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So what is wrong with using High Input to get 10 volts out of HU instead of Pre-outs that have 4 volts?


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I'm asking because I've never once heard of any advice to use speaker output into the high input of the amp even though most HU's are typically 2-4 volts. Up until recently, I've used pre-outs. My Pioneer HU uses 4 volt Pre's which according to my scope typically puts me around the half mark on my gains. One thing I notice is that without any audio playing, I could always hear a slight white noise from my tweeters which was louder or softer depending on the gain but to achieve proper gain, it was quite audible if the car was quiet. I'd get that from all amps, JL Audio Slash, MTX Elite or even my old Punch 60ix which was actually worse BTW. As I've owned a lot of amps over the years and still have them. 

 

Since many amps accept up to 10 volts of input and my HU's speaker outs are about 10 volts, I tried it out and was able to keep my gain at 0 on the amp. It sounds really clean and I don't hear any white noise through my tweeters when the car is quiet and the amp is on. So if the goal is to keep the noise floor low as possible, this made me want to know what the reasons are for using pre-outs instead if they are lower voltage?

 

 

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You bring up an interesting point between high and low level.

The only answer I say about your question is your speaker wire isn't shielded like RCA cables are.

It's odd that you would have amp whine w the rca and not with the unshielded speaker wire. Unless the voltage signal increase overcomes the floor noise?

I saw a video from 5 star on youtube and he had a great explanation of amplified noise as you turn up your gain.

anyway, the 10v you mentioned from the high level coming from radio, is that full tilt?

I have a rfx-8140. it has 8v balanced and 17w unbalanced. never knew how to use the unbalanced. you need an adaptor to use it.

Edited by Deeznutz
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Probably some noise being picked up on the line level side.
 

You want to avoid using speaker level inputs when possible because you get all the noise from the amplification. 
 

it’s not really an apples to apples comparison to compare preout voltage and speaker level voltage. 

Edited by MrSkippyJ

 

F150:

Stock :(

 

2019 Harley Road Glide:

Amp: TM400Xad - 4 channel 400 watt

Processor: DSR1

Fairing (Front) 6.5s -MMats PA601cx

Lid (Rear) 6x9s -  TMS69

 

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21 hours ago, MrSkippyJ said:

Probably some noise being picked up on the line level side.
 

You want to avoid using speaker level inputs when possible because you get all the noise from the amplification. 
 

it’s not really an apples to apples comparison to compare preout voltage and speaker level voltage. 

 

What noise is it? Sounds super clean to me. Having the gains higher, I can hear the hiss white noise. I've always heard it going back into the 90's and from what I've understood that as being the "noise floor" which is why we used to use Pre amps to take the low voltage signal to 8 or 10 volts which effectively allowed for a lower gain on the amp...so what am I missing here?

Edited by omnibus
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22 hours ago, Deeznutz said:

You bring up an interesting point between high and low level.

The only answer I say about your question is your speaker wire isn't shielded like RCA cables are.

It's odd that you would have amp whine w the rca and not with the unshielded speaker wire. Unless the voltage signal increase overcomes the floor noise?

I saw a video from 5 star on youtube and he had a great explanation of amplified noise as you turn up your gain.

anyway, the 10v you mentioned from the high level coming from radio, is that full tilt?

I have a rfx-8140. it has 8v balanced and 17w unbalanced. never knew how to use the unbalanced. you need an adaptor to use it.

 

It's not amp whine. It's a White noise which I attribute it to being the noise floor itself and increases the higher the gain is..even with shielded RCA. It's high pitched and usually heard in tweets when no audio is playing...I'm sensitive to high pitch noises so maybe it bothers me more than most. Back in the day, we used pre amps, I used to have a Pheonix Gold pre amp that was adjustable up to 10 volts. So it would take the 2 volt input form HU and amp it up so that the longer run of the RCA's to your amp didn't introduce the noise floor.

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There is more possibility of introducing distortion and burning up your subs. Many test have been done and high speaker output tend to distort at a very low volume level in the deck 

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If memory serves.....

With speaker outputs on the deck, the 'negative' wire isn't a ground. It's a reference signal. DC voltage applied at half-voltage between 0v and rail power. If reference>signal, then speaker is driven in negative direction. If reference<signal, speaker driven in positive direction sort of thing.


Whereas on RCAs, the sheath is actual ground and doesn't carry any reference voltage. Hence the presence of a turn on pop if the amplifier turns on before your head unit - needs a few milliseconds to correct for the DC offset.


So if you were to say, solder speaker outputs on the deck to a snipped RCA cable for input, you'd be applying DC power to a ground circuit. Depending on how the amplifier is designed, it may or may not cause bad things to happen. Blow a ground fuse, melt a cable, cause physical damage to amplifier or head unit. Theoretically, the head unit should be providing the ground to RCA cables, not the amplifier. So it might work without issue, but the circuit itself was never designed to have an electrical potential applied to it in that manner. So YMMV if any blue smoke escapes.

Edited by SnowDrifter
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21 hours ago, omnibus said:

 

What noise is it? Sounds super clean to me. Having the gains higher, I can hear the hiss white noise. I've always heard it going back into the 90's and from what I've understood that as being the "noise floor" which is why we used to use Pre amps to take the low voltage signal to 8 or 10 volts which effectively allowed for a lower gain on the amp...so what am I missing here?

 

You really aren't missing anything to be honest. You get less "noise floor" using the higher voltage speaker outputs for your inputs since you can run the gain lower. The trade off (typically) is that you are now amplifying a much dirtier signal. Most deck amplifiers are pretty terrible and their frequency range is usually a decent amount narrower than a preamp's range. If you compare a speaker level and a preamp level of equal voltage, in most cases the preamp will sound better. There are lots of factors and variables that can make one better than the other though.

 

All that being said, if it sounds better to you then there really is no reason to change. Your "noise floor" will be similar across the 2 signal types with similar voltages. AKA a speaker level of 10v and a preamp level of 10v should have similar noise floors, the biggest difference will be the quality of the signal. 

 

Edit: Just saw SnowDrifter's resonse. 

Too add, I am speaking of using an amps high level when using speaker outputs and preamp inputs when using preamp outputs. Not running speaker level outputs into preamp inputs. 

Edited by MrSkippyJ

 

F150:

Stock :(

 

2019 Harley Road Glide:

Amp: TM400Xad - 4 channel 400 watt

Processor: DSR1

Fairing (Front) 6.5s -MMats PA601cx

Lid (Rear) 6x9s -  TMS69

 

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  • 2 weeks later...

Or just ad some Kind of balanced line input processor or line drive but stay with the RCS’s unless your running an amp that has a balanced line input on it. Like. Pld

xtant amps you could run speaker wire and conver to rca at the amp and they would still sound good. But other then that stay away from speaker level amp inputs 

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