A new BeePre sings

physicsmajor · 2839

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Offline physicsmajor

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on: August 16, 2016, 08:58:29 PM
Finished my build, tested, and installed yesterday.

Outstanding documentation, per the usual. I applied the BeeQuiet during the build, so had to juggle the manuals a bit. Took a little more time than it would have otherwise, but triple checking again saves the day. No problems with the build at all. All of the tests passed, LEDs lit, etc.

Modifications:
  • I moved the pair of balanced sockets to the input position and wired for two single-ended outputs. My main system biamps using two single-ended amps, so this made more sense. Currently lurking on auction sites, etc. for a pair of input transformers to actually wire up the balanced inputs.
  • I used a pair of Russian K73 PETP caps instead of the stock Dayton ones in the parafeed positions. The axial variant of the K73 fits perfectly here, but the leads are too short. So I extended them with some of the Teflon solid core wire in the kit.

I got a pair of the 0.5 lb red lead rings Doc B. recommends on Ebay cheap. Never used the kit without them, but the ringing/microphonics is only really evident when moving the attenuators - and damps out in about 3 seconds. Using the standard stick-on feet, at least for now.

It sounds really, really fantastic. I think what impresses me most is how it handles fine detail, particularly very subtle textures on top of an otherwise black background. Fingers repositioning in acoustic string music, etc. - or at least that's what hit me first.


As an aside I just have to tell everyone: If you're doing this stuff, seriously go get a pair of nice surgical needle drivers. As a joke I tried a pair of Codman 47 Classic Plus needle holders with tungsten carbide inserts on this build, and was astonished. It's so much easier to guide and wrap wires. They lock in place to hold a part (I'm looking at you, power supply diodes) or thermally insulate a component. Add in a pair of round-nosed pliers, typically sold for jewelry making, and your kit-building life will be so much easier... and raise the quality of your builds.
« Last Edit: August 16, 2016, 09:02:51 PM by physicsmajor »



Offline 2wo

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Reply #1 on: August 17, 2016, 04:37:14 PM
Finished my build, tested, and installed yesterday.

 As a joke I tried a pair of Codman 47 Classic Plus needle holders with tungsten carbide inserts on this build, and was astonished.

Wow. tool envy(;...John

John S.


Offline physicsmajor

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Reply #2 on: August 17, 2016, 07:11:56 PM
Not trying to flaunt - on Ebay or various other sites you can pick a nice set of needle holders up for around $20. That's akin to a nice set of pliers, and at that price well worth the investment. My wife also finds them useful for many other hobbies, and I've used these to fix a number of other things around the house, too.



Offline physicsmajor

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Reply #3 on: August 20, 2016, 05:49:48 PM
Depending on time of day and what other electronics are in use around the house, it seems some noise can pass through my existing filter and cause a low frequency hum. It's well below the level of the audio, but at its worst can become noticeable between tracks and in very quiet sections.

So I'm looking for an isolation transformer. I want to make sure to get a properly rated one, but don't see the BeePre's power consumption specified. And even if it was, I'd still be here asking because of turn-on transient draw.

What is the correct minimum wattage for a BeePre-dedicated isolation transformer?



Offline elko

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Reply #4 on: August 25, 2016, 01:44:38 AM
I am having some hum issues to. Can't figure out where or what the source is. I suspect its something outside the amplifier and even outside my house.

I am thinking about a isolation transformer to. Found a great deal here in the Netherlands for a 1600VA. That seems plenty to me.

 The only doubt i have is that the hum only occurs in the left channel. Sometimes its quite loud and the amplitude varies with the height of the line voltage. When the voltage drops the hum gets louder. It always stays above 230v (Dutch standard voltage). I don't think that the lowness (still above standard) in voltage is the source, but just an indication that some big powerline polluting device is turning on.

« Last Edit: August 25, 2016, 02:42:52 AM by elko »



Offline Doc B.

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Reply #5 on: August 25, 2016, 07:57:35 AM
Have you swapped tubes side to side to see if the hum follows one of them?

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.


Offline physicsmajor

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Reply #6 on: August 27, 2016, 12:44:34 PM
In my case the hum is about the same on both sides. It exists independent of volume setting. Martin Logans aren't the most efficient speakers in the world, but my amps are quite high gain which accentuates this.

I do believe it's polluted power, though, as an aquarium pump increases the hum by around 3 dB when switched on. Given the 1.5 amp fuse is a 250VA iso transformer OK for the BeePre?



Offline Paul Birkeland

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Reply #7 on: August 28, 2016, 11:18:01 AM
A 250VA isolation transformer will work well.  In your case, I would look for an isolation transformer that could raise the voltage slightly.  One that maybe had taps for different voltages on one side would be helpful.  (220:235 would be ideal, or you could buy a 500VA unit, which would have higher output since you wouldn't be loading it down much)

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline elko

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Reply #8 on: August 31, 2016, 08:52:07 AM
That 1600VA is a bit overpowerd. Never thought about the size and weight of a transformer of such capacity. I would really like to know if an isolation transformer is a solution for your problem

Ps. Switching tubes doesn't make hum switch along. It just stays left.



Offline physicsmajor

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Reply #9 on: September 13, 2016, 03:41:46 PM
Update, with three main findings:

Iso transformer took some time getting here, but I have a non-isolating Variac I wanted to try adjusting the voltage a bit. There is a definite proper operation sweet spot, where things are happiest, but it didn't solve the hum I was hearing. Go below this and you get a nasty hum at a well-defined threshold; above it just seems to increase a little (but I didn't push too far either way).

Iso transformer helped a little, but didn't get rid of the problem entirely.

Then I noticed that my 300b's weren't fully seated. The silicone dampers both had little gaps between it and the tube's ceramic bottom, even though I had used what I thought was significant force and also have the 0.5 lb ring weight on top. I cautiously but firmly seated them... and now the noise floor is inaudible until your ear gets within about 18 inches from the woofers.

Still got it on the iso transformer, but I honestly think my particular hum was mechanical. For those with hum, first triple check that your 300b's are very well seated. These sockets' connectors are rather stiff, and caught me off guard.



Offline Paul Joppa

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Reply #10 on: September 13, 2016, 07:04:58 PM
That is an interesting, and valuable, finding. Such a mechanism is logical but new to me. Thanks for your persistence and for sharing it on the forum!

Paul Joppa


Offline jjvornov

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Reply #11 on: September 22, 2016, 04:47:28 AM
I've seen the same thing. I have one tube that likes to move up and out of its socket. When the hum and noise start coming from the channel, I push the tube back down and it stops. Since I have the weights, I'm thinking about trying without the ring damper to avoid the problem, but it just sounds so perfect as is, I haven't tried yet.

But the weights made a big difference. The funny thing was that the vibration/feedback was really bad on certain recordings like Keith Jarret's Koln Concert. It has that glassy piano sound that became distorted before the weights were added. I can see how the frequency of ringing I heard tapping the tube was resonant with the sound of the piano.

James