# HU Pre-out Voltages & Amp Input Voltages



## Dean (Oct 27, 2006)

1) If a given HU has pre-out rating of 8V, is that the maximum but not the constant operating voltage? I think yes, but I couldn't find an answer.

1a) Related, when you "turn up the volume", what is happening? Yeah, yeah, the speakers get louder, I know, but what is happening? Voltage increase or something more complex?

2) If a given HU has pre-out rating of 8V, MUST it be paired with an amplifier that covers that range (e.g. 2v-10V)? I think yes, that would be best, but perhaps not necessary.

3) Hoping that my presumptions to questions 1 & 2 are correct, would it be safe enough to pair that 8V pre-out HU with an amplifier that has a pre-in voltage rating of 200mV-6V, knowing that if I cranked it up to 100% volume I could damage the amp? Again I think yes. Gawd I hope so... it is working so far. 

Thanks,


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## VR028 (Feb 17, 2012)

well to answer question 2. i dont think its necessary. ive used a 5v jvc head unit on a alpine amp which stated 4v max with no problems.

my advice would be to try it all on the lowest gain setting first and work your way up untill youve set the gains correctly


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## Serieus (May 27, 2011)

Dean said:


> 1) If a given HU has pre-out rating of 8V, is that the maximum but not the constant operating voltage? I think yes, but I couldn't find an answer.
> 
> 1a) Related, when you "turn up the volume", what is happening? Yeah, yeah, the speakers get louder, I know, but what is happening? Voltage increase or something more complex?
> 
> ...


1) it's the max, i.e. on a 0db test signal with the volume control and all other settings (eq, etc) all set flat, it *should* read whatever the preouts are rated for -- this can vary of course, just as amps come with birth sheets that are rated either higher or lower than their rated output, head units will also read lower or higher. note that it seems the majority of head units clip before their volume is maxed out, so you won't ever even see that actual voltage anyways.

1a) voltage is increasing in increments. if you think of volume as voltage, you're sending a theoretical 8v signal at full volume to your amp, which is amplifying that to, say, 20v to go to your drivers. the gain is to match it up to your preout, so you'd set it to the 8v position if your head unit actually put out 8v unclipped signal, in order to get the outputs on the amp to read 20v. basically, it doesn't matter what the gain range is, as long as you can get it to read the amount of voltage you need on the outputs for its rated power.

2) that's ideal but for example, the alpine pdx series is (i believe) 0.2v-4v but i believe it can be used with 8v preouts. mainly it's just a matter of setting the gains for a low volume in that case so you don't overdrive the amp. if you're pushing 8v to an amp that is rated for 4v, then yes, you're going to have a problem, at least on test tones -- on music, it may or may not be an issue since music is dynamic.

3) you're fine on music, especially given that the general recommendation here is to set gain with your volume at around 75% which automatically puts your preout voltage much lower than 8v.  beyond that, i believe most decent amps have some sort of protection although i don't know for certain -- otherwise, as long as it's not clipping, you should be fine although someone else may be able to answer this one better than i!


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## nosaj122081 (Apr 7, 2012)

It's OK to use a HU that outputs a greater voltage than the amp's input range, as long as you don't turn the volume past a certain point.

Do you have access to an oscilloscope? If so, very easy, run a sine wave through the HU, turn the volume up while monitoring the scope. When the peak value reaches the the maximum input value of the amp, bingo, that's your top volume.

You could use a DMM to do the same thing, bear in mind that when you look at AC voltage on a DMM, you're looking at the RMS voltage, not the peak voltage. Multiply the RMS voltage shown on the DMM by 1.414, and that will give you peak voltage.

Personally (and this is just my opinion), I would use a 0dB sine wave to test the HU's output, but a -3dB to set the gains.


Conversely, again with a scope, you could hook the whole mess up, with the gains set all the way down, and turn the volume of the HU up until it clips. Voila, max volume value.


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## Dean (Oct 27, 2006)

Thanks, folks, I feel better. 

I have read about gain setting, and there are many opinions on what to do. DMM, oscilloscope, piezo tweeter, etc. Seems the scope is the best way. I still have studying to do on crossovers too. I read and understood it years ago, but this project was put on hold and I forget.

*nosaj122081*, no I don't have access to an oscilloscope, though I have previously considered getting one for working on cars and have been looking again. Someone on this BB mentioned a Velleman HPS10, which I have found for ~$120. Looks like that would do all that I need. Would you happen know of any others that are in or below that price range?


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## kyheng (Jan 31, 2007)

Just grab a Pioneer amp's operating manual and have a read up on the gain settings, it should able to clear your doubts on this...


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## Dean (Oct 27, 2006)

You do like Pioneer, now don't you. 

I'll look on-line for a Pioneer manual... after I find a suitable Pioneer HU.

Dean


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## kyheng (Jan 31, 2007)

Nope, on this is the amp's manual....
I like Pioneer higher end Hus only, not the current line ups....


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## --Kei-- (Sep 8, 2011)

You'll not need to turn the volume up on the headunit as much to get loud on an amp with a 4V max input voltage. Basically you'll have less "range" to the volume control before you enter clipping. If the headunit displays the volume in -xxdB or just a number and you can measure for clipping, you can find the maximum point on the headunit volume control that you can go to.

I'm running a 4V RMS, 8V max DRX9255 into my old alpine amplifiers with a max input voltage of 2V. It all works fine with the gain controls set to minimum.


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## nosaj122081 (Apr 7, 2012)

Dean said:


> *nosaj122081*, no I don't have access to an oscilloscope, though I have previously considered getting one for working on cars and have been looking again. Someone on this BB mentioned a Velleman HPS10, which I have found for ~$120. Looks like that would do all that I need. Would you happen know of any others that are in or below that price range?


Velleman makes good equipment, I've never used their scopes, but have some of their other items. IMO, a scope is a good investment if you mess around with electronics/electricity, once you have one, you'll come up with more uses for it than you would imagine. I use mine a lot, they're really versatile. I've used, and liked, units manufactured by Leader, Hitachi, HP/Agilent, and Tektronix, you couldn't go wrong with any of those brands (among others, but that's what I've laid hands on).

You can get a lot of different scopes for less than $200, the big CRT scopes are going the way of the dodo for tiny-ass digital units so they're saturating the used market. 

My personal scope is a Hitachi VC-6524, it's a bigass CRT dual trace digital storage unit. I really like it, since it's a storage scope you can "save" the waveform and use built-in tools to more-precisely measure voltage, frequency, and/or period. It would have cost more than I wanted to spend, but the college I went/am going to switched to these badass little Tektronix 4-channel fully-digital scopes (that weigh NOTHING and are functionally AMAZING! Of course I think they paid like $3000 each though), they were so old they were just getting written off the books and I'm pretty close with the professor that runs the dept., I begged and pleaded and he threw me one (they were just getting piled up in a corner of a closet to decompose back to dust anyway). Really though, for car audio, a basic scope will get the job done just fine, the bells and whistles are just a nicety.

Just make sure that you get one that has been verified tested and functional, test equipment has a bad habit of getting DESTROYED!


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## Dean (Oct 27, 2006)

nosaj122081 said:


> You can get a lot of different scopes for less than $200, the big CRT scopes are going the way of the dodo for tiny-ass digital units so they're saturating the used market.


Funny you mention old CRT 'scopes as I have been cruising eBay and Craigslist and there are boat loads of them. Problem being, as you mention, not a lot of tested functional. Many are simply tested "power on" and that's it, and "No Returns" or exchange only, but shipped at my cost.

Also, I'm not sure what I should be looking for. As I mentioned, I want to use it on my car for other things as well. Issues have been resolved after components are "scoped" at the shop I use, like faulty sensors, injectors, and wiring. I want to be able to do that myself and want to make sure I get a scope that is capable. I'm not an electronics guy, though, so all those specs mean nothing to me at the moment. I need to do some learnin', but in the meantime my sound system is waiting...


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