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      10-26-2009, 09:15 PM   #1
kaigoss69
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Logic 7 amp output (V) at select volume levels

I did this test to find out if I am currently overloading the high-level inputs of my Blaupunkt amp and whether the voltage of the sub-out channel would be too close the the max input voltage of my new JL HD600/4 amp. For reference, my Blaupunkt THA1250PnP amp has a max input voltage of 8V and the JL Audio HD600/4 11V. I measured the L7 sub-out channel only, using a digital voltmeter set to "AC" and playing a sine wave sweep between 20 and 120 Hz through the CD player. The DSP was set to "music", the bass setting at "0" and the 80 and 200Hz EQ points "0" or flat.

The volume of the HU can be set as follows:

- Turn radio on

- within 8 seconds, push the "m" or "TP" button and hold for 8 seconds

- a "secret menu will appear. Use the "+" or "-" buttons on the far right to skip to the volume display. It will say something like "DSP = 1 V=29". The volume level may be lower, depending on where it was set when you last used the radio.

- now go ahead and rotate the volume knob and you will see that the setting will change by "1" with every single click of the volume knob. Set it to 29 or above and turn the radio off to exit the secret menu (the HU volume will be "29", the max. setting after turning it on again (to protect your ears in case you left it blasting the night before!))

- now you know that the initial volume is "29" and you can set it to "40", for example, by rotating the volume button clockwise by 11 "clicks".

OK, here are the results:

V = 30: 1.27V
V = 35: 2.26V
V = 40: 4.20V
V = 45: 6.90V
V = 50: 12.30V
V = 55: 12.86V

Interesting that the voltage did not increase significantly beyond V = 50. I am guessing that the HU limits the output at that point.

By the way, the max. voltage produced during the sweep seemed to be at around 40 to 50 Hz.

I then went back in the car, popped in a music CD, and played music at the above levels. I turned it up to the point I would consider to be the absolute max. I would ever use. This setting was 50. The music was painfully loud to my ears. Normal listening would normally take place between 35 and 45.

From all this I can conclude the following:

I do not need a line output converter with either amp as long as I am limiting the volume to V = 45. I would set the gains on the new JL Audio amp with that same input volume setting and increase the gains to the "unbearable" level to make sure that I am never feeding too much voltage or even distortion to the input of the JL amp. As I am also amplifying the front stage speakers with the JL amp at the same time, I can match the output to the sub channels, or vice versa. If I was not doing that, and still using the L7 amp to directly power the front speakers, I would have to keep the gain on the sub amp lower so that the front stage can "keep up" with the subs, and risking the occasional overload of the amp's input stage.

Anywhoo, hope someone out there will benefit from this.
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      10-26-2009, 10:06 PM   #2
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Thanks... what about measuring the voltage at different levels of bass adjustment?
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      10-26-2009, 10:16 PM   #3
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Quote:
Originally Posted by Technic View Post
Thanks... what about measuring the voltage at different levels of bass adjustment?
Perhaps I'll do that also, just out of curiosity.
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