posted
If the pre amp output of a deck is 4V and the input stage on the amp is between 500mV and 2.5V, even if I turn the gains way down...Will I still overload the amp? What if I threw a pre amp in there that raised the level up to 8V?
------------------ Knobs Rule! Keep it simple, clean, and loud!
posted
I have wondered that also. Only think I can think is you have 4 volts out but that then when you figure in the resistence of them outputs thats not 4 volts any more.
Make sense?
------------------ Robert (Rob) - 1996 Chevy Cavlier 2.2 Member Of"Team Gates" and "Team Shockwave[\b]" USAC Sactioned Judge
posted
Proaudio, what the heck are you talking about? Do you know how crappy the outputs/rca's would have to be to drop the voltage that much and such a voltage drop from the inital 4v output of the deck would result in horrible results
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Posts: 97 | From: Tomah, Wisconsin BASS: It's not a friggen FISH, redneck! | Registered: Jan 2000
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posted
Well what I am talking about is the output resistence on some decks in 50 ohms and some is a hell of alot more. That is what I am talking about.
------------------ Robert (Rob) - 1996 Chevy Cavlier 2.2 Member Of"Team Gates" and "Team Shockwave" USAC Sactioned Judge
posted
Ok, heres another question off of the top of my head. If the head unit pushes 4 Volt Pre out, is that volatage split in half? So basically 2 volts per side?
------------------ Ratfink, ICQ # 34918107 Yahoo Messenger- ratfink67 ------------------------- *Government Policy* If it isnt broke-Fix until it is. ------------------------- "Of all the things I`ve ever lost, I miss my mind the most.." ~~~~~~~~~~~~~~~~~~~~~~~~~ "Ever stop to think, and then forget to start again???"
Posts: 373 | From: Twin Falls, Idaho | Registered: Jun 1999
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posted
You state that the input sensitivity on your amp is adjustable between 500mV and 2.5V. When the input sensitivity control on the amp is set to maximum gain (500mV), it will take a 500mV rms signal to drive the amplifier to it's maximum output. When the input sensitivity control on the amp is set to minimum gain (2.5V), it will take a 2.5 volt rms signal to drive the amp to full output.
Let's assume that your deck is capable of producing 4 volts rms. Actually, the output voltage from the source unit is adjustable from 0 to 4 volts rms via the volume control. If you connect the source unit to the amp, and the amp's input sensitivity is set to minimum (2.5 volts rms), the amplifier will be driven to full output BEFORE the source unit achieves it's maximum output voltage of 4 volts. This won't hurt anything.
If you have an ac voltmeter, you can connect it to the output of your source unit and find out what volume setting produces 2.5 volts. Use a disk like dB Jams (where the tracks are recorded at 0 dB - the maximum recordable signal) and adjust the volume until you measure 2.5 volts rms. Most AC voltmeters don't have the capability for measuring rms voltages, but if you use a sine wave as the test signal, the results will be the same. Let's say that the volume display on your source unit is 23 when the output of the deck is 2.5 volts. This means that when the volume is set to 23, the amplifier will be driven to full output. If you turn the volume up further, you risk driving the amplifier into clipping.
Of course, things aren't quite as simple as they seem. Most CD's are not recorded at full output (0 dB). This means that you may need to turn your volume control a little further to achieve full output. In addition, our ears are not very sensitive to distortion at the high spl's that will be occuring. Some listener's actually like a little bit of "overdrive" as it makes their system play louder. Woofers, by their very nature, tend to filter out the high-frequency harmonics that occur when clipping is taking place.
My advice is this. Always turn the input sensitivity controls on the amps all the way down whenever possible. This will result in minimum system noise, engine noise, alternator whine, etc. You goal should always be to drive the amp as hard as possible.
For more information relating to topics such as this, please refer to:
posted
sorry i made a mistake when i posted, but my question was. when you have 4 volts from the head and you put in a line driver that is 8 volts, will you end up with 12 volts?
------------------ if it,s not bone crushing it,s not loud
posted
No, the output level of the line driver cannot exceed it's maximum voltage of 8 volts.
You should be careful "overdriving" amplifiers. Not because you will damage the amp, but because your Signal-to-Noise ratio will suffer. For example, if your amp can accept a 4 volt rms signal and you drive it with an 8 volt rms line driver, your S/N ratio will be hurt by the following amount:
dB Volts = 20 * log (V1/V2) dB Volts = 20 * log (8/4) dB Volts = 20 * log (2) dB Volts = 20 * 0.3 dB Volts = 6
Answer: 6 dB
Singal-to-noise problems accumulate through each device. Therefore, if the maximum input signal to the line driver is 2 volts, and you drive it with a 4 volt source unit, you will suffer an additional 6 dB of signal degradation.
What does this mean? In the first example, you will have 6 dB more noise (hiss, whine, etc.) than you would if the system levels were matched properly. In the second example, you would have an additional 6 dB loss resulting in a total increase in noise of 12 dB.
Imagine what would happen if you had a source unit, equilizer, line driver, active crossover networks, and amplifiers in your system and the levels between each device was not set correctly!
------------------ "Keep it Loud and Make me Proud!"
posted
Grrr...that is not good. Why do MMATS and MCINTOSH amps have such low input sensitivity?!! I've only experienced better sound with higher input voltage in other amps, so why do they have to make it so plugging their amps into my system that took advantage of this instead produce negative effects?
Thanks for all the help Wayne, and it never occured to me to travel down the WEB-line to the articles section!
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Posts: 97 | From: Tomah, Wisconsin BASS: It's not a friggen FISH, redneck! | Registered: Jan 2000
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posted
lets say that the input sensitivity on the amp was 0.5-10 volts and the output on the head was 5 volts.would it be safe to have the gain of the amp at the half way point?
------------------ if it,s not bone crushing it,s not loud
posted
It would probably be safe but I doubt it would be optimal.
Many times, the input sensitivity control on an amp (or other device) responds in a non-linear fashion. It all depends on the circuit that is being used and the "taper" of the potentiometer (the knob you turn.)
Here's how I would do it if I didn't have any tools.
1. I pick out my favorite CD.
2. I would turn the inputs on the amp all the way down.
3. I'd turn the volume on the source unit up as high as it would go without distorting. (With the amps turned down, you should be able to listen without getting your head blown off.) Keep in mind that many source will start clipping before their volume control is turned all the way up. If you hear distortion, back off the volume until it goes away.
4. Now, with the system playing, turn up the input controls on the amp until you can't take any more. (It's as loud as you ever want to play it.)
Hope this helps.
------------------ "Keep it Loud and Make me Proud!"
posted
Ok while the pros are here I wouldn't mind asking a question on this topic I have been wondering for a while already .. Assume the following equipment: HU with 4V output, Pheonix Gold PLD1, amplifier with "rated" max 4V input (ie Rockford amps). My question is, is the PLD1 going to be useful here? Assuming that PG rates the PLD1 at 8V RMS output, and the RF amp only will recognize a rated 4V input. Would the head unit be satisfactory or what benefit would there be from using the PLD1 in this situation (assuming only one amp in the setup). And is it possible to damage or make the amp clip from inputting to much? Thanks for any help guys!
------------------ ---RougeDude--- "If it's not loud enough your probably already broke!"
posted
If your source unit has the ability to produce 4 volts RMS, and your amplifier can be adjusted to accept a 4 volt input signal, it looks like you have an ideal match without any type of line driver.
So, why would you want to use a line driver in a scenario such as this?
First, the output impedance of many source units is not very low. In the perfect world, the output impedance of the source unit would be 0 and the input impedance of the amp would be infinite.
The output impedance of the source unit will have as much, if not more, impact on noise immunity as the output voltage itself. (Resists noise from being induced into the RCA cables.) If the output impedance of the deck is low, the system will be more immune to induced noises than if the output impedance is high. In addition, a deck with a low output impedance will have the capability to drive more amplifiers than a deck with a higher output impedance.
So, you may ask, why don't source unit manufacturer's make "low output impedance" decks? Well, some do. Many don't. Probably the biggest reason that manufacturers don't provide low output impedance decks is because of reliability. The line drivers inside of the source unit are really little amplifiers. Now, you may recall that an amplifier delivers more power when the impedance of the load is reduced. Now, imagine what would happen if you shorted the RCA outputs of the deck to ground. The little amps inside of the deck would try to deliver lots of power and would probably break. Therefore, many manufacturers insert a series resistance in the output of each line driver in the deck to establish what the absolute minimum load impedance to the deck will be. For example, if the series resistance is 100 ohms, the load on the line driver amplifier can NEVER be below 100 ohms; even if you short the RCA outputs to ground.
While this technique may be good for reliability, it really bites for noise immunity. Decks that utilize low output impedance generally have more expensive output circuitry to prevent damage in the event of a short circuit.
An external "line driver" can be used to drive the lengthy run from the source unit to the amplifiers. If the line driver has a low output impedance, it can offer some noise immunity when used in conjunction with a high output impedance deck. Just make sure you install the line driver as close to the source unit as possible.
Another thing to look at in a source unit is the resistance between chassis ground and audio ground. Take an ohmmeter and measure the resistance between the chassis of the deck and the shield of the output RCA jack. It should read a dead short. (0 ohms).
In any system, audio ground should be established at one place and one place only. Ideally, audio ground is established at the source unit.
What will happen if the resistance between audio ground and chassis ground is not 0? The system will very likely suffer from noise problems. To fix this problem, simply run a wire from the shield of the RCA cable to the chassis of the radio.
Why do manufacturers insert a resistance between chassis ground and audio ground?
In some cheap amplifiers, audio ground and power (chassis) ground are ALREADY connected together internally inside of the amplifier. When you connect this amp to a deck with a common chass / audio ground, a "ground loop" will be established. This will result in all kinds of noise problems. So, in an effort to eliminate these noise problems, installers sometimes "lift" the ground to the amplifier WHILE THE AMP IS ON. Now, guess where the amp is sourcing it's power ground? You guessed it! The shield of the RCA. Let's assume the amp is capable of drawing 5 amps of current. This means that 5 amps of current is flowing through the shield of the RCA cables AND the pc board inside of the source unit. This almost always results in a burned trace inside of the source unit. To prevent this, many source unit manufacturers insert a series resistance with the shield of the output RCA connectors.
------------------ "Keep it Loud and Make me Proud!"
posted
Thank you very much Wayne for taking the time to type out that lengthy response. I feel I have a firmer grasp on the situation now. However, I was also wondering the affects of using a line driver with a higher rated output than the acceptable input on the amp (ie as in the example above). Is it possible to input to much (voltage wise on the amp)? Thanks again!
------------------ ---RougeDude--- "If it's not loud enough your probably already broke!"
posted
Overdriving an amplifiers input will not damage the amplifier to my knowledge, however, once the input reaches it's limit, it saturates, and the output will always be clipped. I've heard of people overdriving they're amplifiers by as much as 3x what the normal input is without damaging the amplifier.
------------------ STILL waiting to hear a GOOD pair of HLCD's!!
If it dont fit, force it... if it breaks, it needed to be replaced anyway...
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