high level of background noise from Befaco A*B+C [SOLVED]

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fredke
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high level of background noise from Befaco A*B+C [SOLVED]

Post by fredke » Tue Mar 27, 2018 5:04 am

Hello there.

I would like to know if anybody has had the same experience as I with the Befaco A*B+C :

I find it great for mixing and tweaking voltages, but I can't mix audio with it because it adds too much background noise.
It's like it's adding white noise...

I have never heard such a noisy module - except for those which are supposed to be noisy ;-)

(Ok, *maybe* it would pass in a live concert, but it's impossible to make a clean recording from it.)

Any feedback and ideas welcome.
Last edited by fredke on Tue Jun 05, 2018 7:49 am, edited 1 time in total.

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Shledge
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Post by Shledge » Tue Mar 27, 2018 5:38 am

Completely silent and clean for me.

Sounds more like either:
- faulty module
- grounding issue
- crap PSU

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Post by starthief » Tue Mar 27, 2018 8:18 am

It's likely to be your power supply or distribution.

Somebody geeky and smart about power -- probably Genus Modu, but maybe Rabid Elephant or Graham Hinton -- wrote something about running audio through offset modules often being highly susceptible to noise on the 0V rail. Far more so than a standard VCA would.

If you can eliminate the offset entirely -- maybe plug a dummy cable into the C inputs? -- that might quiet it.

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Post by pugix » Tue Mar 27, 2018 9:28 am

Standard trouble shooting for this sort of problem is to try the module in a different case, or with a different power supply. If the problem shows up in all environments, it's the module, otherwise the problem is with the environment where it occurs.

And include the external audio path as something to change, too.
Richard
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Graham Hinton
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Post by Graham Hinton » Tue Mar 27, 2018 9:38 am

fredke wrote:I find it great for mixing and tweaking voltages, but I can't mix audio with it because it adds too much background noise.
It's like it's adding white noise...
Has it always been like that or has it changed?
If the latter, it is probably a faulty IC.
starthief wrote:It's likely to be your power supply or distribution.
No, it isn't. Wideband noise is not a symptom of either at fault. PSU problems tend to be one frequency, distribution problems may be a mixture of distinct frequencies.

That's why it is important not to be vague describing noise problems if you want help.

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Post by starthief » Tue Mar 27, 2018 9:40 am

I stand corrected :)

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Post by fredke » Tue Mar 27, 2018 10:47 am

First of all, I am new here and I appreciate to find such a responsive community... Thanks !

Ok, so it's not normal.

Since it's more a white noise than a hum, I don't think it's the power supply. Also, I have mounted the module in 3 different cases (Arksine, Ginko, Mantis), and the noise remains the same.

Even when killing the offset with a dangling jack in input C, the problem remains unchanged. In fact, in stays the same no matter if I inject signals, insert dangling jacks or leave it unplugged.

Did I mention that both outputs exhibit exactly the same noise issue ?

So all the explaination that is left is a faulty module, I suppose.

Since I DIYed it myself, could I have done something wrong ? Did I overheat a component ? What do you think ?
(Only electronically educated answers please - I can do wild guesses on my own ;-))

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Shledge
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Post by Shledge » Tue Mar 27, 2018 10:55 am

Sounds like it's faulty then. Contact Befaco and I'm sure they'll sort you out.

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Post by brandonlogic » Tue Mar 27, 2018 11:22 am

I have the exact same problem with mine. noisy, high noise floor. sounds like white noise. I thought it was normal, its just a noisier module, i use it more often with cv than audio so never bothered contacting befaco.

But others are saying its clean/no noise, perhaps i should contact Befaco as well.

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Post by listentoaheartbeat » Tue Mar 27, 2018 11:34 am

fredke wrote:Since I DIYed it myself, could I have done something wrong ? Did I overheat a component ? What do you think ?
Of course you could have done something wrong. Which is why the thread title and first post are really unfair towards Befaco – it doesn‘t say anything about DIY so potential customers of their built and tested modules might be irritated for no reason.

If you want qualified feedback about potential issues with your build, I recommend posting a detailed description, high resolution photos, and audio in the DIY section.

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Post by brandonlogic » Tue Mar 27, 2018 11:44 am

listentoaheartbeat wrote:
fredke wrote:Since I DIYed it myself, could I have done something wrong ? Did I overheat a component ? What do you think ?
Of course you could have done something wrong. Which is why the thread title and first post are really unfair towards Befaco – it doesn‘t say anything about DIY so potential customers of their built and tested modules might be irritated for no reason.

If you want qualified feedback about potential issues with your build, I recommend posting a detailed description, high resolution photos, and audio in the DIY section.
mine is not diy and i have the exact same problem.

just sent them a message to see whats up. thanks for the reminder.

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Post by CaneMan » Tue Mar 27, 2018 12:38 pm

(oops. wrong post)

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Post by Graham Hinton » Tue Mar 27, 2018 1:22 pm

fredke wrote: Ok, so it's not normal.
Well, maybe it is... Looking at the schematic, there is a +24dB gain stage on the outputs which should be totally unnecessary with an AD633.

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Post by fredke » Tue Mar 27, 2018 2:14 pm

listentoaheartbeat wrote:
fredke wrote:Since I DIYed it myself, could I have done something wrong ? Did I overheat a component ? What do you think ?
Of course you could have done something wrong. Which is why the thread title and first post are really unfair towards Befaco – it doesn‘t say anything about DIY so potential customers of their built and tested modules might be irritated for no reason.

If you want qualified feedback about potential issues with your build, I recommend posting a detailed description, high resolution photos, and audio in the DIY section.
You are right, I should have been more precise. To be honest I can't remember whether I bought it pre-assembled or assembled it myself.

(EDIT: I just had a look at the PCB and it's definitely too clean to be a DIY of mine. So I bought it pre-assembled.)

Anyway, I contacted Befaco 2 days ago and they just replied :

"Some users have reported this behaviour before! we are currently working on a new version of the module that solves noise issues.
If your unit is DIY I can suggest a few changes for you to try and see if noise levels go down."

This would also explain Brandonlogic's experience.
Graham Hinton wrote:Looking at the schematic, there is a +24dB gain stage on the outputs which should be totally unnecessary with an AD633.
Maybe that is what they mean. Anyway I've asked for their mod suggestions, and will post them here once I get a reply
- which apparently may take a couple of days.

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Post by slow_riot » Tue Mar 27, 2018 2:52 pm

Graham Hinton wrote:
Well, maybe it is... Looking at the schematic, there is a +24dB gain stage on the outputs which should be totally unnecessary with an AD633.
AD633 has very high wideband noise already too.

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Post by Shledge » Tue Mar 27, 2018 4:59 pm

If it's by design, then why is it not an issue for other people? Mine for example is completely clean.

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Post by Shledge » Tue Mar 27, 2018 5:09 pm

Actually on further inspection...

There is some noise, but it's fairly quiet. I have to really turn up my headphone amp to even notice it. I have never noticed until this topic came along. :despair:

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Post by slow_riot » Wed Mar 28, 2018 4:44 am

Shledge wrote:If it's by design, then why is it not an issue for other people? Mine for example is completely clean.
Typical noise performance for the AD633 into 24dB gain will give 30mV peak to peak wideband noise, but this will vary from part to part. Psychoacoustics are highly subjective, too.

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Post by Shledge » Wed Mar 28, 2018 5:03 am

Either that or people have different ideas on what is acceptable. I don't mind background noise if it's barely noticeable when the signal is hot - you won't hear it in a mix anyway.

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Post by starthief » Wed Mar 28, 2018 6:16 am

Based on the thing about the DAC in Plaits, I suspect people also use wildly different gain staging and dynamics processing, among other things.

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Post by slow_riot » Wed Mar 28, 2018 6:37 am

Shledge wrote:Either that or people have different ideas on what is acceptable. I don't mind background noise if it's barely noticeable when the signal is hot - you won't hear it in a mix anyway.
Yes, personal taste in this realm gives a lot of room for different interpretations, in many cases leaving in an imperfection can result in a more appealing sound. However in this context I think the AD633 performs best at unity gain, with level control on the inputs rather than the output if necessary. It seems like Befaco have reached that conclusion too after user feedback.

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Post by pugix » Wed Mar 28, 2018 10:54 am

fredke wrote: I contacted Befaco 2 days ago and they just replied :

"Some users have reported this behaviour before! we are currently working on a new version of the module that solves noise issues.
If your unit is DIY I can suggest a few changes for you to try and see if noise levels go down."

I've asked for their mod suggestions, and will post them here once I get a reply
- which apparently may take a couple of days.
I'm very interested to find out what they say. I built two DIY.

The concept for this module is really quite good. Too bad that the implementation of it seems not so good.
Richard
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Post by fredke » Thu Mar 29, 2018 3:37 am

[EDIT: the schematics below is a beta version of the mod. As you'll read further in this thread, it only solves the problem partly. Now Befaco has a much better mod, which you'll find down this thread too.]

Ok, so I've got a reply from Befaco.

I would need to replace some resistors, remove some others, and bypass a couple.

It seems easily doable, but the risk of damaging my (not DIY) module is not null. Furthermore, they provide a schematics rather than a picture of the PCB, wich increases the risk of me making a mistake...

Since they offered to provide further assistance if needed, I'll ask if I can return it to have it modded by them, and at which cost if any. I will let you all know.

Meanwhile, for those who are electronically inclined, here are their schematics and instructions :
(I'd be curious to know what it all means: does it have something to do with the AD633's gain ?)

Image
Image

"You get resistor names and its original value in grey. New resistor/capacitor values are written in black.
Then you have a few resistors crossed. Just remove them. and one of them that need to be bridged with a wire.

I would suggest to do the modification in one side to see if it improves the situation, and if so, go for the second channel."
Last edited by fredke on Tue Jun 05, 2018 8:12 am, edited 3 times in total.

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Post by fredke » Thu Mar 29, 2018 3:46 am

Shledge wrote:Either that or people have different ideas on what is acceptable. I don't mind background noise if it's barely noticeable when the signal is hot - you won't hear it in a mix anyway.
Of course, but in this case there is also a quality disparity between units. I was probably unlucky, and you were more lucky.

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Post by pugix » Thu Mar 29, 2018 8:46 am

Wow, that is a lot of changes. It would be easy to miss some of them. Befaco should give you a list of the changes, too.

I just listened to one of mine. I can hear some noise, with nothing patched in, when I turn the C pot to about 9 or 3 o'clock (straight up is 'off'), but not in other positions. I am not going to make those circuit changes.
Richard
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