Low-noise opamp for battery-powered preamp.

[quote author="eded"]i would suppose bcarso (but i'm just a learner) the issue with the linear op amp is the slew rate. is this correct ?[/quote]

Yes, that's the one that stands out.

[quote author="AMZ-FX"]I wrote the noise calc for my own personal use... it needs the Noise voltage in nV/√Hz and the Noise current in pA/√Hz, along with the resistor values.

There is a similar one online at: http://tangentsoft.net/audio/calc.html

I got the noise specs from a datasheet on the RC4560... I ran the calculations before I had Dave's schematic for reference so I just picked some values to use... the relative performance of the opamps should be about the same even without the schematic values.

regards, Jack[/quote]

Thanks. This datasheet: http://focus.ti.com/lit/ds/symlink/rc4560.pdf doesn't say much about either voltage noise or current noise (other than what one could infer about current noise from the bias current magnitude) and just has that peculiar "RIAA" thing. Maybe you have a better datasheet. That's one of the reasons I asked.

So what your numbers earlier are for is rms noise in a 1 Hz BW? And they are assuming a given transformed source resistance?

[quote author="featherpillow"]You don't say what your preferred current draw is, Dave. I've been toying with a similar thing lately. LM6132 is OK, but I'd look into the LMH6655 first, because it has less noise. It's been pretty stable in applications I've tested it with, using supply rails of +/-8vdc and +12vdc with divider. The 6132 can be kind of bitchy sometimes if it doesn't like the PCB layout. the 6655's noise is about 4.5nv/rt hz. It's not rail to rail O/P, I don't know if that matters to you or not. Oh, and it's SOIC package only, so you'll probably want one of those Brown Dog adaptors.

link:
http://www.national.com/pf/LM/LMH6655.html[/quote]

Just check the noise graph, the 1/f noise starts rising at about 20K. Not too good for audio.

And the 1.7pA/root Hz current noise is pretty foul as well; e sub n/i sub n is 2.6k, and the current noise probably has a similar or worse rise below 10kHz.

Not a lot of loop gain at low frequencies either.

But it is fast, I'll give it that.

Hello,
i realize it's an old thread but i was wondering if the schematic was still available
Thanks
francois

Hi, I know this is a very old thread, but I am interested in NewYorkDaves BattPowerMicPreamp.png schematic. Is there someone who can help me out with this? Thanks!

which battery?

TL081 begs for a 9 volt, 

mire stuff here,

http://groupdiy.com/index.php?topic=20038.0

no wait, i mean here>

http://groupdiy.com/index.php?topic=16909

Hello CJ , thanks for the information! I am planning a battery-powered field recorder with a built-in headphone amp for 250 ohm headphones and an ad/da converter to use it with my iphone or ipad.
The operating voltage should be about 18 volts , so two 9 volt blocks are planned .
Right now I 'm thinking about the realization of the bipolar supply voltage for the operational amplifiers.
So I want to study the old threads here,  unfortunately all exciting schematics for this topic are no longer available .

The last few days I spent on the website of Samuel Groner, his design with the 2sk170 and the 5532 will be the basis of my mic pre . The hpa will be a cmoy, the converter is a  BB2902.

cheers  8)

Hi. I have attached a circuit that I built a few years ago and am using it each week for one of my mics on my webcast. It will run on two 9 volt batteries or a regular ac  power supply. I am sorry but I don't know the amount of gain that it puts out but I have a dual level pot and it is no where close to maximum. The noise level is very low. If you have any questions whatsoever, don't be afraid to ask. Len.

Hey, a call from the past! Thanks a lot for the circuit, Lennie! Cheers

Lennie said:

Hi. I have attached a circuit that I built a few years ago and am using it each week for one of my mics on my webcast. It will run on two 9 volt batteries or a regular ac  power supply. I am sorry but I don't know the amount of gain that it puts out but I have a dual level pot and it is no where close to maximum. The noise level is very low. If you have any questions whatsoever, don't be afraid to ask. Len.

Click to expand...

A few questions... like why post in this (old) thread?

The 5534 is neither very low noise (around 9dB noise figure as low Z mic preamp), nor battery friendly.  In fact the pin outs described in that schematic do not agree with 5534, perhaps they mean the  5532 dual? That makes more sense since 5534 is not unity gain stable and would need compensation to operate as unity gain inverter, the 5532 is unity gain stable.

The gain in your circuit is roughly (100k/220)x2....  The input loading seen by the mic is around 400 Ohms... Nominal target impedance for loading mics is a bridging termination (10x), so should be more like 1.5k-2k.

I have seen that topology used in low performance fixed install mixer amps, but instead of 220 ohm input resistors, 1k input resistors load the microphone with a more appropriate 2k termination.

Glad that it works for you.

JR

PS: I used a bare 5534 as a mic preamp in a DJ mixer kit design I published back in 1978 (different topology), intended for use with hi Z, 600 ohm mics.

Lennie said:

Hi. I have attached a circuit that I built a few years ago and am using it each week for one of my mics on my webcast. It will run on two 9 volt batteries or a regular ac  power supply. I am sorry but I don't know the amount of gain that it puts out but I have a dual level pot and it is no where close to maximum. The noise level is very low. If you have any questions whatsoever, don't be afraid to ask. Len.

Click to expand...

Apart from what JohnRoberts notes - you could lose the 100K and cap from pin 5 to ground.
You have ac coupling in any case to remove dc offset. And if that were the point - equalising the impedances seen by both inputs then the value would properly be 50K (2 parallel 100K).

Newmarket said:

Apart from what JohnRoberts notes - you could lose the 100K and cap from pin 5 to ground.
You have ac coupling in any case to remove dc offset. And if that were the point - equalising the impedances seen by both inputs then the value would properly be 50K (2 parallel 100K).

Click to expand...

??! care to explain?...