[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

[Billy]

Hi Nescio

Here’s a post from the old forum with lots of circuit information from Tonmann

https://guitarpcb.webs.com/apps/forums/topics/show/8230458-swah-super-white

 

[Billy]

Excellent looks superb Mark

I’ll be sure to try your mods when I build mine

[Billy]

Hi Pierre,

Post some photos of your build

Both sides of the pcb and offboard wiring so that it can be traced

Post all of your IC pin voltages both the PT2399 and TL072 it’s very difficult to help without seeing your build

It would be better to start a new troubleshooting post for your build so that more people will see it

[Billy]

Looks good

I’m guilty for foraging parts off of working builds I haven’t yet boxed as well as those bottom drawer jobs, I’ve a few of those!

 

 

[Billy]

Just for info Greg, you may already know this but with less resistance you increase negative feedback and decrease the op amps gain factor in this case x 1000

220K would be gain 46

220R would be 0.046

And that would obviously affect what’s going back via the negative feedback loop from output pin 7 to – input pin 6 and throw it all out

I’ve told this one before,  I’ve built 100s of pedals yet still managed to put not 1 but 3 incorrect resistors in a delay build, checked multiple times but still took a while to find them

We all do it………

Many times, at least yours was only 1 colour band out

 

[Billy]

Your voltages look good Greg

Your R10 looks like a 220R instead of a 220K

 

[Billy]

Your eyes ain’t that old Ray I downloaded the photo zoomed in and still thought the battery was going to the middle lug

Now that I look at the solder lugs I can see it’s not sitting sideways

[Billy]

Double check none of your DC jack lugs have continuity

The battery +9v and top +9v should only have continuity until you plug in your adaptor, check once you plug in your adaptor there’s no continuity between the battery power and main power terminals on the DC  jack

[Billy]

Hi Jon

You’ll need to order some op amps

The ones you have are dual op amps you need single op amps an LM741 and TL071

Just for info op amps come in single, dual and quad packages meaning they either have 1, 2 or 4 op amp circuits internally in the same package and therefore the pin outs are different

The TL series are easy to tell the difference

TL071 with the 1 denoting 1 internal circuit (single) 8 pin package or DIP 8, DIP = dual inline package meaning the pins are on both sides, the 8 denoting the number of pins in this case 8 dual inline so 4 per side

TL072  with 2 denoting 2 internal circuits (dual) 8 pin package or DIP 8

and obviously the  TL074 with 4 denoting 4 internal circuits (quad) 14 pin package or DIP 14

Unfortunately not all manufacturers make it easy to know which package it is, but most suppliers do state whether it’s single or dual

The confusion arises because the same physical package is used with single and dual op amps ie they both have 8 pins

There is a little information on op amps in the beginners guide to effects pedal components on the guides page

If you look at the pinout diagrams for the TL071 and TL072 on Google you’ll see the different pin allocations etc

 

[Billy]

No they’re bigger values Robrhy in nf

2u2 = 2200

4u7 = 4700

They would have been electrolytics in the original

From the schematic  your + side would go to the bottom pad on all 3 using electrolytics

You will be able to get 2u2 in MLCC type, 4u7 will be more difficult to get in MLCC

Barry’s very handy capacitor guide is here

The GUIDES PAGE – Mandatory Reading for all!

 

[Billy]

I’m off work for 5 days

It normally only happened with me at work going through tunnels on trains where you would loose WiFi  signal strength

Not very frequently to be honest and not just GPCB so not a major problem more of an annoyance than anything else

Sometimes when answering a post after writing a novel reply when I hit submit the comment doesn’t appear now that’s infuriating but again definitely only at work and not your site

I also can’t watch videos etc when using my work WiFi so I’d say the problems are not at your end

None of it happens using my home WiFi

[Billy]

I’ve seen it and I use Chrome it’s definitely a slow page loading thing

[Billy]

There should be a 3 digit code on your trimmer 254 check to see what code it has on it

[Billy]

In comparison to my first effort that’s magnificent

Part of the fun’s those wee mishaps and learning from them

Nothing better when you try something and it bursts into life well done to you

[Billy]

Don’t know if I could operate that Wilkie never mind build it

I’m sure if they dig that up in the future they’ll be scratching their heads on some tv programme making comparisons to the Antikythera mechanism!

Superb work even Pete Cornish would be envious

 

[Billy]

Your LED needs to be common anode, centre pin positive two outer pins ground

[Author]

Posts