Help needed with residual noise/noisefloor

sl-15 · 3849

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Offline sl-15

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on: June 25, 2023, 03:41:13 PM
I finished my BeePre2 a few weeks ago and noticed a hum/noise right away that gets louder with the volume.
During a built I triple check ever step. I use a Pace soldering station set between 650F and 800F depending, I clean all connections and leads and I use Cardas leaded solder. All the voltages and resistances during my build passed.
I use a SS power amp with a lot of power. The hum/noise is noticeable in between songs or in quiet passages when watching movies.
I have a hard time figuring out what kind of hum/noise it is, it definitely has a buzzing component.
I recorded it and also recorded the residual noise with my extended Foreplay 3 as a comparison (no problems there). But I noticed I can not upload audio files here.
The same happens with my Crack. If I have my BeePre up half way and the Crack half way up music is at good listening level through HD650ies. At that volume I also hear the noise in quite passages and in between songs.
It does not matter if the input is shorted or if a muted source is connected.
Here is what I did so far:
I visually inspected every solder joint again, passed.
I measured all the ground connection continuity, passed.
I listened with Crack and headphones with no source, so I just could hear the noise and pocked every connection with a chop stick. No change in the sound, no crackling.
I would appreciate some guidance on how to troubleshoot this further. I can re-flow all the connections if deemed necessary. I was thinking about doing the BeePre 2 Modification for Highly Sensitive Systems? I am very curious if this is a solder connection problem or if it might be something else. Thanks for any input.
I attached a photo of my oscilloscope reading, left and right channel, source is shorted. Not sure if this is helpful.

Stefan Hampel
Soundsmith Carmen, modded Technics SL-1200mkII, Thorens TD 125 mk2 with SME V, Eros, Extended Foreplay III, BeePre2, Crack, Pioneer Spec 4, Sonus Faber Electa


Offline Paul Birkeland

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Reply #1 on: June 25, 2023, 03:45:27 PM
If you don't have the second upgrade installed, the noise floor will drop a fair amount once you get there.  Otherwise if you decrease the value of the 130 ohm resistors on the 5 lug strips by the 4 pin sockets to more like 22 ohms, that will also drop the noise floor.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline sl-15

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Reply #2 on: June 25, 2023, 04:13:21 PM
Okay thanks. Is this pretty much the Modification for Highly Sensitive Systems as in the sticky post from you? Or are you saying to just replace the 130 ohms with 22ohms?

Stefan Hampel
Soundsmith Carmen, modded Technics SL-1200mkII, Thorens TD 125 mk2 with SME V, Eros, Extended Foreplay III, BeePre2, Crack, Pioneer Spec 4, Sonus Faber Electa


Offline Paul Birkeland

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Reply #3 on: June 26, 2023, 03:59:51 AM
Correct, it is that modification.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline sl-15

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Reply #4 on: October 16, 2023, 12:07:53 PM
I finally had an order big enough for mouser and got the 27ohm resistors to install as recommended. It was tricky to get them installed next to the exciting resistors, I think I would have been faster removing the 130 ohm ones and replacing with 22ohms. But the result is the same and now the BeePre2 is nice and quiet. It is so much better now, not that the music sounds better but the lack of the background noise in quiet passages gives it a much more professional feel. :)

Stefan Hampel
Soundsmith Carmen, modded Technics SL-1200mkII, Thorens TD 125 mk2 with SME V, Eros, Extended Foreplay III, BeePre2, Crack, Pioneer Spec 4, Sonus Faber Electa