mxr distortion 2 schematic

[scaesic]

i have the schematic for this pedal but it doesnt apear to be enough informationj to build.

for example theres no size for the transformer.

and theres leads coming off circuits that it doesnt tell you where they are going.

theres also a symbol i dont recognize, like a cpaacitor but in a v shap instead of a straight line, i think its some sort of a connection maybe but im not sure. it also doesnt tell you where the input and outputs are....

anyone got a schematic for this diagram or can take a look at it and explain it a bit more?

http://www.diystompboxes.com/pedals/dist2.GIF

[Rich G.]

Those >> symbols represent wires, jumpers, or ribbon cables.  You can replace them with straight line.

[scaesic]

what are they required for? using the same pcb in different circuits?

thats one large portion of the circuit diagram out of the way then, hehehe.

anyone else know if those leads with the little triangles on them are all earth connections? its something i thought about but im not sure :s

transformer size is still a mysetery to me too, and the quad analouge switch. is that just one quad analouge switch in there? and every A is a new connection to it?

[Rich G.]

They're usually required to show a connection to something external.  Most of the ones here look like the signal leaves the board then connects to a pot.

[scaesic]

what pots do they connect to :S

sure its alright to just leave them out?

[Rich G.]

All the pots are clearly labeled on the schematic with a box around them.: [DRIVE], [FILTER], [RESONANCE], [OUTPUT]

Yes, it's ok to replace ">>" with a wire.  In fact, consider ">>" to be a wire that leaves the circuit board and connects to something external like a pot, switch, or jack.

[scaesic]

i figured it out with yr help (didint ntoice the matching symbols on the pots), cheers.


anyone help me a little further?

what transformer should i use for the power supply? (in uk)

wheres about is the output and input?

theres a lot of wires flying off circuits that dont say where theyr going, they have little triangles on the end of them, are these earth connections?

is the footswitch the switch on the far top left?

whats the switch on the far top right? and is that a resistor attached to it? if so whats the value of it.

does anyone knwo how to wire up one of those quad analougue switches?

hmm, sorry to be such a pain, the schematics not exactly very user friendly

[scaesic]

any ideas?

[Torchy]

If you take out the off-board wiring symbols, and get rid of the logic switching you get this (I think, perhaps someone more knowlegable than me can check this ...)

http://server6.uploadit.org/files/Torchy-dist2.jpg

1. The v.reg is 15V so the transformer should supply 20V for headroom.

2. Input is top left, output is top right.

3. The "triangles" are ground connections.

4. Vs is the half-supply-voltage (or Vref) from the TL072 in the PS circuit.

[stm]

You need around 20Vdc (rectified) after the diodes (CR devies on the schem), just befor the 15V voltage regulator.

The transformers are specified in terms of the AC voltages.  To obtain around 20Vdc with the rectifier circuit shown, you need a transformer with an output of 15VAC, since 15V*sqrt(2)-0.7V=20.5V

Sqrt(2) is to go from AC to Peak voltage. The "magic" 0.7V discount takes care of the voltage drop on the rectifier diode.

Assuming your mains voltage is 220V (or is it 230 or 240?), you should specify your transformer as  220:15+15, alternatively designated as 220:15-0-15

The above voltages for the secondary indicate it is a center tapped transformer. Eventually a 14+14 to 16+16 secondary would be fine. Just don't forget to indicate the transformer is center tapped and you need 15VAC on each half.

[scaesic]

ok, just a quick question. if i get rid of the led indicator, can i have my footswitch just at the top and get rid of all that logic switching?

also, where do i get the supply for my tlo72's, they need +V and -V dont they?

where shoudl i connect my ground connections to aswel? theres 3 different symbols, im assuming i have to keeep them seperate to avoid any ground loops?

p.s our voltage is 230 (supopsedly)

im realyl starting to think im not going to be able to do this without a better schematic....

[moosapotamus]

Please don't take this the wrong way... I'm not crazy about dealing with mains wiring, myself. But, at least I know what a ground symbol looks like on a schematic. With so many questions, I'm inclined to recommend avoiding anything that requires mains wiring.

BTW - nice clean-up, Torchy.

But, that doesn't have to mean that you should avoid this circuit altogether. In other words, why does this pedal NEED to have a mains transformer just to get 15V, anyway? Wouldn't a suitable DC wallwart, or even two batteries, do just as good a job?

~ Charlie

[scaesic]

Please don't take this the wrong way... I'm not crazy about dealing with mains wiring, myself. But, at least I know what a ground symbol looks like on a schematic. With so many questions, I'm inclined to recommend avoiding anything that requires mains wiring.

BTW - nice clean-up, Torchy.

But, that doesn't have to mean that you should avoid this circuit altogether. In other words, why does this pedal NEED to have a mains transformer just to get 15V, anyway? Wouldn't a suitable DC wallwart, or even two batteries, do just as good a job?

~ Charlie

i know what a ground conenction looks like too, but incase you didint realise there is two ground symbols there, and a third when you take into acount what torchy said.

now im assuming that these grounds need to be kept seperate. i knwo il be able to get a ground from the guitar cable into the amp, and also via the power supply, i also knwo that its likely they are given different symbols because you need to keep them seperate in order to avoid a ground loop which would cause horrendous hum when turned on.

there are so many questions because the diagram is quite complicated, and very ambiguous in places, iv sat here and worked out most of it and intend to make my own schematic eventually, and opefully pcb.but i just thought id get through it a lot quicker with some help....

im was also wondering if id be able to just buy my own power supply.
but i thoguht itd be likely the schematics are given for it as you cant buy the same kind commercially...

[moosapotamus]

Cool. I would actually be into building one of these, myself.

On second look, the ground connections are a bit confusing... the fork is chassis (or, star) ground and the arrow is circuit ground, but sometimes it's also necessary to keep the power supply ground separate from the circuit/audio ground. However, a separate power ground is not indicated. Hmmm...

You can get a Power One power supply from Digi-Key (for example). I'm not sure it would fit into a stompbox, tho.

But, still... instead of the transformer, I would be more inclined to just use a 18V wall wart going into a 7815 regulator with some 100uF caps on the input and output, and keep the Vref as is.

~ Charlie

[Peter Snowberg]

I like using external wall-warts because you get less hum that way.

When it comes to grounds and effects, just about 100% of circuits have their grouds connected together at some point.  There are two basic styles of grounding..... bus grounds, and star grounds. A star ground has all the ground wires coming back to a single point. The advatage there is that power being drawn from one part of a circuit will not show up in the ground wiring of another part of the circuit. Bus grounding takes the view that these little currents don't matter too much and every circuit ground just connects to a big ground wire.

When you have a box with a PCB and lots of off-board parts like pots, jacks, and switches, a combination of the two styles is often seen. Ususally in one corner of the schematic you'll see a point that connects to both ground symbols. In this case it's right next to the input jack.

In general, you can treat the standard triangle shapped ground symbol as a bus ground and the pitch-fork shapped symbol as a star ground but in reality these symbols mean "circuit board ground" and "chassis ground".

That schematic is a little weird in that it shows three symbols. I would just treat the triangles and the triangle shape made of three lines (the standard ground symbol) as the same thing.

Also, I would avoid putting a transformer in the box with a ground connection to the plug. That is almost asking to have hum in the circuit. An 18V wall wart is your best choice.

Take care,
-Peter

[moosapotamus]

Hey! I just noticed something...
I'll bet you could replace that switch on the output buffer with a clean volume (blend) control.  

~ Charlie

[scaesic]

sounds like it could be an idea for a good mod, but i think il try and do the original first.

what are peoples thoughts on doing away with the logic switching and just having the footswitch in the position thats in the clean up version (earlier in this post).

i may be wrong but all i can see that it does is introduce the "on" led, which for all the complication it adds, i could do without. im probably wrong though...

[scaesic]

p.s i live in britain, ie no walmarts.

would one of these do though

http://www.maplin.co.uk

(High Quality Switched-Mode Mains Adaptors in search)

id have to make sure theres not too much power coming from it somehow, and i need 13v.

on the led circuit, the base and the collector of the transistor are going to little triangles, but they look kind of like arrows too, so what do you think guys? bottom left circuit. are those all grounds?

[Torchy]

Power Supply
The required Vs for this circuit is 15V. Why do you want 13V ?
Pick a wall-"WART" (not MART btw) that delivers regulated 15V at 100mA - there are plenty about.

LED circuit ...
The transistor is the "driver" for the logic switching at the top of the schem. The collector symbol is "A" - this controls the logic gates on the immediate right (the square boxes, the horizontal line connections are marked "A/-5-" and "A/-6-". The base of the transistor has the symbol "B". This goes to the logic gates top left. The vertical line connections are labelled "B". Depending on the conducting state of the trasistor (ei on/off) and hence the voltage levels at the base and collector, then the gates are on or off.

I took out the transistor control circuitry and logic gates out and replaced them with two halves of a dpdt to clarify the schem. Sorry if it wasnt that clear.

Also note that the signal grounds and chassis grounds must be kept separate and NOT be connected together. This is to avoid a ground loop inducing hum into the audio path. Upshot is you cannot connect the negative pole of the power supply to the case ... use an insulated jack.

Another thing ... the earthy side of R22 (the output level control) goes to signal (chassis) ground and not the power supply ground. The input jack appears to have a short to ground on it - this is a break contact on the input socket.

[scaesic]

would i need to add those resistors and op amp to stop from loading the circuit or will a wall wart power supply do on its own?

the circuit looked like it said 13v to me :s

i can only seem to find 300mA 15v adapters too.