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o.k., much appreciated djazz, i'll do that.  once again, thanks to yourself and all here for the help getting me this far.

An update here: I had blown the BC337 transistor, so with that replaced, I am at least getting audio through the circuit now.  Woohoo!

However rather than boosting the signal, it's giving me a signal that's quieter than the original. 

The pot does work, and turning clockwise increases the signal from inaudible to a max of just very quiet. 

I've tried replacing the BC327 transistor and the IC chip too, but no improvement, still the same behaviour. 

Any ideas on what I've done wrong?

Thanks, djaaz, that would be much clearer alright - apologies.

So, I think it should be:

Q1:
E: 2.9V
B: 0.91V
C: 8.9V

Q2:
E: 2.9V
B: 0.86V
C: 0V


And thanks NorthCoast, I'll get replacements for those transistors and post an update here one way or the other.  Thank you for all the help!

Thank you all so much for your patience and help here. 

@jimilee: do you mean where the wire from lug 3 goes to on the circuit board?  from the top side, there isn't much solder there, alright, but from underneath it looks good.  i checked for continuity between the top side of those pads and the lugs on the potentiometer itself, and all have continuity. 

@NorthCoast: 
- Thanks re the transistor naming sleuthing!
- re voltage rating on C5 and C6, apologies again here for the newbie question, but do you mean de-solder them from the board first and then check the voltage (as described here, for instance: https://www.electrical4u.com/how-to-test-capacitors/)?  Or visually verify what's written on the capacitor? (in which case, it's 35V)
- i had a look at any potential physical contact between C5/C6 and neighbouring resistors, but there's clear daylight between everything.

- i've measured those voltages (to be clear, all measured without any of the IC, Q1 or Q2 in the circuit, rather than removing a single component at a time):

Q1:
Left: 2.9V
Middle: 0.91V
Right: 8.9V

Q2:
Left: 2.9V
Middle: 0.86V
Right: 0V

IC: (anti-clockwise, starting from bottom right, as per this graphic: https://startingelectronics.org/beginners/components/IC/8-pin-IC-outline.png)
1: 0.82V
2: 0.8V
3: 4.47V
4: 0V
5: 0.78V
6: 0.01V
7: 0.01V
8: 8.9V


I've also realised initially mixed up the placement of Q1 and Q2.  I thought they were identical components, but obviously one is a PNP and the other a NPN.  If I'm very fortunate, maybe nothing else will have blown, and getting replacement transistors in the *correct* place might solve the issue.  I'll order a spare TL072 while I'm at it, in case I've fried the IC too.

I can't thank you all enough for your help with this.  Good to be learning on this learning curve!

thanks, djazz!  can you point me in the direction of how to check i'm not going to blow the next one?  is it a matter of visually inspecting all the soldering, or is there a process to follow around the circuit with a multimeter or something like that?

Thanks, djazz, it looks like I've blown one of the transistors, which leads me to another newbie question: do the numbers/letters AFTER BC327 mean anything on the transistor?  The one I've blown is marked "BC327-25 T6 E" on the casing, but I can't find a local replacement with those exact markings.  Is, for instance, a BC327-40 BU transistor o.k., or does the "40 BU" mean something incompatible? 

Super, djaaz, much appreciated, and I'll disappear down the rabbit hole for a while and see what I can find...

sure thing:

I had a closer look and it doesn't look like there's any stray contacts from my dodgy soldering, as far as I can tell.

I tried passing audio through the circuit.  Bypass works fine .  However I'm getting nothing once the switch is engaged.  I presume this is because I blew something in the circuit (there was smoke from *something* the first time I powered up the circuit!).  If I remember correctly, the smoke looked to be coming from somewhere around C2/C5, but I can't be sure.  Is there any way I can track down what I've blown, or do I need to remove individual components from the board to check them? 

Thanks, NorthCoast, that's exactly what I need to know.  I've just replaced the LED, put in that 2.2k resistor, and SUCCESS!  The LED is lighting up and staying lit.  Thank you so much for the help with this.

Oh, that's super about the 3PDT grounding - I am indeed only getting that continuity when the switch is engaged - thank you again!

I'll take a closer look at the potential contact issues flagged by djazz now before I count my chickens...

thank you NorthCoast & djaaz, really appreciate the help on this.

@NorthCoast: yes, the LED flashed once the first time i pushed the 3PDT switch.  i'll replace that resistor leg with the 2.2k ohm resistor now and see if i get anything, but i fear i've blown some components.

@djaaz: thanks for looking over the pictures so closely, that's great help and i'll see if there is contact there, and see if i can manage to desolder any offenders...

I'm a total newbie with a soldering iron, and I'm trying to build Merlin's Glassblower booster from THCustom.  I managed to make some magic smoke on my first attempt at powering it up, so trying to figure out now what I've done wrong!

1) I've done some continuity tests with a multimeter, and getting a beep for everything that should be connected to ground from the circuit diagram.  But I'm also getting a beep between ground and BI or board input.  Is that correct, or does it indicate that I've shorted something out?  I'm also getting a beep from three of the 3PDT legs (if it were a smartphone keypad, they'd be numbers #1, #5 and #8)

2) Also, on the 3PDT board, it looked like a white LED was supplied with the kit, so I used a resistor leg to short across the RLED pads.  But I notice now that I have one 2.2k resistor left over from the kit - should I have used that in the RLED spot?

3) I've also put the multimeter across each capacitor on the board, and each one is giving me some kind of readout, so does that mean the capacitors are o.k., or is it still possible I've fried some of them?  And is it likely I've fried some other components, the transistors or the IC, for instance?  Is there a way I can check those with the multimeter?

For reference:
- for wiring the jacks, battery & power socket, I was following this: http://www.diy-musikding.de/content/001-Basics/battwire.pdf
- for populating the board, i followed these instructions: https://diy.thcustom.com/?wpdmdl=3881

Apologies for my newbie-ness, and I'll probably end up ordering a replacement kit from THCustom, but I'm also keen to learn from my stupid mistakes rather than repeat them.  Thank you for any help you can offer!