Bottlehead Forum
Bottlehead Kits => BeePre => Topic started by: Paul Birkeland on May 08, 2021, 11:22:15 AM
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For some users of the BeePre 2 with highly sensitive systems, the following modification will lower the noise floor of the preamp for the cost of a few resistors. You will need four 27 Ohm Vishay PR-02 resistors. I recommend part number PR02000202709JR500.
In the BeePre, install one resistor between 22U and 25U, another between 24U and 25U, another between 27U and 30U, then another between 29U and 30U. I recommend positioning the resistors at 24/25 and 29/30 above the resistors already there so they are out of the way (see the attached photo). If you have trouble getting all the leads through 25 or 30, the unbanded lead of the 220uF cap can be moved to the lower terminal to make more space.
This will drop a bit of buzz that resides in the noise floor that I have a tough time picking up in any of the test systems I have here, but could certainly come through with headphones or highly sensitive speakers.
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Hello
I’m getting the resistors today and will install them tonight.
I just wanted to double check one thing before installing. From the instruction you gave one goes on U22-U24 and the other on U24-U25. (Than mirrored on the other channel).
From the picture you attached it seems to me that one goes on U22-U25 and the other from U24-U25. Am I mistaken?
Thanks in advance.
Best
AB
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You're correct, I just amended the original post to reflect that.
-PB
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You're correct, I just amended the original post to reflect that.
-PB
That's what I was attempting to tell you the other day. Guess I should have posted here instead.
-phil
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Yeah, I immediately thought about that and figured out what you meant with that drawing.
Incidentally it will be helpful to have your preamp visit on Friday, as I believe the second BeePre upgrade may naturally remove this noise on its own.
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You're correct, I just amended the original post to reflect that.
-PB
Great Paul, I’ll install the resistor tonight and report back.
Cheers
AB
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Incidentally it will be helpful to have your preamp visit on Friday, as I believe the second BeePre upgrade may naturally remove this noise on its own.
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Will the BeePre upgrades be available soon? If so I will wait for them instead of doing this mod
Debra
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Yup, it's getting close.
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Great Paul, I’ll install the resistor tonight and report back.
Cheers
AB
What an outstanding result!!! I couldn’t be happier. The noise dropped by a lot! To give an idea, before installing the resistors I had a -12db pair of attenuators into the Kaiju and I had hum at half way volume of be beepre2. Now I removed the attenuators and I get a slight noise at 3/4 of the volume pot (it would be impossible to even try to listen at that level).
To summarize, very happy!! Thanks PB and BH team.
Best
AB
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Great news, AB! I'm so glad that this worked for you. I'm over the moon with my BeePre2 as well. I have slight hum too, but it's not a problem. I'm using solid state amps and inefficient (87db) speakers so it's only audible between tracks when the volume > than 50% (which is approaching my maximum comfortable listening level). I ordered these parts but will hold off until after the upgrades!!!
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The second upgrade will also take care of this issue.
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Got my BeePree operational tonight. I am experiencing a hum/buzz that sounds like the previously mentioned buzzy bees (sorry). If I add these resistors, should they remain in place once the upgrade is released?
I hear the hum coming from all three sources on my efficient speakers.
It’s feeding a Kaiju that has been operational for a couple weeks. The system hasn’t exhibited any undesirable background hum until I added the BeePre. I definitely have to get this thing running quieter.
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Yes, just add them in and enjoy.
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This modification did exactly what I hoped. The volume dependent buzz from the speakers was dramatically reduced. It is only audible with full gain on the Kaiju and 3/4 volume on the Beepre and no audio playing. Speakers are Klipsch Cornwall w/ fresh tweeter, mid horn driver, woofer, and crossovers from Crites Audio fwiw (96db I think).
This DEFINITELY increased the enjoyment in listening to the new equipment. THANK YOU!
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I just added the resistors. Nice modification, really lowered the noise floor with my Jagers
Thanks
Debra
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PB,
Is there an equivalent change for the original BeePre (with BeeQuiet)? I have to put a -12dB L-pad at my amp to drop the hum noise so it doesn't bug me. I'd love to handle that at the preamp end. Lower gain is not an issue.
And I've eliminated all the usual noise suspects. And have a nice 120V of regenerated power.
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The original BeePre solves that particular problem in a different way, so there is no equivalent.
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I recommend part number PR02000202709JR500.
Does it have to be specifically Vishay or any other metal film 27R 2W 5% should do?
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Any one will do.
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Any one will do.
Modification performed and tested. Solid -13.5 dB noise decrease for me based on attenuator settings, a great improvement when used with headphones, especially at low volume listening.
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I finally got around to installing these 4 resistors and it made an enormous difference. I don’t have sensitive speakers (87db) but it is an obvious improvement in lowering the noise floor. In between tracks or in quiet passages one could easily detect a buzzing noise from the listening chair. Now, at loud listening volumes (without music playing) I can barely detect noise with my ear an inch away from the drivers. My only regret is waiting so long to do this mod. Great work, PB!
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I did the Modification for Highly Sensitive Systems, and it works great! My question is, with each upgrade, does it ever get removed? I did the stepped attenuator/Constant Current Source upgrade, and now will do the Output Hybrid Shunt Regulator and low impedance balanced output upgrade. Do I just keep the resistors from the Highly Sensitive Systems in place? Or should they be removed with one of these upgrades? Thanks in advance. Eric
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You can leave the resistors there. When the second upgrade is added, they are not explicitly necessary anymore, but they also don't hurt anything.