diode help please!

[amp_surgeon]

so i just finished soldering it up and its not working . sounds like a transistor round the wrong way. but i socketed them so i could switch round , and still no joy. i wounder if the trans i substituted bc548,from the original 2sc828. or the fet vn10km from the orignial 2sk30a. when i take the fet out of the socket then put it back in , it sounds like it works for a moment. any idea? anyone. cheers

 

 

From the datasheets I'm looking at, the BC548 has a pinout of emitter/base/collector from left to right when facing the flat side of the package. The 2SC828 is emitter/collector/base. This may be one problem. Aside from that, and the fact that the BC548 has a higher max hFE, they look reasonably compatible.

 

The VN10KM does NOT look like a suitable substitute for the 2SK30A. The VN10KM is a MOSFET designed for switching applications. The 2SK30A is a FET designed for low-noise preamplifier applications. MOSFET's and FET's are not the same type of device.

[jonjohn]

 

The VN10KM does NOT look like a suitable substitute for the 2SK30A. The VN10KM is a MOSFET designed for switching applications. The 2SK30A is a FET designed for low-noise preamplifier applications. MOSFET's and FET's are not the same type of device.

 

thanks for that

i thought it might have some thing to do with the fet. only because of when i pull it in and out it worked for a moment.

the transistors didn't work at all one way. do you have any idea of a good fet substitute?

what about a stp6ne06? i dont have a credit card so i am trying to get every thing herehttp://www.jaycar.co.nz/

[jonjohn]

this is there fet pages http://www.jaycar.co.nz/productResults.asp?FORM=KEYWORD

*edit*well that didn't work. but if you type "fets" in keyword search, it shows up

[amp_surgeon]

thanks for that i thought it might have some thing to do with the fet. only because of when i pull it in and out it worked for a moment. the transistors didn't work at all one way. do you have any idea of a good fet substitute? what about a stp6ne06? i dont have a credit card so i am trying to get every thing here http://www.jaycar.co.nz/

 

 

I didn't see the STP6NE06 on that site. I saw the STP60NE06, which is a power MOSFET in a TO-220 package. Definitely not what you need. In fact, all of the FET's on that site are MOSFET's, with the exception of the 2N5484, which is an RF amplifier.

 

When I need a suitable substitute for a semiconductor which isn't being made anymore I usually use NTE components. They specialize in making replacement parts, so they can cross reference just about any discrete semiconductor, even if it's no longer made. Their cross reference for the 2SK30A is the NTE459. You could also use the NTE458, but you have to rotate it 180 degrees to get the proper pin configuration. See if you can find a supplier on your side of the world that carries them.

[jonjohn]

thanks for all your help. it is very appreciated .

i will see what i can dig out.

[jonjohn]

ok. been searching a bit but don't really know what i am looking for in the spec sheets. but would this do?

http://www.fairchildsemi.com/ds/2N/2N5459.pdf

 

just unscrewed my wau wau fuzz and had a look, the one in my pedal is a k30a here is the data sheethttp://www.alldatasheet.com/view.jsp?Searchword=K30A

[amp_surgeon]

ok. been searching a bit but don't really know what i am looking for in the spec sheets. but would this do? http://www.fairchildsemi.com/ds/2N/2N5459.pdf just unscrewed my wau wau fuzz and had a look, the one in my pedal is a k30a here is the data sheet http://www.alldatasheet.com/view.jsp?Searchword=K30A

 

 

The first point to note is that the pinouts are not the same. The 2SK30A has the gate on the middle pin. The 2N5459 has the gate on right pin when viewing the flat side of the package.

 

The maximum gate voltage (relative to source or drain) on the 2N5459 is only half that of the 2SK30A; 25V compared to 50V. This shouldn't be a problem in this circuit since the highest voltage in the circuit is 9V.

 

The most important characteristic now is how much affect the gate voltage has on the current flow through the channel. On the 2SK30A datasheet this is plotted in a chart titled "ID - VDS (LOW VOLTAGE REGION)". On the 2N5459 datasheet there is chart titled "COMMON DRAIN SOURCE". We can get a rough idea of the operating range for a given gate voltage by looking at the channel current vs. voltage at the pinch-off point (the knee).

 

Without going into a detailed analysis, it looks like the change in the channel current for a given change in gate voltage is about 50% higher on the 2N5459. This may not be a problem in your application, since the FET stage is immedately followed by a level pot, so you can compensate for the additional gain. If I were building this circuit, and I had the 2N5459 available, I'd give it a shot.

[jonjohn]

ok got it going , but it doesn't have as much volume as it should i think , but thats ok , it has enough.

got one more question...

the section i have circled is the tone change part . what i was wondering is, would it be possible to have a pot instead of a switch.

so when the pot is hard one way it is like the switch one way and the pot the other way the same as the switch the other way,

i am finding the switch is good one way but when i switch it the tone is too mid scooped , i think being able to adjust it with a pot so i can get in between the extremes would be good.

is this a simple thing to do, or at all possible with out a lot more circuitry ?

*EDIT* i'm guessing a pot between the two caps would do it , but what value and which lugs? the outside lugs maybe?

[amp_surgeon]

With the switch closed the total parallel capacitance is 0.122uF. The values in the tone stack are then pretty close to the tone stack used in the "Tone 2" position on the FY-6. The mid scoop is pretty extreme.

Ok, anyone else feel free to correct my theory and/or math here...

The tone stack forms a sort of RC notch filter. The 22K resistor and the 0.022uF capacitor form the low side of the filter, and the 0.033uF capacitor and the 10K resistor form the high side. The formula for determining the cutoff frequency of each half is 1 / (2 * pi * R * C). The cutoff frequency for the low side is 328 Hz, and the cutoff frequency for the high side is 482 Hz. Not much of a notch there.

Now, when you flip the switch the two capacitors in parallel add, forming an effective capacitance of 0.122uF. The low side cutoff is now about 60 Hz. That's a pretty big chunk of the mids. To get the cutoff back up to 328 Hz while leaving the 0.122uF capacitor in there you'd need to reduce the resistance to a little under 4K.

You should be able to get a reasonably decent tone control by replacing the 22K resistor with a combination 3.9K resistor in series with a 25K pot, and then jumper across the switch connection so that both capacitors are always connected. Try clipping the pot and resistor in before soldering it up, just in case I'm way off base here.