MXR - Custom Badass '78 Distortion  [schematic]

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Re: MXR Custom Badass '78 Distortion

Postby Ice-9 » 17 Jun 2011, 10:23

askwho69 wrote:
Nocaster wrote:Hey guys. I am the OP of the pics. Sorry I haven't been able to provide anything more than that. I'd be happy to take it apart again and list out all the values if you want. I'll admit that I have not gone down the road of trying to draw a schematic from a pedal before and I really don't have the time to attempt to do so right now. But if there is anything else I can provide (values, more pics, etc.), just ask. Sorry if this was a let down. I just thought the pics might have made it easily identifiable to the experts here! :mrgreen:



How nice mate! that would be good :D

+1 thank


+2 Thanks, I also wonder if it would be possible to remove the 3 pots and take some more pictures so that it may be possible to draw a schematic from the pictures.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?
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Re: MXR Custom Badass '78 Distortion

Postby Ice-9 » 22 Jun 2011, 21:30

Is there anything new happening with this pedal yet on the revesing of it ? If there is no work happening at the mo i may have to buy one to strip down for the forum. :D
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?
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Re: MXR Custom Badass '78 Distortion

Postby Beto Crazy » 25 Jun 2011, 00:51

Could you give us the numbers that appear on top of integrated circuits, capacitors, resistors and transistors?

Example: R22 = 103
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Re: MXR Custom Badass '78 Distortion

Postby Ice-9 » 06 Jul 2011, 22:35

Ok so i have took the plunge and just bought one of these pedals on ebay from the USA with the sole intention of pulling it to bits, so as soon as it arrives I will start to reverse it, probs about 10 days from USA delivery to the UK. My only concern is that SMT capacitors don't have value markings like other components do, so it may prove a bit tricky to get there values.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?
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Re: MXR Custom Badass '78 Distortion

Postby Beto Crazy » 13 Jul 2011, 14:27

I noticed this detail, the capacitors are not marked with the values​​, you may need to use a Capacimeter.

Looking forward

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Re: MXR Custom Badass '78 Distortion

Postby Ice-9 » 25 Jul 2011, 18:27

My new shiny 78' Distortion arrived today, so I got to work taking it to bits and getting a couple of photos of the PCB. I removed the components that block the view of the tracks, so I hope these pictures help with getting a schematic of this effect.

I have had a quick look myself and this effect doesn't look like a modded DS1, the tone stack for instance isn't the same type as the DS1 and a lot of other things look different.

Image

Image

Image
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

For this message the author Ice-9 has received thanks:
x-tn (28 Jul 2011, 12:33)
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Re: MXR Custom Badass '78 Distortion

Postby Ice-9 » 25 Jul 2011, 18:31

Also I forgot to mention that the clipping looks at first glance to be switched between 2 leds D3-D6 and 2 diadoes U2-U4.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?
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Re: MXR Custom Badass '78 Distortion

Postby Güero 2.0 » 25 Jul 2011, 21:01

Where's the muffin bottom?
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Re: MXR Custom Badass '78 Distortion

Postby Ice-9 » 25 Jul 2011, 21:54

Picture of PCB bottom

Image
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?
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Re: MXR Custom Badass '78 Distortion

Postby Ice-9 » 25 Jul 2011, 23:20

I am trying to identify all the transistors and diodes but the markings are a bit different to what i'm used to so if anyone has any info on the following.

Q1- GY5
Q4-1NZ
Q6- 1RP

D2- KA2 - I found this and it looks like a single diode 4148 in a sot 23 package
U2- !G12 sot 23 package
U3- JTW 07 sot 23 package
VS1- AD
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

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Re: MXR Custom Badass '78 Distortion

Postby Beto Crazy » 26 Jul 2011, 01:21

I think it will be difficult to identify them by name. Try to identify the function they fulfill in the circuit, perhaps more "easy".

VS1 and VS2 are zener diodes? U2 and U3 are drivers / switch for the LEDs D3 and D6?
D1 is a bicolor LED? Q5 is a buffer? Q1, Q2, Q3 and Q4 - by/pass system?

Tomorrow I'll try to look better the circuit to see if I can find out about these components.



Thanks for the effort, congratulations for the initiative.
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Re: MXR Custom Badass '78 Distortion

Postby Beto Crazy » 26 Jul 2011, 02:09

U4 é um regulador de tensão?
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Re: MXR Custom Badass '78 Distortion

Postby Beto Crazy » 26 Jul 2011, 02:12

:slap: Sorry ... U4 is a voltage regulator?
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Re: MXR Custom Badass '78 Distortion

Postby Ice-9 » 26 Jul 2011, 09:55

Beto Crazy wrote:I think it will be difficult to identify them by name. Try to identify the function they fulfill in the circuit, perhaps more "easy".

VS1 and VS2 are zener diodes? U2 and U3 are drivers / switch for the LEDs D3 and D6?
D1 is a bicolor LED? Q5 is a buffer? Q1, Q2, Q3 and Q4 - by/pass system?

Tomorrow I'll try to look better the circuit to see if I can find out about these components.



Thanks for the effort, congratulations for the initiative.


I have done a bit of the schematic and should have mentioned whereabouts and what each component in the circuit does

VS1-2 are indeed diodes, which are on the input and output to ground. I didn't know they were zenners though. Thanks
U2-U3 they are in the clipping part of the circuit as are D3-D6 led clippers.
D1 is a standard red led
Q5 is the first buffer on the input, not sure if its a fet or a bipolar but i am guessing at the moment its possibly an MPS-A14 or similar as the circuitry around this is the same as in the MXR dist III.
Q3 looks like a fet on the input which when in bypass pulls down the signal on the input to ground.
Q2-Q4 look like part of the bypass and led circuitry
Q7 is in the second gain stage
U4 does in indeed look like a voltage reg or polarity protection.
I have all the values for resistors and will post them when I get a chance
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?
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Re: MXR Custom Badass '78 Distortion

Postby Beto Crazy » 26 Jul 2011, 14:53

Looking at the best circuits, diodes VS1 and VS2 are not zenners, but something like 1N4148, serving to polarize the FETs Q1 and Q3.
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Re: MXR Custom Badass '78 Distortion

Postby Ice-9 » 26 Jul 2011, 16:30

Here is another picture of the pcb with the crunch switch removed

Image

nd here is a first draft of a section of the schematic , this is as far as i could get at work today, if anyone spots any faults or additions please update or redraw.

Image
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

For this message the author Ice-9 has received thanks:
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Re: MXR Custom Badass '78 Distortion

Postby Ice-9 » 26 Jul 2011, 16:34

I missed out D2 which runs from pin5 U1 to ground.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?
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Re: MXR Custom Badass '78 Distortion

Postby Ice-9 » 26 Jul 2011, 23:23

I've pretty much finished the entire schematic which I think is correct. I have a few things to go over before I draw it up in its complete form. I have omitted the switching circuits as most will be more interested in true bypass. I removed the 4 pin packages U2 and U3 and used a DMM to try and find out what they are, they seem to meter out as 2 seperate diodes in each package and when I have drawn them up from the pcb traces it seems to bear out that this correct.

I will try and draw this up tommorow at work and get the schematic posted.
One last thing, I haven't been able to check cap values yet as my DMM measures caps by pushing the leads into a slot in the meter, I will have to make up some special leads to measure SMD caps.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?
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Re: MXR Custom Badass '78 Distortion

Postby coldcraft » 27 Jul 2011, 03:05

i wonder if those diodes could be forming a rectifier bridge. I've read that one way to prevent AC power from killing DC circuits is to have a rectifier in the way. It will still pass the DC just somewhat lower.
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Re: MXR Custom Badass '78 Distortion

Postby Ice-9 » 27 Jul 2011, 09:33

coldcraft wrote:i wonder if those diodes could be forming a rectifier bridge. I've read that one way to prevent AC power from killing DC circuits is to have a rectifier in the way. It will still pass the DC just somewhat lower.


Your on the right track there Coldcraft, two of the diodes are forming a bridge with the two leds, then the other 2 diodes are switched in another config. I need to go over the clipping section to confirm the schematic before posting.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?
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