Preamp jc 120

[Kirkus]

The one made by Neil
I do use 1/2 watt resistors though but i doubt that that's what's giving me trouble

[Sensei Tim]

most likely the 15k resistors that are going to the drains on the transistors are not biasing them properly.  you'll need to replace them with sockets and try a bunch of different values to see what works.

Where did you source your transistors from?  are they 2sk117's?  were they sourced from a reliable seller?  it could also be that they are fake/out of spec transistors and won't work regardless of the bias transistor.

[Kirkus]

Yeah i bought 2sk117's from a local trustworthy store
I will check the voltages on the transistors and see if they are properly biased by the resistors (i will go for about half the voltage of the power supply)

[Sensei Tim]

use 100k pots or trimmers and bias with that, then measure the value and use that value resistor.

On Mon, Jul 29, 2019 at 12:06 PM Kirkus [via Guitar FX Layouts] <[hidden email]> wrote:

Yeah i bought 2sk117's from a local trustworthy store
I will check the voltages on the transistors and see if they are properly biased by the resistors (i will go for about half the voltage of the power supply)

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[Kirkus]

ok so i use a 22v power supply
2 of the transistors read 22 volts at the drain leg. 1 reads 11.4 or so and 1 is at 8 or so
could you tell me the value that worked for you mate?
Maybe it could work for me too (as adding pots or trims sound like a lot more work than replacing a resistor)

[Kirkus]

I forgot to mention that when i first applied power to the circuit i made a mistake and plugged it wrong way
As a result, the 100uf electrolytic capacitor blew and i replaced it
The top right transistor (as we look at the layout in the first page) reads exactly what my power supply reads which is 22.3 volts
Top left is at 11.8 volts
Bottom right is at 8.7 volts
Bottom left also reads the full 22.3 volts
Did i damage those 2 transistors reading the full 22.3 when i connected the power the wrong way?
Please help this is driving me crazy!

Update: Turns out one resistor was in the wrong hole...

Voltages on transistors drain are about half the power supply except Q2 which still is at full 22.3 volts

At least now i get some sound coming through with 22 volts power supply but close to none with 9 volts...

Emphasize on "some" as it is really low...Any suggestions on what to look for?

 This is my second built ever (first being the Dr Boogie) and i need all the help (knowledge) i can get folks

[Kirkus]

I just finished my second attempt on that build
It seems to work...At least the signal does go through but it's kinda low...
I plugged it straight to reaper using a power amp plugin and a cabinet loader and it's lower than if i just plugged my guitar without the pedal...
Is this how it is supposed to work?
If not how do i even start troubleshooting?

[Travis]

As far as I can tell there is no reason to believe this layout is verified at this point

Q2 drain is directly connected to the power supply so you should expect the full voltage there.

To start troubleshooting compare the schematic to the layout and your build

[Kirkus]

Thanks a lot for your answer Travis!
I noticed that earlier today (the fact that Q2 is directly connected to power)
The question that remains though is what could possibly cause the volume on the pedal (at max) to be lower than the dry signal of my guitar (which is loaded with passive pickups)
The thing is I no longer have an amp at home and I plug to vsts...

[Sensei Tim]

I built the original circuit and had to swap drain resistors to get it to work properly, so it's “verified”

Assuming that you don’t have any errors in your circuit the most common things would be either 1) transistors aren’t biased properly or 2) the transistors are fake/out of spec.

On Sat, Aug 3, 2019 at 12:49 PM Kirkus [via Guitar FX Layouts] <[hidden email]> wrote:

Thanks a lot for your answer Travis!
I noticed that earlier today (the fact that Q2 is directly connected to power)
The question that remains though is what could possibly cause the volume on the pedal (at max) to be lower than the dry signal of my guitar (which is loaded with passive pickups)
The thing is I no longer have an amp at home and I plug to vsts...

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[Kirkus]

What kind of resistors should I go with Sensei Tim? Higher resistance or lower? Do I replace all 3 15k resistors?
As far as the transistors are concerned, they are real 2sk117's but they are the BLs and not the GRs as I couldn't find the GRs but I was told that it would be ok

[Sensei Tim]

You’ll have to experiment and see.  

On Sat, Aug 3, 2019 at 10:27 PM Kirkus [via Guitar FX Layouts] <[hidden email]> wrote:

What kind of resistors should I go with Sensei Tim? Higher resistance or lower? Do I replace all 3 15k resistors?
As far as the transistors are concerned, they are real 2sk117's but they are the BLs and not the GRs as I couldn't find the GRs but I was told that it would be ok

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[Travis]

If you’re trying to raise the voltage, use a lower value resistor. If you’re trying to lower the voltage, use a larger value resistor

You could temporarily replace the resistor with a ~25K pot, adjust till you’re happy, measure the pot and replace with a fixed resistor

[Kirkus]

Ok so i found a proper 30 volt power supply which makes no whining noise whatsoever!
Transistors are biased at half of the supply!
Output volume is still significantly lower than the input volume!
If this is normal and i'm troubleshooting a well working board i'm gonna lose it...
If this is not normal though i could really use some help!
I've triple-checked all of my connections and they all check out
I would like to remind you that i'm testing the board on Reaper DAW and not on an actual amp
Thank you all in advance and excuse me for repeating myself.

[Travis]

Assuming the layout/circuit actually works, it’s certainly possible that you have a cold solder joint or short

It wouldn’t be a bad idea to take an old toothbrush and clean the flux off the bottom of the board with some isopropyl. This will help reduce the possibility of shorts and let you get a better look at things.

It would be a good idea to check for shorts using the continuity test (diode symbol) on your DMM

Take a really good look at your solder joints. It looks like you’re using a soldering iron or solder that isn’t working too well. Your solder is not flowing nicely. When you look at a suspect joint, you could check continuity from the component leg at the top side to another part of the track on the bottom side

[Travis]

It also looks like you’re using solid wire which breaks easily

[Kirkus]

Hello again Travis and thank you for your response!
Let me start by saying I'm terrible at soldering! Absolutely terrible!
When I was building the board I had my dmm by my side and made sure that each and every leg I soldered had a good connection to the copper by touching the leg and the strip I was soldering on with the multimeter on the continuity setting!
After soldering each leg I also made sure that I had no unwanted bridges to the neighbor strips.
I don't have any isopropyl right now tbh to clean up the flux, unfortunately...Can I use plain blue alcohol?
Lastly, the solid wire I use is rather flexible and doesn't break by bending so far.

[Kirkus]

Ok so I went out and bought some isopropyl (as I didn't wanna take my chances with things like acetone etc.)
Cleaned the board thoroughly with a soft toothbrush and it's clean from flux residue now!
I also used a blade to go between the strips to make sure I have no bridges.
Then I used a camera as a microscope to make sure that there are no unwanted connections, and there aren't any!
Volume still low...Reaper reads about minus 8-12 decibels when I use the board compared to when I just plug my guitar without the board.

Please! Can anyone who built this confirm whether or not this is normal? I'm running out of troubleshooting here

[Sensei Tim]

Assuming there are no errors in your component placement, I still think it’s either the transistors or how they’re biased.

[Kirkus]

Sensei Tim if you could please share the voltages your transistors are biased at, it would really help me get an idea...