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Lexicon LPX-5 no wet signal

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Lexicon LPX-5 no wet signal

Postby CS70 » Fri Nov 29, 2019 4:52 pm

A couple years ago I picked up an LPX-5 for free. I tried it once and it did not work out of the box - and since I was in a hurry, I put it in a drawer and happily forgot about it. This morning I saw it and thought of checking it out.

There seems to be a strange behavior which I am not sure means the unit is broken or just mis-configured.

In order to test it, I simply picked up the signal from a headphones out and plugged it into one of the Lexicon's inputs and connect headphones to the Lexicon's outputs via a Y cable. According to the manuals ( https://lexiconpro.com/en/products/lxp-5 ) that makes it work in mono mode - just fine for testing purposes. I figured since there's a wet/dry mix knob, I don't need to use an insert but can simply wet an existing signal.

An indeed signal is passing fine - I can hear the test track in the headphones. The gain structure seems fine as the "overload" led is not lighting and the green "signal present" led pulses okay with the signal. The unit seems to be working just fine, the pots aren't even scratchy.

The problem is that there's no effect. Moving the mix knob from 100% dry to 100% wet progressively reduces the volume, until at 100% wet, the signal is muted. I've been using only the "preset" positions, not the user-customizable ones as obviously there could be all sort of odd parameters there.

Checked over the internet, and it seems that over the years a few people have experienced the same issue. Learned that a possible cause is that the "defeat" footswitch was left accidentally in the on positions the last time the unit was used. So I fished out an old VOX dual footswitch (the left button should be latching) , connected a cable, and indeed the footswitch light was on when I connected it! Eureka! Turned it off by pushing the footswitch... and no change. Still no wet signal, in any position. :(

According to the manual, it's possible to control stuff like whether or not the 2 effects are bypassed or defeated by using an appropriate combination of knob positions.

It seems relatively simple - for example for the "Delay/Reverb" effect (which is the 2nd = effect B I guess), move the "preset" knob to "EDIT B" while pushing the "learn button", then move the "select" knob to 12 or more, then move the "adjust" knob to toggle on/off.. but dong so, nothing changes.

I have the feeling I'm missing something. Or maybe the unit is just broken? Seem strange that it passes dry audio just fine.

The unit was new when the only knob of a piece of studio equipment I was familiar with was the door knob of the recording room... is there anyone who used it in its heyday and remembers how it works?
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Re: Lexicon LPX-5 no wet signal

Postby James Perrett » Fri Nov 29, 2019 10:12 pm

CS70 wrote:I have the feeling I'm missing something. Or maybe the unit is just broken? Seem strange that it passes dry audio just fine.

The dry signal is likely to go through a very simple all analogue signal chain. It is even possible that there are no IC's in the chain at all. The wet signal goes through a much more complicated digital signal chain with a different power supply.

My first thoughts are;

a) is the display working as expected?
b) do you hear any noise in the 100% wet position?
c) can you check the power supply voltages?
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Re: Lexicon LPX-5 no wet signal

Postby BillB » Fri Nov 29, 2019 11:27 pm

It may not make any difference, but from your description, you’re not really connecting it as intended - line (or instrument) in and line out. If testing, I would be inclined to connect exactly as indicated in the manual. Perhaps a drum machine to the inputs, and output to an Amp or mixer... might prove to be irrelevant, but it is good to rule out the connections and sources before trying to resolve settings etc.
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Re: Lexicon LPX-5 no wet signal

Postby CS70 » Sat Nov 30, 2019 1:08 am

James Perrett wrote:
CS70 wrote:I have the feeling I'm missing something. Or maybe the unit is just broken? Seem strange that it passes dry audio just fine.

The dry signal is likely to go through a very simple all analogue signal chain. It is even possible that there are no IC's in the chain at all. The wet signal goes through a much more complicated digital signal chain with a different power supply.

My first thoughts are;

a) is the display working as expected?
b) do you hear any noise in the 100% wet position?
c) can you check the power supply voltages?

Thanks James,

a) There is no display, just a couple LED and they seem to be doing their thing
b) No, perfect silence. That's what suggested me somehow the effect is defeated, but as you say, it could simply be that the as I turn the mix towards wet, the signal is progressively diverted to a not-working, perfectly silent path
c) Not with a voltmeter (dont have one) but it's the original power supply - what possibility are you thinking of?
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Re: Lexicon LPX-5 no wet signal

Postby CS70 » Sat Nov 30, 2019 1:12 am

BillB wrote:It may not make any difference, but from your description, you’re not really connecting it as intended - line (or instrument) in and line out. If testing, I would be inclined to connect exactly as indicated in the manual. Perhaps a drum machine to the inputs, and output to an Amp or mixer... might prove to be irrelevant, but it is good to rule out the connections and sources before trying to resolve settings etc.

Hmm... the manual explicitly say that you can connect only one input? (and I tried also connecting the stereo headphone out to the both L and R inputs via another Y cable)
It also explicitly says (I think) that you can connect it either as an insert or direct, and even shows (as expected) that in the former case you should use 100% wet, in the latter the recommended range of mix is between 10 and 14 o'clock.

If you're thinking voltages, the headphone out I use is from the monitor controller, and it has plenty of juice, it can easily overload the input if I raise it. The S/N ratio on 100% dry is very good, so don't really see how could it be a cabling issue?

Thanks anyways :)
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Re: Lexicon LPX-5 no wet signal

Postby CS70 » Sat Nov 30, 2019 1:19 am

I just found the service manual online ! There's a diagnostic mode as well, and schematics (well, can't read them but anyways..)

It's now at my dropbox at https://www.dropbox.com/s/8tkog4ii7ui6jd7/lxp5.pdf?dl=1

Too late to explore now, but tomorrow is another day! :D
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Re: Lexicon LPX-5 no wet signal

Postby CS70 » Sat Nov 30, 2019 1:29 am

..and yeah from what I understand it looks like the signal paths are very distinct and the dry/mix pot simply moves the signal between the two. Probably the chip is gone.
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Re: Lexicon LPX-5 no wet signal

Postby BillB » Sat Nov 30, 2019 1:33 am

Thanks for sharing the service manual. I was googling for a factory reset but didn’t find anything. The service manual does have a ‘no wet signal troubleshooting’ starting at P2-21.
Also worth noting that you aren’t alone
https://forums.prosoundweb.com/index.php?topic=143160.0
This is for an LXP-1, but there are similar questions for the LXP-5.

But no obvious resolution. Hope you get somewhere with it :thumbup:
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Re: Lexicon LPX-5 no wet signal

Postby CS70 » Sat Nov 30, 2019 3:04 pm

Been reading the manual and it was like a trip on memory lane, there’s a few z80 inside..
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Re: Lexicon LPX-5 no wet signal

Postby James Perrett » Sat Nov 30, 2019 10:33 pm

CS70 wrote: c) Not with a voltmeter (dont have one) but it's the original power supply - what possibility are you thinking of?

It is well worth getting a multimeter - even the £2.50 cheapie from CPC will do for most things.

https://cpc.farnell.com/duratool/d03046 ... multimeter

I bought one from Maplin when I needed something quickly and I use it quite a bit. I wouldn't use it on high voltages but it seems fine up to 100V or so. The only thing missing is a continuity buzzer.

The first thing to do when faced with a dead piece of gear is to check all the power supply voltages as power supplies are one of the more stressed parts of most circuits. No noise at all on the output makes it more likely that there's a supply missing.
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Re: Lexicon LPX-5 no wet signal

Postby Eddy Deegan » Mon Dec 02, 2019 3:45 pm

CS70 wrote:Been reading the manual and it was like a trip on memory lane, there’s a few z80 inside..

Ahh, charming little beasties. I love the fact that the family is still going strong after over 40 years!
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