Hi Everyone
I have a few question about measuring the voltage gain of an amplifier.
My goal with this is to set limiters on my frequency splitters the right way to not blow or burn my speakers (more on that later).
How I measured my Amplifier:
I first measured an XLR cable with a true RMS meter. I generated a 50hz sinewave until I got 0.5V.
Afterwards I connected 2 XLR (with each 0.5V output) to my amplifier set to bridge mode.
Out of the amplifier came 73V.
Questions:
Some more background:
My setup:
Speakers:
2x JBL PRX412m for the high frequencies (link)
1x JBL SRX828P (passive) (link)
Amplifiers:
1x the t.amp E-1200 for my tops (link)
1x Crown XTi 6002 for my subwoofer (link)
Frequency Splitters:
1x the t.racks DSP 206 (link)
1x the t.racks DSP 408 (link)
I have a mixer, which receives signal from a DJ controller.
The mixer then will send the signal to the DSP 206 which will send the signal to the DSP 408.
The DSP 408 will then send the signal to the amps which are connected to my speakers.
Limiting:
My goal is to set my limiters (excursion and thermal) on my frequency splitters (excursion on the DSP 206 and thermal on the DSP 408). The limiters should be set to a level, where to gain of the amplifier can be set to the maximum. This way I do not have to watch my amps all the time and I can still be sure that my speakers are protected.
I've used the limiting guide by linea research (link). Since I want to set my limiters before my amps I have to take the amplifier gain into account (see page 2, bottom chapter of the file).
The problem is now, that I don't know my exact amplifier gain in bridge mono mode. In the owners manual of the XTi there is only a gain for 8 ohm output. However I run my amp for my sub in 4 ohms. So I just measured the voltage gain. In this guide is also stated that some amplifiers have not a fixed voltage gain. So measuring is the best option.
After my measuring I've got the following values (these are all measured with the gain turned all the way up):
the t.amp E-1500 (set to stereo mode): 0.5V into channel 1 generated an output of 57V at channel 1
Crown XTi 6002 (set to bridge mono mode): 0.5V into channel 1 & 2 generated an output of 73V at channel 1
This brings me back again to my questions above. How do I calculate the gain of my amplifier?
Since I have put the XTi to bridge mode I would assume, I have to calculate the gain with an input of 1V. Which means a gain of 73x (equals to 39.48 dBu)
However my gain of the t.amp would be calculated with an input of 0.5V because it was running in stereo mode.
This would mean the voltage gain of the t.amp is 114x (equals to 43.36 dBu).
I hope my questions are understandable and I would be glad for any help.
I've also put some "abstract pictures" of my setup in the attachments, which may help to better understand the setup and how I measured.
Cheers.
I have a few question about measuring the voltage gain of an amplifier.
My goal with this is to set limiters on my frequency splitters the right way to not blow or burn my speakers (more on that later).
How I measured my Amplifier:
I first measured an XLR cable with a true RMS meter. I generated a 50hz sinewave until I got 0.5V.
Afterwards I connected 2 XLR (with each 0.5V output) to my amplifier set to bridge mode.
Out of the amplifier came 73V.
Questions:
- How would I now have to calculate my gain? Since I put in 2x 0.5V to a bridge mode amp I would assume the channels are summed up and I'd have to calculate my gain with 1V input. Which would result in a gain of 73x (equals to 39.48 dBu).
- How would I calculate the gain with the amp set to stereo mode? (assuming I put in 0.5V in each channel and measure and get e.g. 50V out)
Some more background:
My setup:
Speakers:
2x JBL PRX412m for the high frequencies (link)
1x JBL SRX828P (passive) (link)
Amplifiers:
1x the t.amp E-1200 for my tops (link)
1x Crown XTi 6002 for my subwoofer (link)
Frequency Splitters:
1x the t.racks DSP 206 (link)
1x the t.racks DSP 408 (link)
I have a mixer, which receives signal from a DJ controller.
The mixer then will send the signal to the DSP 206 which will send the signal to the DSP 408.
The DSP 408 will then send the signal to the amps which are connected to my speakers.
Limiting:
My goal is to set my limiters (excursion and thermal) on my frequency splitters (excursion on the DSP 206 and thermal on the DSP 408). The limiters should be set to a level, where to gain of the amplifier can be set to the maximum. This way I do not have to watch my amps all the time and I can still be sure that my speakers are protected.
I've used the limiting guide by linea research (link). Since I want to set my limiters before my amps I have to take the amplifier gain into account (see page 2, bottom chapter of the file).
The problem is now, that I don't know my exact amplifier gain in bridge mono mode. In the owners manual of the XTi there is only a gain for 8 ohm output. However I run my amp for my sub in 4 ohms. So I just measured the voltage gain. In this guide is also stated that some amplifiers have not a fixed voltage gain. So measuring is the best option.
After my measuring I've got the following values (these are all measured with the gain turned all the way up):
the t.amp E-1500 (set to stereo mode): 0.5V into channel 1 generated an output of 57V at channel 1
Crown XTi 6002 (set to bridge mono mode): 0.5V into channel 1 & 2 generated an output of 73V at channel 1
This brings me back again to my questions above. How do I calculate the gain of my amplifier?
Since I have put the XTi to bridge mode I would assume, I have to calculate the gain with an input of 1V. Which means a gain of 73x (equals to 39.48 dBu)
However my gain of the t.amp would be calculated with an input of 0.5V because it was running in stereo mode.
This would mean the voltage gain of the t.amp is 114x (equals to 43.36 dBu).
I hope my questions are understandable and I would be glad for any help.
I've also put some "abstract pictures" of my setup in the attachments, which may help to better understand the setup and how I measured.
Cheers.
Attachments
Gain=Vout/Vin. So you put 1V RMS (.5 on each input) in and got 73V out, so you're correct that your gain is 73. Your gain in stereo mode per channel will be Vout per channel/.5 if you put .5V in. And so for the t amp your gain calculation is also correct.
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Be sure it is not clipping. If you put 10V in and still get 73V out, that's not right.
Agree.
You should scope it to know it´s not clipping, but a "Plan B" solution is to feed it enough voltage to reach 1/2 to 1/4 the voltage you already found, say to 20 or 30V RMS or so, and measure needed driving signal.
Math is the same as before: Vout/Vin but now you can (presumably) avoid clipping.
You should scope it to know it´s not clipping, but a "Plan B" solution is to feed it enough voltage to reach 1/2 to 1/4 the voltage you already found, say to 20 or 30V RMS or so, and measure needed driving signal.
Math is the same as before: Vout/Vin but now you can (presumably) avoid clipping.