|
Post by JohnH on Feb 1, 2006 21:59:08 GMT -5
OK - back again. and it works as designed, with a significant clean boost. Not bad at all, although not enough on its own to get into overdrive.
One thing I noticed - my JFET is curved on one face to help identify the pins. Is yours? Getting it the wrong way round is easy, and causes excatly your syptoms.
John
|
|
|
Post by night0wl on Feb 1, 2006 22:05:23 GMT -5
yeah my JFET has a flat side and a curved side...
I have the flat side facing the 1M resistor (input side). I'll try swapping and see how it goes.
Thanks John
Cheers
|
|
|
Post by UnklMickey on Feb 1, 2006 22:07:16 GMT -5
OK - back again. and it works as designed, with a significant clean boost. Not bad at all, although not enough on its own to get into overdrive.... HEY, it's been 29 minutes since your last post. you only built and tested it? What?, no harmonic distortion numbers? no frequency response curves? what have you been doing all this time? LSHIASMP
|
|
|
Post by JohnH on Feb 1, 2006 22:10:12 GMT -5
Sorry but i have to eat sometime. Plus the dog needed a walk.
|
|
|
Post by JohnH on Feb 1, 2006 22:15:19 GMT -5
OK - heres the problem. The gate, which is connected to the 1M resistor is not in the middle. Looking from above as it would be mounted on the board, with the flat side to the left and curved to the right, the pins are, top to bottom:
Drain - connected to output and trim pot Source - connected to 1.5k resistor and 22mfd cap Gate - connected to 1M resistor
John
|
|
|
Post by UnklMickey on Feb 1, 2006 22:19:55 GMT -5
Sorry but i have to eat sometime. Plus the dog needed a walk. lol no, wait: rofl no, wait: lmao no, wait: lshiasmp no, wait: i smell something bad, and i didn't have gas! i better change my drawers! see you guys tomorrow.
|
|
|
Post by night0wl on Feb 1, 2006 22:28:13 GMT -5
thanks for the help John. I will try a new board hopefully tomorrow. I have a full weekend of gigging to do starting this arvo so I might not get time. Then we're going to QLD for a week (bloody heat!) so I want to get the booster going b4 we go on Sunday.
I'll let you know how I get on.
Thanks again, Shane
|
|
|
Post by JohnH on Feb 2, 2006 19:43:24 GMT -5
A few last things from me, having looked again at my breadboard version:
The boost seems to be much the same in volume and quality with bias at either 4.5 or 6V, so not too critical there.
Current drain is about 1.2mA, which is quite reasonable and probably good for at least 150-200 hours with a 9V battery.
If the 1.5k resistor is increased to 4.7k, however, it seems to work just as well, and after rebiasing, the current drain is down to 0.4mA, for longer battery life.
I reckon the 22nF cap on the output is a bit mean, and is slightly curtailing bass response when feeding the 100k volume pot. It sounds fuller with a larger cap, say 100nF or more. J
|
|
|
Post by night0wl on Feb 2, 2006 23:24:33 GMT -5
Ok I had another go... I wired the JFET how you described (Drain - connected to output and trim pot, Source - connected to 1.5k resistor and 22mfd cap & Gate - connected to 1M resistor) and I thought I had it all done and ready to go. BUT... no sound! Nothing! Although the bypass still works a treat! I was sure it would work this time because I had redrawn the diagram on paper to follow, then took care soldering to make sure there was no spills or bad joins and wired it exactly how it looks on paper. Now I know the feeling of frustration when these projects don't go right I will draw a layout of my diagram and post it. Shane
|
|
|
Post by UnklMickey on Feb 2, 2006 23:41:47 GMT -5
see if you can get your hands on another meter too.
that will help in the troubleshooting.
|
|
|
Post by night0wl on Feb 2, 2006 23:47:29 GMT -5
I will definately get another meter unk. I am slowly realising how important they are! Ok here is what i did.... I also tried wiring it without the first capacitor (straight to the 68k resistor) with no luck. Maybe there is something obviously wrong with the layout and I just don't see it?
|
|
|
Post by UnklMickey on Feb 2, 2006 23:55:34 GMT -5
i'm just about to bug-out for the night. it's midnight here. one question before i leave.
are all the holes from left to right a common connection in the row. or are there wires under the board that make the connections between components?
|
|
|
Post by night0wl on Feb 3, 2006 0:01:25 GMT -5
unk, they are rows of connections
|
|
|
Post by UnklMickey on Feb 3, 2006 0:08:21 GMT -5
okay, i'll compare the drawing to the schematic and make sure the picture matches up.
you should double check and make sure the actual layout matches up with the drawing.
it might be a good idea to draw lines on the top of the board to make it easier to keep track of the rows when you place the components. maybe you're already doing this.
|
|
|
Post by night0wl on Feb 3, 2006 0:11:35 GMT -5
thanks unk. I have triple checked the drawing to the board layout and it is all exactly the same. Good idea with the lines, I will try that from now on.
|
|
|
Post by JohnH on Feb 3, 2006 1:42:52 GMT -5
Very strange - your layout looks OK to me, and matches the conections to my JFET. My one also matches this data sheet: pubpages.unh.edu/~aperkins/pdf/MPF-devices/MPF102.pdfIs yours the same? Other things to try, run a knife blade along each space between tracks, to scrape off any residue that could cause an unwanted partial connection. A working meter would be really good to check the drain bias. If the bias is not within a reasonable range, it wont work. With the 1.5k at the source, the trim pot will be needing to be set to quite a low resistance, probably around 3k to 5k, so near to one end of its travel. Even without a meter you might be able to twiddle the trim pot until it gets into the right zone. John
|
|
|
Post by night0wl on Feb 3, 2006 10:07:12 GMT -5
I would have thought all MPF102 JFET's would be the same?
I went over the board a few times with a magnifying glass, scraping anything that might have been making a partial connection and I also turned the trim pot all the way from left to right and back but nothing. When the trimpot is turned almost all the way down (anti-clockwise) it makes a little pop sound. If I stop it right on that sound it is like a buzz, kinda like touching the end of a guitar lead when it is plugged into an amp.
I just got access to some J201's so I am not sure whether to keep trying this setup or wait til the J201's come in. I am also getting a decent meter so I can check all connections.
Thanks, Shane
|
|
|
Post by UnklMickey on Feb 3, 2006 13:58:58 GMT -5
...I also turned the trim pot all the way from left to right and back but nothing. When the trimpot is turned almost all the way down (anti-clockwise) it makes a little pop sound. If I stop it right on that sound it is like a buzz, kinda like touching the end of a guitar lead when it is plugged into an amp.... i compared your drawing and the original circuit. i agree with John. things look as they should be. with the FET mounted on the TOP of the board, with the flat on the left side, the connections from (top to bottom) would be drain, source, gate. that popping and buzzing is a bad omen. when i try to imagine what might be going wrong here, the first things that come to mind are: - could this be a device with a different pinout, but with similar characteristics to the MPF 102?
- is the device defective?
- is the 22 mfd cap shorted?
when you get a new meter, we'll be able to check the voltages at the gate, source, and drain, to determine what's happening. i'm a bit concerned about the third possibility on the list. if that is the case, the source won't be able to be more positive than the gate. the only thing limiting the source-drain current will be the drain resistor (trimpot) since that has already been adjusted to zero, the internal resistance of the battery is now the limiting factor. in view of this, and the sounds you reported, it could be this FET is already toast. for further testing, you should remove the 22 uF cap. that will not allow as much gain, but the circuit will still function and bias voltages won't change. re-install it after you get the circuit to work properly. i would also suggest putting a 1k resistor in series with the trimpot. this will limit the drain current to about 10 mA, if other things fail. maybe JohnH has some information about checking the FETs with an ohmmeter before installing them in a circuit, to weed out ones that are defective. in any case, i hope we can help you to get this thing working. FET based designs will allow you to use much more finesse in processing signals than the bipolar ones like 5th gear et.al. you won't be able to get as much gain from a single stage, but that's a small price to pay, considering the other advantages they have. unk
|
|
|
Post by JohnH on Feb 3, 2006 14:38:18 GMT -5
Yes it is still a mystery. I would also think that if your FET has that case shape, then the pins should be the same. It may be fried.
We know the design works, and that your layout is OK
The only way I know to check a JFET is to put it in a simple circuit, basically the same as yours, on a breadboard. Unlike bipolar transistors, I do not know how to check them directly with a meter.
A meter that works may be the key.
So have you found a source for J201's? - Id be interested to know. They seem to be the preferred type for these circuits, and they provide more gain.
J
|
|
|
Post by night0wl on Feb 3, 2006 16:56:13 GMT -5
Thanks unk and John. I went through it all again just now, bypassing the switch (just incase it was the switch that was the prob) and re-checking all the solder joints for wrong connections etc but nothing One thing I wasn't sure about using in the circuit was the 22uF electro cap. It is grey in colour and says "22uF 50v eec 85°c" on it. Maybe too much voltage?? They were the only 22uF caps I could get and I thought they would be ok to use. John, I have a wholesale account with RS Components and the J201's are on the list and in stock/available. I will order some when I get back from my trip in a week. If you would like some I can order extra and send some down? I won't have time to try any more experiments until I get back from this trip so I'll get back on to it when I get back. Cheers, Shane edit: Can these FET's be damaged from a too hot soldering iron? And, what is the difference/benefits of using FET's over bi-polar?
|
|
|
Post by JohnH on Feb 3, 2006 17:20:23 GMT -5
Shane - that electrolytic should be fine. as long as that 50V value is greater than the 9V battery, then it is OK. Thanks for the tip about RS components, I have not tried them. Ill see if I can order from them, but if not Id be happy to reimburse you for an addition to your order, thankyou for offering and Ill let you know in a PM. Good luck with the gigs. cheers John
|
|
|
Post by JohnH on Feb 3, 2006 17:30:29 GMT -5
Your other questions. Yes semiconductors can be damaged by too much soldering heat. I have not found these JFETs to be significantly tricky in this respect however, as compared to bipolars. The thing is to get the component positioned, and make a quick accurate application of the iron to the leads and track, applying solder at the same time, then withdraw as soon as you have the solder flowed. Then wait half a minute or so for it to cool down before the next lead.
The JFETs have two main advantages that I can see. One is very high input impedance, so you can use them to receive an input from your pups, without loading them. Bipolar circuits can be designed to have this also, but it comes naturally with JFETs. More importantly, when they start to saturate, they do so with a smooth tube-like character, which makes a great OD sound, or adds warmth if not driven so hard. Bipolars by contrast, tend to clip hard and nasty, and add very little character (hence we dont liek our Solid State amps as much as tube amps).
Im currently having a lot of fun developing a circuit which is alot like two of those fetzer circuits end to end, to make an OD pedal - right now it is my favorite toy.
John
|
|
|
Post by UnklMickey on Feb 3, 2006 17:51:19 GMT -5
Shane, newbies often overheat the semiconductor component and even damage switches during soldering.
to give yourself an advantage while you're in the process of honing your skills, you can give some protection to the transistors by clipping an alligator clip to the lead on the top side of the board. when you're soldering on the bottom side, the heat traveling up that tiny lead will take a long time before it can get the alligator clip up to damaging temperatures. you'll be finished soldering the bottom of the lead to the board long before that happens.
also, use a damp sponge and often wipe the tip of your iron on it to clean it. melt just a little solder on the tip, and since it's clean, you will be able to quickly and EVENLY apply the heat to both the board and the component. that way you can "get in, and get out".
about the electrolytic caps. if the voltage rating is way too high (like using a 450 volt cap on 5 volts), they might not deliver quite as much capacitance, but they won't be like a short.
if they are installed backwards, they often will act like a short.
often the NEGATIVE connection is the one marked with an arrow. so look closely at the markings.
good luck, and have a great trip.
unk
|
|
|
Post by night0wl on Feb 3, 2006 17:52:27 GMT -5
Sorry for being a little off topic here...
Would it be possible to use J201's in place of the MPSA13's in the 5th gear OD I made?
|
|
|
Post by JohnH on Feb 3, 2006 18:06:41 GMT -5
Sorry but no - JFEts and bipolars are totally different animals! J
|
|
|
Post by night0wl on Feb 3, 2006 18:25:00 GMT -5
thanks for the tips unk.
The cap I used has a black stripe down one side with a grey oval and a black - in the grey circle. I assumed the stripe with the - was neg so that is how I placed it on the board.
Shane
|
|
|
Post by UnklMickey on Feb 3, 2006 18:30:49 GMT -5
Sorry for being a little off topic here... Would it be possible to use J201's in place of the MPSA13's in the 5th gear OD I made? Sorry but no - JFEts and bipolars are totally different animals! J yeah! it's like an friend of mine used to say, "they're exactly the same, only different." XD among other things the gate of a (N-channel) jFET is biased more negative (or less positive) than the source. the base of a NPN bipolar transisitor is biased more positive than the emitter. FETs have more in common with tubes than bipolars. when you get more experience, you might be able to do a re-design around the 5th gear using FETs, but IMHO the 5th gear is a bit strange anyway. when you become a little more experienced, you'll want a lot more finesse than that.
|
|
|
Post by UnklMickey on Feb 3, 2006 18:32:49 GMT -5
thanks for the tips unk. The cap I used has a black stripe down one side with a grey oval and a black - in the grey circle. I assumed the stripe with the - was neg so that is how I placed it on the board. Shane cool
|
|
|
Post by night0wl on Feb 13, 2006 5:15:41 GMT -5
OK... I received a meter, breadboard and other little goodies today so I decided to make another fetzer circuit on the breadboard. It worked! BUT....when I soldered it together on the vero board, i got some strange noises. I trimmed the drain to 4.5 and the boost works but there is kinda scratchy sounds coming and going. It happens when I move the trimpot around the 4.5v area. One second there is sound, then it pops out and there is nothing. when I get the boost right on 4.5 it works but the scratchy sound keeps coming and going. It is pretty loud to, enough to interfere with the guitar signal. The trimpot is a 100K ohm Piher Horizontal Trimpot from here code is RT4366. Could there be something wrong with the trimpot? The scratchy noise only happens when the trimpot is touched. I checked the solder job and it seems OK. Any thoughts? Thanks, Shane
|
|
|
Post by JohnH on Feb 13, 2006 6:37:36 GMT -5
Shane - moving the trimpot will make a scratchy sound, which happens to most pots when they are moved and have some dc running through them. The question is , do you get any unwanted noises when the pot is not touched, after setting the bias? if not, then all is OK. The trimpot is not intended to be moved after setting initially. It sounds however like maybe you do have a trimpot that is a bit intermittent, perhaps with a dirty track. Is is any better after a few turns back and forth?
Pots designed to be moved in operation, like a volume pot, have capacitors to block the dc.
John
|
|