If I want to use the +33 - 33 V rails from my power amp (lm3875) to power my preamp (which uses an lm1458 ) will the lm337 and 317 do the job? and would I have to use the chassis ground to ground my premp and voltage regualtors as well? I think these regulators are more realiable than using zenors, but feedback is appreciated.
Thanks
Thanks
i might eventually build a spearate power supply for it, but for now I just want to use the same supply I'm using for the power amp to see if the thing even works........I need dual 15 V rails, but those regulators are giving me some trouble.....I calculated the resistor values as specified on the data sheet, but I can't get more than 6 V on the ouput for the positive part.....maybe the resistor values i used arent the best, I'm not sure...still haven't tried the negative voltage. Anyone have experience with the lm317/337?
Problem is going to be amperage...
LM338 is more commonly used - 5A steady state, and what counts is the voltage drop not the ultimate output voltage. Pedja Rogic has published a simple and very effective variant with this. CarlosFM has also published a variant of the same with some of his tweaks. Both follow the schematic in the datasheet at their core.
I am using some LM338 based supplies in my latest amp project. Good stuff.
C
LM338 is more commonly used - 5A steady state, and what counts is the voltage drop not the ultimate output voltage. Pedja Rogic has published a simple and very effective variant with this. CarlosFM has also published a variant of the same with some of his tweaks. Both follow the schematic in the datasheet at their core.
I am using some LM338 based supplies in my latest amp project. Good stuff.
C
Hi,
if you know the cuurent draw of your pre-amp, which should be
constant as it should be class A, then simple RC filtering (R is
determined by the current and the voltage reduction you want,
C is added to suppress residual ripple) is surprisingly effective.
Alternatively R can be reduced to give a voltage drop of say 6V,
in this case the RC filter is used as a pre filter voltage dropper
for the regulator proper, which can be standard types.
/sreten.
if you know the cuurent draw of your pre-amp, which should be
constant as it should be class A, then simple RC filtering (R is
determined by the current and the voltage reduction you want,
C is added to suppress residual ripple) is surprisingly effective.
Alternatively R can be reduced to give a voltage drop of say 6V,
in this case the RC filter is used as a pre filter voltage dropper
for the regulator proper, which can be standard types.
/sreten.alizawi said:
yes they'll work fine, and whether using chassis ground depends on your definition of, and implemenation of chassis ground. If we can assume a center tapped or dual secondaries transformer, the ground can be directly taken, there is no need to tie direct to chassis ground, particularly if your chassis is at earth ground you might want the typical cap and resistor isolation for it.
You haven't defined the current consumption of your preamp though, but since it doesn't have an inherant high-current need, it is generally presumed that the dozen mA or so it'll use, will be easily handled by an LM317/337 combo dropping it some.
Hi,
The current they draw from the Vrail/s varies with output current to satisfy the load.
I know of one single ended topology that does draw constant current but it is rarely implemented (as indicated by my earlier guess). The only way to make a ClassA push pull amplifier draw constant current is to design it as a bridged pair fed from common Vrails.
this is not accurate. At a guess more than 99% of ClassA single ended amplifiers and all ClassA push pull amplifiers are not constant current.
The current they draw from the Vrail/s varies with output current to satisfy the load.
I know of one single ended topology that does draw constant current but it is rarely implemented (as indicated by my earlier guess). The only way to make a ClassA push pull amplifier draw constant current is to design it as a bridged pair fed from common Vrails.
richie00boy said:
Hmmm......
If that was the case then a push pull Class A amplifier when
faced with low impedances loads would never enter class B.
It is the fact that output current is diverted from the standing
current that causes Class A to enter Class B for output currents
beyond the standing current.
So current draw from the supply for Class A is constant in Class A.
A class A stage in Class B for part of the cycle is not constant current.
/sreten.
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