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Class AB Audio Amplifiers

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uzernaam

uzernaam

Member
Joined 2010
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?
 
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AndrewT

R.I.P.
Joined 2004
uzernaam said:
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?
Click to expand...
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.
 
uzernaam

uzernaam

Member
Joined 2010
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"
 
C

Cristi

Banned
Joined 2008
connexelectronic.com
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.
 
T

TCx

Member
Joined 2010
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.
 
A

AndrewT

R.I.P.
Joined 2004
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.
 
T

TCx

Member
Joined 2010
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?
 
T

TCx

Member
Joined 2010
Thanks. I meant particularly the LM4702 based amps from Connexelectronic, specifically the "2x100W LM4702 MOS with Heatsink". It seems that voltages up to +-60V are safe for transistors, just wanted to know if there is any other part on the board which could limit max. usable voltage.
 
C

Cristi

Banned
Joined 2008
connexelectronic.com
The output power in case of class A operation is much lower, about 20-25W on 4 R and it depends on maximum bias current which the transistors accept. also, must use a large heatsink, with better than 0.25*C/W thermal resistance. i am not a fan of class A, and i have made some experiments for the sake of the art. i believe that at least similar performances as a class A amplifier can be achieved with a good performance class AB amplifier.
 
M

magma

Member
Joined 2009
hi cristi


Connexelectronic

or
Connexelectronic

which power supply would go best with each?
63Volts is fine for me

does the mosfet require 2 independant power supplies like
this
Connexelectronic

or will the single supply 6*10000uF / 63v be fine with the mosfet and the SAP?

i wish to buy either the mosfet or SAP 4702
please advice about correct power supply

the manual here
http://www.connexelectronic.com/documents/LM4702_MOS_Audio_Amplifier_Module.pdf

recommends two power supplies for the mosfet(4*..... + 2 *....)/63v
when will these be avaible
 
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C

Cristi

Banned
Joined 2008
connexelectronic.com
The SAP15 amplifiers does not require 4 rail power supplies, but for the MOS and BPL versions is recommended to use 4 rail supply, unless SMPS is used.
I recommend to use at least 6x10000uF at 50V for SAP15 amplifiers, and at least 2x10000uF 50V + 4x10000uF 63V for the MOS and BPL amplifier versions. In fact, beside the available capacitors combinations for the linear power supplies, almost any other combination is possible with existing and available capacitors which can fit on the board footprint. just keep in mind the minimum required capacitance and rated voltage, and if the capacity is huge (like 6x18000uF) must use a PSS on the mains side before the transformer.

For the LM4702 amplfier, any version, can also consider to use a smps, since this is a class AB amplifier and voltage regulation is not a must, the A350SMPS or A500SMPS can be used. http://connexelectronic.com/product_info.php/products_id/111?osCsid=1ikvno4j5l4a85akd57lpui0c5
 
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M

magma

Member
Joined 2009
Cristi said:
The SAP15 amplifiers does not require 4 rail power supplies,

I recommend to use at least 6x10000uF at 50V for SAP15 amplifiers, and at least 2x10000uF 50V + 4x10000uF 63V for the MOS [/url]
Click to expand...

thanks for the clarification crisiti

i would like to order either
the LM4702 SAP15 (without heat sink)module and the linear supply 6x10000uF at 50V or 63V as you have suggested

OR
the LM4702 MOSFET (without heat sink) and the 4 rail supply - 2x10000uF 50V + 4x10000uF 63V
as you have adviced


POWER SUPPLY to be the 230V version please

which combination do you have available?
please send me the links so i may order
rest we can discuss on PM if you wish
 
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