Sunn T questions and help

[Anonymous]

Hey gang, I’m building the Sunn T right now and there are some questions I wanted to clarify before proceeding. I’ve built two other kits from GuitarPCB and have all of the appropriate directions and documentation to assist but there’s a few things I have to ask. There’s no gut shot pictures I could find online of this built to help me get a better sense of what I’m doing and it’s a bit more difficult than I expected. I don’t want to mess anything up out of ignorance. I’ve attached a picture of the PCB and other hardware laid out in the enclosure for reference to the questions.

1. What do I mount the PCB onto since it’s not going to be attached to the potentiometers?

2. I guess I know how to wire the switch from the directions, but I’m not sure what On/On/On means or how to interpret the wiring diagram.
3. How should I have the trim pots set up for the best sound? I read that you want to test to voltage on the FETs and keep them in the range of 4.5-5.5 and I assumed that’s dictated by the trim pots?

4. Does anyone have any tips for the most efficient way to wire the potentiometers to the PCB? That is likely going to cause me headache.

Thank you in advance for the help, this forum is a godsend and I really appreciate the guidance from everyone.

[Anonymous]

1.  When the wires from the board to the pots go under the board, they will provide a cushion. The board will probably not move around too much.  Or, try Barry’s new Gum Wadz!  They will hold that board down against the pots for sure!
2.  The ON/ON/ON type of switch will provide signal flow in all three positions.  Left, Middle, and Right.  The middle position will activate BOTH circuits. The diagram in the build doc shows blue line s that indicate the internal connections of the switch.  You can use a DMM to test the continuity between switch terminals to confirm which switch type you have,
3.  Start with the trim pots set in the middle position.  Measure the voltage between the Drain of the FET and any ground.
4.  It helps to premeasure the wire lengths before soldering the pots.  It is OK to have them pass under the board.  Read the GUIDE PAGE for the basic build instructions.

[Cybercow]

FWIW, here’s a gutshot of my Sunn-T build. I laid my enclosure out as landscape instead of portrait though. I affixed the main PCB to the enclosure with double-sided sticky foam.

[Anonymous]

Finished up the pedal this afternoon. Kind of hate it right now. Wiring it has been an absolute slog to hell. It also doesn’t work properly, as I expected it not to due to the chronic problems I’ve had with this entire build. Because of how messy it became during assembly I just don’t know if I will ever be able to screw the back on the enclosure, might need another way to seal up the enclosure safely without squashing too much or breaking anything. Sigh. Anyway, when plugged in and powered but not engaged there is no bypassed clean tone, when engaged I get clean tone. All knobs and the 3-way switch affect no change in sound while engaged. I have not turned any of the three trim pots yet, I honestly don’t understand what I’m doing with them or looking for while turning them. I will include my voltages for the FETs and some pictures in case there are additional issues you wonderful sleuths can spot, sorry for how insanely messy this gut shot is. Sorry for the bad mood post. Thank you all again for the invaluable help in getting a frustrated novice back on track. Left to Right.

Q1: 

0

.3

5.5

Q2

0

.3

4.75

Q3

0

.3

6.2

Q4

6.2

6.8

9.5

[Billy]

When you adjust the trimmer you’re setting the bias voltage of the transistors in order for them to conduct and amplify correctly

The drain pin is on the right hand side, from right to left the transistor pins or leads would be Drain Gate Source per the pcb silkscreen

 

You would place your black meter probe on any ground point and touch the drain pin with your red probe with your meter set to 20 vdc

DC symbol is this

Because your circuit is in its enclosure you could simply put your black probe in one of the empty screw holes as a ground connection giving you 2 free hands to probe the transistor pins and turn the trimmer until you get the specified 4.5 to 5.5v on the drain pins

from the build doc:

Adjust Bias by using Trimmer 1 for Drain of Q1. Trimmer 2 for Drain of Q2. Trimmer 3 will adjust the
Gate of Q3 and Drain of Q4 silmultaneously. You will want about 4.5v to 5.5v on all lead measurements.

Your lack of bypass signal would indicate a fault  between the 3PDT  middle common row and bottom row

You can continuity check your middle common row switch lugs with the bottom row to make sure it is in bypass when you get no signal

I’m assuming you think it is bypassed according to your LED colour it is however easy to fit your bi colour LED the wrong way around so as I say a continuity check will confirm it’s in bypass when you get no signal and not efffects mode

[Anonymous]

I just built this one recently – harder than it looks, right?  I sympathize.  When I looked at my layout (I used the same size enclosure) I decided to run wires from the top to push down the PCB even though I realize that’s probably not best practice.  Also, that doesn’t really help now…

About the ‘engaged=clean tone’, ‘no bypassed clean tone’ part – are you sure this isn’t really the other way around?  That is, maybe the engaged position has no sound (solder joint somewhere) but you are, in fact, getting a bypass sound?  Do you possibly have the LED connected to the wrong solder pads?  This just seems like it would make more sense (and something I did when I built it).

Here’s just a quick note about the toggle: you really need to test it with a DMM to be SURE what is connected in each toggle position.  Mine wound up being connected differently than the layout in the documentation.  The zig-zag pattern in the doc could be ‘opposite’ the pattern for your toggle.  Test connectivity here just to be sure.

T

[Anonymous]

I’ve adjusted the trim pots so that the Q1, Q2, and Q3 Drain legs measure between 4.5-5.5 but Q4’s Drain stays at 9.5 no matter what, but I got Q4’s Source within range.

I double checked the LED twice before soldering it in, so it’s not backwards. I checked to make sure the 3PDT is getting power, it is, but when I test the lugs all of them come up 0v. I can post how I wired everything if that would help? I don’t think anyone would be able to parse out much of my wiring from photos due to the disorganized nature of it.

In all settings with the DPDT toggle switch, I get 0v on all lugs. I’m not sure what’s going on there but I can’t imagine that having the DPDT switch wired wrong (very possible) would affect so much. I will include a picture of how I have it wired which should be the same as what I saw in the directions, though it does look different from what Cybercrow posted.

Anyway, fantastic support help you guys. I am so sick of this build and just want to move on, so thank you all for the help. I desperately need it.

Wiring layout:
I (3pdt) -> Input tip
G (3pdt) -> Input sleeve
BI (3pdt) -> IN (main pcb)
G (3pdt) -> GND (main)
G (3pdt) -> middle right lug of DPDT
O (3pdt) -> Output tip
BO (3pdt) -> OUT (main)
OUT (main) -> Output sleeve
GND (main) -> DC gnd
+9V (main) -> DC 9v
+9V (main) -> +9V (3pdt)
IN (main) -> top right lug of DPDT
IN BRT (main) -> middle left lug of DPDT

[Billy]

Did you continuity check your connections

That’s the easiest way to check your switch connections are working as they should

You can see from the build doc how each position of the DPDT should connect shown by the blue lines, for example

Flip it up middle and bottom lugs should connect

Flip it to the centre position  lugs should connect diagonally as shown and down middle and top should connect

Also worthwhile checking your 3PDT for continuity

Here’s a PDF in case you’re not used to continuity checking

https://drive.google.com/file/d/1Upc_3zXdSRHGC3ILdiYD4deBSl7fGhlO/view?usp=drivesdk

Just for info you wouldn’t want any voltage on your switch lugs it would cause unwanted noise and popping

 

[Anonymous]

While not engaged there is continuity between: 1-2, 1-4, 1-7, 1-5, 1-8, 2-4, 2-5, 2-7, 2-8, 4-7, 4-8, 4-5, 5-7, 5-8, 7-8.

While engaged there is continuity between: 1-4, 1-5, 1-6, 1-7, 2-3, 2-8, 2-9, 3-2, 3-8, 3-9, 4-7, 5-7, 5-6, 6-7, 8-9.

DPDT: when flipped in either direction the continuity is there between the middle lugs and either end, but when the switch is in the middle the continuity is the inverse of the attached photo when the connection is between the top left and middle, and the bottom right and middle. So I have to completely rewire this switch then I imagine?

I still don’t know what the continuity means for the 3PDT, might have to resolder the board onto the switch then?

Will solving these continuity issues make the thing work outright ya think?

[Billy]

 

May sound daft but make sure your in cable is actually going to your in jack with it the wrong way up the in is actually on the right hand side a very common mistake with your enclosure upside down you would still get bypass signal in this situation

You may have the wrong DPDT or simply have it wired upside down when in the centre switch position you want it to connect as shown middle left to bottom left and middle right to top right

Obviously with continuity checking you’ll know if turned the other way whether it’ll connect correctly

Continuity for the 3PDT you’re just checking that the middle common row has continuity with the top row switched one way ( purple lines, effects mode) and middle has continuity with the bottom row switched the other way (red lines, bypass )

In effects mode your guitar signal goes into lug 2 via the in jack and is connected to lug 1 circuit in

Through your effects circuit out via circuit out lug 7  to your out jack lug 8 then your amp at the same time 4 LED cathode connects to 5 ground lighting your LED effects colour

Thrown the other way 2 in jack / signal in,  now connects to 3 goes along the jumper to 9 which connects to 8 your out jack, bypassing the effects circuit and at the same time 5 now connects to 6 lighting your LED bypass colour

So using your meters continuity test you can check to see if it’s correct and these connections are made

On your 3PDT board just put any probe on each middle lug your other probe onto the corresponding top lug check all 3 beep then click the switch and check the middle 3 lugs beep with their corresponding bottom 3 lugs

[Anonymous]

‘Will solving these continuity issues make the thing work outright ya think?’  Maybe, maybe not – this may bring you to the point of hunting a bad solder joint somewhere with a signal tester.

Just a quick word of encouragement: don’t give up on this circuit.  When I first fixed my issues and tried the Sunn T by itself, I though meh…  Then I started stacking into it – medium & high gain boosts, a rat, tone benders.  Here is where you will find the magic of this circuit.

T

[Billy]

Checking for continuity is just to ensure things are electrically connected as they should be and confirming switches etc work

It’s basically just a case of fault finding in a logical manner and as Tom says may lead you to a cold solder joint, short and so on

Obviously we don’t have your build in front of us, so go on the information and pictures you provide which is exactly what we need to hopefully get it fired up

Because you said you don’t get bypass signal etc checking your 3PDT continuity will confirm it’s definitely in bypass mode and perhaps indicate a switch fault or hidden solder bridge

Switches can be damaged internally from solder iron heat and you could have a solder bridge on the underside of your 3PDT pcb so doing these checks will either confirm there’s a problem or eliminate it as the cause

For example we know the 3PDT middle common row should only connect to one or the other throw and not both at the same time so if you had the middle connecting to both it’d indicate a fault in that area

Frustrating as it is you seem to be getting there and learning as you go so as Tom says don’t give up

I being the strange individual I am, enjoy troubleshooting and putting stuff I’ve previously learnt to the test and learning new stuff and techniques

We all get those what seem impossible to find faults regardless of experience

[Anonymous]

Hey guys!

 

I’m currently building a SUNN T as well. I was also puzzled by the DPDT switch, so I read this thread and researched a bit.

I continuity checked mine and, when flipped to the middle, it is the other way around from the drawings in the guide, same as you.So my guess would be this: we need to wire the top left to the middle right. The in goes to right middle, the bright to left middle and the normal to bottom right.

This way, in the up position, input goes to normal only, in the middle position, the input goes to both and in the bottom position, input goes to bright only.

I’ve made some drawings to explicit, sorry for my poor drawing skills 😛

This shows the result of the continuity check and what I think wiring should be.

This shows the result (hopefully).

Let me know if that sounds correct to you guys! I haven’t tried yet, my enclosure is still drying 😉

Best of luck for you built! I hope you’ll get it live soon! 🙂

 

[Anonymous]

I took three months off and I am back at this build again. Just removed all wires and am going to try this again.

[Anonymous]

BRAVO!  Just remember “How do you eat an elephant?”

“one bite at a time!”

You may have multiple issues to solve.  Do not despair!  Billy is giving you good advice.

(Ya can’t beat those Scots!)

[Anonymous]

My problem with every other pedal I’ve made is always wiring so I figured that had to be the culprit. I’m going to try rewiring tomorrow without mounting anything into the enclosure just to decrease the chances of error and having to take it apart again.
I’m also not totally sure where to wire with the PCB on the 3PDT because the wiring diagram shows how to wire without using one and this build is complicated by the toggle switch wiring.
Again, I am a big time novice still who’s three months out of the game so I’m really trying to make sure I don’t make any stupid mistakes.

[Anonymous]

So the DPDT connects to Brt, In, and…Ground?

Additionally, the Input setup I have is:

Tip->I

Sleeve->G

And BI on the footswitch circuit isn’t connected to anything. Seems wrong. Anyone have a tip on that as well?

 

[Author]

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