Beepre after 2 months

[Thermioniclife]

Hey folks,
I thought I would take the time to give you my thoughts on my Beepre after having it up and running for 2 months.
Right from the start it ran fine, no problems or voltage anomalies. Sounded nice and was quite quiet.
Having said that it is very microphonic. I installed the .5 pound flask weights and they helped a great deal.
I then got the sorbothane hemispheres that Doc recommended and I feel that they did little to help. I think the remaining microphony is sound waves striking the glass envelope of the 300b. its like having reverb on. It is most noticeable when changing tracks or channels on the input device. its a shame.
Has anybody tried to place a glass, plastic or other type of tube around the 300b to possibly thwart some of the sound waves from hitting the tubes? I don't have a signal generator but it would interesting to see at what frequencies cause the problem and try to nullify them, enough about that for now.
Not having the ability to leave well enough alone I installed a pair of Hammond 157m chokes in the power supply along with 56 ohm 10w resistors to keep the DCR at 300 ohms. and as Doc said in another post, I think all it did was add extra gravity and expense to the project (as I stated earlier the circuit is very quiet in its stock form) but they were fun to install and I didn't let any smoke out.
If there was an improvement it was minor, it didn't make it worse so I will call that a win.
I will pursue my quest to mitigate the remaining microphony and report back if successful.
On a side note I was using a pair of Paradigm atom v6 for speakers in my living room which is about 18 by 19 feet sq. with a pair of 300b monos.
Paradigm claims 90db 1w 1m but that seems a little inflated to me, I would think more like 86-87db. but those 5 inch drivers just did not cut it in that size room. So I sprang for a pair of 95Db Tekton mini Lores. The lows and midrange sound nice but the high frequencies are a little thin. I believe the xover is just a simple cap. I know I will get inside them and probably screw them all up.
Perhaps I will call Eric at Tekton and see if he has any ideas. He is a nice guy as I have spoken to him a couple of times and he was very gracious.
I will attach pics of the choke install for others that want to make their Beepre's heavier and more expensive.
Happy Holidays one and all.
Lee

[Paul Birkeland]

Hello Lee,

You might take some time to consider where your BeePre is in relation to the speakers, as positioning can influence how pronounced the microphonics are.

Are you using the lead weights and the O-rings under each tube?  Those two together seemed to do the trick for me.

-PB

[Thermioniclife]

Hey Paul,
I am indeed using the weights and Orings. This helped a great deal to mitigate microphonics from physical shock such as tapping on the chassis or heavy footfalls.
I currently have the preamp behind the speakers and the Mini Lores have a front facing port.
The room has a large braded rug that covers about 80% of the hardwood floor underneath.
I also have very heavy drapes on the 2 picture windows in the room.
Does my idea to try to shield the 300bs from sound waves seem like a fruitless folly to you?

[Paul Birkeland]

You could give it a shot, just trying perhaps a small cabinet with some doors. 

[Thermioniclife]

Roger that.
Btw I forgot to mention that I have EH gold tubes in my amps and I swapped tubes with the pre and same condition exists.
I have read on this forum that some are using 6a3 tubes in the Beepre but the subject of the 6a3 microphonics was not mentioned.
have you tried them and if so what are your thoughts about 6a3 microphony.

[Thermioniclife]

on a lighter note I posted about the new build and mentioned the microphony and another member suggested a sound proof box.
I replied that I had just sold my sound proof box because I didn't need it anymore because I broke up with my last girlfriend.
I shoulda kept it!

[Paul Birkeland]

I have received some 6A3s finally, after wanting to try them for a long time, but I haven't yet given them a go.

[Thermioniclife]

Ok, let me and all know your thoughts on sound quality and microphony when you get a chance.
Have a good day.
Lee

[Paul Joppa]

With respect to 6A3s, I'll just mention that pretty much all directly-heated tubes are microphonic, because the filaments are very thin and have vastly less mechanical stiffness than the other components of the tube.

[Thermioniclife]

Oh hello Mr. Joppa
Nice to hear from you. I love the Beepre except for the Microphony. It's quite quiet and has enough gain for my needs.
I am just trying to get the microphony to a minimum.
I doubt you remember our conversation regarding the virtues of keeping the grid of a 300b at ground during the initial power up of a 300b amp but you validated my thoughts, I hope I thanked you properly at that time. It was probably 15 years ago. I used an industrial timer and a relay and it worked quite well. You will get a chuckle that I also tried to employ a similar circuit on a dc coupled circuit, no joy, but that was a learning experience for me.
I used to have a Foreplay 3 and an early SEX amp but they were stolen from me while I had them in storage.
I would still like to get ahold of another Foreplay 3 if you have one kicking around. I just ordered a S3x and c4s last week and will enjoy the build. I am currently enjoying a crack with speedball.
best wishes to you and yours for the holidays and the new year.
Regards,
Lee Rodenburg

[RPMac]

I’ve had my BeePre running ever since the first kits were shipped out. Built completely stock except I bypassed the selector switch(I only use one input from my BH-DAC) and I used silver-plated copper mil-spec wire in signal path. The only modification was 10 uf Russian caps.

I have no microphonics...I just tapped the top of the 6A3s in use(Sylvania/Philco coil spring). No problem with any tubes I’ve used in it and no tube treatments. It sits on some packing strips that are somewhere between dense foam rubber and styrofoam and all are on a marble top table.

The only thing I’m doing different is that I’m running it and my other tube amps on balanced power.

I also bought a Stereomour from Doc which uses a 3B7 driver which can be very microphonic. The 3B7 that came with the amp wasn’t microphonic, but it went bad on me. The replacements I had were very microphonic to a little less microphonic, but the longer the replacement was used, the less microphonic it became.

Do I know why I don’t have a microphonic problem? No, but all DHT is wonderful.

[Thermioniclife]

Hey PJ and PB,
I got a pair of Tung-Sol black glass 6a3's and tried them in my Beepre.
they solved the problem of the sound waves striking the glass envelope completely mitigating the reverb effect.
makes me Happy.
But on another note they sound a little thinner in bass response than a 300B.
I have not had much listening time on them so we will see.
Peace, Love and Happiness to all at Bottlehead and all in the Forum for the Holidays and the upcoming New Year.

Regards,
Lee

[Todd R]

Did no one think about using tube dampers?
https://herbiesaudiolab.com/collections/tube-dampers

[Doc B.]

He's using dampers, the lead weights we recommend. The Herbie's are OK for some really HF stuff that the 300Bs sometimes generate, but they don't really have the mass to help with the lower frequencies that are primarily set off in the 300B filaments. In rereading this thread the description of the issue and of the setup seems to indicate that the preamp needs to be moved farther away from the speakers.

[Thermioniclife]

Hey Doc,
The flask weights helped a great deal with the 300b's with foot falls but not for the vibration of the tube due to sound waves striking the tube it self. I purchased a pair of vintage 6a3's that are dead quiet regarding that problem. Alas they sound a little thin compared to the 300b. My uneducated guess is that the current manufacturers of tubes probably do not use the best materials to construct their tubes and subsequently could be prone to these issues.
I would speculate the issue is caused by the grid vibrating in relation to the plate. Or the cathode vibrating regarding the plate.
Having said all of this I will say the BeePre is a very nice preamp and will stay in my system. I plan to build an audio rack to hold my 300b mono's, the Beepre and source equipment, perhaps I can place it in a more advantages location, hopefully in a null node in the room.
By the way loving my new S3x. Just ordered another yesterday and will use them as mono pair.
the one pictured has a BeeQuiet attenuator and 3 inputs and will be the master, the next will be the slave and have a single input from the master.