@billy
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I’m not 100% on whether it would be too much Fig
Hence the afaik
As you know calculating gain with a 220K feedback resistor and 4K7 input resistor gain would be 47 and with a 560K = 119 for an inverting op amp set up
So over double fairly significant as far as I know the gain would be increased and bandwidth reduced but seeing as they can multiply gain in 000s I don’t think it’d affect or destabilise it massively but I don’t know for sure
Wilkie will know tell us Ray
Your R3 looks like 47K I think you’ve mixed it up with R15
R15 looks like 4K7 and should be 47K
R3 looks like 47K and should be 4K7
Easy enough to do they’re very similar colour bands
That would affect the op amp biasing
From your description of the fault it does sound like the op amp is misbiased
Easy enough to check take voltages on the IC input and output pins you should get half power around 4.5v
Pins 1,2,3,5,6,7 should have around 4.5v With pin 4 ground 0v and pin 8 power +9v
Just for info when troubleshooting the very first thing to do is visually check all components are the correct value and orientation youll find resistor colour band charts on the guides page
Using a 560K in place of a 220K would increase the gain significantly but shouldn’t mis bias the op amp afaik that resistor would be in circuit regardless of the switch position the switch looks like it connects the diodes in and out
What voltage do you get to the swah pcb +9v and gnd pads
Take voltage readings on the IC and transistor pins, that may indicate your problem area
Q1 D G S Q2 and 3 C B E and all IC pins
Have you verified all component values are correct and orientated correctly it is fairly difficult to see your picture using my phone at work
Make sure your I and O wires go to the jack tips and not the ring connection just insert a jack and follow the connections round to their solder lugs
As Fig says your LED anode + is soldered to a ground pad if it’s the white wire
I’d say the best thing to do is place your white wire in D1 middle solder pad and run a wire from your LED cathode to the pad you’ve currently got your white wire soldered to
Then solder the black wire removed from your LED cathode to S5 leaving the other end where it is 3PDT lug 5, but snip off the strand of bare wire it looks like it may be touching 3PDT lug 6, S6 can be left empty because you are not using a bi colour LED you already have your current limiting resistor soldered to the main pcb (R10)
Your yellow wire already goes to S5 as it should
Your pots are wired the wrong way around they should go to the underside of the pcb if you look at the left pot solder pads you will see a small 1 for pot lug 1 here’s how the pot lugs are numbered for future reference
If it’s a build for yourself I would just leave them working backwards rather than risk damaging solder pads trying to desolder them pcb mounted pots are tricky to desolder if you are confident with desoldering then have a go but it’s not really a problem having them work backwards imho
If it sounds good to you the FET biasing isn’t written in stone it’s more of a guide
As it says in the build doc you’d want Q1 and 2 biased slightly higher than Q3 if you can do that and it sounds good I wouldn’t worry too much about the voltage
Your trimmers should have a 3 digit value code 10K would be 103 the first 2 digits being the significant numbers and 3rd the amount of zeros = 10 + 3 zeros = 10,000
Nitsuj
Welcome to the forum
We’d need to see a picture of your in and out jack wiring and DC jack wiring so we can trace where it goes to
The white square in and out T for tip pads should go to the 3PDT pcb in and out lugs
Check all the mechanical parts on the enclosure especially the pivoting part
It’s very difficult to trace your circuit on a breadboard hard to see values etc but if you’ve done everything advised in the build doc then I’d be looking at the enclosure mechanisms
We know for some reason VB seems to be a problem and the junction of R32 and 33 isn’t giving us the required VB
It’s got to be something common to all builds anyway there’s a possibility of too high a resistance in the voltage divider path so to eliminate that possibility
As you know off by heart now I’d think!
No power to circuit
Check the resistance from the VB junction bottom pads of both R32 and 33 to pin 5 IC1 in each case it should be the the same around the resistor 56K value
You may have to wait for your meter to settle down it will jump around a bit then slow down and eventually stop
The voltages aren’t giving up their secrets so let’s see if resistance won’t resist and give us a clue!
Also check what power is coming out of your adaptor whilst connected to nothing, as you’ll know – simply plug it in stick your ground probe into the centre and touch the sleeve with your red probe, meter obviously set to VDC then plug into your pedal and take voltage on the DC jack lugs and board +9v and ground (I’m a wee bit lost can’t remember if you’ve got it wired to a test box or not) just to see if anything is dropping out, in each case keep your probes on for about a minute to see if it changes
I’ve been down with the flu the last few days defo flu not the dreaded covid thankfully
Hi Jamie
Welcome to the forums
I’d just buy common anode it’ll save messing around
If you look at the build doc LED section you’ll see how to recognise the red side, middle pin is common anode shortest outer pin effect on colour and medium outer pin red or bypass colour shown below
The red side cathode would connect to the bottom bypass 3PDT row because you’re using the vari brite pcb you would place that side in the white boxed solder pad
If you switched power all of your ground connections would be affected including your in and out jack grounds all your grounds are connected to each other so as you say much easier to go with common anode
Chuck
Yes that’s series resistance just for info:
It depends on what you’re trying to do the way you’ve got it wired as you know would give you a variable resistor in place of R2 your series resistance would be added in both directions and no jumper would be required
In this case between lugs 1 and 2 and 1 and 3 both CW and CCW it wouldn’t add anything between lugs 2 and 3 in either direction
So if you were using it so that when turned down it wouldn’t completely turn off, on a gain pot for example that should work
If you added resistance to lug 2 turned either way it would add resistance between lugs 1 and 2 and 2 and 3 but not 1 and 3 basically it’ll only affect whatever lug connects to the lug with added resistance
The best thing to do is get your meter out solder resistors on, use a clip as a jumper and experiment
That’s what I do because I can never remember what happens
Post a photo so that we can see and trace the DC jack and 3PDT wiring to the in and out jacks and pcb in and out T pads
You will fix it
Did you reflow R32, 33 and C13, 14 and 15 and carry out the continuity checks Cybercow suggested
It’s frustrating but you learn a lot debugging I find
Let us know you’re findings
You could remove the MN3007 only and see if that affects voltages it does share a common ground if it is a fake it may well be causing chaos
You can also do your resistance checks around the power section again as you know without power check from a reference point and see if you get expected resistance along that path e.g. R31 from 9v to the side connecting to C13 should be around 47ohms if it’s an easy path to check ie no paralell resistance to consider worth doing the checks
This will highlight shorts, bridges, open circuits etc with R31 for example if you get a much higher resistance you know it’s the correct value so maybe a dry joint causing high resistance to current flow or a dodgy resistor or a bridge etc
Your dropping 3 volts at R31 shouldn’t be that much with a 47 ohm resistor
What resistance did you get from VB to pin 3?
Is R1 definitely 220K was it just reflection making the 4th band look grey
From your voltages what we can say is your power supply is putting out 8.7v which goes into R31 then drops 3v through it, from what I can see R31 is the correct value yellow purple black gold brown but it’s not easy to see it’s slightly out of focus so we need to find what’s causing 3v to be lost it could be R31 or components around it C13, 14 your op amp pins 8 and 4 etc everything thats connected to that node
It is a fairly complex circuit but good point is you’ve got signal flowing from in to out you’re not far away from solving it 9 times out if 10 it is something simple like a dry solder joint, or incorrect value, it’s finding it that ain’t so easy
Use the schematic and trace it back Paul to see where it’s dropping out start at where 9v goes into R31 through it along to R32 and to + sides of C13 and 14
Reflow solder joints on those components
Done that on more than one occasion Paul
If your R1 4th bands orange it’s all good your R17 is definitely 220K so may just be the reflection
Also check the voltage you get at the junction of R32 and 33 bottom pads I think, obviously continuity check that’s where they’re connected to see if you get VB there as you should
As Cybercow says re the trimmer it would also affect your voltages to what extent I dont know
Found this for expected voltages note it’s 9.13v power going in
