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Old 1st November 2010, 05:13 PM   #41
jonners is offline jonners  United Kingdom
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Thanks Andrew. Your post encouraged me to try again, and I succeeded using an older version of Safari on a different computer. Strange....
 
Old 2nd November 2010, 04:27 PM   #42
Cristi is offline Cristi  Europe
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If the document is not loading, please try to refresh the page or download with FDM or similar download manager, the server is slow...
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Old 5th November 2010, 01:02 PM   #43
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What is the minimum voltage you can run the 4702 series boards and still get predictable & stable operation?

Also, I noticed the 49810 boards require two sets of input voltages, one slightly higher than the other. What would happen if you used the same voltage rails for the power and driver stages?

Last edited by uzernaam; 5th November 2010 at 01:17 PM.
 
Old 5th November 2010, 02:27 PM   #44
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by uzernaam View Post
What is the minimum voltage you can run the 4702 series boards and still get predictable & stable operation?

Also, I noticed the 49810 boards require two sets of input voltages, one slightly higher than the other. What would happen if you used the same voltage rails for the power and driver stages?
the LME498xx series do not require two different supply voltages. They all require a dual polarity supply within the range stated by National.
National will also state the range of dual polarity supply voltage for the 4702.
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Old 6th November 2010, 04:58 AM   #45
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From the product info for the 49810 amp module:

"To supply power for the amplifier, 4 voltages are needed. Two positive voltages and two negative voltages with respect to GND. The value of these voltages needed for the 300W amplifier version are +-61V DC for the Power Stage, and +-67V DC for the Driver Stage and for the 500W amplifier version, the voltages are +-78V for the Power Stage and +- 84V for the Driver Stage. The reason why two different supply voltage values were chosen, is that the Amplifier Driver IC to be able to provide enough voltage excursion for the Power stage, to avoid early clipping and saturation of the amplifier"
 
Old 6th November 2010, 07:15 AM   #46
Cristi is offline Cristi  Europe
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Same as i described in the manual, for best performances, i recommend to supply the LME49810 power stages separate than the driver stage. the power supply current demand at high output power levels might lead to large voltage drop, 5-10V when the amplifier is powered from a linear power supply, and keeping the driver stage supply voltage higher, will not reduce the output power if the supply rails voltage drop.
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Old 6th November 2010, 09:09 AM   #47
TCx is offline TCx  Czech Republic
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Well, what happens if I power some of the LM4702 based amps by the +-54V version of A350SMPS, for example? (the same voltage for both driver and power stage) It is intended for home stereo amp so only a fraction of the amp's nominal power is needed anyway. How much will available power decrease? And would it have any negative influence on sound quality? Thanks.
 
Old 6th November 2010, 10:09 AM   #48
AndrewT is offline AndrewT  Scotland
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you are misinterpreting that National extract.

It does not say the lme498xx series chip require 4 supply voltages.
It does not say that the lm3498xx plus the discrete output stage requires 4 supply voltages.

It does say that if you want maximum output voltage from the lme chip and and you do not want the output stage to saturate then adopt a 4supply voltage topology.

Many amps do have the option to separately power the voltage amp from the output stage.
It tends to be more common for the voltage amp stage to have the higher voltage.
National's argument supporting the higher output stage voltage is valid if you want to avoid saturation, but do keep in mind it is not a requirement for the lme to operate.
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Old 6th November 2010, 11:40 AM   #49
TCx is offline TCx  Czech Republic
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Thank you for explanation. I actually mean how much effectively available power I can get without saturation, i.e. with good sound quality. I already found it in the datasheet - it should be about 90W. That's OK.
So my question is - is one voltage of up to +-60V for both driver and power stages safe?
 
Old 6th November 2010, 11:50 AM   #50
AndrewT is offline AndrewT  Scotland
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the lme498xx series are specified for 40 to 200V.
+-60Vdc (=120V) is within the specified range.
You must choose your output devices so that their temperature de-rated SOAR meet the speaker and supply conditions.
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