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I finished wiring up this pedal today, but it doesn’t work. There’s continuity from jack to jack but when I test on the main PCB there’s no continuity between resistors, transistors, even the potentiometers. I don’t know where to start other than pulling all the components and re-populating the whole thing.
At first glance, your missing diode D1. I would look at the bottom and make sure there are no solder bridges or wire strands toughing other pads.
That said, is there a build document for the version 4 Mastodon? I’m building one too and all I can find is version 3. The component layout is different and maybe that’s all.
Thanks.
Are you getting power to the pcb check on the main pcb 9v and ground pads some boards require D1 installed they’re either series 1N5817 (required) or parallel 1N4001 (not required) the quickest way to check is to see if you get voltage to R3
Your pcb is V4 so D1 is a 1N5817 and needs to be soldered in hence why I asked if you get power into the pcb if you don’t have the diode you can solder a jumper in its place
The polarity protection diodes were changed to 1N5817 because of its lower forward voltage allowing less voltage drop into the circuit
Apologies for the Build document.
I have updated it so you can download again. You may need to refresh first?
https://guitarpcb.com/wp-content/uploads/2018/06/BD_Mastodon.pdf
As Billy points out you need to install the 1N5817 in D1 or simply add a jumper to bypass the circuit protection diode if you do not have one.
You may also want to add some more solder to these connections on the 3PDT switch (IMHO). (See Photo)
Your guitar signals AC so you don’t want DC on the out pad
Are you actually getting audio through the circuit in effects / bypass mode
Do your 2 pots on the underside of the pcb also have the plastic caps on them
You should obviously get bias voltage on both transistor collectors etc If you get no voltage on Q2 collector try reflowing solder joints on R4
You can check resistance along that trace, don’t power the circuit and check resistance from a 9v pad to Q2 collector where you’d expect around the value of R4 22K
Also check resistance between Q1 collector and Q2 base where there should be little to no resistance
If you get high resistance readings or OL (over limit) theres obviously a problem along those traces poor solder joints or solder bridges or damaged traces all your resistor values look correct so I wouldn’t suspect an incorrect value to be the problem
Q2 base voltage should be exactly the same as Q1 collector
The circuit is basically a modded fuzz face with extra pots and EQ
So I’d think you’d want similar to fuzz face voltages 1.4v on Q1 collector, base 0.6v emitter 0v, Q2 base 1.4v, collector 4.5v emitter 0.8v mastodon voltages would be affected by the pinch and wool pots so may not be exactly the same
I’ve had slight success! Bypass has always worked, effects were silent until this morning. Now I get the effect but it cuts out intermittently. When I get back to my workshop I’ll double check the measurements you mentioned. I’m extremely grateful for this help, I would be lost otherwise
Ok effects is gone again. I’m reading over 200k resistance on Q2 collector
I don’t think my Q1 ist seated well in it’s socket. Depending on how I shift it I either get voltage on the base or I don’t. Should I pull the socket? Q1 collector is a solid 1.4v
I’m almost at the finish line. The effects are sort of coming through, as long as the back plate isn’t on. But when they come through they are crackly and die out every 9 or 10 seconds. I’m not getting voltage on Q1 Base, and the voltage I’m reading across Q2 ist Power than it should be. Looking at the schematic I see C1 is immediately before Q1 Base. Could that be the issue?
*the voltage I’m reading across Q2 isn’t as high as it should be
There’s continuity between the power pad on the main PCB and Q1 collector and emitter, but no continuity between the 9v power pad on the main PCB and the Q1 base
Confession up front: I haven’t built one of these since the 2A version in 2015 that soldered directly to the stomp switch.
Did you get this as a kit or did you buy the board and an source the parts yourself? The reason I ask is the resistor installed in the 3PDT board does not look like the typical 4.7k that’s recommended for LED protection – at this point it’s not doing anything, but it’s not right.
I’d recommend that you recheck/reflow all the solder joints on the back of the main board paying special attention to the sockets. Also do the same for the 3PDT board and check carefully for stray strands that may be touching something. If you didn’t already follow the advice to solder one leg of the transistors to the socket, don’t do that (personal bias) but do pull each transistor and add a slight kink in the legs so that they fit very tightly into the sockets – don’t go crazy with the bends.
Head smack.
Forgot to mention that if the Pinch pot is turned down the pedal will sound like it’s seriously not right.
Chuck
What voltages are you getting on the transistor pins you shouldn’t get continuity directly from 9v to Q1 collector R3 should connect to 9v with the other side to Q1 collector and Q1 emitter should connect to ground check you don’t have continuity on Q1 pins
Make sure you don’t power the circuit when checking continuity and taking resistance readings
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