How low value resistor can 5532 operate

[preciousmolina666]

hi guys im a self proclaimed sound engineer 10 years of exp,
i tried to run my design on spice and built it and its ok i think, i know a litle in opamp,
i want to design the high gain using 5532 with an ultra low low low noise
i did some research, but i need help,an advice on a pro like ,whats the tradeoff if i use this that etc


im using non invert, 9v bipolar supply, 600ohm dynamic mic,
i want to achive 50db flat,6V p-p output with minimum parts since johnson noise is my cocern


1) R1 10k is still flat and trsparent for me, i tried to change it to 100k it added noise, is 10k ok?
2) R2 50ohm can i lower it more? what parameter should i look on datashhet? whats the concequences?
3) R4 100ohm Is this necessary? BTW may next stage will be the same like this non-inverting gain
4) Potiometer is 10k, should i omit R5 10k?
5) what is the ouput amphere of 555 timer bipolar circuit? can this drive 5532 on 1000x gain?

[induction]

Welcome to the forum.

Without a schematic, those component numbers don't mean very much to us.

[preciousmolina666]

ow thanks, cant attach some files, i put it and dropbox

[R.G.]

Likewise, I'd have to see the schematics to help with the comments on resistor values. I think I know what you mean, but I can't tell for certain.

In general, though:
For 50db of gain, the input side of the amplifier matters dramatically more than the output side. The source impedance of the signal source matters a great deal as well. You have to consider the equivalent input noise voltage from the source and the equivalent input current from the source; this can make a difference with whether you want very high or very low input impedances on your amplifier and on the design of the biasing.

It is nearly always better to use the lowest possible resistances at the input side, as this lowers the thermal noise of the input resistors. However, this directly conflicts with the need to not load the input signal source. Again, the signal source impedance makes a big difference.

A potentiometer on the input or output will wind up lowering the signal-to-noise ratio of the whole mess. But the 5532 can drive quite low impedances on its output, at the expense of using lots more power from the power supply. If you have a potentiometer on the output, you could use as low as 1K, presuming that the load on the pot's wiper can be driven successfully by it.  This may not matter unless you can work out an optimal setup for setting gain and biasing for the input.

For the input, it nearly always works out better to get high impedance by using a bootstrap configuration instead of high input biasing resistors.

But that's about all that I can guess without more info. What's your signal source?

[preciousmolina666]

Hope this link work

https://www.dropbox.com/s/l31aqthk4dyhnaw/Untitled.jpg
dropbox.com/s/l31aqthk4dyhnaw/Untitled.jpg


https://www.dropbox.com/s/3f1bzrvw1zfaa3t/negative-supply-voltage-low-current.jpg
dropbox.com/s/3f1bzrvw1zfaa3t/negative-supply-voltage-low-current.jpg

[preciousmolina666]

bootstrap configuration? is that same in instrumentation bootstrap/ground driver? 
my input source is fix in mic 600ohm, so i need 6k input impedance i think
my circuit is working but i want to lower the value of resistor more, so the noise will reduce
my project is working low noise but i want it more like Rf=10ohm, Rg=10k, Rin=6k, pots output 1k
im afraid whats the trade off, what should i look for?

ne5332 datasheet said:
flat frequency up to 16khz at 50db: passed
slew rate: passed
output voltage swing @6V: passed
what else should i look for?

My soundcard input can handle up to 24V swing

[PRR]

> ultra low low low noise .... using 5532 ....  600ohm dynamic mic

True 600 Ohm mikes are very rare. Most mikes are nominal 200r and really 100r to 300r.

'5532's audio-band hiss is 3.5nV/rtHz and 0.4pA/rtHz so the optimum source impedance for low hiss is 8750 Ohms. We can expect hiss to stay low for 3:1 up or down. It will be noticeably degraded by 10:1 away from optimum. 8K to 600r is 13:1 away. (200r is 40:1 away!)

'5532 is NOT best for 600 Ohm sources.

Yes, many-many quite useful preamps have used '5532. The best (least hiss) invariably have a transformer to couple 200r to 6K impedance (~~1:5 ratio). Naked transformerless '5532 "work" quite well for many uses. The excess hiss is usually inaudible in live PA, at least when the crowd comes in. But you seem to be wishing for "ultra low low", not just "good enough".

There are much better mike preamps around. Google "$10 mike preamp". It is well suited for 150-600 Ohm sources. While this is balanced input, you just may want that feature. (Buzz is "noise" just as much as hiss.)

If you must cling to opamps (which are mostly not laid-out for very low voltage hiss), at least use one with low voltage hiss. LT1028 is a classic. 0.85nV/rtHz is _4_ times lower than '5534. About half the hiss voltage of a 600r source.



____________________________________________________

Let's kick your ball around.



R1 should be as BIG as possible, at least 10X your source impedance. Making it small *seems* to reduce hiss voltage, but it reduces signal strength faster than hiss. You don't necessarily want low hiss, you want best S/N. Don't load-down the signal! 10K is fine. With the low-hiss volt devices, 47K may be "large" in that you will get significant DC errors.

Conversely R2 should be small, 1/3rd to 1/10th of the source impedance. Again there are conflicting issues. I would pencil R2 as 100r, 1/6th of the source.

R3 is your GAIN control. Yes, if you increase R3 the hiss output WILL go up. But so does the signal. S/N is unchanged (nearly).

R5 is just pointless. Why is it here?

P1 is a bad place to control gain. If R3/R2 is fixed, and high ratio, you are likely to OVER-load before you even get to P1. Since microphone output levels vary all over the place, this will be a problem.

Make R3 a variable resistor. For practical reasons, I think it may be a 50K Audio taper pot (rheostat connected) plus a 470r stopper. This gives (with R2=100r) gain of 5, 50, and 500 all on one knob.

With R5 and P1 ripped-out, you DO want R4 at about 100r. If the final output goes to bad places (like long lines or switching), R4 allows the opamp to still do its thing, at least well-enough to not go crazy (oscillate).

C"?" maybe should be larger than you think. If you just scale it for 20Hz into 10K you might pick 1uFd. However the opamp sees 600r at mid/high frequencies and a rising impedance below 300Hz. Its hiss will rise due to input hiss current. This gives a bass-heavy "rumble" hiss. In many practical studios this might be masked by room ventilation blower rumble. But I would pencil 10uFd unless I knew the application, venue, and results well.

C4 may be less critical but still should be "large". 100uFd was not big enough for 20Hz with R2=50r (33Hz cutoff). It is marginal with R2=100r, but I would go 250uFd. IAC this will be an electrolytic and I am sure you want to minimize electro distortion; we do that by over-sizing electros so they distort only in the sub-audible band.

[preciousmolina666]

>5532 is NOT best for 600 Ohm sources
what ohm he can? where in datasheet does it specify? btw i read it in manual my mic is 500ohm
OP27 and TL071 are my only option, audio transformer i think that will my next quest

>C"?" maybe should be larger than you think. If you just scale it for 20Hz into 10K you might pick 1uFd. However the opamp sees 600r at mid/high frequencies and a rising impedance below 300Hz
i see how Cin and R1 filtered its ok with me but "600r ar mid/high rising impedace" idk this my ball hurts

>IAC this will be an electrolytic and I am sure you want to minimize electro distortion; we do that by over-sizing electros so they distort only in the sub-audible band.
i dont know this,nice info , i think i need this in my 3rd stage circuit

>Conversely R2 should be small, 1/3rd to 1/10th of the source impedance. Again there are conflicting issues. I would pencil R2 as 100r, 1/6th of the source.
my source impedance is 500r mic? so 1/10th is 50r, im dying to know this why not 50r or lower cause if 100r my rg would be 100k and it added noise

So Overall
Rin 10k impedance
Rg  100k
Rf   100r
R? 100ohm
1kpots

Im almost done on my first stage thanks