New 4B cubed problem?

doublenaught · « **on:** 1 Oct 2016, 04:17 pm »

After reading the great reviews and receiving advice on this forum, I just purchased a demo 4B cubed to replace my Sunfire amp. It has paperwork showing that it was returned because of a noise in one of the channels. With the preamp off I could hear a slight buzz in the left speaker when I got close to it and a much fainter hum in the right speaker. Both are much quieter than the hum the Sunfire has been emitting. My question is: since I got a very good deal on it being a demo, should I return it to the seller or send it to Bryston for service? Or should I not bother with either because it isn't audible while listening to music? I'm assuming the overall sound is what it's supposed to be. It will take some getting used to after 25 years of listening to the Sunfire. Thanks.

James Tanner · « **Reply #1 on:** 1 Oct 2016, 06:02 pm »

Quote from: doublenaught on 1 Oct 2016, 04:17 pm

After reading the great reviews and receiving advice on this forum, I just purchased a demo 4B cubed to replace my Sunfire amp. It has paperwork showing that it was returned because of a noise in one of the channels. With the preamp off I could hear a slight buzz in the left speaker when I got close to it and a much fainter hum in the right speaker. Both are much quieter than the hum the Sunfire has been emitting. My question is: since I got a very good deal on it being a demo, should I return it to the seller or send it to Bryston for service? Or should I not bother with either because it isn't audible while listening to music? I'm assuming the overall sound is what it's supposed to be. It will take some getting used to after 25 years of listening to the Sunfire. Thanks.

Hi

If you unplug the inputs to the amplifier do you still hear the buzz?

james

doublenaught · « **Reply #2 on:** 1 Oct 2016, 06:20 pm »

Hi James, thanks for the reply. No, it's dead quiet in both channels with inputs unplugged.

jtinto · « **Reply #3 on:** 1 Oct 2016, 06:32 pm »

I bet you have really sensitive ears ...
You describe something that I also hear with my 4B SST2: dead quiet, but an ever so slight 60Hz hum when either an xlr or rca input is connected. It's likely a ground loop but I haven't been able to rid mine. I don't worry about it. It's so low that it doesn't affect the music at all.

doublenaught · « **Reply #4 on:** 1 Oct 2016, 06:40 pm »

I actually have high frequency hearing loss. I just got close to the speakers because of the previous customer's complaint. If it was a ground loop problem wouldn't I hear it in both speakers?

James Tanner · « **Reply #5 on:** 1 Oct 2016, 07:28 pm »

Quote from: doublenaught on 1 Oct 2016, 06:20 pm

Hi James, thanks for the reply. No, it's dead quiet in both channels with inputs unplugged.

HI

Ok then it has to be something in the system in front of the amplifier - try plugging in one component at a time and see if you can isolate it - preamp with no connections then connect each component in turn.

Also hiss can be RF pickup on the cables or a very efficient speaker which means you are hearing the noise floor of a component attached to the amplifier.

james

doublenaught · « **Reply #6 on:** 1 Oct 2016, 08:05 pm »

I can still hear the buzz with no components plugged in. I tried different input cables with no change. Swapping left and right input cables still had the buzz in the left speaker. I swapped speaker cables from right to left and the buzz shifted to the right speaker.

James Tanner · « **Reply #7 on:** 1 Oct 2016, 08:29 pm »

Quote from: doublenaught on 1 Oct 2016, 08:05 pm

I can still hear the buzz with no components plugged in. I tried different input cables with no change. Swapping left and right input cables still had the buzz in the left speaker. I swapped speaker cables from right to left and the buzz shifted to the right speaker.

So the buzz followed the speaker cable?

james

doublenaught · « **Reply #8 on:** 1 Oct 2016, 08:44 pm »

No, the buzz was consistent through the left output terminals through whichever cable was connected to them. When I switched the right speaker cable to the left amp terminals the buzz was in the right speaker instead of the left.

James Tanner · « **Reply #9 on:** 1 Oct 2016, 09:50 pm »

Quote from: doublenaught on 1 Oct 2016, 08:44 pm

No, the buzz was consistent through the left output terminals through whichever cable was connected to them. When I switched the right speaker cable to the left amp terminals the buzz was in the right speaker instead of the left.

Ok so something in the left channel is causing the buzz but it does not seem to be the amplifier.

What is the rest of the system?

james

doublenaught · « **Reply #10 on:** 1 Oct 2016, 10:07 pm »

I have a CAT SL 1 Ultimate preamp, Spendor S100 speakers and Audio Sensibility speaker and interconnect cables.

audio.bill · « **Reply #11 on:** 2 Oct 2016, 01:12 am »

I'd suggest the next step of troubleshooting would be to switch the L/R interconnects between the CAT preamp and the Bryston amp (at one end only) to see if the buzz switches channels.

doublenaught · « **Reply #12 on:** 2 Oct 2016, 02:04 am »

Quote from: audio.bill on 2 Oct 2016, 01:12 am

I'd suggest the next step of troubleshooting would be to switch the L/R interconnects between the CAT preamp and the Bryston amp (at one end only) to see if the buzz switches channels.

I switched cables at the amp end and the buzz was still in the left speaker. I hear the noise even when the preamp is unplugged from the power outlet

audio.bill · « **Reply #13 on:** 2 Oct 2016, 02:53 am »

I'm unsure what could be the cause of the buzz at this point, James or support at Bryston should be able to provide further assistance.

1ZIP · « **Reply #14 on:** 2 Oct 2016, 05:01 am »

You said it was returned because it was noisy. What did the dealer do to correct the problem before he sold it to you?

James Tanner · « **Reply #15 on:** 2 Oct 2016, 10:43 am »

Hi

We can certainly check it out fr you - the test sheet should be in with the amplifier and it will show the signal to noise measurement.

james

doublenaught · « **Reply #16 on:** 2 Oct 2016, 10:50 am »

Quote from: 1ZIP on 2 Oct 2016, 05:01 am

You said it was returned because it was noisy. What did the dealer do to correct the problem before he sold it to you?

There was no service record included but I will call them Monday and find out.

doublenaught · « **Reply #17 on:** 2 Oct 2016, 11:29 am »

Quote from: James Tanner on 2 Oct 2016, 10:43 am

Hi

We can certainly check it out fr you - the test sheet should be in with the amplifier and it will show the signal to noise measurement.

james

Thanks James. I'll contact the dealer tomorrow when they are open. My main reason for this post was to find out if the small amount of noise I'm hearing is acceptable or something I should be concerned about. I truly appreciate all the assistance you have given.

doublenaught · « **Reply #18 on:** 2 Oct 2016, 11:42 am »

I just found one more interesting piece to this puzzle. The left channel noise disappears when the right interconnect cable is disconnected.

audio.bill · « **Reply #19 on:** 2 Oct 2016, 03:06 pm »

Well that's really interesting! If I had to venture a guess at this point it would be a faulty ground connection in one channel of the amp that's causing a ground potential difference between the two channels.