April 19, 2021 at 7:02 pm #18276
Good evening all,
I am wiring up a combo build and am having some trouble with the Mini Me.
The bypass is working fine and the signal passes through fine when the effect is engaged but the sound is essentially the same as the dry signal. Would anybody know what would cause this issue from their experience?
I will work to provide some photographs and voltages later (voltages on Q1) and the CD4047 are lower than what is listed out in the build sheet.
P.April 19, 2021 at 8:54 pm #18277
Could be several possibilities Paul but it sounds like you have no modulation
Did you adjust the trimmer to find the sweet spot
Is it a kit there was a spate of kits containing incorrect values
One of the most common errors is not wiring ground to the G2 pad top left of the pcb and also not placing the jumpers correctly for the BBD IC2
But as I say there are other possibilities
When you post your pictures make sure all components can be seen clearly and post images of both sides of the pcb and all offboard wiring to jacks DC jack 3PDT etc so that it can be tracedApril 19, 2021 at 10:58 pm #18279
Thanks for the reply Billy. THat is correct, there is no modulation at all. This is not the kit so it is possible I may have used a wrong value resistors somewhere. Here are some photos. My voltages are as follows.
IC1 IC2 IC3 IC4
- 3.93V 5.96 1.81 1.81
2. 0.05 1.75 1.82 0.67
3. 0.00 0.04 1.76 0.00
4. 0.00 0.00 5.95 0.00
5. 0.17 0.00 5.96 0.00
6. 0.09 0.00 5.97 0.00
7. 3.91 0.04 0.00 4.83 (value oscillates)
8. 7.28 0.04 0.00 7.27
Q1 Q2 Q3
E 0.16 2.65 5.95
B 0.09 0.00 0.27
C 0.00 7.27 7.27April 19, 2021 at 11:06 pm #18280
G2 is connected to ground at the 2.1 power jack.
Using the MN3007 for IC2 and the jumpers are oriented vertically. I originally had a jumper at D4. I inserted one after reading a post from Cybercow that he prefers to use one regardless of the kind chipused for IC2. The build document said a diode could be used as well.
Please find a video of the issue here.April 20, 2021 at 7:16 am #18288
What’s your voltage both sides of R1 and did you test each board before installing into the enclosure
Your voltages all look too low but it appears with the fluctuating voltages the LFO is working all pins apart from 4 ground and 8 power on IC1 should be around half power your voltage divider resistors R32 and 33 look the correct 56K value so checking R1 voltages will let us know if you’re getting VB (bias voltage/ half power) to IC1
Its difficult to see R1 – 220K which should be red red black orange brown your 4th band looks grey which is 2M2? Could just be the reflection but that would definitely account for your low voltages
Easy enough to check resistance along that path without desoldering anything, with no power to the circuit take a resistance reading from VB the right side of R1 to IC1 pin 3 should read around 221KApril 20, 2021 at 8:47 am #18290CybercowModerator
Paul -after hearing your sound clip, I think the chorus IS working. To me it sounds like the trimpot just needs to be dialed in. One of the more frustrating points of this build (for me anyway) is that single-turn trimpot. The sweet spot is an EXTREMELY narrow position on the sweep. You have to fiddle with it in very tiny increments. Try starting with the trimmer t bout 10:00 o’clock and VERY slowly turn it clockwise – it should catch at around 1:00 o’clock – but you have to be patient and do it very slowly. Let us know how it goes.April 20, 2021 at 11:03 am #18293
The other two boards are working just fine on their own. It may sound silly but don’t want to disclose them until I share them in the build thread.I will take a reading from the VB side of R1 and pin 3 of IC1 to see what I get. I’m pretty sure I didn’t throw a 2M2 at R1 but it wouldn’t be the first time Iused a wrong value resistor either; I usually start populating with the lowest values and work my way up.
I’ll give this a whirl. I did try to dial the trimpot back and forth but heard no discernable difference across the sweep. The voltages are low so something is off; though it’s probably very touchy as you say.April 20, 2021 at 12:29 pm #18294
Done that on more than one occasion Paul
If your R1 4th bands orange it’s all good your R17 is definitely 220K so may just be the reflection
Also check the voltage you get at the junction of R32 and 33 bottom pads I think, obviously continuity check that’s where they’re connected to see if you get VB there as you should
As Cybercow says re the trimmer it would also affect your voltages to what extent I dont know
Found this for expected voltages note it’s 9.13v power going inApril 20, 2021 at 2:18 pm #18295
Thanks for confirming the value of R1, you beat me to the punch. I am not getting the 220k reading from the right side of the resistor to pin 3 of IC1.
i will check the voltages of R32/R33. I did refer to the older document for the voltages and they are considerably lower for IC3 and Q1. I try a continuity check.
Dialing in the trimpot still has no effect I’m afraid. No matter how slow I go, there is no discernable modulation that comes into the signal.April 20, 2021 at 4:34 pm #18298
Measured the voltage at the juntion of R32 nad R33 and am getting 0.02V. I am at a loss at what guessing what could be sapping the voltage.April 20, 2021 at 4:46 pm #18299
Use the schematic and trace it back Paul to see where it’s dropping out start at where 9v goes into R31 through it along to R32 and to + sides of C13 and 14
Reflow solder joints on those componentsApril 20, 2021 at 11:38 pm #18322
Started tracing, ..
8.72v at the right pad of R31.
5.54V at the left pad of R31.
5.54V at the anodes of C13 and C14
Measuring the right pad of R34 grounds circuit out.
5.54V at left pad of R34
5.54V at the top pad of R32
0.00V at the bottom pad of R32
0.00V at the top pad of R33
0.02V at the bottom pad of R33
0.02V at the anode of C15April 20, 2021 at 11:39 pm #18323
It sounds like R33 is the culprit. I did replaced it however and produced the same result. Is it possible there is a damaged trace from R32 to R33? Would a jumper fix this?April 20, 2021 at 11:54 pm #18327CybercowModerator
A quick and temporary solder-tac jumper couldn’t hurt to try. I’ve inadvertently created micro-fractures in over-working PCBs.April 21, 2021 at 6:55 am #18342
Your dropping 3 volts at R31 shouldn’t be that much with a 47 ohm resistor
What resistance did you get from VB to pin 3?
Is R1 definitely 220K was it just reflection making the 4th band look grey
From your voltages what we can say is your power supply is putting out 8.7v which goes into R31 then drops 3v through it, from what I can see R31 is the correct value yellow purple black gold brown but it’s not easy to see it’s slightly out of focus so we need to find what’s causing 3v to be lost it could be R31 or components around it C13, 14 your op amp pins 8 and 4 etc everything thats connected to that node
It is a fairly complex circuit but good point is you’ve got signal flowing from in to out you’re not far away from solving it 9 times out if 10 it is something simple like a dry solder joint, or incorrect value, it’s finding it that ain’t so easyApril 21, 2021 at 11:17 am #18346
Billy and Cybercow,
Thank you for your continued patience and help with me on this.
R31 is definitely 47 ohm, IT measures 0.045K on the DMM.
The resistance between pin 3 of IC1 and VB (pin 5, correct?) is 0.220M on the dot.
What do you make of the non voltage reading at R33?April 21, 2021 at 3:21 pm #18350
Update: I took out R31 and threw in a jumper. 8.72 V gets through the whole power supply until the junction of R32 and R33.
Somethign is definitely inhibiting the VB+ however. I don’t get any voltage readings at R33 and C15 or at R1 or pin 5 of IC1.
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