15V for opamps from 35V ?

[jimbo1968]

How do I get 15V to power my opamps filters from the 35V supply in side my chipamp?

Regulators? Would they need heatsinking?

Potential divider? what size resistors?

TIA. Jim

 

[sss]

78xx15 and 79xx15 regulators will do yhe job , no heatsink is needed if u will just power one or 2 op amps

 

[jimbo1968]

Thanks.

It will be powering maybe 5 opamps, but can be attached to a heatsink so no problem.

 

[richie00boy]

Have a look at my quality PSU for op-amps, with board layout www.readresearch.co.uk You would just need to hook the DC supply into where the rectifier diodes would go, very easy.

 

[jimbo1968]

Have a look at my quality PSU for op-amps, with board layout www.readresearch.co.uk You would just need to hook the DC supply into where the rectifier diodes would go, very easy.

Before I build it, did you hear the difference between this and a simple 7815/7915 ?

 

[peranders]

78xx and 79xx can take max 35 volts in so it's just about. LM317/LM337 is more suitable I think.

 

[carlosfm]

78xx and 79xx can take max 35 volts in so it's just about. LM317/LM337 is more suitable I think.

Of yourse you can (and you should) use series resistors.

 

[demogorgon]

Before I build it, did you hear the difference between this and a simple 7815/7915 ?

I wouldn't think so, considering opamps rather good ability to reject powersuply noise.

for a discreet design, i would agree, but opamps? no, i would just stick with the 78\79xx.
if however your standards are a tad higher, go for the lm317\337 series regulators. they have considerably better specs.
they need reference resistors though.

my thoughts
Marius

 

[richie00boy]

I'll have to admit I haven't directly compared the two side by side. I do know though that the LM317/337 combination measures better in the noise department and has a more tightly controlled output. I also like to just squeeze those extra couple of volts headroom.

 

[valveluver]

A LM 7815 should work,

If all you need to power up is a handfull of 5534 or 5532s you probably dont need a heat sink

 

[peranders]

As we said is 35 V dangerously near the limit of the 78xx/79xx but as Carlos point out a series resistor may be inserted but you must know the load in order to calculate the resistor value.

The only disadvantage as I see it is more parts around the LM317/337 but in this particular case it's only one more

 

[Reactance]

Dont forget to decoupling caps near the Vin and Vout near the voltage regulators.
Cheers!

 

[sndscietist]

granted i'm still just the new guy here, i have a little insight to this problem. i have been repairing Peavey amplifiers for a little over 3 years now. i'll use the CS series as an example their rails are aprox +/- 59 VDC it's split like this, the output gets the full +/- 59 then there is a series resistor the next stage goes to the driver board for the driver output transistors. they drop the voltage a little more then there is another resistor to drop it to the final range. (looking at the schematic now) for their needs they use a 10 watt 10 ohm and then a 5 watt 1k. but case and point series voltage dividers are probably the safest and cheapest way to go

 

[jackinnj]

You can use an 80V transistor and a zener diode to make a power-zener.

 

[sbrads]

A few years ago I modified a Crimson Elektrik moving coil head amp's 15v power rails. I tried a zener + transistor (noisy), 7815's (extremely noisy) and ended up with LM317's fed from 50v via a dropper resistor plus filter caps as by far the quietest and simplest supply. Any hiss from the regulator got straight through the discrete mc circuit and was very audible, and decoupling caps across 7815's doesn't do a thing to reduce it either. LM317's are the way to go.

 

[sndscietist]

LM317's are the way to go.

now correct me if i'm wrong but don't LM317's use the same PWM style as 78xx series regulators. which means they should have the same harmonic output at X voltage. it was my understanding that the only difference with the 317's was that they were variable. and that much like triacs they only varied the pulse width.


like i have said before i could be way way off but that was what i always thought

Adrian

 

[richie00boy]

The 317 and 78xx are linear regulators. Any triangular hash at their output is simply due to the feedback scheme employed. The 317 is a totally different beast to the 78xx and this is reflected in the performance.

 

[kevinkr]

Take a look at Linear Technology's line of linear regulators, they have much lower noise than the venerable 317/337, tighter regulation and lower output impedance as well.. Try LT1086 and LT1185..

Kevin