Is there a way to find out your preamp/RCA voltage with a multimeter?

Flyin11

Member
2007-09-26 1:29 pm
Ok...I know how to try and set your gains with a multi-meter but I was wondering if there is a way to use it to find out what voltage your RCA's/preamps are putting out? I know I had a discussion a while back about my headunit voltage and how you wouldn't really see 5v unless you had it maxed out in volume. So, I might be looking at another amp and don't want to get into a situation with it if it says 4V max input sens and my HU has 5V. Although I had this setup with a Alpine amp before and had no issues. Just wondering though so I can test and make sure....
 
I don't deal with car amps, and I don't know what this has to do with input sensitivity, but if I wanted to know the output levels of something, I would get a recording of a 440Hz sine wave (long enough to be useful, a couple minutes?), and play it. Then with the voltmeter set to AC, just read the terminals. You might not want to have you speakers on, it would probably be loud.

You should be able to find a test tone like the one above on the net somewhere. I'd try and avoid a higher frequency tone because your meter might not be accurate higher up..

Enjoy :D
 

Flyin11

Member
2007-09-26 1:29 pm
Thanks but that's not what I was referring to. That's how to set up your gains. I was wondering if there was a way to find out the voltage coming out of your RCA's from your headunit. I saw on another site someone said that you can set your multimeter to read AC voltage and use the positive probe and touch the pointed part of the RCA and then use the negative and touch the outer round part of it and it gives you the voltage coming off the RCA. Someone then replied though and said to be extremely careful cause if you touch one of the parts incorrectly you can burn out the RCA's in the headunit. I would want to be careful so I was wondering if anyone knew anything about this or if there's a way to do it? I'm wondering what mine is sending as I don't have my volume up max at all and never come anywhere near it so I don't really believe the 5V rating Kenwood gives me in the manual as you probably won't hit that unless you are at full power and you still might not get 5V out of it.
 
I'd agree, 50-60hz will probably give the most accurate reading unless you have a true RMS meter.

I'm not sure about other head units but most Pioneer head units will produce the maximum undistorted output at 1 step below the maximum volume (using a 0dBfs tone). For it not to be driven into clipping, you will have to have all EQs and bass/treble settings at 0. The loudness coutour will have to be off.

There is no danger of damaging the RCA outputs unless you allow them to come in contact with a power source (uninsulated 12v wire, speaker outputs of the amplifier...).

This is a 60Hz tone. Burn it to a disc and use it for testing.
http://bcae1.com/temp/60hz60seconds.zip
 

Flyin11

Member
2007-09-26 1:29 pm
Thanks :cool: Will give it a go later on. Tried a 60hz tone before and it didn't sound great to me after I started playing my music again so I've been using a 28hz tone and get a much better bass response. My system seems to like either 25hz or 28hz. Will stick that back in again and see what the RCA's are reading.
 

jol50

Member
2007-11-08 2:14 am
Flyin11 said:
and don't want to get into a situation with it if it says 4V max input sens and my HU has 5V.

You should not have to worry about that. Not 100% but I don't know if a HU can even put out its full rating playing music. Ones I have measured on RCA before I got a good dmm were millivolt. But it should not matter as you really should never turn the HU all the way up, and should never have to turn the amp gain all the way up either. Back in the 80s we ran 5v line drivers with no problems. Don't recall there being more than 2v HUs then.

You use a 50-60hz tone because odds are the meter can read standard AC current Hz better, it should have no effect on your system what you test with since RCA will not be hooked up anyway if you are reading voltage of it. Also, any numbers printed on an amp pot for crossover frequency or gain level...don't trust they are accurate. Better to set crossover by ear or with tones than what most amps say, even some crossovers.
 

Flyin11

Member
2007-09-26 1:29 pm
Yeah, I know...The meter fluctuates and doesn't really give you a solid reading but I just judged it by when it stops fluctuating and stays still longer than when it is fluctuating, just for a second or 2, that's where I stop and get it to where I want it. I'm not complaining, I know that it's not totally accurate that way but it sounds great anyways and I like how it is sounding. I can't go 60hz or over anymore...It just doesn't compare and I don't get the sound I'm looking for ;)
 

Flyin11

Member
2007-09-26 1:29 pm
Tried this yesterday and it wasn't reading correctly...I had it on AC voltage (Is that wrong?) and touched the round part of the RCA with the red lead and touched the outer part with the black and it was fluctuating at 00.1 and 00.2 volts. Tried it with my crossovers off and everything flat on the headunit and same result with a 60hz tone. Was I doing something wrong? That doesn't sound like a right reading...
 

Flyin11

Member
2007-09-26 1:29 pm
The 60hz tone is just for the testing...so the multi meter will get a stable reading. The crossovers thing was just me trying to see if it would make it read correctly but it didn't make any difference whether I had them set the way I wanted to on the headunit or not...I still got them readings. That's all...

Let me know what you find out ppia600...
 
Also be sure to have none of the deck's rca outputs connected to anything except the meter while checking output. (still haven't checked mine, I've still got some engine parts to take out) The voltage will vary depending on the load your amps present to the deck's circuit.



Update: Just tested, with my rca's still plugged into the door and deck speakers amps the sub preout was averaging 4.5v ac with the volume at 25. This was with any frequency I picked from 20hz up to about 50 which is where I decided to stop. The deck's maximum volume would be at 35. I don't have the loud on, but the bass is +4 at 60hz. I'm pretty sure your deck will do a good 5v, Flyin.
 

Flyin11

Member
2007-09-26 1:29 pm
Are you suppose to try and test the RCA's while they are actually still plugged in? If so, where do you touch the leads? I was told to touch the round part with the + probe and the - touches the outer shiny part. If it's plugged in, you can't touch the round pointy part of it cause it's pushed in.

If it's putting out 5V, that's what concerns me, even though it's what the HU is suppose to do because I hooked up the Alpine amp I got but it's input sensitivity is up to only 4V. I know we discussed this before and a lot of people were saying to not worry about it, that it would just convert the signal to 4V if it is a 5V signal. It does worry me though, cause my other Rockford amp I had, even though it was rated 170watts total power less than the Alpine and it was a Class AB, it was putting out much more bass than the Alpine. The Alpine is a lot cleaner and I feel the power from the kick drums a lot more but I can't get the bass out of it that I had with my Rockford. I think it's because of the input sensitivity and that's why I wanted to try and do this test. I'm thinking I'm still going to have to go for another amp that has up to 5V input sensitivity to get what I wanted but I'm going to have to wait until we get our tax rebate checks from the government in May-Early June before I can do anything again. Looks like I screwed up again but oh well, live and learn :smash:
 
Using a 4v input level amp or 10v input level amp will still sound great if you set them correctly. You DON"T have to use all 5v of the deck either way. They give you that much voltage so you can overcome any ground loop noise by turning the amp's gain down, and also to gain a little "headroom". That's why there's a large range of adjustment for the volume level. (My kenwood has 35 steps, some decks have 100 smaller steps) The maximum I usually ever run my deck, just making my mids scream a little, is at about 25. And since cd's are eq'd differently it will vary from one to the next. Think of it kind of like having a larger sub amp than you need, it doesn't hurt to have a little more power. (read my sig at the bottom, lol)
I tested the sub pre amp out with them unplugged. The front and rear rca's were still plugged into the mids amps though.