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 10th September 2014, 09:12 PM #1 diyAudio Member   Join Date: Sep 2011 LJM Gain L25-D Gain Help Just noticed the gain on L25D modules is 40 volt. My Rotel units are 27.2db. Calculating that is: Rotel:22.908677 Voltage Ratio Gain 27.2db Gain L25D: 40 Voltage Ratio Gain 32db Gain. LJM lists the L15D as a 36db gain. This seems to be a problem causing full power draw of my 1000w Power Supply at -15db from full power. Is there a method to change the gain on L25D's? Hopefully I can make it adjustable for my different pre/pro's. Thank you! Last edited by mstang1988; 10th September 2014 at 09:51 PM.
diyAudio Member

Join Date: Apr 2010
Location: Brisbane
Quote:
 Originally Posted by mstang1988 Just noticed the gain on L25D modules is 40 volt. My Rotel units are 27.2db. Calculating that is: Rotel:22.908677 Voltage Ratio Gain 27.2db Gain L25D: 40 Voltage Ratio Gain 32db Gain. LJM lists the L15D as a 36db gain. This seems to be a problem causing full power draw of my 1000w Power Supply at -15db from full power. Is there a method to change the gain on L25D's? Hopefully I can make it adjustable for my different pre/pro's. Thank you!
Change R7 to 6 k or so that lowers your gain . The ratio, R8/(R7+R2),
determines the voltage gain of IRAUDAMP7S. ( see MY DESIGN L20D IRS2092+IRFI4020H 200W8R for resistor numbers )

Cheers ,

Rens
__________________
If you measure, you know; if you guess, you don't

diyAudio Member

Join Date: Sep 2011
Quote:
 Originally Posted by doctordata Change R7 to 6 k or so that lowers your gain . The ratio, R8/(R7+R2), determines the voltage gain of IRAUDAMP7S. ( see MY DESIGN L20D IRS2092+IRFI4020H 200W8R for resistor numbers ) Cheers , Rens
Thank you! I don't think I'm calculating this correctly. Any chance you can help?

Parameters:
Supply Voltage: DC +-60V to +-80V, the recommended voltage +-70V
Output power: 250W 8ohm, 350W 4ohm
Voltage Gain: 40
Input sensitivity: 1.6V
Output current = 14A of the (25C), 10A (85C)
Noise Residual Noise: 200 μV (22 Hz - 20kHz, AES17 the filter Self-regime of the oscillating frequency)
THD + N, 100W: 0.008% 1kHz, Single-channel driven
Total Idle Power Consumption 7W No input the signal
The Channel Efficiency 90% Single-channel driven

Power=Voltage^2/Load Resistance from what I can find
So if the ramp does the rated 350 watt RMS at 4 ohm and 250 at 8ohm I get:
SQRT(1400)=37.42v
SQRT(1500)=44.73v

Voltage Gain = 20*LOG(Vout/Vin)

Voltage Gain = 20*LOG(37.42/1.6)=27.38
Voltage Gain = 20*LOG(44.73/1.6)=28.94

However if I look at the listed voltage gain from above it says 40. In addition when I put it in a calculating program of voltage gain to DB it gives the original converted numbers I posted. Am I missing something?

diyAudio Member

Join Date: Sep 2011
Quote:
 Originally Posted by mstang1988 Thank you! I don't think I'm calculating this correctly. Any chance you can help? Parameters: Supply Voltage: DC +-60V to +-80V, the recommended voltage +-70V Output power: 250W 8ohm, 350W 4ohm Voltage Gain: 40 Input sensitivity: 1.6V Output current = 14A of the (25C), 10A (85C) Noise Residual Noise: 200 μV (22 Hz - 20kHz, AES17 the filter Self-regime of the oscillating frequency) THD + N, 100W: 0.008% 1kHz, Single-channel driven Total Idle Power Consumption 7W No input the signal The Channel Efficiency 90% Single-channel driven Power=Voltage^2/Load Resistance from what I can find So if the ramp does the rated 350 watt RMS at 4 ohm and 250 at 8ohm I get: SQRT(1400)=37.42v SQRT(1500)=44.73v Voltage Gain = 20*LOG(Vout/Vin) Voltage Gain = 20*LOG(37.42/1.6)=27.38 Voltage Gain = 20*LOG(44.73/1.6)=28.94 However if I look at the listed voltage gain from above it says 40. In addition when I put it in a calculating program of voltage gain to DB it gives the original converted numbers I posted. Am I missing something?
Ok, it can't possibly be voltage gain causing my issues. I tested voltage at 82db on my rotel at .7v where it cuts out via output. 2.9v in the garage all the way up where it doesn't cut out. Rotel is 3.5v all the way up but it cuts out way before then.

diyAudio Member

Join Date: Apr 2010
Location: Brisbane
Quote:
 Originally Posted by mstang1988 Ok, it can't possibly be voltage gain causing my issues. I tested voltage at 82db on my rotel at .7v where it cuts out via output. 2.9v in the garage all the way up where it doesn't cut out. Rotel is 3.5v all the way up but it cuts out way before then.
I think you're pushing the current limits of the A1000SMPS ( see attachment )
Can you do an impedance measurement of your speakers ? just download REW and follow instructions. take the minimum impedance and calculate the current at max RMS output and see if this fits in the current limit of the A1000SMPS .
I use this wonderful PSU for years now to supply 5 x L15D's at +/- 50Volts and it's (almost) impossible to trip the current limiter , but my speakers are all above 8 ohms .
with the above impedance you could calculate a gain factor which prevents the current limiter to trip .

Good luck !

Cheers ,

Rens
Attached Images
 A1000SMPS.jpg (249.4 KB, 103 views)
__________________
If you measure, you know; if you guess, you don't

diyAudio Member

Join Date: Sep 2011
Quote:
 Originally Posted by doctordata You asked how to change the gain , so I answered your question I think you're pushing the current limits of the A1000SMPS ( see attachment ) Can you do an impedance measurement of your speakers ? just download REW and follow instructions. take the minimum impedance and calculate the current at max RMS output and see if this fits in the current limit of the A1000SMPS . I use this wonderful PSU for years now to supply 5 x L15D's at +/- 50Volts and it's (almost) impossible to trip the current limiter , but my speakers are all above 8 ohms . with the above impedance you could calculate a gain factor which prevents the current limiter to trip . Good luck ! Cheers , Rens
Thanks for helping, absolutely! Just frustrated is all. I will see if I can do the REW sweep. I only have a Macbook Air with a single output so I'll have to figure that out. What will be the best way to do the impedance checking? I have my Fluke 116 and can set it on impedance and minimum.

diyAudio Member

Join Date: Apr 2010
Location: Brisbane
Quote:
 Originally Posted by mstang1988 Thanks for helping, absolutely! Just frustrated is all. I will see if I can do the REW sweep. I only have a Macbook Air with a single output so I'll have to figure that out. What will be the best way to do the impedance checking? I have my Fluke 116 and can set it on impedance and minimum.
You could use REW as a signal generator on your MAC . Use a known series resistor ( around 10 ohms in series with your speaker) and keep the voltage on your mac output constant while sweeping . Measure the voltage over the speaker terminal and you can calculate speaker impedance .

Cheers ,

Rens
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