Please login or register. They are either expensive or kind of difficult to find. It's the last part of my order that I need and the only one that the store I'm using is out of.
Thank you! Pin out is different, and it depends on the application but recently I used a j in place of an mpf beacis has a great Pinout guide for most trannies made up until a few years ago. It's a good starting place. Pedal building is like the opposite of sex. All the fun stuff happens before you get in the box. RobA Electron Doctor Posts: Quote from: mrbridgewater on April 02,PM. Affiliations: Music Unfolding musicunfolding. It depends on what you're building. If you're using ppf to wav converter in a buffer, there are better FETs.
If you're building it in a boost, there MAY be better choices. If you're building it in an overdrive, there isn't really a good sub for the J Their gain is much higher than almost every other FET, and their input headroom is also much lower. This means that when you're cascading them, they produce more gain AND distort easier, so you need fewer stages to achieve higher gain sounds.
The closest you can get on pure gain specs without finding something truly exotic is the 2SK, and they still only have just over half as much gain. Also, as has been noted in many threads in recent years, through-hole FETs are obsolete and consequently difficult to source. They're going to be expensive. But it's a 50c part You can also buy SMD Js and use an adapter board. Chromosphere posted about those recently. Or check out chromosphere's SMD j with adapter board option.
I just snagged 20 of em-His prices are good too! Clayford Electron Doctor Posts: Clay. I'll vouch Chromosphere all day every day. Great guy to deal with.Introduction I've been performing experiments with guitar preamps and on-board electronics since, oh, the Nixon adminstration or thereabouts. Sometime around I designed this preamp circuit, and have been using it mostly unchanged ever since.
In I posted a schematic of the preamp to one of the Usenet groups and the circuit became somewhat popular. The goals of the preamp are: Sounds great. Of course. Discrete because I don't like the sound of opamps, and FETs because the devices operate in a manner somewhat analogous to vacuum tubes.
Substituting the 2N5457
Runs off a 9v battery. In practice a decaying 9V battery, possibly as low as 8. Very high 3. Medium 6. There's no need for an especially low output impedance as we're only using the preamp to counter the effects of cable capactance and loading. You don't need much gain, and given the guitar signal level and the 9v supply voltage, there isn't room for much gain.
Low noise. Graceful overload. Overload happens; the circuit should clip gracefully and recover gracefully. The preamp can also be phantom powered and mounted in a phone plug.
It's a simple unassuming common source FET stage that looks and performs somewhat like the first 12AX7 stage in a Fender preamp. You can get a copy of the data sheet from the Siliconix web site. R1 determines the input impedance and, for the case of open inputs, capacitively coupled inputs or piezoelectric pickups, references the FET gate to ground. R1 can be almost any value, and in some cases, such as if the preamp is connected directly to an electromagnetic pickup, can be eliminated entirely.
I originally used 10 Mohm for this resistor, but more recently I've been using 3. R2 biases the FET at around 0. R3 is the FET drain load resistor. The value is chosen for roughly 6. The value of R3 also determines the output impedance.Back to Projects Page! Minimum R ds on or On State Resistance. The above value can be determined by reading specification sheets for the selected transistor.
In cases where it is not known, it is safe to assume it is zero. The other important characteristic is the absolute maximum drain current. Listed below are absolute maximum drain currents for some common N-channel transistors:. When designing a JFET circuit, it is highly recommended to prevent the absolute maximum current from being exceeded under any conditions.
In design calculations. We will allow no more than 5 ma of drain current under any circumstances. For resistor R3, the gate resistor, we will use 1 Meg for a very high impedance across the gate. The gate resistor is normally anywhere from 1 Meg to K. The higher values allow the JFET to amplify very weak signals but require measures to prevent oscillations. The lower values enhance stability but tend to decrease gain.
Sometimes the value of this resistor needs to be adjusted for impedance matching depending on the type of signal source involved. Because we will only allow 5 ma of current through the drain to source, we will calculate the total resistance for resistors R1 and R2. We will assume the Minimum R ds on to be zero. To prevent oscillations a 10 ohm resistor and a uf capacitor were added to isolate the circuit from the power supply.
Slightly larger or smaller capacitor values will also give acceptable results. The optional 4. The addition of this capacitor may introduce a small amount of unwanted white noise and should only be used when an absolutely quiet preamplifier is not required.
It is very suitable for extremely low level audio applications as in audio preamplifiers. The JFET is more expensive than conventional bipolar transistors but offers superior overall performance. Unlike bipolar transistors, current can flow through the drain and source in any direction equally.
Often the drain and source can be reversed in a circuit with almost no effect on circuit operation. Transconductance The ability of a JFET to amplify is described as trans-conductance and is merely the change in drain current divided by the change in gate voltage.
It is indicated as Mhos or Siemens and is typically 2. Because of the high input impedance, the gate is considered an open circuit and draws no power from the source. Although voltage gain appears low in a JFET, power gain is almost infinite.
A Discrete FET Guitar Preamp
Drain Characteristics Even though no voltage appears at the gate, a substantial amount of current will flow from the drain to the source. In fact, the JFET does not actually turn off until the gate goes several volts negative. This zero gate voltage current through the drain to the source is how the bias is set in the JFET.
Resistor R3, which is listed in the above diagram, merely sets the input impedance and insures zero volts appears across the gate with no signal. Resistor R3 does almost nothing for the actual biasing voltages of the circuit. When the gate voltage goes positive, drain current will increase until the minimum drain to source resistance is obtained and is indicated below: Minimum R ds on or On State Resistance The above value can be determined by reading specification sheets for the selected transistor.Please login or register.
Pages: [ 1 ] 2. Tuxedo3 Stompbox Star Posts: I've read some posts about this but wanted the opinions and experiences you all have had, what are good replacements for those 2 transistors? Luke Electron Doctor Posts: I've used his J SMDs boards and transistors a few times. They are a fantastic replacement. Sent from my iPhone using Tapatalk. Quote from: flanagan on September 16,PM. MPF can be an excellent replacement.
Not sure on the availability though.
Substituting the 2N5457
I bought my last batches of all of them when the EOL was announced. I own madbeanpedals duh. I am part owner of Function F X. Mouser carries 2ns in through-hole. Central Semi started making them. If you are willing to buy 10, they are 77 cents a piece.
Not necessarily cheap, but if you have a SMT and an adapter board, that adds up, too. Function f x Follow me on Instagram as pickdropper. BrianS Electron Doctor Posts: This sort of mimics what Pickdropper is saying. Smallbear has both transistors. I use the SMD equivalents of both. Soldering them is ok but it takes some getting used to and a little time chip on board and then the 3 leads. The chips are tiny.
Depending on how many you need I would really look at the price difference and if you could live paying the. If it cost you let's say. Of course I didn't factor in shipping costs l believe you can get each SMD on Arrow with free shipping. Anyway just my half cent on the subject.
From the last series of through-hole J's I bought, 9 out of 10 where out of specYou can still buy the 2N from Central Semiconductor, but they are very expensive — too expensive for Stompville to consider buying sufficient quantities to match them up into pairs and quads.
The question is, can we substitute the 2N without adjusting other component values? The answer varies from maybe through probably to absolutely, depending on the requirements of the circuit. Regarding absolute maximum ratings and thermal characteristics, the 2N is fairly modestly specified so the PF, J and J are as-good-as or better in all areas. From the Stompville matching archive, typical samples of 2N have an Idss between 2.
Corresponding Vgs off range is Stompville samples of 2N with Idss between 4 and 5 mA have a cutoff voltage a little under Stompville samples of PF with Idss between 4 and 5 mA have a cutoff voltage of about Although the Vgs off values for the J look comparable to the 2N and the Idss is specified as 2.
So, where does this leave us? Well, we could consider substituting a low-Idss PF for a 2N in any circuit design. We could possibly substitute a J or J for a 2N provided our circuit is immune to the Idss difference. You must be logged in to post a comment.
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Recent Posts. Teisco CheckMate 22 schem Hi, I want to make a few low wattage guitar amps. Live and learn. I just asked about buying such an FET at 3 different stores. At one they had tons of FETS, but said they didn't sell any of those three. At another store a helpful guy told me they don't sell those, but suggested one of three others that are the same.
I am wondering 1 if these ARE substitutes and 2 how one knows what can be substituted. Doing a web search has so far not given me much information. It seems like there are other choices for FETs around here, but I have no idea how they are different.
I have read the wikipedia entry on FETs but don't really get it.
Besides, the substitutes recommended by component stores are selected on totally other principles than "tone" and you should be familiar with the parameters a FET in some specific circuit needs to have. But that's another story. My main point is to say that in most cases the J is a very poor performer because it's selected "out of habit". For the given application buffer in low voltage circuitry you could randomly pick almost any FET and expect it to operate pretty well.
In most cases it will also surpass the performance of J Quote from: teemuk on April 10,PM. Master Posts: 87 Chip Points: Conguito Regular Posts: 13 Chip Points: 0.
The perfect substitutes for the J are: BFW13 and 2n But you have to pay attention to the position of the pins, they are not in the same position as in the J These are very good substitutes for J with almost identical performance. However, if you understood R. The J was a bad choice in the first place. Heck, pretty much anything.
Like R. Quote from: R. Quote from: xylix on April 11,PM. SMF 2.Skip Intro. Now, with Easy to Find Parts! Some time ago, J. He posted the circuit on the Web. Overnight, this circuit became very popular. And it's still a winner today.
The reasons why are easy to see. This amp is easy to build. The circuit works like a champ. And the JFET's tube-like warmth sounds great. Plus, the high-impedance input won't load your guitar.
At the other end, the medium output impedance combats high-frequency losses due to loading and long cables. And by the way, this FET preamp is great for microphones, too! Bad News The J is a very special device and an excellent choice.
Yet it's uncommon to hobbyists. But my site solves the mystery. Buy It Today. Use It Tonight. I've read the forums.