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Old 31st August 2006, 12:36   #1
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Default Amplifier tuning

Hi Moderators, the amp tuning thread was closed and hence i opened a new thread, if possible merge it with the original amp tuning thread, if this discussion adds value. Sorry for the inconvinience.

I just wanted to confirm my amp tuning process based on Kureti's note published earlier in this forum in the amp tuning thread. Also require some clarifications on this

When tuning the amp should we look at the rating of the amp only or the speaker also.. and should i consider RMS power or peak power for the calculations.

for eg: My system config consists of :

JBL GTO 75.4 amp - Rated at 142 W RMS X 4 Channels @ 2 Ohms or 284 W RMS X 2 channels @ 4 ohms
JBL GTO 607c - 70W rms - 2 Ohms
JBL PS552 coax - 55W rms - 4 Ohm
JBL CS 1204B Sub rated at 250W rms - 4 Ohms

The setup is configured such that the front comps are driven by the front channels of the amp and the sub is driven by the rear channels of the amp (in bridged mode). The rear coax are driven by the HU. This amp has 2 gain adjustments, one for the front and another for the rear channels

The first thing to do would be to see how much I can turn up the volume before distortion sets in, in the rear speaker since they are directly powered by the HU. The rear speakers are rated at 55W RMS- 4Ohms. The HU is rated at 22W - 4 Ohm per channel. So it would be 22*4= 88 sqaureroot for this would be 9.38 volts.

For this setup for the front channels, since the amp is rated at 142 W per channel but the speaker is rated only for 70W shouldnt i use 70W in the calcualtion.
So it would be 70*2= 140 sqaureroot for this would be 11.83 volts.

Similary for the rear channels, since the amp is rated at 284 W per channel (in bridged mode) but the speaker is rated only for 250W. I would use 250W as the power for working out the voltage for tuning purporse..
So it would be 250*4= 1000 sqaureroot for this would be 31.62 volts.

So first I would connect the Multimeter to the rear speaker wires (after disconnecting the speaker and then play the 1Khz test tone then increase the volume till the multimeter reads 9.38 volts. This I assume will the maximum volume i can play on the HU without causing distortion. I would keep the volume a little below this.

Then for the front channel with a test tone of 1Khz I would try and set the output to 11.4 volts.. whereas for the rear channels which power the sub with test tone of 50Hz i would set the output to 30.98 volts.

Once this is done I would fine tune it as per my liking for eg: reduce the gain on the front channels to allow for more bass.

Is this process correct or am i missing something ??
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Old 31st August 2006, 13:09   #2
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Originally Posted by jinu_joseph
The first thing to do would be to see how much I can turn up the volume before distortion sets in, in the rear speaker since they are directly powered by the HU. The rear speakers are rated at 55W RMS- 4Ohms. The HU is rated at 22W - 4 Ohm per channel. So it would be 22*4= 88 sqaureroot for this would be 9.38 volts.
the start is wrong but the method is right....

If u measure the speaker level for setting the HU volume the HU amp will hinder u in this process. The volume can go further than that ....but since u r driving the rear speakers u will have to consider them also so while setting the gains....

Now if u do what u have said above u will never able to hear the rear speakers because if u increase the volume the front and the sub will play louder than the rear speaker so u will have to reduce the gain on the amp to match the front and rear speakers...

or u can do one thing do the matching of the gain and try to fade of the rear when the rear ones are not required.....
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Old 31st August 2006, 13:28   #3
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LBM my thinking for the start step was that, the max volume my HU can reach is based on the limitation set by the HU and rear speakers, because if the rear speaker limit is crossed then there will be distortion in the rear speakers. So the first step is just to identify the limit to which I can take the volume. However if I was also driving the rear speakers from a amp then this step would not be required.

Practically speaking since the rear speakers are rated at 55W there should be no problem even if i turn the volume all the way.. (except ,maybe the distortion introduced by the HU amp), but no harm checking.

But you are right since I am driving the rear speakers on the HU I will never hear the rear speakers over the front speakers and sub which are driven by the amp.. Like someone said earlier.. the rear speakers are used only as fillers..
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Old 31st July 2007, 19:30   #4
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hi guys,

im reviving the thread because i cant set the gains properly. and sam no page digging expeditions here.lol :-)

i not using the DMM or DSO method. im trying to set the gains by using my ears and the thing between the two :-)

i used a test tone of 1 khz 0db to set the comps. i could hear clipping.
the problem is im not being able to set the gain for the sub. i tried using a test tone of 50hz and went uptill 125hz. i couldnt hear the clipping.

125hz is the max i can use because the HU's pre out voltages are different for the full ange and sub outputs. i have to use the sub output and the max cut off is at 125hz. i dont have a DSO nor a dmm with true rms capability.

can the gurus tell me how clipping sounds at the sub level or is there a way out?

and how do i tell i have reached the max unclipped volume of my HU? i connect my laptop with the true rta program. The HU started to clip at 40-41 volume and the max is 62(its not the percentage) but the line out of the laptop wasnt calibrated.

so i request all the gurus help me set my amplifier gains properly.

i somehow messed up the tuning which JB and gunan did and im regretting it.(JB you didnt use your DMM so gift it to me na, you have good ears to do the job..kidding :-)

cheers
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Old 1st August 2007, 13:38   #5
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Originally Posted by clipto333 View Post
i used a test tone of 1 khz 0db to set the comps. i could hear clipping.
the problem is im not being able to set the gain for the sub. i tried using a test tone of 50hz and went uptill 125hz. i couldnt hear the clipping.

The HU started to clip at 40-41 volume and the max is 62(its not the percentage) but the line out of the laptop wasnt calibrated.
I'll just list what I do. Maybe it will help.

First I set my the amp that drives my front components at 70%. Then I play some music. Then I use my HU to HPF the front components. starting at full range to 63Hz/2nd order rarely do I need a higer freq or steeper slope (not with 6" in the front and my relaxed levels)

Then i bring in the sub and use TA to get that to sound right using the levels on the amp. You dont want to hear the sub but you should notice it's absence.

Lastly I bring in the rears just to add ambience and rear fill.
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Old 1st August 2007, 14:15   #6
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Originally Posted by navin View Post
I'll just list what I do. Maybe it will help.

First I set my the amp that drives my front components at 70%. Then I play some music. Then I use my HU to HPF the front components. starting at full range to 63Hz/2nd order rarely do I need a higer freq or steeper slope (not with 6" in the front and my relaxed levels)

Then i bring in the sub and use TA to get that to sound right using the levels on the amp. You dont want to hear the sub but you should notice it's absence.

Lastly I bring in the rears just to add ambience and rear fill.
I do the same thing except I dont use rear speakers...
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Old 1st August 2007, 14:35   #7
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I do the same thing except I dont use rear speakers...
does not your son complain?
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Old 1st August 2007, 14:52   #8
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does not your son complain?
Sir my Daughter is nine months old. But I think later on I think I would have to have the rear speakers also.
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Old 1st August 2007, 16:20   #9
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Sir ..I would have to have the rear speakers also.
And a good car seat.
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Old 1st August 2007, 17:30   #10
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Originally Posted by navin View Post
I'll just list what I do. Maybe it will help.

First I set my the amp that drives my front components at 70%. Then I play some music. Then I use my HU to HPF the front components. starting at full range to 63Hz/2nd order rarely do I need a higer freq or steeper slope (not with 6" in the front and my relaxed levels)

Then i bring in the sub and use TA to get that to sound right using the levels on the amp. You dont want to hear the sub but you should notice it's absence.

Lastly I bring in the rears just to add ambience and rear fill.
hi,

all this means my levels are too high. i can tune the setup from my HU.

but my question is still unanswered. how can i detect clipping at sub bass frequencies i.e. below 125Hz. cant go above 125 using the sub outs.
(im gonna rob you off your T&M equipment one day lol..kidding)
the only way i think is DSO which i dont have :-(

can i use my laptop as a DSO? is there a way to decrease the power output of the amp so that it is suitable for the sound card input?

is there ne other way? gunman/jb/b&t/sam/deralte and all other gurus please help me out on this. otherwise ill have to take a sanyas from ICE. im going mad lol

cheers
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Old 2nd August 2007, 12:18   #11
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but my question is still unanswered. how can i detect clipping at sub bass frequencies i.e. below 125Hz. cant go above 125 using the sub outs.
amp clipping is not easy to detect unless the amp is in serious overdrive in which case the bass will sound grungy as the amp will be putting out a lot of harmonics.

however in most caases the speaker overloads first that means that the speaker hits it's physical limits before the amp clips.
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Old 2nd August 2007, 15:39   #12
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amp clipping is not easy to detect unless the amp is in serious overdrive in which case the bass will sound grungy as the amp will be putting out a lot of harmonics.

however in most cases the speaker overloads first that means that the speaker hits it's physical limits before the amp clips.

so how do the other guru set their amp gains? Is the DMM method accurate? i dont think so. why? because some amps are under rated and some over rated. and for my amp the continuous output is given at a voltage of 14.4 which a car charging system cannot provide and i dont know how to work out the output at 13.8v which is the optimal output for charging a battery. i even dont know the o/p of my car alt. i can measure it though.

also the cliping i heard on the comps using a test tone of 1khz was definitely of the amp. sub bass is the problem. ill have to look out for a dso here. BTW how much would a cheapest scope cost for this kind of a job?

on more thing. some say when the HU clips just back off a little so there's no clipping. i think this is wrong. because the rec levels of some cds are low and the HU goes into clipping.

the only solution is to use a dso then or go to delhi and get the levels set by the deadly duo. :-)

cheers
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Old 2nd August 2007, 15:57   #13
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Originally Posted by clipto333 View Post
also the cliping i heard on the comps using a test tone of 1khz was definitely of the amp. sub bass is the problem. ill have to look out for a dso here. BTW how much would a cheapest scope cost for this kind of a job?
@Clip, if you are using a test tone, you don't need a DSO. Any old oscilloscope would do, even the vintage tube-type scopes. Ask around, you can find one in Jalandher also - hook up with a lab a$$ at the REC or any ITI, they should be able to help you find one.
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Old 2nd August 2007, 16:32   #14
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@Clip, if you are using a test tone, you don't need a DSO. Any old oscilloscope would do, even the vintage tube-type scopes. Ask around, you can find one in Jalandher also - hook up with a lab a$$ at the REC or any ITI, they should be able to help you find one.
really? they must be cheap second hand right? yes there is rec(regional engineering collage) here. ill see if the lab a$$ can find me one.
also what is the advantage of a DSO to the vintage type?


thanks deralte phappe lol
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Old 2nd August 2007, 17:02   #15
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really? they must be cheap second hand right? yes there is rec(regional engineering collage) here. ill see if the lab a$$ can find me one.
also what is the advantage of a DSO to the vintage type?
Sure, second hand should be cheap enough. And, I think there are more than 2 engg. colleges & polytechnics in Jalandhar.

The only advantages of the DSO are storing waveforms as a picture for printing or later reference, and greater flexibility of the sync signal from digital sources, like bit pattern etc.

Otherwise, one can do most work with the older (storage/plain) oscilloscopes from BPL, Aplab, Philips or Tektroniks.
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