Bottlehead Forum
Bottlehead Kits => BeePre => Topic started by: rt60 on June 11, 2013, 08:57:30 PM
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When I first built the BeePre, all of the voltages checked out fine, and it's been sounding beautiful for the last month or so. But then suddenly the left channel became very quiet and muffled. I tried switching around the tubes and inputs, but the problem stayed in the left channel.
I did a few voltage checks, and most notable is the left filament regulator board has kreg=0.75V and +reg=94.5, while the right side regulator board has values of kreg=4.3V and +reg=146V. I checked the voltages coming out of the transformers, and they were the same on both the left and the right. And like I said, switching tubes did not significantly alter the voltage measurements.
Has something gone wrong with my left regulator board, or could the problem be somewhere else? I haven't gone through and tested every terminal, but I can if that would help.
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Pull the EL84 on the muffled channel, power it up, then see how the voltages look (the 94.5V should pop up to ~180V). You can run the preamp like this for a fair amount of time without concern for damage.
-PB
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I removed the EL84 from the "bad" channel, and that channel's regulator board had readings of +reg=192V and kreg=0.57V. I then did the same test on the "good" channel and measured +reg=192V and kreg=1.16V. Does that answer anything?
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Oh, that is actually very, very helpful.
Next, see if the low voltage follows one of the EL84's. Also, listen to the preamp w/o the EL84's to be sure the muffling is gone (it should be).
If the low voltage doesn't follow one of the EL84's, but stays on one side, I would start pointing fingers at the TL431.
-PB
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The low voltage is not following one of the EL84s. I swapped them around, but they both produced approximately the same measurements. The low voltage always stays on the left side. And when I removed both EL84s and listened to the preamp, the muffling seemed to be gone.
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I am about 90% confident that the TL-431 on the lower voltage channel needs to be replaced. We can mail one to you if you like.
-PB
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Ok. I'll try replacing it. Should I email Eileen for the part?
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Ok. I'll try replacing it. Should I email Eileen for the part?
E-mail replacementparts (At) bottlehead (dot) com
-PB
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It was the TL431. I was able to find a local electronics supplier to get the part. Once I replaced it, the left channel went back to normal. Thanks for the help!
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And that, folks is what is so good about this site! There are a few too many 'hit and run' dealers out there. Here, you will find knowledge and support. I feel compelled to mention this occasionally on this site for those who are new here.
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The more time I spend here, the more I am impressed by the time, patience, insight, helpfulness and dedication of the Bottlehead team. It is astonishing and inspiring.
Thanks!
Adam
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oops, I think I have a similar issue.
two quirks : every hour or so of playing time, I have a 30 second burst of static (very annoying, continues even with volume turned down to zero), I have to turn off the amp for a couple minutes.
the second one is the left channel going almost mute from time to time (sometimes 30 minutes, sometimes after a couple hours of uptime). tried swapping the tubes to no avail.
which voltage should I check, and any thoughts on the static/crackle issue ?
thanks
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Always start with checking all of your solder joints. Noise that happens after the amp warms up is often due to thermal expansion in a solder joint that isn't 100%.
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It's a good point. I had the same trouble with one of my Quickie projects. "Ah, it COULDN"T be my soldering." Well, in the volume control set up that I was using, there a lot of joints, but all of them looked great. They weren't, and after rewetting them all, heaven returned.
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thanks guys...
i went and checked everything yesterday, and lo, my trusted Nakamichi PA7 my dad gave me 30 years ago has a channel that goes dead after warming up a while.... the 'Pre is blameless for the channel going mute !!!
for the static noise, still sound's like the pre is the culprit. all solder joints look good, I'll give them a go anyway, but it's a very tubey noise (similar to the one all tube thingies do when they startup, except it happens from time to time even if it's warm). one of the tubes being weak / starting to go ?
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The more time I spend here, the more I am impressed by the time, patience, insight, helpfulness and dedication of the Bottlehead team. . . .
In my case medication helps. And every so often two fingers of Bourbon.
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old scotch or armagnac does it for me -smile-
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by the way doc, you were right, didn't see anything special, but resoldered about half the joints just to be sure, and lo, no more cracks and snaps !!! makes you humble about soldering skills...
so. recap, beepre ok, nakamichi dead. I stole my son's parasound zamp (puny but musical 40watt-er), makes music, but my DIY fullrange speakers (using a nice Davis 20DE8 unit) don't really sing, mids ok, but puny bass. better than -dread- no music.
I just tried my dad's QUAD 909 workhorse, the music is great, but the noiseflor is attrocious. with the source off, i can hear the white noise three feet away from the speaker. I had none with the nak or the parasound, I guess the quad's sensitiviy is very high. Any thoughts on a fix, there is no gain adjustment on the amp.
cheers all.
by the way, who's using what as far as transistor or class D amps ?
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LOL. So basically you stole your son's amp AND your Dad's amp? You must be a popular guy. ;) I'll have to tell your grandchildren to be careful around grandpa! ;D
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borrowed, and I'll pay back with interest (itune credit for one, a nice armagnac for the other).
Appart from that, any thoughts on an attenuator between the beepre and the quad ? a 6 or 10db job to lower the noise floor ? Would serve a double purpose, as I rarely can go up more than 10% volume level, and it's tricky to play not too loud.
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I think johnsonad mentionned something like a "LPad" for a similar problem. Can I get info on this mythical beast ? (sorry for spamming)
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People here are probably tired of me recommending them, but I've had good success with these (http://www.amazon.com/Harrison-Labs-Line-Level-Attenuator/dp/B0006N41B0/ref=sr_1_1?ie=UTF8&qid=1379024471&sr=8-1&keywords=harrison+labs+12+db) in other applications. Don't go with less than 12 dB.
Best regards,
Adam
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Yeah, $25 for what is essentially four resistors is reasonably steep, but they are incredibly convenient.
-PB
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what resistor values are adapted to the bee ? I'll build them around a cable! or would it be more convenient to solder them directly before the RCA output inside the bee ??
i was thinking of a 10k/3.3k for 12db att
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10K/3.3K is a great place to start. These are best soldered into your amplifier, or at the amplifier end of your interconnects. (Remember - we want the BeePre driving the cable/amp, not the L-pad)
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This reminds me of an idea that I had quite some time ago. Since a soldered connection is usually the best, I thought of taking one end of an interconnect apart, and then soldering it to the output of the pre-amp. Of course, you will always be stuck with the chosen length of that interconnect.
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I do that all the time. I used to worry 'what if the cable isn't long enough' but Duh, make it the right length or unsolder it and put in a new one...John
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Hmmm, maybe the next step is power cords permanently mounted the equipment. Pretty big step, but I bet we can sell it....again.
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the davis speaker is the one used in the MV One. A specialized shop in paris sources it, and gives away for free the full MV One schematic that Davis has chosen to give them with ok to distribute. I just built them over the last two weeks, my very first homebuilt speakers (and 2nd Hifi DIY experience after the Bee....). Cost me 2000 euros of drivers, and 200 bucks of assorted wood, glue, laquer.... the MV One retails for 8000, so I guess its a good deal.
source http://www.lamaisonduhautparleur.com/HpDavis.php
sound is gorgeous, and its the first time Ive gotten away from panels in the last 10 years (maggies for 9 years, and last year with 3 different ML i didn't warm to). the speaker is direct connect to the amp, no filter, no nothing. fluild music, warm and musical mid range, almost as good as maggies, no sibilence in the highs that go waaaay up wthout being metallic. Lows, cant say as I have no good amp, cf rest of my post. By the way, the LPad did not do it. i had to go up to -20db to get the noise out, but at that level, no dynamics left. with the Quad, noise withstanding, I'd say very good lows down to 100, a bit less under. Very listenable, like my first 1.6's.
at the audioporn dealer that made me choose that model, thunderous lows i'll be trying to get.
I'd really love to hear what you guys use for amps.
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specs on the 20DE8 (in french, but the curves are universal)
http://www.toutlehautparleur.com/images/Davis_Acoustics/20DE8_Stereo_Image_N54.pdf
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by the way, gave back my son's parasound and my dad's quad, and got myself a nice CODA S12...
more will follow (i started, talking about it in the Davis thread Doc created), but I integrated it with a BW sub and a DSpeaker DSP for room acoustic correction in the very bottom. BLISSSSSSS
(sorry for yelling my enthousiasm).
and i'll roll a few 300Bs for good measure (not thrilled with the EH that shipped with the pre, a bit too microphonic for my taste). I got some shuagang 300b-98Bs and a PSVANE Ti2 pairs on loan.