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Two amp questions:

Discussion in 'Amps and Cabs [BG]' started by cgworkman, Feb 7, 2006.


  1. cgworkman

    cgworkman

    May 14, 2004
    Ohio
    1. What 'signal to noise' rating (in dB's of course) is considered good?

    2. Many have said that for maximum headroom you should run your master high and your gain low - but I've had several soundmen tell me recently that it should be the other way around. Which is true?

    Thanks in advance.
     
  2. depends on wether you like a clean or a dirty bass sound .. the masters on high and the gain on low will be clean , while the masters on low and the gain on high will give you a dirty sound ..
     
  3. theshadow2001

    theshadow2001

    Jun 17, 2004
    Ireland
    I dont konw in decibels what a good signal to noise ratio is is considered good but obvioulsy the more signal and the less noise the better.

    As for gain its all about balance. I believe and Im no expert on the matter but you have gain control due to varying input levels from different instruments so a hotter output like an active bass would use a low gain setting and vice versa for passive. I think that the ideal is to keep the gain set so that your input signal is averaging out at about unity or 0 dB's from there you set your master to whats required. This means that your amplifying signal and not noise. The gain if set correctly will have little to do with headroom which will come from the power amp or your master out. If you set the gain too high your going to reduce your head room if you set it too low your not going to amplify enough signal you'll turn up too much and run out of headroom again and you could also be amplifying noise as well as signal. So you can see what I mean by setting gain is about balance.

    The fact that you can use the gain to overdrive some amps might of been discovered by messing around but its not its intended purpose.
     
  4. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Good PA power amps are able to deliver 100 dB signal-to-noise or better. I think that ratings of 90 dB on bass amps are not uncommon, even on fairly good products. Studio gear could get up into the 130 dB regime, but there is a point of diminishing returns because your bass is a noise source by itself, even if it is passive.

    A problem (here we go with another ratings rant) is that SNR does not really tell the whole story, because the noise performance of the amp in real use depends on control settings and the actual signal level delivered by your bass. A general piece of advice is if your bass has fairly strong output signal, you are probably OK with any respectable amp.
     
  5. cgworkman

    cgworkman

    May 14, 2004
    Ohio
    Can one 'rating' render a given amplifier substandard?

    Also, back to one my questions - If a pre-amp has both gain and master controls and it's paired with a power amp that has a level control - where and how should these three controls be set? Should the power amp be set to max or the preamp's master volume. etc?
     
  6. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    The answer is: it depends.

    The gain on the preamp is there to compensate for the output level of the bass.

    The master on the preamp is to compensate for the power amp. Some need a hot signal, some don't. Notice that larger power amps tend to need a hotter signal.

    The volume on the power amp is to control the volume ;)

    All the above assumes you want a clean signal. If you want a dirty signal, and the preamp is designed for that, you may want to crank the gain. In other words, until you have the equipment togeather, you cannot know what settings are best. Each piece of equipment is different, which is why we need controls in the first place.
     
  7. theshadow2001

    theshadow2001

    Jun 17, 2004
    Ireland
    To be honest I wouldnt max anything out. Its usually not a good idea to crank anything to full with bass gear. I would set the gain around 12ish probably a bit less. Then turn the master out up until the clip goes on the power amp during extreme transients like a really good hard slap of the E string. Then I would adjust the output of the power amp to suit what ever your needs are. But thats just me.

    I really find that annoying when there's no provision made to set up proper gain structure on equipment. How hard would it be to stick in a clip indicator hear and there and few a LED output displays telling how many dB's your running
     
  8. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    No single rule will cover all situations.

    A good method : if you want clean sound, turn up masters or power amp inputs until you hear excess noise, then back off a bit.

    Turn up gains until you get what you want volume wise.

    If gain is then set so low that its very sensitive, turn down master and turn up gain until it's reasonable.


    If you want preamp grunge, back down master and run gain up.....

    If your amp has input signal indicators (many Ampeg do, for instance) then turn up until they show you have a reasonable signal, then set master to get what you want. You can bend that rule if you want something different.


    If you turn up masters or power amp level controls too far, you get too much noise from the rest of the circuits, and you have to keep the gain too low.

    And, most of it makes very little difference on the job, where there usually is more noise from the people than the equipment. Then you start playing..................
     
  9. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Only if it's a meaningful rating, and only because some aspects of amp design, such as minimizing noise, have ceased to be rocket science. For instance, a PA power amp with a low signal-to-noise rating would at least require an explanation in terms of what sonic benefit is gained in return for substandard noise performance.
     
  10. As far as setting the gain and master optimally for a clean sound, you want to set the gain until it's just below clipping to get the hottest signal to the amp without clipping and then adjust the master to the overall volume you want.

    Check any amp manual.
     
  11. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    This is correct if "clipping" is a well defined condition. But many amps use the soft clipping behavior of Class-A gain stages to add some pleasing distortion. In such cases, it's not a simple matter of going for the hottest signal, because the front end gain is working as a de facto distortion control. I you have such an amp, then you are probably better off setting the master and front end gains to moderate settings, and then work them against one another until you get the distortion tone that you want. If you want un distorted sound, you are most likely to get it with a relatively high master volume setting.

    Also, most contemporary amps are quite forgiving of the relative settings of these controls in terms of signal-to-noise performance.
     
  12. I specifically stated the procedure was for a 'clean' sound and it also maximizes the signal to noise ratio. Distortion is another matter. Being concerned about the signal to noise ratio when running a distorted signal is pointless.