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Old 2nd September 2009, 04:03 PM   #1
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Default Line Driver

Just curious, but why is the output voltage on most car audio line drivers only 9 volts? I never see any higher output voltage greater than 9 volts, unbalanced, on commercially built units.

I am not talking about balanced line systems.

Thanks.
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Old 2nd September 2009, 04:23 PM   #2
Glowbug is offline Glowbug  United States
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I don't think I've seen many amps that are able to deal with a higher input signal than 9V.

Why do you need that much voltage?
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Old 2nd September 2009, 05:22 PM   #3
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The 9 volt limit is usually due to the driver chip operating voltage rails and distortion considerations of the driver chip.
Plus I also have never seen a reason for any higher voltage output. Most amps like JL and such have a 9 volt range selection for their input gain circuitry so it can accommodate such unusually high drive levels.
Please remember that every amp I have ever seen also has a input buffer just to manage very low signal levels. The high drive level is useful to over come high noise levels in most cases.
Most home and commercial gear only requires a 1 volt signal to drive the amp to full power depending on how you set the gains. Setting a amp at minimum gains will allow you to use a high drive level, but here again it is for noise issues not dynamic musical enhancement.
If you really need higher voltage then you should look into balanced line drivers. Some of them can output up to 14 volts and up, but these are used in sets a transmitter and a receiver to recover a usable signal for a standard RCA input to use. Unless you using certain amps like Zapco high end series , and SoundStream Ref and Rub series and the like. These all have a balanced input on them to allow for the use of Professional rated balanced line driver gear.
Unless you have a specific noise related or input compensation need for high drive levels, I would not even use a line driver. They will just most likely overload your inputs on your amps and cause all sorts of issues on system setup.
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Old 2nd September 2009, 05:48 PM   #4
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SPL thugs always think they need 10000000000Vrms line levels when what they really need (if anything at all) is a buffer with enough current drive to handle the multiple parallel amp inputs they usually have.

I've personally never had any noise issues with <2Vrms signals anyway.
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Old 2nd September 2009, 08:09 PM   #5
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An amplifier in it's simplest form is just a voltage multiplier.

Voltage out = gain x voltage in.

Max output voltage is limited by the specific amplifier design, so an input voltage higher than what the amp is designed for won't result in more power output.

Using a 9V line driver, you could conceivably add a high current voltage follower (gain = 1) and get about 20 watts/4ohms without even using an amp...
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Old 2nd September 2009, 10:58 PM   #6
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Quote:
Originally Posted by Glowbug View Post
I don't think I've seen many amps that are able to deal with a higher input signal than 9V.

Why do you need that much voltage?
Like I said above, "just curious."
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Old 2nd September 2009, 11:22 PM   #7
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You guys seem really smart.

I am not really sure that I posted in the correct section, if not, please redirect me.

My initial post above was just an "observation" on my part.

My design project reads as follows:

Project:
Design a 12 volt preamp which has an output voltage that is variable from 1 - 30 volts RMS, unbalanced.
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Old 2nd September 2009, 11:36 PM   #8
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David Navone has a home audio preamp from QuickSilver audio that has a 65 volts output voltage, but it is almost $4,000.00.

Here is an excerpt from the QuickSilver site:

Full Function Preamplifier

Quicksilver's new phono-inclusive preamp is a technical tour de force. Mike Sanders' unique design delivers the pure tube sound Quicksilver is known for, without the limitations common in other tube preamps. The high output impedance common with tube preamps can cause problems when mating to many solid state amplifiers. The ultra-low 1.5 Ohm output impedance of the Full Function preamp allows it to drive any amplifier known and using virtually any length or type of cabling.
Sonic performance is maximized through the use of extremely short signal paths, minimal switching and no transistors, regulators or circuit boards. A massive power supply resides in a isolated subchassis within the main preamp.

Hand wired, point to point circuitry
Passive and active RIAA Phono Equalization
Ultra low 1.5 Ohm output impedance
18dB Gain - Line, 47dB - Phono
Line Tubes: 2 x 12AX7, 2 x 6H30
Phono Tubes: 1 x 12AX&, 1 x 6N1P
60 V Maximum Output
17"W x 5.25"H x 11"D
Handcrafted in the U.S.A.
$3200

What is something like the above used for?
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Old 3rd September 2009, 02:47 AM   #9
Glowbug is offline Glowbug  United States
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Because he can?

Seriously, I have no idea why someone would need that.

It's sort of a solution looking for a problem...
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Old 3rd September 2009, 03:45 AM   #10
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Quote:
Originally Posted by Glowbug View Post
Because he can?

Seriously, I have no idea why someone would need that.

It's sort of a solution looking for a problem...
And, believe me, it sells. That is not a new design. Quicksilver Audio has been making those things for many years.

David Navone has always advocated that there is no subsitute for a high signal at the source, whether it be car audio, home audio or pro audio.

Just an excerpt:

"In car audio, home audio, and pro audio, there is no substitute for a source with a high signal level output. All factors equal, the deck with the highest signal level will always provide optimal performance. The Quicksilver audio in David's home listening room is capable of 65 volts of signal with a source impedance of less than 100 ohms. This is a good preamp."
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