Gday just a few questions...
The attached file is a dr. boogie distortion pedal.
1) The 100k trim what are they? variable resistors?
2) The 1k8 resistors...im assuming that means 1.8k ohm?
3) Are there any special caps/res you need to use? or any will do? i mean electrolitic/ceramic etc.
4) The j201 is a transistor?
5) and the master volume bass treble etc are they variable resistors?
thanks
1) Yes. They are "trimmer" -type variable resistors used to fine tune the bias of gain stages.
2) Yes.
3) IMO, you should avoid electrolytics and tantalums as much as you can: They are unreliable on a long term. Ceramic capacitors will introduce a little distortion. There´s a lot of other options but they tend to cost a little more. I would mind about the proper voltage rating and physical size first then pay attention to details like tone of the capacitor.
4) Yes, it´s a FET-transistor. http://www.fairchildsemi.com/ds/J2%2FJ201.pdf
5) Yes. They are "potentiometer" -type variable resistors. Pay attention to their "tapering". Some have a linear resistance, some logarithmical (audio).
#3
I actually fit Sprague orange drops and silver micas into the circuit. It's a tight fit for the orange drops, but they will fit. You can probably get away pretty well with mylar caps in place of the orange drops if you need to keep the cost down though.
Quote from: teemuk on June 20, 2006, 03:50:25 AM
1) Yes. They are "trimmer" -type variable resistors used to fine tune the bias of gain stages.
2) Yes.
3) IMO, you should avoid electrolytics and tantalums as much as you can: They are unreliable on a long term. Ceramic capacitors will introduce a little distortion. There´s a lot of other options but they tend to cost a little more. I would mind about the proper voltage rating and physical size first then pay attention to details like tone of the capacitor.
4) Yes, it´s a FET-transistor. http://www.fairchildsemi.com/ds/J2%2FJ201.pdf
5) Yes. They are "potentiometer" -type variable resistors. Pay attention to their "tapering". Some have a linear resistance, some logarithmical (audio).
Righto, thanks for your help,
So I would need logarithmical potentiometers?
Are these the type of trimmer i need?
http://www.jaycar.com.au/productView.asp?ID=RT4318&CATID=&keywords=trim&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=
As for the trimmers, try to find multiturn ones. Most trimmer resistors only turn less than 360 degrees (less than a full turn), while multiturn trimmers will turn more - usually 10 to 25 turns. Naturally multiturn ones are more accurate than ordinary trimmers. Carbon is the cheapest resistive material and will "degrade" as a trimmer - this is something you do not want. Prefer plastic, wirewound or cermet. Once again, one choosing criteria is whether the trimmer actually fits to it´s place. Someone suggested sealing the trimmer position with nail polish or similar substance. I think it´s a tip of the month.
The potentiometers marked with "A" (Audio) are logarithmic. The "L" stands for linear. Usually you should be able to guess which ones are logarithmic pots even when it´s not marked to the schematic since the human way to sense loudness is logarithmic. For example, volume or gain potentiometers are usually logarithmic. And again, a good rule has to have some confusing exceptions:
Old code: A = Linear, C = Logarithmic, F= Antilog
New code: B = Linear, A = Log, Antilogs are not produced
Alternate = Lin, Log - pretty self explanatory.
Righto thanks mate, would you just be able to have a quick check and see if these will do the job?
For Gain, master volume and bass
http://www.jaycar.com.au/productView.asp?ID=RP3624&CATID=&keywords=potentiometers&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=
For Trebble (there is no 220k, will this do? 250k)
http://www.jaycar.com.au/productView.asp?ID=RP3620&CATID=&keywords=potentiometers&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=
For Mid (no 22k)
http://www.jaycar.com.au/productView.asp?ID=RP3514&CATID=&keywords=potentiometers&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=
For the 100k trimers:
http://www.jaycar.com.au/productView.asp?ID=RT4366&CATID=&keywords=trim&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=
There are multi turn cement ones but it looks like they wont fit on the board.
Thanks mate (Y)
The trimmers that you mentioned will work, though they are not the "multi-turn" type and will be a bit of a pain to dial in.
These are the type that I was referring to.
http://www.mouser.com/index.cfm?handler=displayproduct&lstdispproductid=267703&e_categoryid=318&e_pcodeid=59403
These will be quite a bit easier to dial in the jfet's bias. With short turn trimmers, the voltage fluctuates wildly with the slightest movement of the dial...
Righto, thanks, do you think the potentiameters for gain, volume etc will work?
If you're going to pop these into a foot pedal, I will make 1 suggestion... If possible, use the 16mm pots over the 24mm that you have linked to. There's a total of 6 potentiometers that have to go in the box and the 24mm's are a tight fit in smaller boxes and require pretty precise drilling. The 16's give you some wiggle room on the sides and perform very well. I learned this one on my first build and remembered it for the second and it worked out a million percent better as I don't have a drill press....
If you have more room than say 3 inches across, the 24mm's will be just fine.
The values you chose are right on the mark though. I used 250k and 25k as well.
Yep righto,
Just went to the shop, got all resistors, potentimeters and the dude gave me some transistors which are heaps close to the j201's he seemed to know what he was talking about.
Ill get the caps and trimers tomrow....hopefully this thing works.
Hmm just did a google search and the transistors i got sold were 2n5485
http://www.fairchildsemi.com/ds/2N/2N5485.pdf#search='2n5485'
Would these still be as good as the j201?
http://www.fairchildsemi.com/ds/J2%2FJ201.pdf
They are pretty similar - meaning the substitutes should work without drastic rebiasing of the circuit. Little dissimilarity between specs of different jfet models is quite a small concern since the internal properties of jfets vary a lot and even two jfets of similar model could actually be very dissimilar. In Dr. Boogey circuit the trimmers should handle the fine tuning of bias anyway. I trust they'll work like they are supposed to.
ok, thanks.
The two outside pins on the potentiometers, are these the same?
and for the linear potentiometers...these have 6 pins, what do i do here? solder the matching pins togeather then go about it normaly?
Thanks, sorry about the stupid questions.
Ok, maybe nobody understood me, ill attach a pik.
I have read that you connect the tip to the input, the sleve to ground and ring to the negative battery terminal, how do you know what is what? one terminal is slightly golden (3) what one is this?
Do you connect the negative battery lead to ground?
I have no idea about the pot, is what i have done in the pik wrong?? im guessing it is because my pedal isnt working.
Quote from: lliw on July 02, 2006, 07:41:58 PM
Ok, maybe nobody understood me, ill attach a pik.
That´s a dual potentiometer, which is ideal for stereo circuits, and it has two identical potentiometers inside it. The center tap should be the wiper. At least it has been in every potentiometer i've seen so far. Don't solder pins together - you would connect the two resistances in parallel!
Quote from: lliw on July 02, 2006, 07:41:58 PM
I have read that you connect the tip to the input, the sleve to ground and ring to the negative battery terminal, how do you know what is what? one terminal is slightly golden (3) what one is this?
Do you connect the negative battery lead to ground?
If the polarity of the supply is positive (it is in this circuit) the negative battery terminal IS the ground. Mono plugs connect the sleeve and ring of the jack together so both of them are grounded if either one is connected to ground and a MONO plug is in the jack. If you connect the ring to the battery´s minus terminal and use the sleeve as a ground node the circuit will not be powered unless a mono jack is inserted (the circuit is open until this point) - thus you can make an "On/Off switch".
You can test which pin is which with multimeter's resistance tester: Connect one probe to tip and test which pin it is with the other probe. The resistance should be nearly zero. Same thing with ring and sleeve.
Thanks, I still cant get it to work, when i turn it on there is a small buzzing sound, and no signal from the guitar is getting through.
You connect the negative terminal of the battery to the ground?
Negative terminal has to connect the ground otherwise the circuit is open. Consider the connection of the negative terminal equal to a connection of the positive terminal. No connection = no path to ground for current from the battery = open circuit = no power.
Yer i thaught so, ill have to keep mucking around with it