@billy
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Barry I’ve got the V1 board if you need me to build it let me know and I’ll get to it, just msg me any components you want socketed etc
If it’s gated throughout the entire pot range that would suggest too much resistance ie the transistor can’t reach correct bias voltage
Leave it as it is and check Q2 collector voltage with the pot fully CCW and CW to make sure that’s the only problem
I would just simply wire the pot to TR1 lugs 2 and 3 with no series resistance you shouldn’t have to place a jumper between lugs 2 and 1 if you’re only using lugs 2 and 3
A wee point to remember with 2 and 3 being used resistance will decrease as you turn it CW so obviously fully CW should allow more voltage through
So if you want it to go gated as you turn the pot up use lugs 1 and 2 to increase resistance CW
Hi Alan
Could you post pictures of the pcb and offboard wiring so that we can clearly see all components and trace the wiring
The most common errors with the mini me are not placing the BBD jumpers in or placing them incorrectly and not wiring the 2nd ground G2
Do you get bypass signal
Craig it’s a correct value you’d find a 7K5 easier or you could tepee two resistors in series to get the correct value
If I do that I use1/8th watt resistors if I can which are nice and small a 5K1 and 2K7 would get you there
You don’t have to be exact
Yes Steve the mods would be the same the differences are more to improve the pcb layout I think introducing the board mounted pot etc
That’s a reverse polarity protection diode 1N5817 or 1N4001 I’ve noticed Barry implementing the use of 1N5817 which has a lower voltage drop than the 4001
Either would be fine
Post some nice clear images so we can clearly see the pcb and trace your switch wiring it could be several causes a cold solder joint, switch or wiring fault
From your explanation it’s the diodes in the op amp feedback loop that seem to be the problem D1, 2, 3, 4 continuity check all components from IC1B pin 7 to pin 6 and the switch lugs to make sure there’s a good connection
All values and orientation that i can see look correct
Lug 2 of the volume pot solder joint looks like it needs more solder
Yes I think looking at the schematic you’d leave them out otherwise you’d get the diodes already in the feedback loop plus the ones on the switch position
I don’t think you’d need to jumper anything it looks like pads A and B connect to op amp pins 1 and 2 but continuity check to make sure
Your in jack socket has the ground lug connected to the 3PDT swap the white and black wires around on the jack socket
You can check the stereo jack socket by inserting a jack and following round to the solder lugs like this
If you’re not using a battery you would leave the ring lug unconnected
Cant see R2 clearly should be 200K red black black orange brown
It looks like 2K red black black brown brown but it’s out of focus so may just be the reflection
Your 7660 looks the wrong way around
Notch and dot to the right
It should boost pretty good Mack
It boosts the signal by around 38db afaik
The components mainly responsible for gain would be the emitter trimmer TR2 supplying negative feedback and the bypass cap C5
So I’d try adjusting TR2 and perhaps reflow solder joints I’ve built a few and it always boosts the signal
It sounds like you may have a build error what transistor did you use? If the transistor is in the wrong way it wouldn’t conduct properly
Your VB should be the same as the voltage on IC3B pin 7
You’d get half power 4.5v ish at the junction of the voltage divider R21 and 22 then drop a little after R23
I’m not a 100% If R23 would act as a voltage divider with R22 if it did I’d estimate around 3.6v if your power supply puts out exactly 9v
So whatever you get at pin 7 IC3B is your VB less a little voltage drop through components
Post some nice clear pictures so we can have a look you can check your gain pot as outlined here
Post some nice clear pictures Robert so we can clearly see all components
It’s easy to miss something especially in a circuit with a fairly high component count
I know I’ve done it more than once after checking a zillion times
A C1M or A1M should make it less severe with the more gradual distribution of resistance across the pot rotation
Obviously desolder at the pot lugs and not pcb solder pads to minimise accidental damage
You could of course have a faulty pot so you could check the resistance on the pot to see how it’s distributed as you turn it, put your meter probes on lugs 1 and 2 and rotate it both ways then do the same across 2 and 3 to see how gradually it changes
With a linear pot at halfway you should have around half the resistance
At fully CCW between lugs 1 and 2 should be zero to a small amount of ohms and 2 and 3 full resistance as you turn it CW 1 and 2 should increase 2 and 3 decrease
Post some nice clear pictures Mack so we can clearly see all components and offboard wiring to DC jack (if using one) etc
The power at the battery would be negative ground, so you would get a + voltage reading, it’s only inverted going into the circuit through the 7660S so use a circuit ground point to take voltages
It won’t actually matter youre just simply inverting the meter leads
Bias voltages are a guide I usually bias by ear to where it sounds good to me, sometimes depending on the transistor used it’ll be anything from 4.5v up to 8v
