Question about Lexicon LX-7 7-Channel Amplifier

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Lexicon Lx-7 buzz sound

I have a LX-7 amplifier wich present a subtle buzz sound through each one of the seven channels even do there is no input signal just the speakers cable were connected. Can somebody help me...?

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Hi chupetin2

If the problem is present with ONLY the speakers connected, that is no other powered devices like subs, or input/output cables, it will be a power supply problem inside the amp. If you have electronic fault finding skills, there will probably be a capacitor in a regulated rail that has failed.
If you do have a sub connected, be sure it is powered from the same mains source as the amp, or at least a GPO that is on the same phase. Different phases will induce mains hum, as will multiple earths. Try also temporarily moving the amp(whilst monitoring the hum) from where it is sitting and see if the hum is being induced into the amp by any other devices

Happy to talk to you more about this. Just ask:)

regards
robotek

Posted on Aug 19, 2008

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I have the xp 300 and in stereo mode it only works on one channel or the other, not as 2 seperate channels


If you are saying that it only works on say the left channel in stereo mode, but both channels come on in mono, then there's a fault in the amplifier's pre-amp. These days they are an IC, it can be traced by following the input wires to the point on the PC Board and then looking around for an IC with all inputs going in. If you are lucky there might be two! One for each channel. Replace the one on the dead channel. You can test it, either the single IC or both, touching it's pins with an insulated tool while the amp is on. It will buzz on the channel. Stereo amps have two sets of identical parts, except when an IC is involved. But even then that will have two halves (inside it). You just need to touch the pins of the IC, with the tool, but don't short the pins together! You should hear at least 4 buzzers. One at the right input, one at the left input, one each at the left and right output. If you only get the left an right output buzz, plus the good channel input buzz, you know it's the IC that's gone.

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I am using a Lexicon CX-7 Power Amplifier in conjunction with a Lexicon MV-5 Processor. I have 7 B&W Speakers (2 Fronts, 2 Sides, 2 Rears and one Center). I also have a REL Stentor III subwoofer....


I assume you're wrestling with the choice of using its onboard amp fed by the MV-5 or driving it from the CX-7's unused channel.

Of course either way will work. I'd go with the preamp-to-REL method as the REL engineers undoubtedly gave some thought to the amp design for the price paid.

Attach it to the Sub1 Preamp out

http://www.retrevo.com/support/Lexicon-MV-5-Receivers-manual/id/22990ci271/t/2/

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1 Answer

When switching on system, it makes loud buzzing sound from amplifier? UK 240v


Unplug everything apart from the speakers that is plugged in to the amp and check the wiring of all the connectors. If the buzzing stops when you do so then it is most likely one of the input connectors or cables causing the problem and it is most likely that the shield or earthing wire in one of those cables is aft faulty and needs repairing or replacing. If the buzzing continues try switching the input selector to something else to see if it disappears. If it does then the input channel that causes the buzzing may be faulty and need repairing and if it does not then the amp itself has an issue and will need repairing. In this case it may be a faulty power supply, preamp or main amp module especially if it comes from both or all channels.

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No sound from CD input, all others fine. Very faint trace of sound if volume cranked right up. Problem only on CD input.


If you follow the cd input to the pc board and trace the course of the channels, my guess is you will come accros an IC. Touching the pins of this with a tiny screwdriver (be carefull not to touch two pins at the same time) should produce a buzz on either channel. If it doesn't and there's not another IC further along the path of the signal, (that could be causing the loss) then it will most likely have gone.

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Crate gtx 65 guitar amp mains hum


I had the same problem on my VTX65. I noticed it would oscillate with different effects so I removed the effects module. Problem solved. Now it's dead quiet. I use a Digitech RP500 so removing the effects module was a non issue.

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1 Answer

How do you control the signal coming back from a reverb etc.


The FX connection sounds correct:
To control the fx you need the FX send and return Faders up, and turn up the FX pot on the channels u wish to add FX too.

Compressors can be used in many ways, for system protection, instrument processing, and for containing vocals:
How you connect them to your system depends on what your wanting to compress. If you tell me what you are using it for i could recommend the best option to suit you. e.g vocals FOH / FB- 1 singer 2 singers, Instrument Gating/comp. let me know for more detail??

The most common connection is to insert the compressor over the individual channels you wish to compress using insert leads.

Lets presume your tyring to compress more than 2 channels:
for example- you have a female singer that is mainly soft but hits some really belting notes every now and then, you want to compress her vocal so that the volume in the speakers does not increase as significantly with the loud notes.
Lets say she is in channel 1, you want to send channel 1 to group 1(or 1&2 if they are not individually assignable) and don't send it to ST(stereo).(same settings for any other channels you want to compress)

Connect the compressor via Insert leads to the group inserts.

Assign the group to the Stereo outputs (the group fader now acts as a sub-master for the vocal and will need to be up to hear the vocals)

- If you havn't got insert leads you can also take the group output and plug into the compressor, out of the compressor- into a stereo channel that is assigned to ST. and leave that channel up as well.
-----------------------------------------------------------------------------------------------
Another common connection for a compressor is:
Take the main L&R outputs- plug into the compressor, out of the compressor- plug into Amplifier L&R. This compresses the whole lot and may not be ideal for instruments and CD playback. This option is purely for system protection.

I hope you can make sense of this.
If not- i can provide more detail if you wish.

Goodluck
PTB



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Might be caused by any of the Large Capacitors in the power supply section of the amp.

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Cheers Jeremyt

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