections, as the C4S active loads can be installed and evaluated on their own prior to installing the BeeQuiet attenuator."
That's likely how I would do it.
Then try to figure out how to drill another hole in the chassis, which appears to have plenty of real estate.
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It's easy enough to pop a hole in the wood base and mount the balance pot to that. Heck I even think you could mount it on the side of the wood base.
When you've gotten the first set of upgrades done, I can walk you through how to put the balance pot back in the circuit.
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Guessing that the 'active', or even 'reactive' load on the 300B would make for a larger sonic 'improvement' than the addition of a stepped pot rather than a wiper pot? Good that it's a two-step upgrade.
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In the BP2 circuit, both the plate load and the pot load the 300B. When going from the resistive load to an active load, that frees up our ability to drop the impedance of the attenuator a bit.
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In the BP2 circuit, both the plate load and the pot load the 300B. When going from the resistive load to an active load, that frees up our ability to drop the impedance of the attenuator a bit.
BeePre 2 kit is on order. Can you share the plate to cathode voltage and the plate current and would that change with the active load?
Thanks.
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Plate to filament is a bit less than 100V, plate current is about 33mA. The BeeQuiet upgrade slightly increases the current to 40mA.
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100V at 40mA?
300B running at 4 watts plate dissipation?
That said, I suppose a 300B being used as a driver for a 845 might not look that much different?
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Yeah, it should last a long time. When you don't need to swing hundreds of volts, nor to swing the most possible current, a few watts of dissipation and a decent amount of standing current are more than adequate.
For an 845, you'll need to swing hundreds of volts, though not necessarily a whole ton of current.
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Yeah, it should last a long time.
The new Western Electrics 300B's are rated for.over 40,000 hours of use... using them in the BeePree 2 would probably result in a single pair lasting a lifetime, unless you leave the preamp on 24/7 lol.
Speaking of, I'm assuming tube rolling the 300B in the BeePree is likely more influential on sonics than the Kaiju? Even if only due to the signal being further amplified by the power amp..?
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Speaking of, I'm assuming tube rolling the 300B in the BeePree is likely more influential on sonics than the Kaiju? Even if only due to the signal being further amplified by the power amp..?
It's complicated ... no surprise there! The headroom of the BeePre is pretty substantial, and the tube itself is quite linear, so the actual distortion is very low. And Kaiju does not invert the phase, so the harmonics simply add, and will be dominated by the Kaiju - unless your speakers are so efficient that it has even greater headroom. But if the sonics are influenced by noise or mechanical resonances of the internal tube strucrture, the preamp may dominate.
Bottom line, I'd just say the sonics are differently influential between the two.
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The BeePre is earlier in the chain, so yes I would say to use the nicer pair there.
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the tube itself is quite linear
Even at that uncommon operating point?
Good to know.
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Even at that uncommon operating point?
If you try to swing 100V peak from a BeePre, that won't be great. At preamp signal levels, the operating area is linear.
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Thanks to both Paul's for the input!
Not trying to hijack this thread here, but I had a couple quick questions as I'm likely going to place an order for the BP2.
At what point does the low frequencies begin to roll off? I imagine that since this is operating at such a low output (and is so linear) that it doesn't even drop 1dB until probably 20Hz?
And, is the Bottlehead shop open to visitors? I moved to the area not long ago. :)
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In stock configuration the BP2 should be about -3dB at 2Hz. With the attenuator upgrade, that will move up to 5Hz, but you could put bigger coupling caps in to move it back down if you'd like.
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So based on that, if one really doesn't need anything under 10-20 Hz one could halve the size of the output cap and go with something EXPENSIVE?
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Well, where would you like the roll-off to start? -3dB at 5Hz from a coupling caps means the rolloff starts around 50Hz.
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It's complicated ... no surprise there! The headroom of the BeePre is pretty substantial, and the tube itself is quite linear, so the actual distortion is very low.
This got me thinkin -- is it all that different sounding from a decent solid state pre then? :) Lol I'm mostly kidding, but am kind of curious how they'd generally compare them since the THD is so low, do you actually end up getting some of those nice second order harmonics injected into the signal?
Every BH kit I've heard has done an amazing job of hitting the sweet spot between tube warmth and accurate tonal fidelity, so I have no doubt it's even better with the BP2. Just made me curious why it works so well in this case (from what I've read).
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This got me thinkin -- is it all that different sounding from a decent solid state pre then?
Well, a solid state preamp usually requires many, many discrete components or at least an op-amp (~20 transistors inside one package) to get some gain and decent linear output. The BeePre and the Moreplay do that with just one active device.