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Author Topic: Noise from mix bus..somewhere..
maikol
Administrator
Posts: 77
Post Re: Noise from mix bus..somewhere..
on: May 8, 2016, 08:03

Yeah desoldering gun is mandatory for this kind of project ! :P

I'm not sure un-routing the channels is going to make a difference, but it's worth a try for sure.

And regarding the P1 channels being quiet, I don't think you can draw this conclusion, as if you use them as master faders, they are not routed to the P1 bus right ? ;)

Then about the value of the caps, there are several of them on the whole channel, but the vast majority are of the same value (220uF maybe, I'm not sure anymore, and I'm not near the studio right now). All in all, it's not going to be expensive, just very time consuming.
Paul-
Svenre
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Posts: 62
Post Re: Noise from mix bus..somewhere..
on: May 8, 2016, 11:17

Cool M!
Ok I'll try un routing first and then proceed with the more brute way :-)
Re my P1, I should have reminded you that I recently replaced the L/R channel cards of P1 and the noise remained but disappeared when I muted P1, so that's why I now assume that at least the problem probably isn't the caps at the assignment board on P1.

If this turns out to be the problem I'm totally in for recapping all channels. Starting with the presumed noisy ones, I could then do it bit by bit. In my new life as single I always look forward to the evenings of TV, a cold beer or two and the soldering fumes:-) Here's 24 Don Classics NV73 Neve preamp clone kits ready just yesterday night, waiting for a couple of delayed components from Mouser. I'm building 10 for a couple of friends and the rest for myself. A nice row of Carnhill transformers to the left :-)
Image
maikol
Administrator
Posts: 77
Post Re: Noise from mix bus..somewhere..
on: May 8, 2016, 20:59

Wow impressive kit ! Nice work mate ! 8O

Regarding your P1 conclusions, I think you're misunderstanding how it works. You don't route your P1 channels to the P1 bus right ? Or it would give you a loop and end up with a big larsen effect ? :-)

So muting the P1 channels doesn't tell you anything about the state of its caps on the assignment board, it just tells you that the problems lies before those P1 channels mute happens.

Is this clearer now ?

Anyway, of course is the assignment board is new in those P1 channels, it's probably just fine... ;-)

And about the caps values on the channels, I've looked back at the orders I'd made to Farnell at that time, it looked like this :

1200 CAPACITOR, RADIAL, 35V, 33UF; Product Ra EEUFM1V330
3900 CAPACITOR, RADIAL, 220UF, 10V; Product R EEUFM1A221
600 CAPACITOR, RADIAL, 16V, 470UF; Product R EEUFM1C471
200 CAP, ALU ELECT, 100UF, 25V, CAN; Product EEUFM1E101

Quite a lot of caps, huh ? :D

Let us know what you find !
Paul-
Svenre
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Posts: 62
Post Re: Noise from mix bus..somewhere..
on: May 8, 2016, 21:22

Thanks M!

Well if you say I've got something wrong, I surrender, right away! :-)
Ok..so I assumed that the assignment board is a stage of every channel that lies after the fader/mute switch. I assumed that this was also the case with P1. In that case that assignment board would alway be 'heard', even if the P1 was muted.

I do understand that P1 shouldn't be routed to itself.

One of the first things I did when troubleshooting that noise was to swap P1 (both left and right channels) with P2. Because the noise remained my guess was that the noise came from another place.

You've already provided very valuable info for me to proceed the troubleshooting so I'll be fine for a while and hopefully I'll be able to pinpoint. But to answer your question 'Is it clearer now?' I'm afraid it's not entirely..

I thought the assignment board was a stage positioned after the fader/mute switch. Did I miss something? Or is P1 different?

Edit: Jeeez, just saw the amount of caps you ordered...
maikol
Administrator
Posts: 77
Post Re: Noise from mix bus..somewhere..
on: May 8, 2016, 22:04

Quote from Paul Svenre on May 8, 2016, 21:22
Ok..so I assumed that the assignment board is a stage of every channel that lies after the fader/mute switch. I assumed that this was also the case with P1. In that case that assignment board would alway be 'heard', even if the P1 was muted.

I do understand that P1 shouldn't be routed to itself.

One of the first things I did when troubleshooting that noise was to swap P1 (both left and right channels) with P2. Because the noise remained my guess was that the noise came from another place.

You've already provided very valuable info for me to proceed the troubleshooting so I'll be fine for a while and hopefully I'll be able to pinpoint. But to answer your question 'Is it clearer now?' I'm afraid it's not entirely..

I thought the assignment board was a stage positioned after the fader/mute switch. Did I miss something? Or is P1 different?

Edit: Jeeez, just saw the amount of caps you ordered...

You are right, is it after the mute, and P1 channels are no different than the other ones.

However, the assignment board has different paths for the signal, depending on what you actually choose in the routing section. So a bad cap somewhere in the P1 bus section might not affect what you get on bus 7-8 for example.

And on P1 channels, as you are not routing them to any bus, but rather use their direct output, the signal doesn't go through the P1 bus section, so it might not be affected even if there is something bad in the P1 channel's P1 bus section.

Now, that doesn't look very much clearer, or does it ? :D

Paul-
Svenre
Advanced
Posts: 62
Post Re: Noise from mix bus..somewhere..
on: May 9, 2016, 07:41

Ha ha, no not 100% clear :-) But guess what.. I found the bad channel!!
Oh my.. can't thank you enough Maikol!!! This has haunted me for some time..
Not knowing that a muted channel still could cause noise always pointed me to the wrong direction. And sometimes even thinking it could be digital signal leaking into the analog path..
And FYI I was able to work it out by routing only
I'm going to swap the bad card with a spare and then start planning the mighty re cap.
I was surprised how much noise there is from channels when they are only routed to mix bus.. Do you remember any change after you recapped M? As a side note my saved default mix preset have all channels routed to the mix bus, so I'll change that before anything else :-)
YES!! Thanks again Mighty Maikol!
maikol
Administrator
Posts: 77
Post Re: Noise from mix bus..somewhere..
on: May 9, 2016, 08:35

AhA! Great news Paul ! :-)

Yes after I recapped all the channels, I did notice a significant drop in the noise floor.

I guess if not using the mixbus does give you really lower noise floor, then it's time to at least check those 220uF caps on all the assignment boards (the caps you can see on the picture I posted). I wouldn't be surprised if you find a number of close to death ones there...
Paul-
Svenre
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Posts: 62
Post Re: Noise from mix bus..somewhere..
on: May 9, 2016, 11:00

Follow up: To try to isolate the issue I took only the assignment board from my spare channel and put it on the faulty channel. The issue then remained so I put the assignment card back on and moved on to the In-/Output card and voilà the channel is quiet. Nice to have narrowed it down.
Also ordered 100 each of the caps you specified so I can start practicing, probably this weekend.
maikol
Administrator
Posts: 77
Post Re: Noise from mix bus..somewhere..
on: May 9, 2016, 12:47

Hmm so the issue is on the input/output board... interesting !

Paul-
Svenre
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Posts: 62
Post Re: Noise from mix bus..somewhere..
on: May 9, 2016, 13:11

Yep, will recap it this weekend and then let you know how it's behaving
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