Hi Gain Noise Issues
4CM setups can suffer from additional noise. By nature, 4CM messes with levels around the amplifier and will introduce multiple ground connections in, increasing the chance of a ground loop. These are a pain but can generally be remedied.PRE-CHECKS
If there are any noise issues within the system then you will meet them doubly working with the OD1/2 Orange and Red Channels. Normally, on a healthy JVM, you would expect to hear hiss on the high gain channels - but not significant hum. You would be therefore be well advised to check for excessive noise in the system before you start trying to configure 4CM. To do this:
- Disconnect ALL effects and cables from the JVM and turn on the switchable effects loop.
- Plug in a working guitar with a good lead and turn the guitar volumes all the way down.
- Select an OD Red channel and turn the channel gain level to around 11 o'clock and the volume level to around 2 o'clock. Set the master to around 9 o'clock.
Now listen. You will expect to hear hiss but if you hear significant hum then there is a problem in your system that is not related to 4CM. It may relate to cables, failing tubes, power quality or any number of other reasons and you should check elsewhere in the forum for advice on how to fix this.
If you hear only hiss then you are good to go with 4CM and know what to expect. Connect up the 4CM cables. Set the controls for 4CM. Setup a 'blank' 4CM patch on the HD as per the quick start guide above and power up the amp.
Again, plug in your guitar and cable. And turn the guitar volumes down. Change back to the OD Red channel with gain, volume and tone settings set to where you would normally use them.KILLING HUM AND OTHER NOISES
With the 4CM running, you might hear a lot of hum. There can also be ugly 'ringing' or howling within the patch, the kind of thing that you hear where there is a ground loop or a slightly microphonic tube. Sometimes the noise has a 'phasey', glassy or 'cocked wah' quality to it.
There are three main areas that you need to check:
- Levels. Check everything is set as per the quick start and you are using a 'blank' 4CM patch with only the FX loop and Studio EQ blocks inline and levels set correctly. If you are happy that everything is set right and you still hear significant noise then you need to check for ...
- Bad Cables. Replace any suspect cables with good ones (please don't use cheapo cables with your JVM - you paid a lot for it and bad cables pretty much guarantee extra noise. Splash out on new ones or make your own using good cable and connectors). Check cable runs. Do not run 4CM cables alongside power, wherever possible. If the cables are bundled, try separating them. If that doesn't work then the last thing to check is for ...
- Ground loops.
Ground Loops are caused by having multiple ground connections between the JVM and the HD. These will come in through the main power connection ground for both units and also through the audio cables 2-4 in the 4CM. Ground loops in the power connections can be addressed by plugging the JVM and the HD into the same power strip. Ground loops in the audio cables are a little more tricky. I am aware of two approaches to resolvng them.
First, You can use transformer-based device like the Behringer HD400 hum destroyer to eliminate ground loops within the setup. This can be very effective and I had a good result with one of those (detailed here viewtopic.php?f=7&t=5599&start=0
). Other vendors have similar devices (e.g. Art, Ebtech). Some people think, however, that transformers can have a detrimental effect on the signal and they can also reduce gain by a few dB wherever they connect. I found that the second of these was true but I didn't hear much tone suck personally.
Second, you can disconnect the ground connection within some of the the cables that connect up the 4CM. I tried this on the cables that link in and out of the JVM FX Loop and again it seems very effective (details here viewtopic.php?f=7&t=5610
). This is my chosen method.
If the hum persists, there may be other reasons. Lousy power in a house or venue is commonly suspected of being a cause of noise. Some people say that power conditioners can be great at fixing this (though others say that they are snake oil). I have not tried one.
Finally, move away from the amp if you can. If you are too close, or standing in the wrong place, hum can ensue.KILLING HISS
If you hear hiss only or have managed to kill off your hum, leaving only hiss: good news, you can fix that with noise gates. Start by putting a noise gate block directly after the FX Loop block in the chain. Set the 'Decay' parameter to 0 and then adjust the 'threshold' until the hiss just disappears.
Turn the guitar volume back up but damp the strings with your hand. For most guitars You will hear noise coming through from the pickup and cable. If this is at a reasonably low level, you can kill this noise by using a second Noise Gate at the very front of the Effects Chain. Again, set the decay to 0 and turn up the threshold until the noise just disappears. Now save the patch.
If everything is good and the guitar noise levels were initially fairly low then you should find that OD Red is now very quiet when you are not playing and should sound natural when in higher gain modes. In lower gain modes, avoid a gate unless you need it as it can mess up the note decay and sound unnatural. Remember, you can configure gates on your high gain patches only.Tips and TricksSolo/Level Boosts
Many people with a JVM use the Master 2 to create a second volume level for solo boosts. However, using 4CM an alternative is to boost using a Studio EQ block at the end of the effect chain. The EQ Block does not actually make any changes to the EQ but instead has the gain set about 3-4 dB up. This works for both real and modelled pre-amp patches and is a very transparent boost.HD Master Down and JVM Master Up
The (unmodified) JVM Power amp has a lot of negative feedback and is not prone to distortion. Therefore, power amp distortion has less effect on the sound than in some other amps. You can use this in your favour by turning down the master control on your HD and increasing the Master level on you JVM. This gives you control over master levels at your feet and works particularly well alongside the Solo Level boost trick above.Guitar Specific EQs.
Do you use more than one guitar but need to change the EQ settings on the amp to make them sound right? Well you now have the option to use EQs within patches , positioned both in front of the JVM or in the JVM loop, to tweak the sound in to match the guitar. The HD500, JVM and MIDI
The HD500 can change The JVM Channel, Master 1/2, Reverb on/off and FX Loop on/off whenever you change your patch on the HD500. This is hugely powerful (with some limitations) and is detailed in a separate thread here ... http://jvmforum.com/phpBB3/viewtopic.php?f=9&t=5358&p=53630