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distortion on mixer channel, possible causes?

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distortion on mixer channel, possible causes?

Postby nathanscribe » Thu Nov 28, 2013 10:29 pm

My 3-yr old out-of-warranty A&H Zed R16 is playing up. Channel 15 is exhibiting large amounts of grungy crackle, along with a very low signal level; oddly, there's no trouble at all when PFL is engaged - the gain pot works as it should, the channel fader works as it should, EQ is bypassed and none of the other channels are showing the fault. Having looked at the flowchart in the user guide, I'm no wiser where the problem might lie.

Any ideas what this might be?
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Re: distortion on mixer channel, possible causes?

Postby Hugh Robjohns » Thu Nov 28, 2013 10:57 pm

If pfl is good, then it can only be the fader, the mute button, the panpot, or the bus routing switch. The post fade aux sends sound clean that rules out the fader and mute button. The bus routing switch is probably more likely than the pan pot. Does working either of them change the sound at all?

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Re: distortion on mixer channel, possible causes?

Postby nathanscribe » Thu Nov 28, 2013 11:22 pm

Hmm.

- Pre-fade aux sends are clean.
- PFL is clean.
- Mute and L/R buss switch seem OK - they have no discernible effect on the sound.
- One of the channel control switches turns the fader into a MIDI controller. I'm guessing the audio is then sent at unity gain, bypassing the channel fader, to the stereo buss. In this mode, the sound is clean, and the pan pot works fine.
- The post-fade sends seem OK, they send whatever the channel sounds like.
- In normal use (channel routed to stereo buss, fader used for channel volume) the sound is horrible, and the fader affects the volume of that. It's a great deal quieter than normal, but it does still have some effect.



EDIT: the flowchart shows a buffer after the fader. I'm wondering if that might be the culprit...
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Re: distortion on mixer channel, possible causes?

Postby Hugh Robjohns » Thu Nov 28, 2013 11:42 pm

Can't be the fader or post-fade buffer if the post-fade auxes sound okay and the quality matches the pfl sound.

If the post-fade sends sound horrible then it must be the fader, post-fade amp, or the wiring between them.

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Re: distortion on mixer channel, possible causes?

Postby nathanscribe » Thu Nov 28, 2013 11:54 pm

Hugh Robjohns wrote:If the post-fade sends sound horrible then it must be the fader, post-fade amp, or the wiring between them.

I think that must be it. The post-fade sends sound bad when the channel fader is used normally, but sound clean when the fader is switched to be a MIDI controller (the audio bypasses the fader and buffer, and goes straight to the mute, pan, and post-fade sends). As the post-fade sends mirror whatever clean/grotty sound the channel sounds like, I'm guessing the fault has to lie where you say. That's tomorrow's job, then!

Thanks Hugh, they really should let you out of the office once in a while.
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Re: distortion on mixer channel, possible causes?

Postby Hugh Robjohns » Fri Nov 29, 2013 7:28 am

They do! Today and tomorrow I'm in that there Lon-don town for the MPS show!
Sounds like you've got dead fader or an unhappy buffer... Or the relay/switch is dicky.

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Re: distortion on mixer channel, possible causes?

Postby KeithAC1 » Fri Nov 29, 2013 10:32 am

This is exactly what happened to mine this year on ch 13. Had to have the channel replaced by Audio Technica (official repair company etc), which resulted in a complete nightmare for me as took a long time and was returned to me damaged. I voiced my concerns here on this forum at the time.

I was never told what the problem actually was, however the entire channel's internals were lifted out and swapped for new. I was very fortunate that mine was under warranty, but as I said came back to me damaged so I had to return it to them for a 2nd time. All is good now though, except the fact that the new channel 13's led lights are of a different brightness to the rest of the desk so it looks odd... As long as the channel doesn't sound like a hurricane though, It'll do !!

Good luck!
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Re: distortion on mixer channel, possible causes?

Postby nathanscribe » Fri Nov 29, 2013 11:11 am

KeithAC1 wrote:I voiced my concerns here on this forum at the time.

Wow, I just read that thread. What a mess. Mine came from a local retailer who I'm on very good terms with, but it's out of warranty anyway so I'll take a peek myself first. As long as it's not all SMD in there I might be able to avoid some expensive shipping...
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Re: distortion on mixer channel, possible causes?

Postby nathanscribe » Fri Nov 29, 2013 5:24 pm

OK, so if you want to dive into a world of glued-on-ribbon-cable pain, this is what the Zed looks like inside. The suspected faulty area is beneath a bunch of ribbons and the front edge of the unit. Sigh.

Image
Untitled by nathanscribe, on Flickr
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Re: distortion on mixer channel, possible causes?

Postby damoore » Fri Nov 29, 2013 10:40 pm

Oh dear - I wish they wouldn't glue cables on. I had a Behringer mixer that went wonky and on that they had glued the cables so that you couldn't even open the case properly. Would not buy anything else from them in part because of that. Sad to see that the ZED is the same way, although at least you were able to open it up. I expect it saves them all of ten cents a connector not to have to use proper clipping connectors.
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Re: distortion on mixer channel, possible causes?

Postby nathanscribe » Fri Nov 29, 2013 10:44 pm

They're clipped *and* glued...

Some of them just pull off, so that's OK. It's back together for now, but depending how much the repair centre quote me, I might brave it again later.
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Re: distortion on mixer channel, possible causes?

Postby KeithAC1 » Sat Nov 30, 2013 2:57 pm

nathanscribe wrote:
KeithAC1 wrote:I voiced my concerns here on this forum at the time.

Wow, I just read that thread. What a mess. Mine came from a local retailer who I'm on very good terms with, but it's out of warranty anyway so I'll take a peek myself first. As long as it's not all SMD in there I might be able to avoid some expensive shipping...

If you have looked back at my old thread I'd like to note that although DV247 did go bust during my repair, they were in the end very good help and honored their word as soon as up and trading again. The damage was a result of Audio Technica themselves who sent it back in box that didn't fit and filled with a handful of polystyrene chips. They didn't admit to their poor service until I proved it was their fault (they tried to indicate DV247 were responsible for the unsuitable/loss of packaging when it infact came direct from them back to me).

They were, to be frank, a nightmare to talk to and deal with.
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Re: distortion on mixer channel, possible causes?

Postby nathanscribe » Sun Dec 01, 2013 12:08 pm

Hmm. I'll bear that in mind when I speak to the dealer, see what they recommend.
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