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I could see some knobs on JBL 75.4 upper panel that read "input level" and "freq". can someone let me know their significance please??

i tried reading the catalogue, but cdnt find much.

The input level is the gain control. Just another word for it. It's a secondary volume control that basically tells the amplifier how many times to multiply the ampliftude of the audio signal. Basically how much to amplify the line-level signal. As it is dependent on the HU (1.8V, 2V, 4V, 6V output) you are supposed to adjust it accordingly. Hence it's called an input level. The higher the input level, the less amplification is required. So, highest input level means minimum gain, lowest input level means maximum gain. (highest volume)

The frequency control is wel,l a cut off frequency control. If you use the LPF, then the frequency control determines what frequency and BELOW, go to the speaker connected to the channel.

If you use the HPF then the frequency control determines what frequency and ABOVE go to the speaker connected to the channel.

If the switch is on FLAT, then the frequency control does not work.

I hope this helps. :) BRUUUUAAAHHH!!

1. The "Bass Boost" is present only for the Rear channels. Is this for the sub or does this assume that rear speakers generally need a boost? Interestingly though there is no bass-boost for the fronts, there is an LF setting.

2. Is it possible to delay the front signal over the rear (for the purpose of, say, matching the sub timing to the front stage)? Or is that left to external adjustment before the signal reaches the amp?

Yes, by convention, the rear channels are used either to drive larger speakers, or subwoofers. I guess this is why there is a bass boost option for the rear channel. personally I don't like using it, nor do I recommend people to.

Yes, you are right, by this logic, there shouldn't be an LPF setting for the front, only HP would suffice. I guess this is because the identical active crossover is used in both front and rear channels, for the sake of uniformity in audio reproduction (and i guess uniformity in production too)

That is left to external adjustment.

Der Alte, typically, delay controls are left either to the HU or the digital sound processor (if used). Signal processing features are not usually in an automotive Power Amplifier.

Thanks, Sam.

That makes sense. Anything other than the rudimentary filter / gain settings would take one away from design objective - KISS - and focus costs on the priority features. But one never knows, sometimes strange things are done - so I asked:p.

One of my first challenges (eons back) was replacing a resistor & a capacitor (costing 20c) with a small software filter routine. Took me a while to figure out that the $10K spent on that software development saved $200K in final module costs (2 million units).

that is a huge amount involved there.

thanks SAM...... waise interesting point raised by DerAlte....never noticed it upfront!! thanks for the clarification again.

i recollect you suggesting somebody in some other thread as to cut off levels (freq i think) for front and rear....any suggestions for front GTO607 and rear 937's??

that can be done from the HU level also...

Yes sure, in your Indica, I think the front cut off for the 607C should be 100Hz (simply because you like it loud and your doors are not damped), the 937's can be cut off at 70-80Hz.
And the woofer LPF to be at 80Hz.

These are basic guidelines, not the law. Adjust to taste.

thanks again SAM. yes i like it loud, but my taxi is damped with 80 mils XtremeDead to my satisfaction (i dont hear any rattles/vibrations/like) both at the front doors and boot. I've used the damping sheets liberally.

I plan to run only 937s and 607s off this 75.4. no sub, for that i use a seperate JBL 301.1 :)


LBM bhaiya, my HU is not P80; its only Sony XRCA-620X cassette player (with Mp3 changer). My HU would probably faint hearing names like LPF, HPF and Sub level. lol:

bass treble fader balance are the only few assets that i can count upon.

ok then I though you are asking the question with keeping your next upgrade in mind that is 7950. which has all the things discussed above.:)

there goes like a TRUE friend.... thanks LBM.....am still confused between 5950/6950/7950

simply go for 7950..no second thoughts there..

Go for 7950 as it has 3 pre outs and ipod ready also.

any other difference except 3 preouts??