ok got the voltage readings, i took two measurements:
onset and full clipping...didnt clamp the current though.
car on, voltage at 13.7 volts (both amps)
gain for both amps approx 10 volts
50hz sinewave
4 ohm mono load
_________________________
Standbye rail voltage:
loud : 36.72
amp2: 35.4
_________________________
LOUD AMP
(onset)
output : 29.7
rails : 36.2
(full clipping)
output : 33.8
rails : 35.9
________________________
AMP 2
(onset)
output : 21.5
rails : 35.1
(full clipping)
output : 32.7
rails : 34.8
onset and full clipping...didnt clamp the current though.
car on, voltage at 13.7 volts (both amps)
gain for both amps approx 10 volts
50hz sinewave
4 ohm mono load
_________________________
Standbye rail voltage:
loud : 36.72
amp2: 35.4
_________________________
LOUD AMP
(onset)
output : 29.7
rails : 36.2
(full clipping)
output : 33.8
rails : 35.9
________________________
AMP 2
(onset)
output : 21.5
rails : 35.1
(full clipping)
output : 32.7
rails : 34.8
I think you're going to have to borrow an oscilloscope to determine where the problem is.
At the onset of clipping, the rail voltage should be ~1.4 times the RMS voltage (plus 2-3 volts).
It seems that the output of amp 2 may not be symmetrical. one half of the wave may be clipping before the other. That's the only reason I can think of that you'd be clipping and have such low output voltage.
It's also possible that the output is oscillating. The oscillation may only be on one half of the wave.
See if you can borrow a scope.
If that's not possible, try to download scope software that uses the soundcard of your computer. It won't be able to resolve the oscillation but it should show you if there is significant distortion. The oscillation may show up as a bump or irregularity in the sine wave.
If you use software, you'll need to make up cables and you'll need to include several safety components. Find the software, get it working with preamp level audio and we can work from there.
At the onset of clipping, the rail voltage should be ~1.4 times the RMS voltage (plus 2-3 volts).
It seems that the output of amp 2 may not be symmetrical. one half of the wave may be clipping before the other. That's the only reason I can think of that you'd be clipping and have such low output voltage.
It's also possible that the output is oscillating. The oscillation may only be on one half of the wave.
See if you can borrow a scope.
If that's not possible, try to download scope software that uses the soundcard of your computer. It won't be able to resolve the oscillation but it should show you if there is significant distortion. The oscillation may show up as a bump or irregularity in the sine wave.
If you use software, you'll need to make up cables and you'll need to include several safety components. Find the software, get it working with preamp level audio and we can work from there.
let me triple check the readings one more time...double checked already...but the readings do coincide with the perceived difference in loudness.
i used the amps clipping leds to determine clipping for onset...is that ok? its hard to tell when a sinewave is clipping.
thats why i did a full clipping measurement also...to tell you the truth i cant tell when its clipping with a sinewave....(it may be do to my awesome job of building these subs)
only difference i could hear was when it started to fade...thats where i took measurement....volume 27, a long way from onset.
let me set a lower common gain voltage between the amps, so the headunit can increase volume slower... right now the gains were set with volume at 5....and the amps clip lights come on at volume 7... this is my normal listening style.
i think i may have put the leads in the wrong place also...for the outputs i put the black lead on the rca shield red lead on one output wire...that doesnt seem right to me.
i always thought each lead should be touching each polarity output?
i used the amps clipping leds to determine clipping for onset...is that ok? its hard to tell when a sinewave is clipping.
thats why i did a full clipping measurement also...to tell you the truth i cant tell when its clipping with a sinewave....(it may be do to my awesome job of building these subs)
only difference i could hear was when it started to fade...thats where i took measurement....volume 27, a long way from onset.
let me set a lower common gain voltage between the amps, so the headunit can increase volume slower... right now the gains were set with volume at 5....and the amps clip lights come on at volume 7... this is my normal listening style.
i think i may have put the leads in the wrong place also...for the outputs i put the black lead on the rca shield red lead on one output wire...that doesnt seem right to me.
i always thought each lead should be touching each polarity output?
The clipping indicators are useless. They are simply voltage comparators that light when the preamp level reaches the level that should be producing clipped output. They are not true clipping indicators.
Someone (Richard Clark?) recommended paralleling a piezo tweeter with the woofer. The clipping would be clearly produced by the tweeter. If you try this, insert a 4 ohm resistor in series with it.
RCA to output is OK. You could also connect the meter to the same leads as the woofer.
Someone (Richard Clark?) recommended paralleling a piezo tweeter with the woofer. The clipping would be clearly produced by the tweeter. If you try this, insert a 4 ohm resistor in series with it.
RCA to output is OK. You could also connect the meter to the same leads as the woofer.
I was trying that one day with a cheap/smaller sub amp on a single sub. With a 20-30hz tone it would go up to a point where it got max excursion (sub was much higher rated) then it would make a higher tone with the low bass as more gain was added but not more xmax in the sub. I even set the crossover low to maybe 40hz and it still made this 60hz secondary tone when overdriven, or approximately whatever hz it was. Could have been the cheap amp I used too, it was a little bazooka. I was pretty sure that was clipping, but could have been an artifact of the amp. I will try some other small amps when I get time.
At the onset of clipping, the output voltage of the "loud" amp was 8V higher than the other amp. To me, that confirms that you are not imagining what you claim to be hearing. Have you done the math on what an extra 8V will contribute to the power output?
Also, the rails between the amps are within a volt or so of each other so maybe the 910/911 outputs are indeed more efficient.
An alternative explanation might be what Perry was referring to in that the clipping indicators are merely comparitors, not true clipping indicators. If one is more sensitive than the other, then you are reaching the "onset" of "clipping" a lot sooner on one amp than the other.
Sounds like it's time to get that scope.
Also, the rails between the amps are within a volt or so of each other so maybe the 910/911 outputs are indeed more efficient.
An alternative explanation might be what Perry was referring to in that the clipping indicators are merely comparitors, not true clipping indicators. If one is more sensitive than the other, then you are reaching the "onset" of "clipping" a lot sooner on one amp than the other.
Sounds like it's time to get that scope.
Well I don't know, but how complex would it be to make a test device with an error correction circuit that you hooked to the input and output of an amp? Maybe put a few LED on it indicating % of distortion and optimize it for certain test frequencies....even if it was within say +/-5% distortion it would work for basic testing on a sub amp. Even if it showed a level at half volume to compare to when it clipped, clipping should show in an obvious way. One of you guys out there must know if that is possible to do for a reasonable price, there has to be a lot of people interested in that. You could also make it to hook onto a meter to read a value. Or should I start a new thread with this.....
Your right jol50, that is the million dollar idea, however, using a scope to determine the onset of clipping is fairly trivial, which is why Perry recommended he use a scope in the first place.
For a true comparison I would use a resistive dummy load instead of a reactive speaker load. Just like in a lab environment, you aim to remove as many variables from the experiment and keep only the ones you can control or are testing for.
With a scope not only can you "see" the onset of clipping but you should be able to look for symmetrical clipping as well.
A computer running NI LabView networked with a storage scope, spec an, and a couple multimeters will do the trick! You'll be able to monitor all sorts of parameters, but I'm getting ahead of myself.
For a true comparison I would use a resistive dummy load instead of a reactive speaker load. Just like in a lab environment, you aim to remove as many variables from the experiment and keep only the ones you can control or are testing for.
With a scope not only can you "see" the onset of clipping but you should be able to look for symmetrical clipping as well.
A computer running NI LabView networked with a storage scope, spec an, and a couple multimeters will do the trick! You'll be able to monitor all sorts of parameters, but I'm getting ahead of myself.
I agree that is the proper tool, a scope. I'm just thinking of people with an amp in a car trying to set gains at clipping under real world/real use conditions....where in the end the gain needs to be set in the amp's intended environment of use, if not just for power measurements. It would be useful for an SQ system setup as well for example, though they would want to use one at high frequency as well.
Like I said, even if it got you close it would be ideal for setup. It would need to be portable in a trunk. I read all the time about people checking voltage on outputs, from what I know that is not always very precise.
Like I said, even if it got you close it would be ideal for setup. It would need to be portable in a trunk. I read all the time about people checking voltage on outputs, from what I know that is not always very precise.
if i would have went up one more level on volume control, amp2's reading would have probably looked similiar to the loud one on the first test.
here are more readings from another amp plus the first two...looks more comparable...gains set at 6 volts this time.
this time with the leads on the outputs and the rail voltage oneach rail emitter...still using the clipping indicators, since i havent found a piezo speaker yet.
the loud amp has a bad solder joint where the pot is...it would make a popping noise when i touch a screwdiver to the endplate while adjusting the gain, pushed it forward a bit to make contact and stopped popping, any chance this difference in sound could be from the pots ground joint?
eventhough the measurements below look fairly close, the loud amp is still loudest... maybe this is just do to warn out components in the other amps,this amp just doesnt sound the same... it sounds better.
loud
onset 47.8 72.8
-------------------------------
amp2
onset 48.5 70.8
-------------------------------
amp3
onset 46.35 71.9
-------------------------------
the actual perceived louness is in the same order.
here are more readings from another amp plus the first two...looks more comparable...gains set at 6 volts this time.
this time with the leads on the outputs and the rail voltage oneach rail emitter...still using the clipping indicators, since i havent found a piezo speaker yet.
the loud amp has a bad solder joint where the pot is...it would make a popping noise when i touch a screwdiver to the endplate while adjusting the gain, pushed it forward a bit to make contact and stopped popping, any chance this difference in sound could be from the pots ground joint?
eventhough the measurements below look fairly close, the loud amp is still loudest... maybe this is just do to warn out components in the other amps,this amp just doesnt sound the same... it sounds better.
loud
onset 47.8 72.8
-------------------------------
amp2
onset 48.5 70.8
-------------------------------
amp3
onset 46.35 71.9
-------------------------------
the actual perceived louness is in the same order.
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