[Billy]

That’s what it’s all about Mario learning as you go along

Well done to you

Glad it’s working

[Billy]

Damn deleted the wrong one!

Try adjusting the trimmer until you get just over 2v on Q1 to 4 gate pins

I think your op amp pin numbers are wrong you read them pin 1 left of the notch or dot then down from top to bottom to pin 4 then up the other side bottom to top pins 5 to 8

I think you’ve went down both sides so your pin numbers 5,6,7,8 are actually 8,7,6,5 that would make sense

[Billy]

**EDIT checked the pinouts flip your transistors Q1 TO 4 around**

Some of your voltages are wrong the gate voltages should be just over 2v could be a problem with D1 or the trimmer or the transistor pinout

Check the 5457 pinout is the same first, it may simply be a case of flipping the transistors Q1 to 4

D1 left side doesn’t look to be soldered in correctly but voltage appears ok I can’t see the value of the trimmer which should be 250K the code written on it would be 254

I think you may have IC1 pins 6 and 7 mixed up, 7 is power 9v and 6 output pin which should be around the same as pin 3

Good news is your LFO IC3 appears to be working with the fluctuating voltages

 

[Billy]

Did you adjust the trimmer

Post all your IC and transistor pin voltages

IC pin numbers like this pin 1 left of the dot / notch down one side and up the other side in a U shape

 

[Billy]

Hi Mario

Welcome to the forum

Could you post some nice clear images of both sides of the pcb and offboard wiring to the DC jack, in and out jacks and 3PDT switch so that we can trace it and check component value and orientation

One of the most common mistakes is not installing the ground wire top left of the pcb labelled G

[Billy]

Glad you got it going Bob

We  do like people to let us know if it’s resolved

So cheers and enjoy your new creation don’t forget to let us see it when it’s dressed and ready to go out

[Billy]

Check the voltage on D1 anode + side that may have been damaged should be 5v ish

IC1 – pins 2,3 and 6 should be the same as VB ( around 5V) pin 4 is ground (0V) pin 7 is power supply (9v). Pins 1, 5 and 8 are not used – they could vary from 0V to a few millivolts.

There’s a good chance if you’ve shorted power D1s  zapped

 

[Billy]

Great looking build

Very clean

[Billy]

Tell us more Wilkie

I particularly like the cab sim  addition

But don’t have a clue with DI boxes in general I have had a few people asking about adding xlr etc

[Billy]

I wouldn’t bother taking R11 out if it’s in

Only do it if it sounds bad and you can’t get it to bias

No point in doing anything till you know just stick the transistors in the sockets and see how it sounds

If you already have a 10K trimmer in leave that too

[Billy]

Damn I was writing a novel and Cybercow beat me to it!

The only thing I’d add is perhaps socket R11 and increase the bias trimmer to 20K to help with biasing

Start with the stock 6K8 at R11 check Q1 drain voltage is around 5v and adjust up or down as required

With the Q2 bias trimmer all you’re doing is giving yourself more resistance to play with and if you decide to eventually use the specified transistor types you wouldn’t have to change it

 

[Billy]

You’re giving me way too much credit Fig

Everything I know or think I know I learnt mainly on this forum

Regardless of what they say the guys that really know what they’re talking about are Wilkie and Cybercow and of course the Cap’n – Barry and Bruce

Tonmann was the king sadly no longer frequenting these parts I’d love to know how he’s getting on and hope he’s doing well

[Billy]

As long as they’re PNP they should work  germanium PNP transistors will generally be lower hFE than silicon PNP so I’d try lower gain first 2N3906 are fairly low hFE

They may not sound the same or they may sound better the best thing to do is use SIL sockets and try different ones

[Billy]

With schematics anything that has a flag or label like VB are connected

As Wilkie says that part is the power section usually separate from the main circuit on schematics and very useful for giving you an idea of what voltages to expect at certain parts of the circuit

Most are more or less the same with filtering capacitors in this case C8 and 9 which stop any voltage ripple creating unwanted noise by filtering those frequencies to ground and not into the audio circuit and a reverse polarity protection diode D1 where you’ll notice the cathode side is connected to the +9v rail so if you plugged in an incorrect polarity adaptor (centre positive)  it would conduct through D1 to ground and not into the circuit stopping any potential damage, if you used a correct polarity adaptor (centre negative) D1 would not conduct and power would go to the circuit as it should

If you look at the power section you’ll see +9v goes along to power pin 8 of the IC as Wilkie said, then onto R11 and 12 which form a voltage divider, because they are the same value 10K they half the power exactly so you’d expect all VB points to be around 4.5v I say around because depending on your meter impedance it may load down readings and you will get some voltage drop through components

VB is voltage bias, sometimes labelled VREF (voltage reference) or VR etc and would connect to anything requiring a bias voltage to ensure it operates correctly in this case IC1

All schematic flags or labels of the same type VB, VCC, ground etc should all be connected

You can see VB flags at the non inverting + inputs of IC1 at pins 3 and 5 so you’d know what voltage to expect at each input and output pin

To calculate what voltage you should get at the junction of R11 and 12 if for example they are not the same value resistance you’d use the voltage divider calculation

Which is Voltage supply x R2 divided by R1 + R2,  ( R1 being the resistor connected to +9v (R11) and R2 the resistor connected to ground (R12)

So 9 x 10 = 90 / 20 = 4.5

You only need to use this calculation if the resistors are different values if they are the same it always halves the power supply

To start understanding schematics you should check a completed pcb and compare it with the schematic

Check that all identical flags are indeed connected and you get the same voltage on them etc, it does break up the monotony of staring at a piece of paper, putting the knowledge you gain to practical use with continuity and voltage checks

Another tip for understanding parts of a schematic circuit is to look at the datasheet for example if you had a 7660S IC in the power supply and weren’t sure of its function looking at datasheet circuit examples and comparing them to your schematic would let you know if it’s being used as a voltage inverter or multiplier etc again letting you know what voltages to expect

Anyway this is obviously simplified, I  hope! and hopefully gives you a little more info specifically on the schematic power supply section

 

[Billy]

Your yellow out wire is soldered to the ground pad on the main pcb Andre it should go to the pad with the small T for tip written next to it

I’d personally power and ground the main pcb from the DC jack and jumper it over to the 3PDT pcb

 

 

 

[Billy]

There are a few CAD programs for pcb design

KiCad is completely free and you can get free versions of Eagle and Diptrace although they are not the full version they are fine for guitar effects pcbs

I’d suggest reading comparisons then once you decide which program you are going to use, follow a tutorial that takes you through the process of completing a simple pcb or download and try them all I’ve tried eagle and Kicad

Eagle is probably the most popular it being one of the first ones available I myself use KiCad, with all of them there are different learning curves, Eagle apparently isnt the most user friendly but does have a lot of component libraries available for guitar effects

KiCad full version is free and perhaps doesn’t have as many component and footprint libraries available but is definitely catching up as it grows in popularity in the DIY community and you can of course make your own components and footprints

Diptrace I’ve heard good things about but have never tried it

I think the biggest thing you’ll learn is an appreciation for pcb suppliers especially those that offer a large amount

There’s certainly nothing wrong with having a go especially if it’s a free programme you’ve got nothing to loose

Imo it wont teach you why a circuits laid out the way it is for example why a pots wired as a voltage divider or variable resistor but it will lead you to finding out why

Like most things you can do it parrot fashion although it helps you don’t need to be an expert on how to draw a schematic from scratch you can simply copy a schematic into your software

Again you’ll learn by using Google to find out why a resistor or whatever is where it is and what it’s being used for

There are plenty of user groups and forums and again you’d simply Google eagle tutorial etc to find videos and so on

 

 

 

 

[Billy]

Hi Dan

Best thing to do is socket the diodes and try different types to see how it alters the sound any diode will work

D9 the 1N5817 shottky is a reverse polarity protection diode so that won’t alter anything

Here’s an article with info on the different clipping diode types

https://www.guitarpedalx.com/news/news/a-brief-hobbyist-primer-on-clipping-diodes

 

[Author]

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