Anyone had any experience with this circuit? or know why it is really quiet?

[harryskerritt]

Decided to build the DIY Strap mounted booster made by greg fryer. (https://fryerguitars.com/pedals-tech/)

After building it, the pedal doesn't really work as intended and is really quiet
I've attached an image of the front and back of my board as well as the schematic.
If anyone has built this circuit or just knows how to help it'd be greatly appreciated as this is my first pedal.

  I ordered all the correct parts (apart from the 4.3K resistor, i got a 4.7k as i couldn't seem to find any 4.3k's) and wired it up and it doesn't work. I have added a truebypass switch and LED, both of which work as expected. I also replaced the 47K resistor with a 50K pot (i couldn't get my hands on any 47K pots) like it mentions in the schematic as the end. Due to the wiring for my switch, jacks and pots the front view may be confusing. If needs be i'll add some more photos, but the green and red wire on the far left as the sheild (G) and tip (R) for the input. The red wire at the top is positive 9V. The blue wire, bottom right is ground. Beneath the two big green capacitors is the wiring for the 100K Level pot. the green and red wire towards the left beneath the blue capacitor is the wiring for the 50K volume pot. The black wire beneath those is the LED ground, and the blue wire above that is the output shield. The red wire next to the blue cap is the output tip. I do apologise for the bad photos, and hope my explanation helps.

[GibsonGM]

Hi Harry, welcome!
Can you go here, read it, and post the info asked back here?  Can you use a DMM?  That would be helpful!  https://www.diystompboxes.com/smfforum/index.php?topic=29816.0

You're right, this should not be quiet 

We'll help you figure it out. 

[Vivek]

Welcome to the group !


This circuit has quite a low input impedance. When driven by a guitar pickup, it will exhibit tone suck.


"Really quiet" can mean "Has high Signal to Noise ratio, no hiss, no hum"

or can mean "Has very low output level". I assume this is what you mean.



( I gave you your first "like" on this forum, to acknowledge the experimenter's spirit in building this circuit)

[anotherjim]

Works but quiet might be transistors the wrong way around so collector and emitter are swapped. That works but with really low gain. I suspect BC847 is CBE versus the more common BCE. Can't tell from the pic's what goes where but if they are CBE that puts the collector at the top ends in the component side shot.

Oh yeah, isn't the input bias bootstrapped with the B-E cap? Input impedance is then higher than it first appears, depending on gain. Where's Antonis when you need him?

[Ripthorn]

If you are relatively new to debugging, here's a good guide I put together that walks through a couple of the most common issues

[harryskerritt]

Can you go here, read it, and post the info asked back here?  Can you use a DMM?  That would be helpful!  https://www.diystompboxes.com/smfforum/index.php?topic=29816.0

You're right, this should not be quiet 

We'll help you figure it out. 

In reply to GibsonGM I've answered the questions

This circuit should have a treble boost effect, but currently has a very low output meaning it is hard to tell if the circuit is working.
Name: DIY Strap Mounted Treble Booster (https://fryerguitars.com/pedals-tech/)
I have substituted the 4.3K Resistor for a 4.7K, and the 47K Pot for a 50K one. Along with subsitituing the BC847 with BC547 ( the through hole equivalent ). Along with adding a true-bypass switch and LED.

The battery voltage is 9.09V when unplugged.
The circuit end red lead is 8.98v
The circuit end blac klead is 0v

Q1 Voltage:
C = 2.64v
B = 3.22v
E = 2.60v

Q2 Voltage:
C = 8.93v
B = 0.65v
E = 0.01v

All my electrolytic caps have a higher voltage on the + pin than the negative.

[anotherjim]

Q2 emitter may be short circuit to supply negative.

[harryskerritt]

Q2 emitter may be short circuit to supply negative.

The emitter of Q2 is connected to ground via a resistor.

[duck_arse]

Q1 base voltage is too high, should be around 1V6. hard to be sure, but I think you have missed a connection between the 22k resistor to ground and the Q1 base. can you confirm that connection? collector of Q1 is also wrong, but I don't see why.

also welcome. also, we can't see your offboard parts, we don't know how you have them wired.

[antonis]

Q2 emitter may be short circuit to supply negative.

The emitter of Q2 is connected to ground via a resistor.

If so, there should be "some" voltage reading on Emitter..

P.S.
Q2 is wired as an Emitter follower (buffer) but the single Base resistor bias method sucks,,

edit: Place a 560k resistor between Q2 Base and GND ans also see what duck-arse said about Q1..
(as it is, it's almost saturated..)

[Vivek]

The battery voltage is 9.09V when unplugged.
The circuit end red lead is 8.98v
The circuit end blac klead is 0v

Q1 Voltage:
C = 2.64v
B = 3.22v
E = 2.60v

Q2 Voltage:
C = 8.93v
B = 0.65v
E = 0.01v

Q1 has very little Vce collector to emitter drop. It is almost in saturation. It will give small amplitude, distorted signal

Q2 has too much Vce collector to emitter drop. It is almost cutoff. It will give small amplitude, distorted output

https://learn.sparkfun.com/tutorials/transistors/operation-modes


To get this working correct, Vce for both transistors should be in range of 2 to 6V

Which either means

There is some error in the schematic
or error in the build
or the transistors you used have different hfe


But in any case, this schematic will have very low input impedance and will load the pickup. Which means that when you get sufficient volume out of it, you wont be happy with the tone suck.

[Lino22]

I have a question about the DC filtering here.
I see the 100R is placed between the Q1/Q2 collectors, so the low pass filter works only towards the Q1.
Why it isn't placed between +9 and the first nod, so the R/C would work for both? Or is there a reason for that like suppressing the current going from C2 to C1?

[antonis]

Q2 is wired as a current amp (Emitter follower) so it might dip power supply voltage a bit..
We don't want to pass that voltage "dip" to Q1, which is a voltage amplifier..