demogorgon said:whoa, you just out of nowhere get a call from one of the national engineering staff?
well, i bow my head, and take back what i'v said.
r680 and 33uf it is
-Marius
Well, it was a call in response to a email to a previous contact yes. He also was kind enough to send me a few more samples.
I love National.
Yes, I was very surprised by the datasheet when I first saw it, so that question was at the top of my list, along with one other important one, which was how much impedance is there on those signal input pins? The answer, for all practical purposes, zero.
One other important note, I asked about the Darlington pairs and whether they were strictly necessary or if you could just use ordinary power transistors, you may use ordinary power transistors, but of course the circuit may look different depending on the part.
Cheers!
Russ
One other important note, I asked about the Darlington pairs and whether they were strictly necessary or if you could just use ordinary power transistors, you may use ordinary power transistors, but of course the circuit may look different depending on the part.
Cheers!
Russ
Hi
I don't think so guys, using 1.8K and 10uF will have 8.846Hz corner, lowering the resistor valuse to 680 ohm and keeping the capacitor as 10uF will have 23.417Hz corner, wich will force the diyer to increase the capacitor valuse to some thing like 26uF, say 33uF "Available" to obtain at most 7Hz corner....in deed it don't see any logical reason to increase the capacitor value and lower the resistor from 1.8K ohm to 680 ohm, saying that 1.8K ohm resistor will add more noise than 680 ohm resistor !! What an innovation...this is practical audio fellows, welcome to the club.
The feedback resistor will be 22Kohm, and the other resistor will stay 1.8K ohm, which will lower the gain, this is for two reasons:
1. As the high sensivtivity/bandwidth of this IC is concerned, using lower feedback will ensure that oscillation is avoided, and will give you much more options about the input signal processing and manipulation !
2. Lower gain sounds better than higher one, I tested that with OPA541/9 and STK4141/91/4221, the high gain yields very sharp response and sound quality, also the bass just booms and booms, and is not nice. The lower gain gives me smoother sound quality and rigid/very nice bass response in combination to keeping the input/feedback capacitors as high as 10uF, raising these capacitors to 33uF will have nothing to add other than more theoritical response in the lower end of audio, which is something not required practically, there is no audio CD that contains techno music in which the bass is down to 40Hz, unless you are listening to an orchestra and would like to vibrate your butt small bone with 30Hz.
Exaggerating these components values and ratings is not called trying to find the optimal thingy here, it will have only to make the cost of components and PCB much higher than it worths in deed, whether its extraordinary IC or not, its still audio we are dealing with...
I don't think so guys, using 1.8K and 10uF will have 8.846Hz corner, lowering the resistor valuse to 680 ohm and keeping the capacitor as 10uF will have 23.417Hz corner, wich will force the diyer to increase the capacitor valuse to some thing like 26uF, say 33uF "Available" to obtain at most 7Hz corner....in deed it don't see any logical reason to increase the capacitor value and lower the resistor from 1.8K ohm to 680 ohm, saying that 1.8K ohm resistor will add more noise than 680 ohm resistor !! What an innovation...this is practical audio fellows, welcome to the club.
The feedback resistor will be 22Kohm, and the other resistor will stay 1.8K ohm, which will lower the gain, this is for two reasons:
1. As the high sensivtivity/bandwidth of this IC is concerned, using lower feedback will ensure that oscillation is avoided, and will give you much more options about the input signal processing and manipulation !
2. Lower gain sounds better than higher one, I tested that with OPA541/9 and STK4141/91/4221, the high gain yields very sharp response and sound quality, also the bass just booms and booms, and is not nice. The lower gain gives me smoother sound quality and rigid/very nice bass response in combination to keeping the input/feedback capacitors as high as 10uF, raising these capacitors to 33uF will have nothing to add other than more theoritical response in the lower end of audio, which is something not required practically, there is no audio CD that contains techno music in which the bass is down to 40Hz, unless you are listening to an orchestra and would like to vibrate your butt small bone with 30Hz.
Exaggerating these components values and ratings is not called trying to find the optimal thingy here, it will have only to make the cost of components and PCB much higher than it worths in deed, whether its extraordinary IC or not, its still audio we are dealing with...
metal said:
That will give you a high-pass filter at 23hz, too high.
Using 680 ohm resistors the Ci caps should be at least 22uF.
And then I would use even bigger for the Cin caps.
Those those are optional, they will only remove DC from the source component(s), not the amp.
Avoid the same corner frequency if you must use them.
Something like 47uF would be fine.
That's what you pay for using low value resistors on a chip that has pactically a virtual ground on both inputs.
PS: this imprementation can't be used with a direct volume pot, it needs an active pre/buffer stage.
Hey carlosfm
I was editing/calculating when you posted your reply, re-read my reply now...
Also lowering the input impedance that much, will bring the penalty of impedance mismatch between signal sourcses and the amplifier.
BTW, I was wondering if there is a problem using electrolytic capacitors for the input and feedback networks...If not, then all thingies we are talking about can be easily solved.
I was editing/calculating when you posted your reply, re-read my reply now...
Also lowering the input impedance that much, will bring the penalty of impedance mismatch between signal sourcses and the amplifier.
BTW, I was wondering if there is a problem using electrolytic capacitors for the input and feedback networks...If not, then all thingies we are talking about can be easily solved.
Metal did you miss my previous posts where I did the calculations?
http://www.diyaudio.com/forums/showthread.php?postid=757909#post757909
I wouild never suggest 680R with 10uf...
I proposed 680R Rin, Ri with 21K Rf,Rs with 33uf bipolar Nichicon ES type (muse) caps bypassed with 1uf film caps in the Ci and Cin positions. This gives actually a bit better corner frequency than the datasheet circuit and will be less noisy, and all of the info I got today this morning confirms to me that it is a good choice.
Anyhow I shall know by tomorrow for sure as I have all my parts now. PCBs done in about an hour.
Certainly there are other good choices, but I am quite that I have done solid legwork in choosing what I have. After all I went to those who should know the part best
http://www.diyaudio.com/forums/showthread.php?postid=757909#post757909
I wouild never suggest 680R with 10uf...
I proposed 680R Rin, Ri with 21K Rf,Rs with 33uf bipolar Nichicon ES type (muse) caps bypassed with 1uf film caps in the Ci and Cin positions. This gives actually a bit better corner frequency than the datasheet circuit and will be less noisy, and all of the info I got today this morning confirms to me that it is a good choice.
Anyhow I shall know by tomorrow for sure as I have all my parts now. PCBs done in about an hour.
Certainly there are other good choices, but I am quite that I have done solid legwork in choosing what I have. After all I went to those who should know the part best
Russ White said:
One hour? I wish! I have been working on for 4 days now.
Congratulations...
Russ White said:
Yes national will even call a guy like you should you email them and ask them to.
Sure they will call me, but I don't need the extra samples any way
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