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Discussion in ' DIY ' started by peefAug 14, Super Best Audio Friends.

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Read these "rules" AND introduce yourself before your first post. A healthy approach to understanding measurements Being true to what the artists intended. Earlier last month, a friend decided she was getting a turntable and asked me for advice. Looking at phono stages, I drew a blank. Some general requirements 1. There should be no hum, hiss, or buzz.

Kind of ruins the experience, no? This means the circuit should have excellent PSRR, or an excellent power supply, or ideally both. This also means no ground loops and no EMI. It should also sound like a single ended phono stage. That means more second order harmonic distortion than third, more third than fourth, and so on. RIAA equalization should not rely on feedback. Feedback can be a very lovely thing, but not so much in RIAA equalization.

Notably, feedback RIAA works by varying the feedback ratio according to frequency, such that you have a higher ratio at high frequencies and a lower one at low frequencies. An unfortunate consequence is that your input and output impedances are also frequency dependent. So is your distortion. This seems like a bad tradeoff.

The user should have full control over cart loading, and be able to plug into any reasonable load. Alternatively, this means that input impedance should be very high, and output impedance should be low. We can then tailor the input impedance to our needs with loading resistors and capacitors. But, we should have the freedom to load the cart with no more capacitance than what the cables provide.

Even though Lundahls are lovely. They might look like this: The lower device is a transconductance amplifier. The current is then converted back to a voltage using a resistor, and we can sample the output voltage across it on the -Out and Ref Out nodes. The top device is a transimpedance amplifier.NXP has restructured, spinning off standard products into a new company called Nexperia.

The BF, beloved of physics projects, fiber optic bootstrap circuits and seemingly a particular favorite of WInfield Hill "Art of Electronics" is not going along for the ride. So after panic buying the next logical step is to look back and assess the situation.

In the people on diyaudio became concerned that the noise knee had increased when stated production moved to china. Some information came from the company that the chips were being fabbed in the same place and only the encapsulation point had changed. This seems unresolved. It's quite a difficult test to do and the small number tested may not be representative.

Could dielectric noise be a contributing factor? That would potentially be affected by a change in encapsulation. For my purposes the BF was a little high in input capacitance and I spent some time chasing Sony 2SK's which I found in all Idss grades except -1 and 2SK which so far I have failed to find in any grade.

These have 6 to 7 pf input capacitance versus the BF's 10pf. In the same way the BF bulk application was car radio preamps the 2SK was originally produced for the head amplifier circuit of the Betamax video recorder and found it's way into shortwave sets and the Amptek X-ray spectroscopy literature where is performs the best of all JFETs tested except for a narrow low capacitance range where it's just beaten by the Interfet "NJ14".

Create an account to leave a comment. Already have an account? Log In. I have recently had success using 2SK in place of BF Specs aren't quite as good as BF but it is made for the same application and works well enough in my application low-noise high-impedance audio frequency sensor amplifier.

I also bought some BF's on eBay that have the correct markings but I haven't tested them yet. Are you sure? Yes, delete it Cancel. About Us Contact Hackaday.

BF862 is now End Of Life. Well that sucks.

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Well that sucks. A project log for Chymes Cheap, nondestructive atomic analysis in real time. The important thing of course is not to panic.

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Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up. My schematics and PCB layout are as follows:.

BF862 replacement

My problem is that the measured noise is too high. However, after producing the PCB several times with different layouts and measuring the noise floor at the amplifier output the result was always the same: Approx. Referred to the input that means approx. But the noise floor always kept exactly the same. The amplifier was powered via two lead acid batteries. Does anybody have an idea what the problem could be, i.

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Is it possible that the simulation is wrong? Or could it be that one of my components is not behaving like expected? I also checked all the DC operating points, but they are correct, i. What would you try next? In your case current noise will dominant. Second, you are running the BF in ohmic region, which will degenerate it's noise performance. BF was designed to run near Idss. Third, it looks like that the stability margin of your circuit was not enough.

Which means it has more noise gain than expected. And, remember to make guard rings around to protect the input traces.Welcome, Guest. Please login or register. Did you miss your activation email? This topic This board Entire forum Google Bing. Print Search. Author Topic: Low noise amplifier.

Let's Build a Phono Stage

Read times. Kleinstein Super Contributor Posts: Country:. There a few larger ones larger trans-conductance and low noisebut these are usually really expensive e. The BF is about the best one can get in low noise compared to input capacitance and it is still relatively cheap. So the noise figure might be good only for a very small frequency range.

Marco Super Contributor Posts: Country:. A daring few have dared harness them for "DC" use Phil Hobbs is particularly fond of using bootstrapped combinations for wideband laser diode and high impedance probe amps. Bringing a project to life? Send me a message! Quote from: T3sl4co1l on December 27,pm. Hi Glen from a fellow aussie I have been toying with a low noise front end design for audio band use for several months now, with no success in using an integrated solution.

The big challenge I am trying to overcome is the input voltage swing. Additionally, I am looking to minimise quiescent current draw this will be battery operated. The input is from a single ended source, with impedances that range from tens of ohms up to around 7k. This is due to the varying specs of the microphone preamp output signal, for different model mics.Resources saved on this page: MySQL Show 50 post s from this thread on one page.

We do. To a nauseating amount sometimes, well before UV touches photoresist. With the exception of chopper amplifiers, DC precision will always increase the cost of a part. But yes, people do still buy them. Muses01 looks awfully similar to OPA Would that give us a near optimum MM stage?

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The BF is spec'd at 0. So they may very well be equivalent at 1kHz. I think you could parallel a lot of BFs and still come out ahead. INF the to package must be a good part of the cost, we should ask Interfet if they can put it in a sot package for us. The jfet specialists. TI won't afford to put such a good jfet in their devices :- now why did Bews not used a jfet in there design?

Most of the high end japanese MM phono-amp designs I have looked at all used jfets. Has Doug Self ever used a jfet in the front end for MM phono-amp?

Using a jfet as the first stage of the NE is old technology. See the link page Page 5 of 7. Capt Grogg. So the die for such a device is going to be expensive, and when some systems engineer me takes this concept to a customer, they're probably going to ask why they just can't put a BF in front of a regular op amp?Layout was carefully adapted to ensure track separation due to HV in place.

Result is that the new gyrator board provides all protection needed on the lower device and simplifies the build process. Yesterday I started with the build of a new 01a preamp Gen2.


I made some component changes during the build process thanks to Andy Evans who reminded me of the Russian FT-2 teflon capacitors. I had a pair left of nF FT-3 caps in stock! The bias point is changed slightly up to 5V so the anode voltage is increased to V to get the 3mA of anode current. I preferred the sound and higher bandwidth as well as lower output impedance.

The top anodised plate is 4mm thick and anodised. How does it sound?

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We did some listening tests recently with Andy Evans comparing filament resistors and these ones were real winners for both of us. It always pay pack at some point.


He found a MOSFET which could do high drain currents, it has high transconductance and most importantly the parasitic capacitances were low even close to the BF Hooray, I thought. We may have a great solution here to use the gyrator load for currents above 25mA and with similar performance to the great BF There are some other depletion MOSFETs that can do high currents, however they all have relatively high capacitances and low transconductances when VDS is low, like in the cascoded gyrator circuit.

The 3B7 triode has a pair of DHT triodes on the same bottle. It has a high mu for a DHT about 20 but with that it comes the higher anode resistance. This was a drawback when implementing a choke or transformer loaded stage due to the high anode resistance there is no free lunch am afraid.

Although I tried the 3B7 in the past, I proceeded to get it out from my valve stash and trace it again. Here is a nice set of a Sylvania military NOS one:. A fantastic build of the 01a preamp using the gyrator PCB from Cheah:.A novel single-transistor transimpedance preamplifier has been introduced for improving performance in Fourier-transform ion cyclotron resonance FT-ICR mass spectrometry. A low noise junction field-effect transistor JFETBF, is used as the main amplification stage of this trans-impedance preamplifier, and a T-shaped feedback network is introduced as both the feedback and the gate biasing solutions.

Fourier-transform mass spectrometry FTMS is an essential analytical instrument for detailed analysis of chemical compounds. In terms of sensitivity, the front-end electronics, especially the preamplifier, in a FT-ICR system plays a crucial role. New preamplifier designs may allow single charge detection, which would maximize the potential dynamic range of FTMS instruments.

Similar to the photodiodes in optical communication systems, the signal analyzer of a FT-ICR mass spectrometer, an ICR cell, 12 is a capacitive device. Electrostatically induced image currents are expected at the input of the preamplifier. The parasitic capacitance from the cell can vary from around 10 pF to over pF, 13 depending on the cell dimensions, feedthroughs, and cabling.

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A high capacitance at the preamplifier input limits the bandwidth, causing potential signal intensity loss.

As a result, a transimpedance amplifier, with its ability of effective input capacitance reduction 614 over an existing voltage amplifier VA design, 8 can potentially provide an ideal preamplifier solution for many mass spectrometry systems, including FT-ICR MS. A basic transimpedance amplifier is constructed out of an operational amplifier Op Amp with a feedback resistor, as shown in Fig.

Consequently, the voltage at output becomes.

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An ideal Op Amp has a few particular characteristics, including infinite input impedance and infinite open-loop gain.

In reality, the open-loop gain, Ais a finite large value of typically larger than 10 4. When analyzing the Op Amp circuit, it is common to assume that the input impedance is large so that the current flowing into either the inverting or non-inverting input is negligible. Transimpedance amplifiers with different feedback arrangements I in indicates an ideal current signal source. The single feedback resistor can be replaced by a three-resistor T-shaped feedback network, 1516 consisting of two resistors connected in series, and a third resistor coupled between the junction node of the two series resistors and a reference potential ground in this caseas shown in Fig.

As a result, by replacing the single feedback resistor with the T feedback network, the resistance of the feedback system can be reduced without sacrificing the overall transimpedance in a negative-feedback transimpedance amplifier system.

Thus, with roughly the same theoretical transimpedance, the resistance values of the feedback resistors can be dropped by about fold. Since the bandwidth of a transimpedance amplifier is a function of the feedback impedance, reducing the feedback resistance increases the bandwidth. Despite different technologies being introduced for amplifier bandwidth extension, 17181920 the T feedback network is undoubtedly another simple approach to preserve the bandwidth without sacrificing the transimpedance.

Note that here, the resistors R 1R 2and R 3 can be replaced by complex impedances such as Z 1Z 2and Z 3 in order to obtain transimpedance characteristics which vary with frequency according to particular requirements in a given application.

Reducing the noise from a preamplifier can be a major difficulty for a circuit designer. Typically, noise consists of all of the voltages and currents which accompany a signal of interest, and includes a Johnson-Nyquist noise thermal noiseb the noise from active components or amplifiers such as shot noise and flicker noisec environmental noise, and d the noise of natural quantizing fluctuation.

Caused by the thermal agitation of electrons inside conductors, thermal noise can be described as the noise power P n. To describe the thermal noise output from a resistor, the equivalent circuit of a noisy resistor can be modeled by a noiseless resistor Reither coupling in series with a noise voltage source e nor shunting a noise current source i nwhere.

Note that here the e n and i n are the root mean square voltage and current, respectively. Shot noise and flicker noise are considered electronic noise sources and are commonly seen in an active device. The noise model of an amplifier suggested by Letzter and Webster, 21 including a noiseless amplifier with gain Aan equivalent amplifier noise current generator i naan equivalent amplifier noise voltage generator e naand a noiseless source the input signal source resistor R with its noise voltage generator e n.

It can be known from Eq. At a given temperature such as at room temperatureto change the resistance value in an amplifier system can be an approach to alter the thermal noise voltage or current. To characterize such a change in an amplifier system illustrated by Fig.

On the other hand, to limit the noise generated by the active components can be another approach to improve the signal-to-noise performance of a preamplifier. It can be done by reducing the number of active components being used.