hello I consider this filter
http://www.hanssummers.com/images/stories/cwfilter/files/article.pdf
I guess I could I use another opamp with the same values of external components without affecting it's frequency response?
I think I am going to try the single opamp versions, since it will be easier to align the components and also it will be easier to add more stages or less, to achieve variable bandwidth. Will something like the cheap ne5534 prove better opamp?
Which opamp would you recommend for very low noise?
http://www.hanssummers.com/images/stories/cwfilter/files/article.pdf
I guess I could I use another opamp with the same values of external components without affecting it's frequency response?
I think I am going to try the single opamp versions, since it will be easier to align the components and also it will be easier to add more stages or less, to achieve variable bandwidth. Will something like the cheap ne5534 prove better opamp?
Which opamp would you recommend for very low noise?
Changing to the 5534 would probably be noisier, as the allpass stages are working at 100k impedance. To get lower noise you'd need to scale down this resistor value and multiply up the capacitors accordingly. Or you could use (much more expensive) low noise JFET opamps like OPA827. Definitely ditch the differencing 741 if you want it to sound half-way decent.
Changing to the 5534 would probably be noisier, as the allpass stages are working at 100k impedance. To get lower noise you'd need to scale down this resistor value and multiply up the capacitors accordingly. Or you could use (much more expensive) low noise JFET opamps like OPA827. Definitely ditch the differencing 741 if you want it to sound half-way decent.
So the OPA827 could be proved better without any changes in the circuit? (except from pinout maybe, I have not checked)
any equivalent DIP version?
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Well I think the TL074 is probably low noise enough for something acting as a filter for radio signals - those signals are already far noisier than the opamps here. The difference when switching to OPA827 would probably only be heard on hi resolution audio formats with better than 16bit noise floors.
For single (or dual, or quad) opamps I would go with the TL071 (or TL072 dual, TL074 quad).
The 5534 is power hungry and you would need to ensure stability. The TL0's would drop right in place with no problems.
tbh for it's intended use a 741 (or LM324) isn't going to worsen the overall snr of what comes out all that much.
The 5534 is power hungry and you would need to ensure stability. The TL0's would drop right in place with no problems.
tbh for it's intended use a 741 (or LM324) isn't going to worsen the overall snr of what comes out all that much.
neazoi... the signal you are dealing with is extremely limited.
Anything better than a TL071/2/4 is overkill... you gain nothing performance wise and may lose out in terms of cost, stability and power consumption.
If power consumption is an issue then the low power TL061 and TL062 would be fine.
On the random swapping of opamps see this,
http://www.diyaudio.com/forums/anal...u-have-checked-see-its-stable-havent-you.html
Anything better than a TL071/2/4 is overkill... you gain nothing performance wise and may lose out in terms of cost, stability and power consumption.
If power consumption is an issue then the low power TL061 and TL062 would be fine.
On the random swapping of opamps see this,
http://www.diyaudio.com/forums/anal...u-have-checked-see-its-stable-havent-you.html
If it is ok, could ththese be used with single supply as well in the circuit? (I see a balanced supply in the datasheet)
I agree with Mooly on the overkill of those ADI parts.
Single supply can be made to work yes - you can use something like a 5532 as a virtual ground generator. Otherwise called a 'rail splitter'. Or you can buy a (fairly expensive for what it is) dedicated device from TI : TLE2426.
Virtual Ground Circuits
Thank you so much all of you.
I think I am going to be realistic and go for the cheap and tested on this circuit tl071
I would use some 0.1% tolerance resistors and good tolerance capacitors for the phasing networks to get good performance over temperature. These are cheap these days
I think I am going to be realistic and go for the cheap and tested on this circuit tl071
I would use some 0.1% tolerance resistors and good tolerance capacitors for the phasing networks to get good performance over temperature. These are cheap these days
Exactly! The input signal probably has 20dB S/N and 5% distortion, so lets not get in a sweat about op-amps, component tolerance etc. Given the relatively high impedance a JFET input amp would seem best, and a cheap one will be just as good as an expensive one in this application.
Personally, I'm not too sure about the design. It has a narrow central peak, but broad skirts. I guess the question is how close to linear phase does it get across the passband?
Personally, I'm not too sure about the design. It has a narrow central peak, but broad skirts. I guess the question is how close to linear phase does it get across the passband?
The OP circuit is for CW (ie Morse Code!) demodulation!
Whaddya mean you've never dreamed of greater soundstage depth and added detail for your dahs and dits? Isn't Morse all about PRaT ?
I agree fully with Mooly, the filter is for CW (continuous tone) communications, noise power density is directly related to bandwidth which is very limited. It does exactly what it says, it will retrieve coherent signal from what seems to be under the noise floor which is non coherent signal or what we refer to as noise. any op-amp will do the job equally well at this frequency.
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