I have a factory integrated system with stock radio, USA-Spec iPod integration, Factory amp > LOC > RCA > 4 ch amp. Upon trying to turn up the gains, the max voltage output I get is 2v. I changed my Amp > Ground > RCA > LOC > and bypassed the factory amp. Still only getting 2V at the aftermarket amp terminal with gains up. Someone said I need the factory amp to amplify the signal coming from the radio. But even after I bypass, I get the same low voltage as if the factory amp is still connected. Can anyone confirm this? Also, only thing left to do is to get a new radio. I need input because I have been without sound for about a month now, and I am getting annoyed. Thanks in advance.

 

What's the output voltage range of the LOC? Did you set the input sensitivity on the aftermarket amp to match this?

 

So the output of the aftermarket amp is 2V?

What are you using for source material? Test tones?

2VAC is 1 watt into a 4 ohm load.

Or do you mean the preamp output level of your LOC is 2V? Because that is different, and shouldn't be a problem. Most amps have a gain structure that will allow for as little as ~.25V input.

 

I think the LOC said up to 40w or so

The Output of the the aftermarket amp is 2V with gains turned all the way up. Source is a test tone 1khz. I know, that's crazy low right? I don't want no 1 watt speakers lol.

 

First thing I want to understand is where, specifically are you measuring this. Second, does the output voltage change when you adjust the amp gain? Third, doulbe check that the input sensitivity is adjusted correctly too. The LOC should specify the output (in volts) and then you should adjust the amp input sensitivity to match the output of the LOC voltage range.

If you're truly measuring that low, then you might have a defective component somewhere.

 

I am measuring at the aftermarket amp's output terminals for the speaker wire. That's the whole problem that is baffling me. The output voltage does not change with the adjustment of the amp gain.

 

To add, he LOC gain/sensitivity knob is half way. And this does not matter if it is turned all the way up either. So I am banking it is my factory stereo that is giving me problems. Especially since I still get low voltage when I pass the factory amp in the system.

 

Yeah, that sounds like a bad amp to me.

 

This is the order of components in the system:

Radio > USA-Spec > Factory Amp > LOC > RCA > Ground for Aftermarket amp > Aftermarket Amp

Underlined components are what I have already changed to rule out.

 

The thing is, I have another amp, and that TOO is giving me the same characteristics so I ruled out it is a bad aftermarket amp. Especially since it is brand new. I thought the same thing!

 

Wow so you've done some swapping out already... Well clearly you know how to use a DMM. If you've confirmed that the factory amp and everything downstream is GOOD, then the problem is either the radio or USA Spec (I'm not quite familiar with this device...). Measure the radio pre-amp outputs to see what's happening there.

 

Right? LOL. What should the wires be running from the pre-amp? Never actually knew what to look for.

 

That's a good question. I would expect a couple of volts or so. More importantly, I would expect it to fluctuate with a volume adjustment.

 

I'll check today. It should be a solid volt whatever it is since it is a solid test tone. I will try it at the pre-amp wires coming straight from the radio.

 

The stock radio preamp is 1.0VAC at max volume @1kHz. It is a balanced signal.

What is weird is that adjusting the amp gain has no affect on output. The only way that could happen is if there is no input signal to amplify. But you said it plays, just at really low levels right?

 

Exactly right! That voltage is at the wires alone right? I will tap into the harness for factory amp input to see what it does. When I tested the RCAs one time, I got a reading of 0.2V coming from the LOCs RCAs. The RCA should match the 1VAC? Or be lower?

 

Thanks for the input again guys. Probably the best help I have gotten on any forum with this issue.

 

Thanks!!

The RCA outputs of the LOC will be specified in the description of the part. Which LOC do you have?

And what was the input condition that you measured 0.2V? Max volume?

 

I have a PAC SOEM-4 (4 channel). All tests are at 3/4 volume from my headunit. I don't want to clip and get a distorted signal. So my volume is at 30/40

 

That LOC has adjustable output levels. Did you verify that you can manipulate the output by adjusting the output levels on the LOC?

Also, to confirm, you are using the factory amp speaker outputs right? Because this LOC requires a MIN 5V input for low level signals which you won't get from the TL per JoeQuimby's info above.

 

Hi Ho: I expect that the problem lies in the way you are making the measurement, or rather in the way the data is being interpreted. First of all, a 2V rms signal across 4 ohm speaker is 1 watt rms. This is a very loud signal. (Most people set the output in a car at about 0.1 watts of so.) So, the most likely thing is that you have a supersonic (say 15 or 20 KHz) oscillation caused by probing or connecting something to the system that causes feedback.

That would explain why you get a large, stable reading while not getting much sound. If there is an oscillation, then something is likely saturating and that would tend to suppress the real signal. If you have access to an oscilloscope, connect it where you are currently making your voltage reading and see what is really there.

 

So this is what I CONFIRMED. I tested the voltage of the pre (factory) amp leads and the voltage of output of factory amp. And here are the results:

Pre-Amp:
wht/yel (Left Rear) .06-.07 VAC
org/red (Right Rear) .06-.07 VAC
grn/blue (Left Front) .04 VAC
gry/blk (Right Front) .03 VAC

Factory Amp Output:
Green: 2.3 VAC
Purple: 2.3 VAC
Grey: 7.7 VAC
White: 8.2 VAC
__________________________________________________ __

After passing through LOC:
All channels no more than 1.8 VAC

Now the question is, why is my LOC diminishing the voltage by that much? Given my radio isn't at spec, but the LOC is looking terrible right now. IMO....note this is all conducted at 40/40 volume with 1khz test tone playing.

 

I guess 2v is enough for a pre-amp voltage, but that doesn't change that there is no voltage if at 3/4 volume on the radio. I am so confused...

 

maybe instead of buying a new LOC to test, get a line driver (Rockford Fosgate BLD for example) and hook that up pre-amp and see where you results go. If it works, that's the cleaner approach anyway.

 

line driver or an amp that works with the low output of the HU

 

That's the whole point of the LOC. It converts the high-power speaker level signals to low-power line outputs. That's why it's called a Line Output Converter lol.

1.8VAC on the LOC outputs seems normal to me. Does it go to 0V when you reduce the volume to 3/4? Did you try adjusting the LOC to see if the output level changed? I think there is something fundamentally wrong with this setup or a defective component somewhere... As someone mentioned above, there might also be something wrong with your measurement technique, but I wouldn't expect you to have an oscope just chillin in your garage. What kind of amp is this anyway?

Using a line driver is a good suggestion.

 

I realized that after I said it lol. I think it DOES go to 0v or lower at the factory pre amp because for me to get that low voltage at 3/4, and get decent levels at 4/4. THE RADIO HAS TO BE IT!!!!! What do you think?

 

Honestly, the way I'd set this up from the jump is to take the factory preamp signal right into the amp (provided your amp will play nice with the balanced signal). No LOC. The 1.0V output of the factory preamp is at MAX volume. Your volume scale is not linear it's kind of an exponential scale so I would totally expect the output voltage of the preamp to be well under .5V even at 3/4 volume on the actual number scale displayed on the radio. I have not tested the actual voltage as you turn the volume down, just at the max levels, which are un-clipped BTW. But to give you an example, an aftermarket Kenwood radio with a 4 volt output that has a volume scale of 0-35 will look something like this in regard to volume and voltage:
Volume Voltage AC
35------------4
34------------3.6
33------------3.1
32------------2.5
31------------1.9
30------------1.3
29-------------.7
Etc.....

So at volume 17 (1/2 on the numeric scale) you may only see .1V.

You wouldn't want a linear voltage scale. You'd need like 500 steps for it to function right. (unless you are talking analog control, which we aren't, which is a whole different animal)

What amp are you running? Also, is this a new problem or has it never worked right since the amp was installed?

 

The factory preamp can't go lower than 0V because physics and math.

 

That's good info, but even at full tilt, 2 channels are giving me only .03 VAC at pre-amp and NOTHING at 30/40. This leaves me to think the radio in that channel is the problem. At 40/40, it should be showing 1VAC right? If this is true, the radio isn't even giving good preouts.

I am running the Pioneer GM-8604 4ch D class. This is all coming from my system at one time making a loud whining noise (while no radio on) and frying my original amp. Things haven't been right ever since. Here is the full story on another website: http://www.stevemeadedesigns.com/boa...-channel-pics/

 

IDK what I was thinking here lol. I meant to say 1VAC

 

Does the stock amp already have xovers that could be cutting the 1khz signal strength?

 

disregard that last post. It wouldn't be a factor.

 

Just a friendly suggestion. You might want to try answering some of our questions too.

What kind of amp are you running? Is this a new problem or has this never worked? How are you taking the measurement?

 

I'm trying to get all the help I can get man! That's why I answered in post #30

 

Question. Instead of tuning at 30/40. Should I tune at 40/40 (max volume without clipping)? Maybe the RCA leads are dipping below .1 V and the DMM just shows 0?

 

My bad!!! Now I feel like a douche hahaha.


If it were me, I would tune at 40/40. But it sounds like (assuming your measurement techniques are good), that it is in fact a bad head unit.

 

I finally fixed the problem! You can't tune an amp if the headunit isn't at max power without clipping. Thanks for all the help guys. But I now have another problem LOL. I will start a new thread.

 

What was the problem and how did you fix it?

 

I turned the stereo up to full power. My radio happens to clip at 38 though. Still. The peak RCA voltage will not reach unless it is up at (or close to) max. Therefore, gains cannot be properly set on the amp either.