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Old 31st May 2014, 11:57 AM   #11
AndrewT is online now AndrewT  Scotland
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The output current of an opamp is fed into the feedback and into the load and into any added capacitance.
This Loading can be very significant, particularly with regard to transients in music signals.

The supply rail has to supply the quiescent current to run the opamp AND the output current fed to that complex and demanding load.

You, the designer, have to work out, or guess at, a sensible total supply current for all the opamps and all the different loads.
I'd suggest Iq + 10mA for each opamp.

opa2134 are dual opamps, that is 10 channels for the 5 chips,
6mA of Iq and 10mApk of transient load current times ten ~ 160mApk.
Much of this comes from the chip decoupling.
The regulators see very little of the transient loading.
The continuous load on the regulators could be around 70mA.
A drop across the regs of 10V gives an average dissipation of 0.7W, not worth adding a heatsink.
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Old 31st May 2014, 12:18 PM   #12
Mooly is online now Mooly  United Kingdom
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Quote:
Originally Posted by giro1991 View Post
There was me thinking a transformer was all I needed to convert to DC to form a power supply!
You have to decide whether you need a "kit" or whether you would be happy wiring the separate parts together which is easy.

There is one more alternative, and that is to use a small cheap "wall wart" of say 12 volts DC output and use one of these which generates a -/+ 15 volt rail,

There are only 5 connections. Two for the input and three for the output, plus 15, zero and minus 15 volts.

10PWRA1215D - POWERPAX - 10W REG DIP 12V IN / + - 15V OUT | CPC
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Old 31st May 2014, 08:43 PM   #13
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A PCB mount transformer should be fine. Ill echo some comments here and suggest that its unlikely you'll need heatsinks for the 7812/7912.

I typically use a Block 6 VA 9-0-9v transformers with 7812/7912, or 6VA 12-0-12v with 7815/7915 regs. With the 15v regs i have considered that 9 VA MIGHT be better.

I find that's enough capacity for a couple of quad ICs. If i were powering 4 quads id probably go to 9-12VA.
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Old 2nd June 2014, 10:38 AM   #14
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Alright,
Quote:
Originally Posted by Mooly View Post
You have to decide whether you need a "kit" or whether you would be happy wiring the separate parts together which is easy.
Prefer the seperate parts way

Wait a minute, is a single regulated +/-15v (12v) enough for two xo boards, or?

Not sure what to go for 12 or 15, but i'm sure we mean 15v+/- for the whole ensemble (ie, hpf+xo's)/

Regarding the basic HPF circuit i'm doing - it has a single op amp, a + and - connection, that is the only 'live' part of this circuit (seperate from line level), does this mean its also "dual symetric", i.e. can I just stick hpf to the end of a 15+/- reg? - I can't really see a common line in this circuit.
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Last edited by giro1991; 2nd June 2014 at 11:03 AM.
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Old 2nd June 2014, 10:59 AM   #15
AndrewT is online now AndrewT  Scotland
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higher transformer voltage makes the regulators run hotter.
lower transformer voltage runs the risk of the regulators dropping out when mains voltage goes low.
In the UK the lowest mains voltage is 216Vac.

If you use a 230:12Vac transformer @ full load and 216Vac mains voltage, then you will get ~11.27Vac before the rectifiers. This is too low for 15Vdc output

If you use a 230:15Vac 15% regulation transformer @ near zero load you will get ~19.05Vac before the rectifiers when Mains is at a maximum of 254Vac. This will dissipate ~1.9W, when delivering 160mA

You have to design such that the regulator never drops out during your target operational conditions and never overheats in your worst case conditions.
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Old 2nd June 2014, 11:28 AM   #16
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You don't actually need regulators at all.

A simple 9-0-9 transformer with a rectifier and two caps will work fine.

Adding regulators will improve the fidelity but you are trying to make it work on a shoestring budget.
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Old 2nd June 2014, 12:11 PM   #17
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I merely meant the assembled regulating PCB mooley linked to could be done cheaper -
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Old 2nd June 2014, 01:10 PM   #18
Mooly is online now Mooly  United Kingdom
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Quote:
Originally Posted by giro1991 View Post
Alright,

Prefer the seperate parts way

Wait a minute, is a single regulated +/-15v (12v) enough for two xo boards, or?

Not sure what to go for 12 or 15, but i'm sure we mean 15v+/- for the whole ensemble (ie, hpf+xo's)/

Regarding the basic HPF circuit i'm doing - it has a single op amp, a + and - connection, that is the only 'live' part of this circuit (seperate from line level), does this mean its also "dual symetric", i.e. can I just stick hpf to the end of a 15+/- reg? - I can't really see a common line in this circuit.
Quote:
Originally Posted by giro1991 View Post
I merely meant the assembled regulating PCB mooley linked to could be done cheaper -
Here is what I would do. Power the opamps from a -/+15 vdc supply.

That means you need one of these which is easy to wire and easy to mount,

CTFC12-15 - CAMDENBOSS - TRANSFORMER, 12VA, 2 X 15V | CPC

You also need a 7815 and a 7915 regulators together with two small heatsinks such as,

L7815ACV - STMICROELECTRONICS - V REG +15V, 7815, TO-220-3 | CPC From This Range

L7915ACV - STMICROELECTRONICS - V REG -15V, 7915, TO-220-3 | CPC From This Range

FK 220 SA 220 - FISCHER ELEKTRONIK - HEAT SINK, TO-220, 25C/W | CPC From This Range

And a bridge rectifier which can be mounted on the transformer tags,
2KBP02PBF - VISHAY FORMERLY I.R. - BRIDGE RECTIFIER, 2A 200V | CPC From This Range&MER=e-bb45-00001003

Two reservoir caps,
ECA1VM222 - PANASONIC - CAPACITOR, 2200UF, 35V | CPC

You can add as much extra decoupling as you want but the above is the minimum.
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Old 2nd June 2014, 01:57 PM   #19
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I am thinking of using two ald "scrap" laptop chargers to get 2 x 19VDC then run this through 15VDC regulators... good idea?
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Old 2nd June 2014, 02:41 PM   #20
Mooly is online now Mooly  United Kingdom
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Quote:
Originally Posted by ViennaTom View Post
I am thinking of using two ald "scrap" laptop chargers to get 2 x 19VDC then run this through 15VDC regulators... good idea?
Its hugely dependent on the PSU's (grounding arrangements internally) and your intended use.

I wouldn't even contemplate it tbh.
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