advertisement


One Channel Not Working on Lehmann Black Cube SE

regatron

regatron

Member
Hi All,

I'm new here and new to the world of hifi/vinyl in general. I recently picked up a used Lehmann Black Cube SE to pair with my Rega RP1 with ATVM95ML and Rega Elex-R as an upgrade over the build in phono stage. I have the Black Cube connected to one of the line inputs using Kimber Kables PBJ Interconnect (Ultraplate Standard RCA).

I first tried the Black Cube with all the "default" settings, all DIP switches off (MM setting), high gain mode (default jumper "on" setting), and all other jumper settings off. I tested this for a couple of sides and it sounded great except I noticed that 1) the playback was a good amount louder than usual at the same volume setting and 2) there was a lot more noise when the record was not playing. As a first step, I thought I should try the low gain setting (remove jumper) to try to reduce the noise since I did not need the extra gain for my ATVM95ML since it has 3.5mV of output. (for clarity I plugged the Black Cube into the line input of my amp and not the phono input - not this type of newbie mistake :)

I removed the jumpers and reconnected everything and immediately noticed the left channel was not working. I left it playing briefly at low volume and I heard the left speaker flutter or rumble, like it was intermittently receiving a connection and dropping the connection just as quickly. I was afraid of damaging my systems so I shut the amp off and disconnected the Black Cube.

After some quick search, I read a suggestion to use electronics cleaner. I noticed what I would call "grime" around the dip switch pins on the circuit board so I cleaned it off the the electronics cleaner. After letting everything dry, I tried again and this time the left channel was working but I could hear a periodic fluttering/rumbling sound.

I shut everything down again and decided to revert back to "default" settings. This time, the left channel was not working. Thinking it could be a loose connection, I disconnected everything and reconnected, now BOTH channels are not working! More precisely, both channels appear to be extremely faint. At this point I decided to stop messing with it and look for some help.

Any idea what the issue could be? Any help is greatly appreciated!

Edit: I should note that everything works fine when I revert back to the built in phono stage in the Elex-R.
 
The dip switches are not very good. I had one (sold it on here about 3 years ago now) and after cleaning them with Servisol it was fine. You have to squirt it in via the switches underneath and then work the switches back and forth a few times. Also, you need to use low gain for MM. Where abouts are you based?
 
a.palfreyman said:
The dip switches are not very good. I had one (sold it on here about 3 years ago now) and after cleaning them with Servisol it was fine. You have to squirt it in via the switches underneath and then work the switches back and forth a few times. Also, you need to use low gain for MM. Where abouts are you based?
Click to expand...
Thanks for the tip! I tried isopropyl alcohol on the circuit board and on the dip switches using a qtip. I am unable to find Servisol here, would Hosa Deoxit be the same thing ?

a.palfreyman said:
Also, you need to use low gain for MM.
Click to expand...

I first tried the default setting and everything initially worked, it was when I tried to change to low gain using the internal jumper (removing the jumpers for each of the L and R channels) that the problem started. Only the right channel is working now, even in high gain model (jumpers in)

a.palfreyman said:
Where abouts are you based?
Click to expand...
I am located in Toronto, Canada.

Really appreciate you sharing your experience, thank you!
 
regatron said:
That would be my ideal option but I bought it used in a private sale and will try to work with the seller if I can't find a simple fix.
Click to expand...

Hopefully the advice from @a.palfreyman will work. I think servisol and deoxit do the same thing - aren’t they both electric switch cleaners? Perhaps an expert will confirm…
 
a.palfreyman said:
The dip switches are not very good. I had one (sold it on here about 3 years ago now) and after cleaning them with Servisol it was fine. You have to squirt it in via the switches underneath and then work the switches back and forth a few times. Also, you need to use low gain for MM. Where abouts are you based?
Click to expand...


Well I bought it from you in December 2020 and am pleased to say that whatever you did to it it’s still working well!

J.
 
Update: I tried a round of Deoxit on the dip switches and there was no change, the left channel still did not work. However, I tried moving the RCA input connectors and when I did the left channel came back momentarily!

I then applied Deoxit to the RCA input and output jacks and checked the soldering (though I am no expert). It does not appear there are any issues with the connections from a soldering perspective but I can't be sure, they connections appear solid to me and there is no play on the jacks.

When I connected everything up, I adjusted the left input RCA connector until I heard sound from the left channel. As long as I dont touch anything, both channels work but the left seems, to my ear, slightly quieter. I am now wondering if the differences in tolerances between the Rega RP1 RCA connectors and the Lehmann Black Cube SE RCA input jacks are causing the issue. If I touch the input connectors while the system is playing one or both channels can blip in and out.

On the output side, I am using Kimber PBJ with Ultraplate RCA and they are an extremely tight connection. If I try to "wiggle" the output connections from the Black Cube, there is no change in sound, both channels work and remain unaffected.

Is it simply the RP1 RCAs and Black Cube input jacks dont play nice? Is there a way to confirm there is no internal soldering or connectivity issue on the Black Cube? Any other possible causes?

I am reluctant to simply move on because I'm worried that the connection could drop again and become an intermittent issue. I am also worried that I could blow the speaker if the connection "blips" on and off rapidly while at higher volumes. Is that possible?

Thanks everyone for your help so far!
 
Last edited:
Very possibly either a cold solder joint where the RCA jack is attached to the circuit board, or else a damaged RCA connector. If you can get someone to reflow the solder on the joint that is the first step to take. Plugging in and out cables, especially some that are quite tight can cause stress on the solder joint.
 
fran said:
Very possibly either a cold solder joint where the RCA jack is attached to the circuit board, or else a damaged RCA connector. If you can get someone to reflow the solder on the joint that is the first step to take. Plugging in and out cables, especially some that are quite tight can cause stress on the solder joint.
Click to expand...

Thanks, this sounds like a good next step. Is this something any technician can do?
 
Yes...a decent tech will do this

But why not simply return it and get a refund?

As soon as you start messing with it that option is gone!!
 
Yes, sounds like the input connector has a dodgy solder joint on the signal side. Highly likely if someone has used really tight phono connectors. Needs the joints reflowing as @fran said above.
 
Mynamemynaim said:
Yes...a decent tech will do this

But why not simply return it and get a refund?

As soon as you start messing with it that option is gone!!
Click to expand...

I purchased the unit used in a private sale. The seller claims it was working fine and had tested it prior to selling to me. I would get a refund as my first choice but given the situation, I am trying to find out if there is an easy fix before exploring more remediation from the seller.
 
The solder round the affected joint may also have a more crystalline appearance when viewed under a lens. This is caused when the component moves just before the solder solidifies causing a "cold joint".
 
Thanks a.palfreyman and cctaylor. The reason I ask is I also want to make sure it's not the RCA cables from my RP1 going into the Black Cube inputs. There is a little "play" when they are connected as the connection is slightly loose compared to the Kimber cables connected on the output side. There is a small amount of movement when I "wiggle" the cables.

If I rotate the input cables while they are connected, it seems like I can adjust the connection to a point where I get both channels working.

That said, the RP1 cables worked fine into my two other phono stages (onboard stage with Elex-R and previous Kanto YU4 powered speakers).
 
You must log in or register to reply here.


advertisement


Back
Top