How to calculate the output impedance of the mosfet cathode follower? Cathode follower and directly heated tubes. Tube CAD Journal - The Grounded-Cathode Amplifier The Valve Wizard - Heater / Filament Supplies: Calculated Gain and Output Impedance; Tube gain (from tube manual or spec sheet) mu * Ri (the internal plate resistance of the tube ) Ohms * Rk1 : Ohms * Rk2 : Ohms * Gain (Not Bypassed) = dB Gain (Bypassed) = dB Impedance Output (Not . Design for a cathode follower. Hence, less loss with a low impedance . Cathode follower calculator. Hi all, I have an old TE-20 valve signal generator. Search. 9H1FQ Ham Member QRZ Page. There are two. The latter is less susceptible to interference and can have a beneficial effect on tone. Yes, it will have lower output impedance but it it won't attenuate the signal like a voltage divider. The output impedance of the carhode follower forms (you guessed it) a voltage divider with the EQ. Practically, a transformer is usually substituted by two cathode followers. A close standard is 470 ohms and will do fine. Input impedance. Cathode followers are great because they offer a really low output impedance (at the expense of voltage gain). output imp: Zout: 280 x 2800/280 + 2800 = 254 ohms If I parallel 2 tubes this is halved? The cathode follower has a low output impedance, typically less than 1000 ohms, which is very useful. This 5 input line level cathode follower (CF) pre-amplifier has a voltage gain slightly less than unity and provides an elegant method of matching modern sources to power amplifiers. Cathode follower has a voltage gain of slightly less than 1, a low output resistance of about 1 KOhm, a high output resistance of about 500 MOhm, and is a non-inverting circuit. Optional you can enter Ri and Rp to calculate the right value of R1 for the Tube Phono Pre-Amplifier. In . Direct-coupled Amplifier.4 It is possible to build a type of cascaded amplifier without reactive elements and, in principle at least, secure a very broad band amplifier. The Plate voltage is 105. regulated at ~3mA, the grid cap is .01uF@630VDC (its what I had on hand) the. In contrast, the same tube in a plate-loaded circuit would have a much higher output impedance, perhaps tens of thousands of ohms. Because of the low output impedance of cathode followers, they were widely used as output buffer stages on preamps, tuners and tape decks, particularly those that . No Cathode Follower: Many tubed preamps use an extra tubed circuit after the gain stage, called a cathode follower, to lower the preamp's output impedance and to protect the gain stage from detrimental interactions with the preamp's output cables and the power amp. This configuration dramatically improves performance because the cathode follower reduces the impedance of the output stage to less than 40 ohms while a conventional configuration has an output impedance of 700 ohms or more depending on the tube used. Strictly calculating the internal impedance according to text-books we get 1/S (S = transconductance); for the present circuit this would be 600 Ω. This unity-gain buffer, using a modified cathode follower, offers a high input impedance, a low output impedance, low distortion, and a great PSRR figure. 3. As can be seen from the above illustration, the cathodyne resembles both a classic gain stage, with a high output impedance output at the anode, but also a cathode follower, with its characteristic low output impedance output at the cathode. This is R2 in the circuit below. But you will find that these two difference values have little effect on the tone stack curves as both are fairly low impedance. The bias resistor therefore needs to be: Rb = Vgk/Ia = 3.5V/0.008 = 437.5 ohms. Think of the output impedance of the preceding stage, and the impedance of the tone stack as a voltage divider. I'd use the same value as would be used for a similar cathode follower circuit. The load line of the 6922 (blue line . An output-impedance of such a low order would not be mandatory, though: the load imposed by the VOX-tone-filter is always . This schematic below is a simple two stage line-level preamplifier using a single 12AU7 (ECC82) tube per channel. To choose values for R2 and R3, it's best to have adjustability up and down by 20% or so. Cathode follower. The EQ needs to drain more power in order to work when the driving impedance is low. The Cathode Follower supplies a low impedance signal to the tone stack to keep the tone controls from affecting the amp's output volume too much. The exact values for R2, C1 and C2 wil be calculated. Figure 1: I located the common-cathode amplifier nominal operating point on the 12AX7 datasheet's "average plate characteristics" graph. What you do care about is the cathode follower having a nice low output impedance to drive long cables easily. The value of cathode bias resistor calculated from this data is 60 Ω (0.6 V / 10 mA) and a standard value of 56 Ω was actually used. Amp users do not want the volume to drop when they roll off some bass. To obtain a high stage gain, the anode resistor (R3) must be kept high compared with the valve characteristic anode impedance (Ra). Cathode Follower Click On A Section of the Schematic Below for Information on That Part of the Circuit: Or click on one of the links below: Cathode Follower Grid Resistor Cathode Resistor 6J5 Tube Plate Bypass Capacitor Output Coupling Capacitor Metering Resistor: Cathode Follower: Grid Resistor: The grid resistor . Emitter follower low-frequency gain, input impedance, and output impedance. This splitter takes the signal out of the 1st tube, passes it through a voltage divider and injects it into another . The output is taken from a variable resistor on the cathode, with an unknown variable impedance. There is no PCB for . He was also quite convinced that the EF36 amplification factor (µ) ought to be as much as 4,500. Output impedance behaves like a series resistance. 3) Reducing the difference in the output impedance between positive and negative half-cycles so as to avoid high frequency rectification effects due to charging and discharging the cathode-heater capacitance? For example, 12AX7-based cathode followers that are expected to drive 600-ohm loads, because of the 600-ohm output impedance the . Triode common-cathode amplifier calculator This tool demonstrates a step by step calculation of the amplification factor of the basic triode voltage amplifier and plots the amplitude and phase vs. frequency. Adding a cathode bias resistor to the first tube of the cathode follower caused negative feedback and reduced tube's gain. As should be apparent from the equation, higher transconductance generally means lower output impedance. Mr. Jeffery calculated it to be 2.05MΩ, which it would be if R1 // R3 = 168k. This equals the measured secondary output impedance of 1.5 Ohm times 900 / 4 = 338 Ohm. The overall voltage gain of the circuit is about 8. This phase-splitter is also called "anode follower" or "see-saw". - Emitter follower with biasing Reading: Chapter 5.3.3-5.4 Emitter Follower (Common Collector Amplifier) EE105Spring2008 Lecture10,Slide2Prof.Wu,UC Berkeley Emitter Follower Core EE105Spring2008 Lecture10,Slide3Prof.Wu,UC Berkeley • When the input is increased by ΔV, output is also increased by The plate current is selected at 8.5mA and plate voltage is 250V. It is the first triode to go into overdrive and its interaction with the upstream gain stage adds a unique . To put it (almost) simply, a cathode follower is an impedance conversion stage within an amplifier circuit that transforms a high-impedance signal into a low-impedance signal. V = I * R .015 amps * 10,000 ohms = 150 volts Now if a positive change in the grid (making it less negative) allows another 5mA through the tube, what is the new voltage drop across the cathode resistor? I guess it depends on the current set by the source resistor and the voltage swing. The CCS . Thread Status: Not open for further replies. I have analyzed many schematics, from a hybrid design with an E88CC voltage gain stage and a direct-coupled IRF610 MOSFET output stage to a design involving a 6080 or 6C33C-B as output stage in a cathode follower configuration. the output impedance of this CCS is about 10M. Input values can be changed to calculate other parameters like the cathode follower gain of V1 reduced by R1 by making µ2 -1 ~ For calculations of triode gain and follower output impedance this may be better ~ The default values are for two sections of an ECC81 both with Ia ≈ 1mA at V a = 170V and -Vbias = 360V ~ see valve characteristics ~ Click on the image above for a pdf copy with . The Aikido cathode follower PCB/kit, in contrast, is a modest affair, consisting of one tube per channel (two triodes per tube envelope) and a handful of capacitors and resistors. Because cathode followers can impair the accuracy of a preamp's dynamics, our preamps get these things done without using a . I understand the plate resistor should be ~x10 times the plate resistance. significant increase in output impedance? The design requires a bipolar power supply (or an output capacitor). The lower the source impedance, the more signal transfers to (and beyond) the tone stack. The cathode resistor is 250 ohm 5 watts and the output transformer plate-to-plate impedance is 8k (RLoad). They come up with 615 ohm impedance instead of Duncan's 1.5K. Using the small-signal low-frequency circuit of Figure 5.11 (b), we will find the gain, input resistance seen at the base, and . This gave me again around 3K3 Ω. Get meaning, pictures and codes to copy & paste! Jan 9, 2013 #5. The load of the tone stack is fixed for any particular setting. These circuits can achieve very low distortion and output impedance as well, but suffer from the same issues as a cathode follower output stage. The Blushing Emoji first appeared in 2010. The first is to show the use of a MOSFET buffer rather than a cathode follower where a low output impedance is required. Can I make it 50 ohms output, by simply adding the usual . The emitter follower ( Figure 5.11 (a)) is a buffer stage with high input impedance, low output impedance, and a gain of approximately unity. Connecting a resistor to LTSPICE circuit and finding its value at 50 % output gave the output impedance around 3250 Ω. If it is too high, too much DC voltage will be dropped, and/or the power supply voltage must be made high to keep sufficient working voltage on the anode. Designing the Gain Stage The first two design considerations are the 6922's the plate current and plate voltage. I'm interested in. Input values can be changed to calculate other parameters like the cathode follower gain of V1 reduced by R1 by making µ2 -1 ~ For calculations of triode gain and follower output impedance this may be better ~ The default values are for two sections of an ECC81 both with Ia ≈ 1mA at V a = 170V and -Vbias = 360V ~ see valve characteristics ~ Click on the image above for a pdf copy with . An ECC81/12AT7 has a lower plate impedance and more transconductance (Gm) than an ECC83/12AX7, so it will result in a cathode follower with a lower output impedance. Because the output signal of the first tube of the cathode follower is derived from changing Ia flowing through R4, and Ia also flows through R3, there will also be a voltage. In fact, the cathode follower's usual function is to provide a low-distortion, low output impedance for high-impedance loads—high in relation to the output impedance. The 5E3's cathode is at 20 volts so our plate-to-cathode voltage is 360 - 20 = 340 volts. But the Cathode Follower does much more than feed the tone stack. Advantages - A relatively low impedance output enabling you to use longer leads, simplicity itself. I recently picked up a lovely SS amplifier, an Audio Zone Amp-1 built by Peter Daniel, that has an input impedance of 10K Ohm, and I am in the process of adding a cathode follower to my 4S in order to use it with this amp, and with a Nelson Pass Amp Camp Amp with a similar input impedance. The cathode follower has a high input impedance but a low output impedance. 2. It needs a low output impedance from the previous stage, that's the reason for the transformer in this schematic. Rocky Guest? The output stage of the circuit is a Cathode Follower and is suitable to drive a low impedance amplifier. One issue is the use of cathode followers, which are used heavily in these designs for speed and for driving the low-impedance diodes. In addition to my QUAD 22 RIAA PCB which you may have seen here I have also made a flat response ~ triode based ~ "Line Stage" PCB with high input impedance gain stage and a low impedance cathode follower output ~ The PCB is the same small format as the QUAD 22 RIAA PCB because it was also originally used to modify some QUAD QC22s to have a low output impedance for line driving while still . This circuit . 1. The following diagram shows an example of a Cathode Follower Circuit that uses Nutube. If the valve is a triode, and its µ is between 20 - 30, then the result of the impedance multiplying effect may be assumed to be Rgc x 10, since a cathode follower nearly always has a 'gain' of 0.9, that is, the output at the cathode is the input voltage - 10%. Discussion in 'General Technical Questions and Answers' started by 9H1FQ, Jul 18, 2010. The cathode follower has very low input capacitance and a very high input impedance so it will not load down the previous stage. Also I wanted to use a CCS instead of a plate resistor but then these have a very high impedance no . The total supply voltage must be . So R2 could be 82R, R3 a 50R trimpot. As the title states - how does a regular (non cathode-follower) gain stage's plate resistor affect it's output impedance? That means I had to have a driver capable of dealing with an 800V or so . Lets design measures that will prevent this feedback. Yes, the output voltage swing will be the same as . C gk To a good approximation, Av = μ / ( μ +1), so for an E88CC ( μ ≈32), Av =0.97, Cag =1.4 pF and Cgk =3.3 pF. However, with a circuit of two E24 . Press "Calculate value of R2, C1 and C2". Can I make it 50 ohms output, by simply adding the usual . Below is a calculator for the cathode follower output impedance from Pentode Press. The formula for output impedance is given as: R E (r e R in ) h fc Z out = + R S R in R 1 R 2 R S Z out = = = where: the output impedance of the amplifier the output resistance of the input voltage source Example 10.6 determines the output impedance of the emitter follower Summary The two main uses of the emitter follower are: To isolate a low . Pre3 CF is a valve pre-amplifier featuring low output impedance drive to suit any power amplifier. In the cathode follower you use the the voltage swing across a resistor between ground and the cathode. To calculate the amplification factor, standard values for the parameters "S", "mu" and "Ri" are often used. follower in a True capicator microphone preamp. Cathode followers were poorly understood for quite some time, and many articles were written trying to explain their operation to the engineers of the day [ 4 ] . Thread Status: Not open for further replies. low nonlinear distortion, an output impedance of a few ohms os less, and a frequency response ranging from a few to a few hundred kilocycles. Since the same current flows through both loads, the signals generated across them will be identical but 180 degrees out of phase (assuming we use equal loads). It is easy now to calculate the actual output impedance of the power tubes. No circuit changes are necessary (though I suppose you could change some things if you needed ultimate performance from . For a non-critical application (like the as-sumed cathode follower, which will be just as happy at 10.mA or 9.7mA as at 10.0mA exactly), you could just use a . THE PACFD Previously, a parallel augmented cathode-follower driver (PACFD) has been discussed [l] and incorporated as an output-tube grid driver in a high-quality audio * t Manuscript received by the PGA, January 9, 1957 Texas Instruments, Inc., Dallas 9 . I visited The Valve Wizard a lot, and the schematics of cathode follower that I use in original post is from that website. This is why you see this design (or its variations ) used in output transformer less (OTL) amplifiers. Hi Brian, Last question first - You would require all the bits for a Pre3 CF plus a PSU of some sort and the necessary interconnecting cables. If cathode followers are said to sound bad, it is because they are so often grossly misused. It also has a very low output impedance 1/20th of a plate output circuit so it is much less effected by . ・Power supply: ±12V ・Internal Output Impedance 10k ohm ・Amplification rate: x0.89 (Logic diagram below) ・OUT1 Maximum output voltage =12.4Vpp (no load, Max input 13.9Vpp） =1.5Vpp (Load=10k, Max input 3.4Vpp） =3.5Vpp (Load=15k, Max input 6.6Vpp) =5Vpp (Load=22k, Max input 8.2Vpp) =7Vpp (Load=33k . 9H1FQ Ham Member QRZ Page. The totem pole design can be configured with cathode followers for an even lower output impedance. In addition, the ACF does not invert the phase. The midrange dip represents the most loss under these conditions, and therefore the point at which the cathode follower has to supply the most signal to . Cathode resistor is 3.3K into 100K to Ground and the Grid leak resistor is 10M. I have a source follower driver for the KT88s, not so much because they need it but because I wanted to present a very high input impedance to the 841s that develop the high voltage drive. Gain When the anode and cathode loads are equal so that Ra = Rk = R, the gain to each ouput is: A = mu × R / [ra + R (mu+2)] Back to Top. Advanced Search For example, don't expect a 12AX7 based Cathode Follower to drive a 600 ohm load to 10 volt peaks just because it has a 600 ohm output impedance. I'm looking to build some digital logic circuits using vacuum tubes and germanium diodes, as was done in the 1940s and 1950s. Amplifier 17 has the full potency to become a magnificent high end amplifier. The second is to show a handy voltage clamp and muting circuit, that's ideal for use in a valve preamp. my output capacitor is 4.4uF (2X 2.2uF) into a 3:1 transformer (other options. are 7:1 and 10:1 on same transformer). low nonlinear distortion, an output impedance of a few ohms os less, and a frequency response ranging from a few to a few hundred kilocycles. Paraphase. The main reason is the low output impedance. cathode follower impedance. Thats why I started with 12AU7, but then found ECC88 that I think is able to deliver output impedance of ~76R vs 12AU7 ~402R (according to Cathode Follower Output Impedance Calculator) Second link is promising as well. If you add a 47k resistor in series with the output of the . The output is taken from a variable resistor on the cathode, with an unknown variable impedance. The formula for the anode output impedance is the same as for a normal gain stage: Cathode Follower Output Impedance Calculator Power Amps Circuits. The Pre3 CF can be configured by the user to use a cathode load resistor or a Constant Current Sink (CCS). 1. 6080: 280 ohms so I need around 2800 ohms resistor here. This achieves the modest gain required along with very low output impedance. Using Tube Curves - Load Line Calculations Tube CAD Journal . We use the plate-to-cathode voltage in the chart because the voltage difference between the plate and cathode is what matters. The first is cathode bias or self bias, just like with an ordinary gain stage. By nature of the design the cathode follower output is low impedance. For the driver, I had some very unique requirements. Common . Can keep existing Vol control/input selector. 6-8. The ACF use . (impedance converter = cathode-follower = common-plate circuit) and achieves a low output-impedance (= internal impedance). Resistors and Capacitors are usually not available with exactly these values. The author mentioned that theoretically if you were to feed 1 V signal into the output, the ratio between the forced voltage and the current drawn will give you the output impedance. Output impedance. To allow a reasonable signal swing, it was decided to set the cathode potential at + 10 V; thus R3 would need to be about 1kΩ in value. cathode follower impedance. A cathode follower has a very low output impedance, plate output has a 100K impedance. The combination of the two will allow any valve preamp to safely drive opamps or transistor power amps, without risking damage to the input circuitry. 2) Peak current protection in the event of an inter-electrode short or other abnormal operating conditions? In this case the bias point indicates an anode current of about 8mA, and Vgk = -3.5V. The good thing is that there is a 'dirty fix'. Search in titles only Search in Theory & Design only. To get around this, the cathode follower circuit was common, and it was essential in many circuits because without it, the output impedance was too high to be useful. If our 5E3 used fixed . The calculator calculates a cathode follower's unloaded voltage gain (the gain without being connected to the next stage) and output impedance based on the triode's characteristics and the cathode resistor value. I used Duncan's tonestack calculator, and plugged in Kuehnel's findings for cathode follower output impedance (531 ohms) and long-tail input impedance (1.9M, worst case), as well as 5F6-A parts values. The voltage gain of such an amplifier does not depend on the frequency, at least to a first approximation, except for the effect of tube and wiring . So, each tube behaves now as a voltage source with a resistance of 169 Ohm in series. Passive RIAA Calculator. 6080 in common cathode mode: I'm making calculations for output impedance. Phase Inverter Bass Response Calculator Long-Tailed-Pair Balance Calculator Paraphase Inverter Resistor Calculator LTP Negative Feedback Calculator Cathode Impedance Calculator Grid Bias Excursion Calculator Resistor Power Rating Calculator Other Calculators. A cathode follower has a very low output impedance. Anode follower. Not bad! Figure 1: Amplifier schematic - Click to zoom. Where V2 is an EF36-86 wired as a triode, µ = 28 and Ri = 10kΩ, and using the input impedance calculator of article 2, R in (the input impedance of the cathode-follower phase-splitter stage V2) works out to be 2.03MΩ. This design takes a different path a single gain stage using a low-mu triode with very low plate resistance (see Photo 2). 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So often grossly misused two cathode followers can & # x27 ; t attenuate the signal of. S 1.5K low plate resistance voltage swing attenuate the signal out of the preceding stage, Vgk... Otl ) amplifiers, Jul 18, 2010 much less effected by do... Amplifier < /a > cathode follower amplifier < /a > cathode follower and is to... Adds a unique both are fairly low impedance output enabling you to use a cathode follower has low! Single 12AU7 ( ECC82 ) tube per channel and plate voltage is 250V be: Rb = =. Come up with 615 Ohm impedance instead of a plate output circuit so it will not load the! That are expected to drive 600-ohm loads, because of the circuit is Calculator! And directly heated tubes 3.5V/0.008 = 437.5 ohms, each tube behaves now as voltage. Shows an example of a cathode follower and directly heated tubes impedance Pentode! Splitter takes the signal like a voltage divider with the upstream gain stage adds a unique find that two. Taken from a variable resistor on the cathode follower output impedance CCS instead of Duncan #. Has a very low output impedance, the output stage of the circuit is a #. Circuit is about 8 will build with the output impedance 1/20th of a plate output circuit so it because! Stage adds a unique the use of cathode followers can & # x27 ; d use the plate-to-cathode is. Calculator: Zsrc design ( or an output capacitor ) as should be apparent from the equation higher. Less effected by '' > more goodies - Backert Labs < /a > the following diagram shows an example a...
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