Alpine head unit says 4V pre-out but only 40mV?

[rth]

The sensitivity of my Kicker ix2302 is 150mV-3V and Alpine says this head unit has 4 V pre-outs, which I assumed was either an RMS voltage or a peak voltage that I would see on the RCA cables, so I decided to measure it first to make sure I didn't exceed the amp's input range. I looked at each channel on the pre-out (subwoofer and regular) and at normal volume on the main speakers I'm only seeing 80 mV p-p and when turned way up I see around 300 mV p-p What exactly does "4 V pre-out" refer to if it's not even half a volt peak to peak? I'm having to turn my gain all the way up on the amp to get the level to match the main speakers (unamplified till i fix my ppi). The scope had a hard time triggering on this level so the waveform looked really noisy but looking at the output on the amp I was seeing a perfect sine wave at up to 160 V p-p I was surprised that it looked that good on the amp given how nasty it looked at the low-level input but I guess the scope was not giving me the true story.

Does 300 mV p-p seem low for a pre-out or is this common? I would think a level of several volts would be better to avoid noise being amplified along with the signal, no?

 

[Stocker]

Turn down the gain on your amplifier so you do not deafen yourself.

Turn up the volume all the way, or until the preamp output hits 3V.

Are you using a test tone, sine wave or music as a signal? Looks like a sine wave.

What is the input impedance of the amplifier...could it be loading the preamp output too heavily?

 

[Tim__x]

Many 'scope probes attenuate the signal, perhaps your probe is a 1:10 which would mean your measured 300mv was actually 3v.

 

[rth]

I did have to use a 10x probe to see the amp output due to scope clipping at ~120V but I used a 1:1 probe on the RCA cables and it surely was ~50mV at reasonable volume. My DMM also confirms this, which is why I got the scope out, because it was reading ~30 mV RMS before I cranked up the volume. I am using a 60 hz sine track off a bass test cd and don't worry about the spl on my eardrums because i have it turned up only for testing right now... sounds like booty without an amplified front stage anyway

One possibility is that the cd player is sensing that the rca cable is disconnected and shutting off that output so maybe I will have to put a load on it to see anything, though both the amp and scope should have very high input impedances. I can try turning up the volume more but these factory speakers don't like that 60 hz very much

Taking it back to the basic question: should I see 4 Vpp (or is it 8 Vpp, 4 V peak?) if Alpine says "4 V pre-out"? Have any of you ever looked at the output of your head unit?

 

[Puggie]

I think the Alpine is 4V peak (not peak to peak) but you will only get this with a sinewave recorded at 0dB and the volume turned all the way up. Also if you are using the sub out, that has a 15dB attenuator, usually if you press the function knob you can select the sub out, you will have to turn that up to +15 to get your 4V out of the sub out.

I had an old alpine and I couldn't get the outputs to clip it was awesome, full scale recordings with the volume up to max and the bass boost up full we could get about 11V peak out of it and it was still a clean unclipped sine wave!!!

 

[rth]

WOW

This is my brother's Alpine mp3 player that I'm using so I haven't messed with it much but my older Alpine cd player is still rock solid and I know it had a large pre-out signal because I could leave the gain almost all the way down on the amp and still go boom boom boom

As soon as this PPI amp is fixed (waiting on a new FET driver from TI) I'm going to clip these factory speakers and then I can turn up the volume and see what the hell is going on with this newfangled alpine thingamajigger

 

[MyNameIsJake]

i was always under the impresion that preamp output voltage was used as a carrier for the signal, the higher the voltage the better the signal has of staying clean, if thats not the case, please someone educate me... besides, im at the opinion that nothing beats cables with proper and/or excellent sheilding. this is something that is over looked in a lot of sound systems ive seen, home or car...

 

[rth]

By carrier do you mean "4 V pre-out" would mean a 4V DC offset with the signal swinging around that voltage? That's possible, I wouldn't have noticed it with the scope on AC coupling. I'll throw the DMM on it tomorrow and see if that's the case.

 

[richie00boy]

I was told that it was peak to peak, however Puggie seems to have practical experience to counter that. It won't be DC offset is 4V as that would be completely pointless and worse than the normal 6V/half supply.

 

[rth]

An offset would help reject common-mode noise but you are right, a split supply with as large a swing as possible would be the easiest and best route. I don't guess there could be an offset anyway because there's no zero-adjust on car amps

 

[MyNameIsJake]

By carrier do you mean "4 V pre-out" would mean a 4V DC offset with the signal swinging around that voltage? That's possible, I wouldn't have noticed it with the scope on AC coupling. I'll throw the DMM on it tomorrow and see if that's the case.

by carrier, i mean the pre out yes, but dc voltage in the signal line woud kill anything hooked up to it. if you find DC in your preouts, say around 8-15 mv, i would worry. BUT keep in mind, I AM NOT SURE, ive never really looked into it my self as to what is harmful as dc offset in a line signal, never had to...

I was told that it was peak to peak, however Puggie seems to have practical experience to counter that. It won't be DC offset is 4V as that would be completely pointless and worse than the normal 6V/half supply.

puggie is most likely right, the voltage preout is peak to peak, i own a alpine head, and it produces some of the cleanest signals ive ever had pleasure sending to an amp.

An offset would help reject common-mode noise but you are right, a split supply with as large a swing as possible would be the easiest and best route. I don't guess there could be an offset anyway because there's no zero-adjust on car amps

as far as i know, dc would be harmful to signal processors and amps. the carrer voltage is AC, just not at a fixed frequencey like house power. try your test with the DMM using a sine wave sweeping at 20-200Hz and 20-20kHz than the same using the scope, and turn it up. you should see peak voltages on the meter and the wave on the scope. when you do so set for alternating current. that should get the results your looking for, if not then im baffled...

 

[rth]

Indeed, DC would be a bad thing to have on the line if the devices weren't expecting it, but it would be possible to use a certain DC voltage as the zero reference if all devices were designed to calibrate for it, but there's really no reason to do it this way since even at 12 volts there's plenty of headroom for a signal large enough to reject noise. I have watched the pre-out AC voltage on a dmm already and without turning it up so far as to destroy the high-level speakers I saw about 350mV RMS which would be about 0.5 V peak amplitude... obviously not 4 volts p-p Hopefully there is nothing wrong with this head unit and once I remove the high level speakers I'll be able to turn up the volume far enough to get the pre-out to at least 2 V peak so that I can amplify less noise and mo' boom at the amp

My TI drivers just showed up so hopefully this PPI amp will be rocking here shortly, then the Quart's go in and I can set all gains relative to each other and make this thing sound right

 

[MyNameIsJake]

oops, i failed to realize you had mid's hooked up. try to measure the pre outs with out using the internal amps of the deck, that way your readings would be more accurate, if not id get the deck checked out or try another alpine deck to conferm your findings... this is indeed interesting...

i do agree with you on the dc for calibration, i could see this in some silly high end gear with some sickass processing built in or something, but still, dc in the signal... yack...

 

[MyNameIsJake]

puggie is most likely right, the voltage preout is peak to peak, i own a alpine head, and it produces some of the cleanest signals ive ever had pleasure sending to an amp.

sorry... i meant NOT peak to peak... my bad...

 

[rth]

the answer has come!

Well, there is no more question, this thing will push every bit of 4 volts and then some! I found a setting to turn off the internal amp so I turned it off and cranked the volume up to the max of 35, whereas I'd only been able to go to 15 before. With flat settings I hit 4.73 Vrms (6.69 peak!) and with the bass maxed (not sure what center freq it's set to now) it hit 6.3 Vrms (8.9 V peak!) This was with my DMM and a 60 hz track so there's no telling how bad it was clipping at these levels so I'll put it on the scope when I get a chance and we'll see if Alpine is still ///-\lpine

 

[Stocker]

Sweet.

 

[MyNameIsJake]

now im drooling...

 

[subarusteve]

not sure HOW alpine measures

I used to work for an alpine dealer....their claim is that 4 volts is an unclipped low level signal
in the early days of car audio the output imp. were high and the output voltage was low....amplifier designs were not as advanced as they are now....noise issues were very common...cable designs and better designed electronics have virtually eliminated those issues....on of the big ones was to increase preamp level signal....alpine did it 1st with the veneral 7909....a 20bit 4 volt deck legendary for it's sound.....for many many years to boot...only one other deck came close or exceeded it...the clarion drx 9255....10 years later !!!..the high signal lever means your gonna have to turn down your amp gains...the high preamp voltage won't harm the amp but it will sound pretty bad and clip way to early

 

[MyNameIsJake]

Re: not sure HOW alpine measures

10 years later !!!..the high signal lever means your gonna have to turn down your amp gains...the high preamp voltage won't harm the amp but it will sound pretty bad and clip way to early

ya, i have experenced this, not to crazy bout it... but what are ya going to do. i have a newer alpine mono sub amp that doesn't really have this problem, but my 2 older amps do...