SOLVED Pharmacist pedal lights no effect

[johnzero0]

Hi guys

I wonder if you can help, i just built a pharmacist pedal and after painstakingly ordering the individual components im getting lights but an almost inaudible low volume output with pedal engaged. pass through is working fine.

 

[eh là bas ma]

If I understood correctly, you said :

the signal is allright from R1 to Q4, nothing to report on 99% of the circuit, it suddenly cleans up at C16, and the volume drops significantly on the Volume pot.
However, all components in Q4 and C16 aera are perfectly ok, checked and triple checked, and the Volume pot is ok too ?

There has to be something you are missing...

Edit : I would try to reflow all pads in the aera, and do a continuity test on the rest of the signal path : from the Volume pot to the pcb's pad Out, to both switchboard Out pads, then to the jack Out.
No change on the volume pot if you engage or disengage the boost, i guess ?

 

[johnzero0]

If I understood correctly, you said :

the signal is allright from R1 to Q4, nothing to report on 99% of the circuit, it suddenly cleans up at C16, and the volume drops significantly on the Volume pot.
However, all components in Q4 and C16 aera are perfectly ok, checked and triple checked, and the Volume pot is ok too ?

There has to be something you are missing...

Edit : I would try to reflow all pads in the aera, and do a continuity test on the rest of the signal path : from the Volume pot to the pcb's pad Out, to both switchboard Out pads, then to the jack Out.

Im going to go back over the signal path i think i noticed a slight drop in volume earlier at r11-Q3 but it got louder at Q3 so i assumed it was the point the overdrive effect was added.

edit : “No change on the volume pot if you engage or disengage the boost, i guess ?”
i didnt want to mention boost as seems to be more or less ok, i had to adjust the boost internal trim pot as it was clipping at full now it is fine ie boosting the weak signal, I have not tried to adjust the normal volume pot whilst boost engaged yet.

 

[johnzero0]

Boost engaged all controls work except volume adjusting this doesnt do anything.
Also with boost engaged i am no longer detecting audio signal from Q4 p2 or 3

 

[eh là bas ma]

Boost engaged all controls work except volume adjusting this doesnt do anything.
Also with boost engaged i am no longer detecting audio signal from Q4 p2 or 3

One of the Volume's pads should be connected to both R28 and R29 (Volume pin 3 on schematics). Does this pad have audio signal coming in ?

No audio on this part of the circuit is to be expected when boost is engaged. The Boost 3PDT is switching between these two sections of the circuit, it's either one or the other that will have audio.

 

[johnzero0]

Yes the volume pot pad closest to edge of the board and also the pad next to it has continuity to one side of both r28 and r29

With gain pot turned full on I can hear audio in these 2 locations
And volume pot controls the volume when probing audio on the middle pad on volume pot but the audio is extremely low volume

 

[eh là bas ma]

and also the pad next to it has continuity to one side of both r28 and r29

I am not sure there's supposed to be continuity between the volume's middle and outer pads... I could be wrong, but you may have a short. Clean the spaces between pads (without overheating the board), and have a close look to the pot's legs. Nothing should touch the pot's body and legs in the enclosure, put some tape on the inside if you have to... use any means necessary.

Edit 2 : ...and of course, reflow the volume pads. Make sure the pads are filled, not too much, but enough solder.

the audio is extremely low volume

Check R28 and R29 values, if the resistance is too high, it will decrease the volume.

Edit : i checked with a resistor viewer, and it looks good. Check if one side of R28 is connected to ground. Is the volume dropping at R28 or at the Volume pot itself ? If it's the volume pot, you should focus on it.

Edit 3 : If you really can't find any short on the pot, in last resort, I would try an other one. If you are confident in your desoldering skills, you can try to take it off. Otherwise, you can gently cut its legs with pliers, and it will be easier to take off the remaining bit of legs. You can also use wires.
If you take this path : while the pot is unsoldered and all pads empty, check if the two volume pads (middle and close to the edge) have continuity on the board.

Edit 4 : I checked on a similar volume pot of one of my builds, and there are no continuity between volume pads... I guess that's your issue.
We found it !

 

[jimilee]

If you turn the volume pin all the way down, you will have continuity between pins 1 and 3. If you turn it all the way up, you will have continuity between two and three.

 

[johnzero0]

If you turn the volume pin all the way down, you will have continuity between pins 1 and 3. If you turn it all the way up, you will have continuity between two and three.

Thanks for that input jimilee unfortunately i think that you are right and this is the case, since i have such low volume a lot of my testing is the Vol pot full up.

Something strange on Q4 since on 2 of its legs the audio is what i would expect. i have replaced this component but have the same. i am not sure of the properties of this component perhaps this is normal?

 

[jimilee]

Thanks for that input jimilee unfortunately i think that you are right and this is the case, since i have such low volume a lot of my testing is the Vol pot full up.

Something strange on Q4 since on 2 of its legs the audio is what i would expect. i have replaced this component but have the same. i am not sure of the properties of this component perhaps this is normal?

Depends on which two legs you have audio.

 

[johnzero0]

I have audio on legs 2 and 3 of Q4
That is the Source and Gate of the 2n5457 respectively

Edit: The vol pot has no effect on the volume of the audio in this place and the audio sounds like i would expect this pedal to sound like ie overdriven audio not clipped / faulty sounding.

 

[jimilee]

Honestly, your soldering could use a reflow in all the joints, they shouldn’t be big blobs, they should look like little Hershey kisses and the solder should flow through the board. If you look at two of the pots on the right(from the top) they look to have no solder at all. If you can do all that, I will bet you have better results. After doing this for 10 years, I still have to occasionally do that.

 

[johnzero0]

Honestly, your soldering could use a reflow in all the joints, they shouldn’t be big blobs, they should look like little Hershey kisses and the solder should flow through the board. If you look at two of the pots on the right(from the top) they look to have no solder at all. If you can do all that, I will bet you have better results. After doing this for 10 years, I still have to occasionally do that.

Thanks Jimilee, have done that and checked for bridges and continuity on suspect joints. I believe we have narrowed it down to the last part of the circuit using the signal path kindly supplied by eh la bas ma.

Reading some some similar posts there are some problematic 2n5457s out there, i wonder if my batch from Mouser could be the cause?

although i believe my post on the voltages on legs of the 2n5457s earlier are ok?

 

[johnzero0]

Guys i have built another Pharmacist using the same parts and i have exactly the same issue, so i dont think its a short or a bridge it must be an incorrect value resistor on the board

 

[eh là bas ma]

using the same parts

Do you mean you desoldered every parts from the first pcb, and use them on the second board ?

i dont think its a short or a bridge it must be an incorrect value resistor on the board

If you have tested and measured every components with your multimeter, before soldering them on the board, they are most probably ok...
Can you confirm you have tested every parts ?

Do you mean that you suspect there is an issue the BOM ? I didn't build this circuit, but I think other forumites have built it without having any issue.
You can look for "pharmacist" in the search bar, to find exemples.

Have you socketed your transistors ? Could be an orientation issue... I know there can be some pinouts variations between europe and usa. Or one of them is bad, maybe.

"exactly the same issue" : The signal cleans up at C16 and volume drops down at Volume pot's middle lug ?

You can try to desolder C16, R28, R29, even C17, re-check their values with your multimeter before putting them back, they are the main suspects in this matter.
Also check if you have continuity between all the Ground pads and connections (switches, jacks, pcb, DC power jack).

 

[johnzero0]

Do you mean you desoldered every parts from the first pcb, and use them on the second board ?

I used the same BOM on another board, original board is still populated. After testing output which was extremely low and boost Which worked i used the audio probe, the probe had same result in same areas extreme low possibly clean audio from c16 and onwards including the vol pot. At Q4 i got overdriven audio on 2 legs only (2 and 3).

 

[eh là bas ma]

You mean signal stops here ? Or is it some clean signal ? Does it respond to the Gain control ?

The gain control is before Q2 and Q3, I would expect some overdriven signal on these too... not only on Q4.

Edit : There are a few trimmers, I'd set them all at 12', until everything works. You can fine-tune them to your taste later.

 

[johnzero0]

Yes the audio was very low Hard to tell clean or not but i just tried again. the gain control does have an effect. if the gain pot is not at full i cant hear any signal, turning the amp up and gain pot full i can hear a signal at the point indicated in your diagram leg 1 of Q4 and it is overdriven just extreme low volume.

Edit trimmers have been tested and adjusted during testing but they are all set at noon now

 

[eh là bas ma]

i can hear a signal at the point indicated in your diagram leg 1 of Q4 and it is overdriven just extreme low volume.

To be clear, signal's volume is allright at C15 and Q4 pin 3 ? It's only at pin 1 that the volume is dropping ?

If so, Q4 is probably ok, the issue might be after this point. Q4 pin 1 is connected to Q5, C17, and C16. One of these could possibly be messing with your signal.

I would carefully check this aera :

Check ground connections, components values, continuity tests, reflowing pads...

Edit : Did you audio probe the beginning of the circuit, from the input jack until Q4 ? Isn't it possible that there is an other volume drop before this final section of the circuit ?
I mean there is a possibility that there is nothing wrong with this aera in green : because the volume was supposed to be much louder before getting to Q4... Only way to make sure is to check if there isn't any other suspicious volume drop earlier in the signal path.
The volume at C15 should be at least as loud as at the Input jack's tip, probably louder if the gain is set above 12'.

 

[johnzero0]

I've gone over the audio path again and up to C15 is great and is much louder than input jack tip only starts to go very quiet at leg 1 (drain) of Q4 as stated also I've gone over my readings of Q4 to be sure,

leg 3 gate - 0v
Leg 2 source is 1.3v and
leg 1 drain is 16v.

Leg 2 ( source) of Q4 does connect to R25 and on one side of R25 I have 1.3v and the other side to ground is 0v.

 

[eh là bas ma]

Maybe some clear pictures of the soldering side, showing Q4 and Q5 aera could be useful.

Maybe we can spot something that you're missing.

As I said in reply #58, pin 1 is connected to several other components, the issue could come from one of them.

What are your readings on Q5 legs ?