ok electronics junkies...question time
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ok electronics junkies...question time
sorry for all the "inquiring minds" posts as of late but i'm the type of person that if i'm doing something and i'm not familiar with it i want to obtain as much knowledge as possible.
can you explain the difference in a HU as the pre-out voltage increases, the effect of lower impedence (ohm) ratings on sq and what ratios of pre-out voltage to amplifier voltage should one be seeking?
i read that lower impedance= improved clarity and an amplifier should see a 3/1 voltage ratio (ie: 4volt pre-out HU should see a 1ohm setting at the amp).
thoughts?
gracias!
can you explain the difference in a HU as the pre-out voltage increases, the effect of lower impedence (ohm) ratings on sq and what ratios of pre-out voltage to amplifier voltage should one be seeking?
i read that lower impedance= improved clarity and an amplifier should see a 3/1 voltage ratio (ie: 4volt pre-out HU should see a 1ohm setting at the amp).
thoughts?
gracias!
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Joined: May 2001
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From: Indian Land SC
Sounds like BS to me. And it looks like some of your info got a little lopsided somewhere along the way. HU output voltage has nothing to do with amp output impedance. Or are you talking about amp input impedance? Hmmm.
A couple things to consider -
1. Anytime a signal is amplified, distortion and noise is added. One of the theories I've heard of higher pre-amp putputs is that the power amp can be turned down (amplifies less, so less distortion) but in reality the power amp is amplifying the same amount either way. Let's say you have a 100W amp and it takes 1v input to produce 100W output. Putting 4v in and then immediately reducing it to 1v (by turning down the input adjustment) does absolutely nothing to affect the distortion of the power amp. In fact, since your HU now has more amplification (4v instead of 1v) you have more distortion than before.
2. There is an improvement in "induced noise" by using higher pre-amp outputs. This is probably worth the trade-off in additional HU distortion. Actually the benefit comes not from the higher pre-amp output but from turning down the input on the power amp. Lowering the input lowers the audio signal and lowers any noise picked up by the wiring. The benefit will be minimal and maybe not very noticeable unless you're measuring it with a meter, and in many cases you can get nearly the same effect by turning down the power amp input all the way, cranking the HU up all the way, then adjusting the amp inputs for the maximum volume you will ever listen to. This will minimize amplification of noise picked up by the wiring. Of course it means you'll be turning the HU volume up to a higher level and might not like the sound of it because it will roll off the loudness curve much sooner. There's always a trade-off.
3. HU pre-amp output voltage has nothing to do with power amp output or input impedance. Input impedance of power amps is designed to work with the current capability of the pre-amp, not the voltage. Pre-amps are typically low-current devices so power amps have relatively high input impedances (typically 20k). If you lower the input impedance of a power amp too far it will over-load a typical pre-amp and will cause the voltage to drop and distortion to increase.
4. Again, there is a small (mostly theoretical) noise advantage to using high-current pre-amp outputs and low impedance power amp inputs. Induced noise will usually be low current, so dumping it into a low impedance input will squash some of it. But then to enable the HU to drive a lower impedance power amp you have to build more power amplification into the pre-amp, so your distortion goes up. Damn, another trade-off.
Aside from reducing induced noise a little, I don't see much advantage to higher voltage pre-amps. Unless somebody starts making lower gain power amps to match.
BTW - what is "sq"?
A couple things to consider -
1. Anytime a signal is amplified, distortion and noise is added. One of the theories I've heard of higher pre-amp putputs is that the power amp can be turned down (amplifies less, so less distortion) but in reality the power amp is amplifying the same amount either way. Let's say you have a 100W amp and it takes 1v input to produce 100W output. Putting 4v in and then immediately reducing it to 1v (by turning down the input adjustment) does absolutely nothing to affect the distortion of the power amp. In fact, since your HU now has more amplification (4v instead of 1v) you have more distortion than before.
2. There is an improvement in "induced noise" by using higher pre-amp outputs. This is probably worth the trade-off in additional HU distortion. Actually the benefit comes not from the higher pre-amp output but from turning down the input on the power amp. Lowering the input lowers the audio signal and lowers any noise picked up by the wiring. The benefit will be minimal and maybe not very noticeable unless you're measuring it with a meter, and in many cases you can get nearly the same effect by turning down the power amp input all the way, cranking the HU up all the way, then adjusting the amp inputs for the maximum volume you will ever listen to. This will minimize amplification of noise picked up by the wiring. Of course it means you'll be turning the HU volume up to a higher level and might not like the sound of it because it will roll off the loudness curve much sooner. There's always a trade-off.
3. HU pre-amp output voltage has nothing to do with power amp output or input impedance. Input impedance of power amps is designed to work with the current capability of the pre-amp, not the voltage. Pre-amps are typically low-current devices so power amps have relatively high input impedances (typically 20k). If you lower the input impedance of a power amp too far it will over-load a typical pre-amp and will cause the voltage to drop and distortion to increase.
4. Again, there is a small (mostly theoretical) noise advantage to using high-current pre-amp outputs and low impedance power amp inputs. Induced noise will usually be low current, so dumping it into a low impedance input will squash some of it. But then to enable the HU to drive a lower impedance power amp you have to build more power amplification into the pre-amp, so your distortion goes up. Damn, another trade-off.
Aside from reducing induced noise a little, I don't see much advantage to higher voltage pre-amps. Unless somebody starts making lower gain power amps to match.
BTW - what is "sq"?
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sq meaning sound quality
i guess i'll give an example of what i was told. taking identically matched head units (same eq, same DAC's, etc) and both putting out the same pre-out voltage, let's say 5volts, if amp A is dishing out 5volts at 55ohm impedance and amp B is dishing the same 5volts but at a higher 150 ohm impedance amp A wins out by virtue of lower impedance.
the way it was explained to me was that basically anyone could claim their head units crank out 5volts on the pre-out side but what you arent being told by some is that in order to obtain those 5volts their impedance level may be as high as 300-500 ohms.
shoulda went to school for electrical engineering! damn the luck haha
i guess i'll give an example of what i was told. taking identically matched head units (same eq, same DAC's, etc) and both putting out the same pre-out voltage, let's say 5volts, if amp A is dishing out 5volts at 55ohm impedance and amp B is dishing the same 5volts but at a higher 150 ohm impedance amp A wins out by virtue of lower impedance.
the way it was explained to me was that basically anyone could claim their head units crank out 5volts on the pre-out side but what you arent being told by some is that in order to obtain those 5volts their impedance level may be as high as 300-500 ohms.
shoulda went to school for electrical engineering! damn the luck haha
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From: Indian Land SC
So you're saying the source impedance (of the pre-amp) is what's different in the two scenarios?
I'm sure source impedances are different from HU to HU, but when you're driving a 20k load I'm not sure how much difference 200 ohms makes. And I'll bet that he couldn't tell the difference between the two if he had all day to listen to them. Could it be that the person telling you this is trying to sell you something?
This reminds me of the BS that occasionally circulates about "my 100 watts are better than your 100 watts because they're high-current watts". Right. And my 240HP is better than your 240HP because it's higher torque HP.
I'm sure source impedances are different from HU to HU, but when you're driving a 20k load I'm not sure how much difference 200 ohms makes. And I'll bet that he couldn't tell the difference between the two if he had all day to listen to them. Could it be that the person telling you this is trying to sell you something?
This reminds me of the BS that occasionally circulates about "my 100 watts are better than your 100 watts because they're high-current watts". Right. And my 240HP is better than your 240HP because it's higher torque HP.
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correct, different source impedance. sorry, not up on all the technical speak lol
it wasnt someone trying to sell me anything (believe me i know to take all that with a grain of salt) but rather a discussion on another board i ran across.
thanks for all the clarification though, its reasons like this and knowledgeable folk like you why i find s2ki a great place to pose such inquiries!
it wasnt someone trying to sell me anything (believe me i know to take all that with a grain of salt) but rather a discussion on another board i ran across.
thanks for all the clarification though, its reasons like this and knowledgeable folk like you why i find s2ki a great place to pose such inquiries!
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