Yep, its another gain question

[phish368 10+ year member]

Like each person who post's on here, I tried the search but it did not provide me with an answer to the questions I have:

So here we go. I set up my system last night using a DMM and test tones.

Alpine CDA-9887 HU set to Defeat all, and volume turned up to 27 (3/4 of the way)

1khz 0db test tone ran for front components and rear 6x9's

50hz -10 test tone ran for sub (2 - 10" eD subs)

Amps: JL 300/4 amp for front and rear

JL 250/1 amp for sub

Now on to the questions:

1. I noticed that my JL 300/4 amp showed a different voltage for each channel i hooked the DMM up to. I was going for 4 ohms which is 17.3 on the DMM. Each channel showed me different voltages but they were very close. Is that a common thing? for example: I turned up the gain on one stereo pair and the left channel said 17.3 but the right channel said 17.8. The other stereo pair showed the left channel as 18.1 and 17.3. Granted the amp is old but I wanted to see if this was somewhat common

2. After I set the gains i listed to some music in the car (duh).. I noticed that my rear deck sounded louder than my front components.. To lower the rear deck, which should be done:

a. lower the rear deck channels on the HU through the crossover db levels?

b. lower the rear deck channels on the amp gain?

3. After I set the gains i listed to some music in the car (duh).. I noticed that my sub's were not as loud as I'd like. The sub level on the HU goes from 0 - 15. I placed the sub level at 8 when i was setting the gains with the DMM (thinking i'd get some decent headroom) but when i listed to music I have to turn the sub level to 15 to get some volume. How do I go about setting the sub better? The gain knob is almost at its max (input level on amp is HIGH as the HU send's 4v). Should I switch the input level to low on the amp and try setting the gain again with the DMM? I assume 22.4V is the same whether the input level is set to high or low on the amp? Is it common to move the input level to "low" from "high" even if the HU states its a 4v pre-out?

I know its alot of questions but any assistance would be greatly appreciated.

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[ejschultz 10+ year member]

The only thing I can see with the sub is on the Alpines, the sub preout isn't at 4 volts until the sub is turned up to 15 and the volume is near max. If you measured for the correct voltage, that shouldn't matter though. I gave up on using my DMM to set my gains. I was supposed to be getting like 30 something volts for my subs and I had a hell of a time getting the DMM to read over 10V. You do disconnect the speakers and wire the DMM directly to the amp and measure AC voltage, correct?

To answer your other question, in part, I would assume that all amps have some sort of variance in voltage between channels. Higher end amps may not have as much variance as some cheaper ones. Even though all the transistors and capacitors and really everything else for that matter in the amps are rated the same, they're not identical. Measure the capacitance of two 330 uF capacitors. Even though they're both rated at 330 uF, you'll see some variance there. That's probably where the variance in the channels comes from. A higher end brand with hand selected internals may limit or eliminate the variance you're seeing.

 

[phish368 10+ year member]

You do disconnect the speakers and wire the DMM directly to the amp and measure AC voltage, correct?

Yes sir. Speaker wires were disconnected and the DMM was connected directly to each speaker terminal.

Thank you for the answer on #1. I had a feelings it was nothing to be concerned with but I just wanted to make sure.

As far as the sub issue, i guess my only worry is the Low/High Input selector on the Amp. Currently I have it set to High but I have to turn that gain knob almost all the way up. If i set the input selector to low, i have a lot of room on that gain knob to move and plenty of headroom to tweak.. I was more concerned with the 'best practices" that seem to be stated in a lot of manuals...

 

[ejschultz 10+ year member]

Yes sir. Speaker wires were disconnected and the DMM was connected directly to each speaker terminal.

Thank you for the answer on #1. I had a feelings it was nothing to be concerned with but I just wanted to make sure.

As far as the sub issue, i guess my only worry is the Low/High Input selector on the Amp. Currently I have it set to High but I have to turn that gain knob almost all the way up. If i set the input selector to low, i have a lot of room on that gain knob to move and plenty of headroom to tweak.. I was more concerned with the 'best practices" that seem to be stated in a lot of manuals...

Use the low setting on the amp. The high is for speaker level inputs. The low is for RCAs.

 

[phish368 10+ year member]

Use the low setting on the amp. The high is for speaker level inputs. The low is for RCAs.

Are you sure? I only ask because this is what the manual states:

Input Voltage Range: A wide range of signal

input voltages can be accommodated by each of

the 300/4's input sections (200mV – 8V).

This wide range is split up into two sub-ranges, accessible via

switches located in each input section of the

amplifier.

The “Low” position on each “Input Voltage”

switch selects an input sensitivity range between

200mV and 2V.This means that the “Input Sens.”

rotary control will operate within that voltage

window. If you are using an aftermarket source unit,

with conventional preamp-level outputs, this is most

likely the position that you will use.

The “High” position on each “Input Voltage”

switch selects an input sensitivity range between

800mV and 8V.This is useful for certain high-output

preamp level signals as well as speaker-level output

from source units and small amplifiers.To use

speaker-level sources, splice the speaker output

wires of the source unit or small amplifier onto a

pair of RCA plugs for each input pair.

 

[ejschultz 10+ year member]

Are you sure? I only ask because this is what the manual states:
Input Voltage Range: A wide range of signal

input voltages can be accommodated by each of

the 300/4's input sections (200mV – 8V).

This wide range is split up into two sub-ranges, accessible via

switches located in each input section of the

amplifier.

The “Low” position on each “Input Voltage”

switch selects an input sensitivity range between

200mV and 2V.This means that the “Input Sens.”

rotary control will operate within that voltage

window. If you are using an aftermarket source unit,

with conventional preamp-level outputs, this is most

likely the position that you will use.

The “High” position on each “Input Voltage”

switch selects an input sensitivity range between

800mV and 8V.This is useful for certain high-output

preamp level signals as well as speaker-level output

from source units and small amplifiers.To use

speaker-level sources, splice the speaker output

wires of the source unit or small amplifier onto a

pair of RCA plugs for each input pair.

Yes. I'm sure. Low level inputs are for pre amp outputs (RCAs). High level inputs are for post amp outputs (speaker wire).