It should not be a surprise to anyone that there is more output voltage on the speaker leads of an aftermarket deck. For an Alpine entry-level deck that says 45 x 4 max (16 x 4 RMS) that should work out to be 8 V, according to this this calculator:
http://www.sengpielaudio.com/calculator-ohm.htm
That is four times the output voltage on those preamp outs.
This is where it gets interesting, if you haven't already guessed. Is anything wrong with using those speaker leads as preamp outs on male RCA jacks, and making a direct connection to the next stage in line, eq, xover or amplifier?
Is this a good or a bad idea?
http://www.sengpielaudio.com/calculator-ohm.htm
That is four times the output voltage on those preamp outs.
This is where it gets interesting, if you haven't already guessed. Is anything wrong with using those speaker leads as preamp outs on male RCA jacks, and making a direct connection to the next stage in line, eq, xover or amplifier?
Is this a good or a bad idea?
Sometime last year or a couple years ago when I had an experimental entry level deck on my test bench, I made a direct connection of RCA jacks on the the speaker leads (by soldering them on) and observed over 5 volts on those RCA jacks connected to those speaker leads. No 8 volts and "no barbecue."
However, it was at a lower volume setting - 19 I believe down from 29 of 35. I remember taking them out, now sure why?
I also know that there is d-c on those speaker leads and not sure it a good thing to do, without using a suitable interface and adequate isolation.
However, it was at a lower volume setting - 19 I believe down from 29 of 35. I remember taking them out, now sure why?
I also know that there is d-c on those speaker leads and not sure it a good thing to do, without using a suitable interface and adequate isolation.
I think 8V into a line level circuit will clip.
The line level input is high impedance so no high current will flow.
Personally, without knowing the output driver schematic, I'd put some kind of realistic load on the amplifier output, say 10-50ohms and then resistively divide down the 8V to a more sane 1V line level.
...or turn the volume down.
There shouldn't be DC on the speaker leads. Yes, the speaker leads could well be at Vcc/2 (6V) relative to the chassis but both speaker leads should BOTH be at 6V. Make sure you stick a DC blocking cap in the input to your circuit. A differential input looking at both speaker wires is probably best to minimize noise.
The line level input is high impedance so no high current will flow.
Personally, without knowing the output driver schematic, I'd put some kind of realistic load on the amplifier output, say 10-50ohms and then resistively divide down the 8V to a more sane 1V line level.
...or turn the volume down.
There shouldn't be DC on the speaker leads. Yes, the speaker leads could well be at Vcc/2 (6V) relative to the chassis but both speaker leads should BOTH be at 6V. Make sure you stick a DC blocking cap in the input to your circuit. A differential input looking at both speaker wires is probably best to minimize noise.
defect9 said:
Current is limited by impedance. An amplifier will have a input impedence around ~28k-80k ohm so won't be an issue.
You could very likely damage the equipment still. The amplifiers signal ground is at ground but the deck output isn't as a aftermarket deck is bridged. You would be putting DC into the amplifier input stage, The deck will likely have built in protection but its still nothing you should try.
ocool_15 said:
I hear you brother, but what do you make of this:
"Here’s a thought on those big internal amps, use them as preamps instead - 27 watts into 4 ohms equates to about 10 volts. If you drive a higher impedance, such as that found at the input of an amp (with balanced inputs) or in a LOC, you’ll get even more. When’s the last time you saw 10-volt+ preamps in a head unit? This approach should prevent the unit from becoming overly hot and provide excellent performance from the noise perspective due to the amp’s voltage capabilities."
This is what started the whole thing.
Here's the full review, but ONLY the above pertains to this thread.
http://www.carsound.com/reviews/hd_units/cda-7875.html
I don't think Brian Smith understands amplifiers very well. He seems to think that increasing the load impedance increases the voltage the amplifier puts out. This is not true.
An amplifier can only put out voltage to the limit of its voltage rails. In a car amp, unless there is a voltage booster/step-up circuit, you are limited to ±12V peak best case (bridged mode) That's 8V rms regardless of the load impedance (>4ohms).
I still think this will overload any other amplifier input stage (typically expecting 1Vrms) and cause severe clipping.
An amplifier can only put out voltage to the limit of its voltage rails. In a car amp, unless there is a voltage booster/step-up circuit, you are limited to ±12V peak best case (bridged mode) That's 8V rms regardless of the load impedance (>4ohms).
I still think this will overload any other amplifier input stage (typically expecting 1Vrms) and cause severe clipping.
Lol, we used to do that with LP amps back in the day, with low power HU that were out then. They would eat 5v input with no problem, but we did it more for noise issues due to things like noisy electrical in cars and pioneer HU with no RCA output. It never worked that great because the quality is not there, and you had to be real careful not to crank the HU up high. I would never try it on many amps, most could not take the input like that. Today I'd say it was senseless to do unless you had just the right equipment, I mean why bother? Input voltage has little to do with how well an amp works anyway in the equipment I have used. Or just run a line driver. Another thing is you could get a quality cut down and still run high-er power into the amp, but same issue the signal quality was not there even with top of the line HU back in say '90. Seems like back then everyone wanted to turn the volume knob all the way over, then stuff did blow up running that way.
So you just got ahold of a PAII LP for a ton of cash and it worked way better.
So you just got ahold of a PAII LP for a ton of cash and it worked way better.
Iain McNeill said:
I think you misunderstood what he was talking about. That's okay. It happens to me when I read too quickly. He was not talking about the amplifier at all. He was talking about "input impedance" to any source. A typical amplifier input stage has an input impedance of 20K. AC processors has an input impedance of 10K, a LOC has an input impedance of approximately 10k. The higher the input impedance the greater the voltage drop. I hope we can agree on that. All of this has nothing to do with amplifier power or gain which is usually fixed. That's why he used the examples above and said that you will get more output voltage.
I think using the output of a head unit as a preamp is an extremely bad way to achieve whatever it is you're trying to achieve. Sure it can work, but what is the point?
If for whatever reason you have an amplifier that needs a ridiculously high input signal to reach clipping; then you are better off building a proper preamp/line driver.
<2Vrms will driver the amps in my car to clipping.
If for whatever reason you have an amplifier that needs a ridiculously high input signal to reach clipping; then you are better off building a proper preamp/line driver.
<2Vrms will driver the amps in my car to clipping.
I've done it and the quality was not there, but maybe you can find it with the right equipment. I don't even trust HU amps to run my speakers let alone inputs. Does you little good if it sounds like.....you know. Beyond that I have not had a noise issue in 15 years. I run the RCA right next to the 4ga amp power wire and could care less. If I ever get noise again I'll know the first place to look. And that is with a 2v HU running at half volume max. People talked about it, and I did it, back in the late 80s/early 90s because noise from electrical was a big issue then. I had the second best HU kenwood (9900 or 999?) made at the time and it did not have the SQ RCA had, and I don't think it went much louder if any before noticeable distortion. Unless HU amps are better now. Maybe I'm an idiot, but I still fail to see what huge line voltage has to do with anything SQ related. Fine if you want to ensure your amp is maxed but for a daily driver I can't find any noise from the car in many many years. Even this kicker amp I have now the gains are 1/3 and I can run it into clipping at half HU volume.
theAnonymous1 said:I think using the output of a head unit as a preamp is an extremely bad way to achieve whatever it is you're trying to achieve. Sure it can work, but what is the point?
If for whatever reason you have an amplifier that needs a ridiculously high input signal to reach clipping; then you are better off building a proper preamp/line driver.
<2Vrms will driver the amps in my car to clipping.
Why buy an external line driver when you would be getting one for FREE, at the source.
Whatever I am trying to achieve? I will tell you what I am trying to achieve. As much voltage as I possibly can, pure and simple. I will get to that in a minute.
Let's compare apples to apples. Let's take two separate head units for comparison. One has 2 volts and the other has 4 volts. If we start to turn the dial to maximum, the 2 volt deck will run out of steam a lot faster than a 4 volt deck. When you reach the maximum volume rotation, you will still have like double the way to go on a 4 volt deck. An 8 volt deck and higher, you get the picture. It's like a car with a maximum speed of 55 mph and one with a maximum of 110 mph. Which one would you choose? I would always choose the one with more. Again, it is like having more money in the bank. I will always take more money than take less money, if I had the choice. This may seem silly to you, but it makes a lot of sense to me. High voltage is a BIG deal, at least to me.
Remember, that our hobby, car audio, evolved from other fields like pro and home audio. The technology that you see today we brought from other fields. We didn't invent anything new here. Line drivers that you spoke about has been around for almost 100 years, first used in the telephone industry. The car audio industry did not invent it.
Quicksilver Audio has a preamp that has about 65 volts out, even though it retails for over $1,000.00. It was designed for home audio. Why would one design a preamp with that kind of voltage? Must be for a very good reason, right? If that high of a voltage used to hurt the input of amplifiers, then that company would be out of business a long time ago, by destryoying many amplifiers.
jol50 said:
Could this be a car audio myth? Remember, OEM integration. No problem with SQ here.
jol50 said:
Really, noise has little to do with output voltage and more to do with source impedance. The higher the source impedance, the more chance of noise getting into your system, and no amount of re-routing wires will help you in this situation. The fix? Reduce the source impedance of the deck.
jol50 said:
I addressed this one in the post before this.
Stock equipment is much better now, then again people like the sound of ipods too.infoseeker said:
I don't really know why the old cars had so much noise, if it was the car or equipment. I say the car because you don't get noise in that old equipment today as I have used some HU and amps from back then. But new equipment is better from what I have used.
Hey if you want to do it be my guest, go for it. That is what this place is all about. My issue was with the lack of quality of the HU amps. You have to get a fairly expensive HU just to get clean RCA output though I admit I have not used a HU amp in a long time I'm just assuming. Even with my old 2v HU I can hear differing qualities of the source CDs I listen to, that is good enough for me as then I tend to not like to listen to some of my music because they mixed it poorly. I hate it when that happens.
Or you could just go optical to the amps and not worry about voltage at all.
infoseeker said:
Ah, the voice of reason.
Car audio forums in general lack some of these basic concepts; it is good to hear wisdom. We should all pay attention; foundational understanding such as this will go a long way in building quality noise-free systems in the future.
There's just too much snake oil when it comes down to troubleshooting alternator whine and the like.
I digress.
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