dc/dc step up converter (raplace 9v battery with AA)

[frejoh4666]

So I'm building a project on a PCB-board, and I'm trying to find a replacement for 9v battery that create +-18v.

I'm trying to power a few NE5532 IC-ciruits, so +-15v would be fine. The 9v battery is just a cheap way to get the power, and i rather not use 9v battery.

So I'm trying to power it with AA battery. I would need an dc/dc step up converter, that I can't find anything on. I'm trying to get 3v to 15v then 15v to 30v with 2 AA.

But I'm not sure if this is an good/best idea, or if there is an better way to do it. So does anyone know what I would need to do too achieve this?

 

[audioguru]

The 30V current might be 32mA for four NE5532 ICs that are not working hard.
The stepup converter will have some loss so its input current from two AA cells will be about 384mA and they will not last long.
The voltage converter will probably add some whining noise.

Why do you need such a high power supply voltage for the opamps?

 

[Colin]

How much current do you need?

 

[frejoh4666]

So I was trying to calculate the current more acurate, but something didn't add up. Long story short, it's not +-18v that was used, it was +-9v.

Ok. I'm building an active noise cancelling circuit. The circuit get noise from Mic J1 left and right ear, J2 is music in, and J3 is output. I did not create the circuit, and I'm simulating everything and creating the PCB layout in NI multisim. The circuit is simulated and is working fine, I just don't like to use 9v batteries, and rather try to replace them with something else.

I went through the data sheet for the NE5532, and if I go under +-9v I will get clipping. I can use max 4 AA batteries, but anything more then that is just going to be a bother, and it would be easier to use two 9v batteries. So I can get 6v, that I could turn, 6v to 12v, 12v to 24v, and get +-12v. I was afraid that the loss in step up converter would be to high to gain anything, as audioguru pointed out.

I'm an student for analogue electronics, and this is a side project that I'm doing mostly for fun.

 

[audioguru]

You found a very old circuit using very old opamps.
Datasheet Archive (.com) and Digikey have never head of an NE5322. Even the NE5532 is also very old and uses a maximum supply current of 16mA! It can drive a load as low as 600 ohms but maybe not headphones that are usually 32 ohms (a few headphones are 600 ohms).
You can use a more modern opamp like an OPA4134 quad for the four NE5532 opamps and use an OPA2134 dual for the NE5322 opamps which can also drive a load as low as 600 ohms. Then you can have much lower distortion and much lower supply current (30mA max instead of 96mA max). Then 9V alkaline batteries will last for 24 hrs. to 48 hrs.

Noise cancelling? No. If you hear outside noise when wearing headphones then the microphones glued to them will hear the headphones and cause frequency peaking then feedback that will make you deaf. But you can adjust for a little noise reduction instead.

 

[frejoh4666]

I never thought about the feedback, but that would kinda be a big problem.
Is the OPA4134 quad only surface mounted? those are annoying to solder. But the best way is to use 9v batteries?

This side project is mostly to learn and something fun to do. I did not expect it to be silent if I wear them. In theory however, at optimal condition, it should be silent, but with slow and imperfect components, I would at least expect it to reduce some noise. Unless the delay is to big and it doesn't have the time to play the inverted sound waves.
And thanks for the help.

 

[audioguru]

The OPA2134 dual opamp is still made in an old dual-inline though holes package.

 

[frejoh4666]

An other question. C2 and R4, wouldn't it be more sensitive due to the high ohm resistor? Isn't it better to increase C2 and lower R4. Or I'm I missing something?

 

[audioguru]

C2 is the input coupling capacitor. It feeds audio from the microphone to R4 which is the biasing resistor for the opamp. The OPA4134 opamp has a maximum input bias current of almost nothing (Jfet inputs) so 1M is fine to bias it. The 0.01uF and 1M produces a cutoff frequency of 16Hz so all audio frequencies are passed.
C2 and R4 have nothing to do with signal sensitivity since the 1M resistance does not load down and reduce the level from the microphone like a 1k resistor would. The signal gain of the opamp is determined by R8 and R6 and is 1+ (33k/1k)= 34 times.

 

[frejoh4666]

Ah, thanks for the help.

 

[AnalogKid]

Do you want to build your power system or buy it. Small switching power supply modules that take in 5-6 V and make +/-12 or +/-15 are common.

 

[frejoh4666]

I decided to buy 2 dc/dc step up converters and use 2 li-ion batteries and go 7.4v to 9v and 7.4v to 18v, and get +-9v

 

[audioguru]

I decided to buy 2 dc/dc step up converters and use 2 li-ion batteries and go 7.4v to 9v and 7.4v to 18v, and get +-9v

A 2-cells Lithium-Ion battery is 8.4V when it is fully charged and 6.4V when it should have its load disconnected. Then it averages 7.4V.
Will the stepup converter still work when the battery voltage is 8.4V which is very close to 9V?

 

[frejoh4666]

Don't think it can handle 8.4v. The circuit can have max 10v and min would be when the opamp becomes to slow, and I would guess that would be around +-5v. So then I could just use one converter and and use +-7.5v

 

[schmitt trigger]

I'm an student for analogue electronics, and this is a side project that I'm doing mostly for fun.

First of all, congratulations! There are not that very many people playing around with old analog circuits anymore.

Second, about the microphone feedback that audioguru has mentioned. It is very real. The noise cancelling headphones I've seen, only cancel the lower frequencies for that same reason. You will have to bandwidth limit the cancelling signal, with a low-pass filter for the microphone signal.
Additionally, the microphone itself should be as much as possible, isolated mechanically from the headphones.

Actual values and mic position will be found via experimentation and measurement.
So I think this will be a fun and exciting project, and you'll learn a lot from it.

 

[Colin]

Use 2 of these:
5v REGULATED SUPPLY FROM 3V

This circuit will produce a 5v regulated output from 2 cells (3v). The output current is limited to 50mA but will be ideal for many microcontroller circuits.
The output voltage is set to 5v by the 3k9 and 560R resistors, making up a voltage divider network.