tanwn
Seeker Of Truth
Posts: 3 
|
Post by tanwn on Apr 14, 2014 5:05:25 GMT -5
Can emotiva or someone tell me how I can DIY a xlr pad attenuation such that my XPA gen1 will have a lower gain as a gen2 29db? I just need the resistor values to construct a xlr pad.
|
|
|
|
Post by geebo on Apr 14, 2014 7:18:17 GMT -5
Can emotiva or someone tell me how I can DIY a xlr pad attenuation such that my XPA gen1 will have a lower gain as a gen2 29db? I just need the resistor values to construct a xlr pad. Have you considered line level attenuators? They come in different values and with balanced or unbalanced connectors. |
|
|
|
Post by Chuck Elliot on Apr 14, 2014 10:04:19 GMT -5
My understanding is that the gain structure of an amp is fixed - period!
All a pad or fixed attenuator does is lower the input signal to the amp.
If an amp has a certain noise floor, that noise is present regardless of input signal.
There may be finer points, but I think the above is pretty close.
|
|
KeithL
Administrator 
Posts: 10,261
|
Post by KeithL on Apr 14, 2014 11:02:15 GMT -5
You are entirely correct - the gain structure of a power amp is fixed (unless it has a volume control knob or jumper). However, the output "minimum noise structure" of most source components is also fixed. (In other words, they have some noise floor on their OUTPUT, which is the minimum noise you will ever achieve. When the volume is turned down low, this is the noise floor you hear; when you start turning the volume up, at some point the noise floor of the source - multiplied by the gain applied by the gain stage - exceeds that floor... at which point the noise increases as you turn the volume control up further.) If your power amp has lots of gain, and your preamp has lots of output, you may well end up with a situation where you never have to turn the volume up past halfway to reach full output, but where you hear noise when the volume is down low (you're hearing the OUTPUT noise floor of the preamp multiplied by the gain structure of the amp). If you add a passive attenuator between the preamp and power amp, it reduces both the signal and the noise. The result is that you will then have to turn the volume control up higher to reach full volume, because the signal level is lowered, but the noise floor will also be lowered - so you will hear less noise when the volume is turned down low (or fully off). So, in summary, putting an attenuator between the preamp and power amp reduces the noise floor of the preamp signal reaching the power amp - which you might otherwise hear if the power amp has lots of gain. (It's actually the output noise floor of the preamp that is being lowered, not the noise floor of the power amp.) My understanding is that the gain structure of an amp is fixed - period! All a pad or fixed attenuator does is lower the input signal to the amp. If an amp has a certain noise floor, that noise is present regardless of input signal. There may be finer points, but I think the above is pretty close. |
|
|
|
Post by geebo on Apr 14, 2014 11:10:51 GMT -5
You are entirely correct - the gain structure of a power amp is fixed (unless it has a volume control knob or jumper). However, the output "minimum noise structure" of most source components is also fixed. (In other words, they have some noise floor on their OUTPUT, which is the minimum noise you will ever achieve. When the volume is turned down low, this is the noise floor you hear; when you start turning the volume up, at some point the noise floor of the source - multiplied by the gain applied by the gain stage - exceeds that floor... at which point the noise increases as you turn the volume control up further.) If your power amp has lots of gain, and your preamp has lots of output, you may well end up with a situation where you never have to turn the volume up past halfway to reach full output, but where you hear noise when the volume is down low (you're hearing the OUTPUT noise floor of the preamp multiplied by the gain structure of the amp). If you add a passive attenuator between the preamp and power amp, it reduces both the signal and the noise. The result is that you will then have to turn the volume control up higher to reach full volume, because the signal level is lowered, but the noise floor will also be lowered - so you will hear less noise when the volume is turned down low (or fully off). So, in summary, putting an attenuator between the preamp and power amp reduces the noise floor of the preamp signal reaching the power amp - which you might otherwise hear if the power amp has lots of gain. (It's actually the output noise floor of the preamp that is being lowered, not the noise floor of the power amp.) My understanding is that the gain structure of an amp is fixed - period! All a pad or fixed attenuator does is lower the input signal to the amp. If an amp has a certain noise floor, that noise is present regardless of input signal. There may be finer points, but I think the above is pretty close. Keith, Is there any downside to adding attenuators as far as signal quality is concerned? |
|
