Another RCA Input Voltage Question

soth · Post by **soth** » Sun Nov 18, 2007 7:39 pm

Well from reading Mr.Tibbs post i've done the following.

Set everything to flat on the HU.
Center pole of RCA and shield of RCA.
Set to AC voltage.
Create a CDA of a 60hz sine 0db file.
Set HU to 3/4 of max volume.

HU -> Eclipse CD5000 (suppose to have 8v preouts).
HU -> Has 4 sets of preouts (front, rear, aux, sub)

Patch cables are 20' length.

When I measure the voltage i'm only showing around 1v. I have to turn the bass, midbass, treble and loudness on and then i'm only getting around 3.9 volts. This is also hooked up to my ax406a crossover and I have to turn the input gains up till they clip to get this.

I've got the patch cables hooked into the (front preouts) off the HU. Is that a normal measurement for an 8v preout with a 20' run?

Just has me puzzled for some reason.

Thanks

Post by **Eric D** » Sun Nov 18, 2007 7:45 pm

What model DMM did you use for this test?

Was it a true RMS measuring DMM? Even at 60Hz some DMMs just don’t read accurately. These are generally budget models.

soth · Post by **soth** » Sun Nov 18, 2007 8:01 pm

http://www.computereq.com/detail.asp?ProdID=2274

Not exact model, but according to the manual it does do True RMS readings. The DMM is in my garage right now so I don't know the exact model, but i'll get it tomorrow though.

Post by **Eric D** » Sun Nov 18, 2007 8:08 pm

Well, you have me puzzled as well.

This are the results I got measuring a cheaper Rockford deck. It was rated for 2.4V, and I got 2.45V RMS, so it was on the money. That was with all the bass, treble, and anything else set flat.

I used a 1kHz tone for that test.

Here is the same deck with the bass boosted, while playing 40Hz…

soth · Post by **soth** » Sun Nov 18, 2007 8:20 pm

Well i'll be *****. Could it be that it's the DMM? It only costed 25 bucks. Could the patch cables have anything to do with it? It's the ARX900 series think from PG. Very nice looking to say the least.

Thanks

dedlyjedly · Post by **dedlyjedly** » Sun Nov 18, 2007 8:23 pm

I've seen underwhelming results using an Audio Control RTA to meter the rca pre-outs on Eclipse decks rated at 8v as well. What kind of numbers do you get if you turn up the sub-level adjustment?

soth · Post by **soth** » Sun Nov 18, 2007 8:41 pm

dedlyjedly wrote:I've seen underwhelming results using an Audio Control RTA to meter the rca pre-outs on Eclipse decks rated at 8v as well. What kind of numbers do you get if you turn up the sub-level adjustment?

Haven't tried the sub level to turn it up any. Are you saying I should use the sub level preouts instead of the front to go to my EQ?

Kevin

Post by **mr tibbs** » Sun Nov 18, 2007 8:51 pm

soth wrote:
dedlyjedly wrote:I've seen underwhelming results using an Audio Control RTA to meter the rca pre-outs on Eclipse decks rated at 8v as well. What kind of numbers do you get if you turn up the sub-level adjustment?
Haven't tried the sub level to turn it up any. Are you saying I should use the sub level preouts instead of the front to go to my EQ?

Kevin

Wouldn't that send only a sub signal to the eq and not a full range signal?

soth · Post by **soth** » Sun Nov 18, 2007 8:55 pm

mr tibbs wrote:
soth wrote:
dedlyjedly wrote:I've seen underwhelming results using an Audio Control RTA to meter the rca pre-outs on Eclipse decks rated at 8v as well. What kind of numbers do you get if you turn up the sub-level adjustment?
Haven't tried the sub level to turn it up any. Are you saying I should use the sub level preouts instead of the front to go to my EQ?

Kevin
Wouldn't that send only a sub signal to the eq and not a full range signal?

I'ts a non fader preamp which can be set either mono or stereo.

dedlyjedly · Post by **dedlyjedly** » Sun Nov 18, 2007 8:57 pm

Sorry, didn't mean to confuse you. I forgot you were using the front outputs. When I measured the outputs on those high voltage eclipse decks I never got anywhere near the rated values but did get closer with the sub-level and processing maxed out. I suspect you're getting similar results to mine and that the DMM isn't the culprit. The only conclusion that I could come to was that like amp power ratings not all manufacturers are truly honest with their ratings.

soth · Post by **soth** » Sun Nov 18, 2007 9:08 pm

dedlyjedly wrote:Sorry, didn't mean to confuse you. I forgot you were using the front outputs. When I measured the outputs on those high voltage eclipse decks I never got anywhere near the rated values but did get closer with the sub-level and processing maxed out. I suspect you're getting similar results to mine and that the DMM isn't the culprit. The only conclusion that I could come to was that like amp power ratings not all manufacturers are truly honest with their ratings.

No problem

Here is a link to the HU I have.
http://www.crutchfield.com/S-ecCfYFgZV6 ... ailed_info

So if a HU is rated at 8v and both the left/right channel of the rca is getting around 4v is that 4 volts total or does the L/R both add to get 8? That sounds stupid I know, but some things you get to thinking too much and then you second guess yourself!

So if you were to use the non-fader output (for subs(can be switched to stereo though)) what type of difference it would be compared to front outputs. The non-fader can be adjusted from 0-6.

One of my friends has a 2v HU and he isn't even getting 1/4 of a volt. This was with a different DMM also. He has no line driver either.

Kev

marko · Post by **marko** » Sun Nov 18, 2007 11:04 pm

where did you get the sine wave from? this can make a differance as some peoples claim they are 0db referance but they arn't (realm of excurtion for one

)

i always use the one on my bassmekaniks cd or auto2000, i use 1khz as well....

soth · Post by **soth** » Mon Nov 19, 2007 3:27 am

marko wrote:where did you get the sine wave from? this can make a differance as some peoples claim they are 0db referance but they arn't (realm of excurtion for one )

i always use the one on my bassmekaniks cd or auto2000, i use 1khz as well....

From Erics site at soundbuggy.

Post by **Eric D** » Mon Nov 19, 2007 3:51 am

I think the signals I posted are in MP3 are they not?

If so, what did you use to decode them out to wave? It is possible your software tried to “normalize” these files and they somehow managed to become much smaller.

soth · Post by **soth** » Mon Nov 19, 2007 6:03 am

Eric D wrote:I think the signals I posted are in MP3 are they not?

If so, what did you use to decode them out to wave? It is possible your software tried to “normalize” these files and they somehow managed to become much smaller.

Nero.

I'll check into that and make sure.

soth · Post by **soth** » Mon Nov 19, 2007 6:06 am

soth wrote:
Eric D wrote:I think the signals I posted are in MP3 are they not?

If so, what did you use to decode them out to wave? It is possible your software tried to “normalize” these files and they somehow managed to become much smaller.
Nero.

I'll check into that and make sure.

Nope, doesn't look like the normalization filter was applied when burning a cda in Nero.

Things that make you go hmmmmmmmmmmmm.

Post by **stipud** » Mon Nov 19, 2007 7:15 am

Of course 8v is just a max rating, just like that $15 pyramid amp will do 1000 watts... Decks are almost always rated in max power levels. 50x4 WATTS! WOW!! Except it's really 10x4 watts...

Just like the headunit amp outputs, RCA ratings are no stranger to the max watts fairy.

My guess is the sub channel is CAPABLE of 8v max with the sub gains turned all the way up, at clipping levels. The front and rear channel are probably 4v max in order to save on costs. They probably don't tell you this anywhere either.

In my experience with the cheaper "4v" Alpine decks, I measured about 1 volt RMS out of them at near max volume.

Post by **bdubs767** » Mon Nov 19, 2007 7:18 am

I want me an O-scope

maybe the should be my next investment.

soth · Post by **soth** » Mon Nov 19, 2007 7:25 am

stipud wrote:Of course 8v is just a max rating, just like that $15 pyramid amp will do 1000 watts... Decks are almost always rated in max power levels. 50x4 WATTS! WOW!! Except it's really 10x4 watts... Just like the headunit amp outputs, RCA ratings are no stranger to the max watts fairy.

My guess is the sub channel is CAPABLE of 8v max with the sub gains turned all the way up, at clipping levels. The front and rear channel are probably 4v max in order to save on costs. They probably don't tell you this anywhere either.

In my experience with the cheaper "4v" Alpine decks, I measured about 1 volt RMS out of them at near max volume.

I could go higher on the input sensitivity on the crossover, but I left it right below where it was clipping. Didn't want to do that

You would think that you would get at least 6-7v though. I'll have to test the rca preouts on the back of the unit instead at the end of the 20' patch cable and see what I get and compare the two.