Warden compressor Vero build help

[duck_arse]

phew.

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Thanks for taking the time to write that detailed explanation. That cleared a lot up for me. Ok, so I removed the caps you specified and here are my voltages (exactly what you just explained)

Tl072
1, 9
2,9
3, 4.5
4,0
5, 8.8
6, 9
7, 9
8, 17.92

Mpsa18
C 10 5
B 4.2
E 7.4

5089 (both)
E 0
B 0
C15.1

[duck_arse]

well now, that prooves something, doesn't it? no, really, doesn't it?

if I squint hard enough I can make those readings look suspicious, but they are the best we've seen, so let's carry on. next step, just to humour me again, please measure the resistance across the pads where each of those caps came out while they are still empty - they should ALL read open/overload/nonsense. any showing a stable reading across the empty pads is suspicious.

so they all read open, yes? now replace a cap, the 100nF in the gain leg first, power on and remeasure the IC voltages. power off, replace the input cap, power on and measure ...... then the pin1 cap ...... the pin 6 cap .... and pin 7 last. if the voltages change at any step, stop and report. nearly there.


[edit :] just so we don't tempt fate, and to rule out possibles, replace with new caps if you can.

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Yes, yes it does. I think it was a faulty 1uf elec cap, but I still went through the motions as instructed. Resistances seemed right so I moved forward and was placing the 100nf cap back to pin 4, checked my voltages and now everything is about half of what it was.

1, 4.46
2, 4.46
3, 2.17
4, 0
5,4.35
6, 4.45
7, 4.45
8, 8.83 (which has consistently been close to 18v the entire time)

So of course, I remove the 100nf cap and voltages did not change back. They stayed exactly where they were while it was in. The mpsa was damn near in half as well

Mpsa18
C 5.4
B 2.1
E 3.38

5089s
0
0
0

Now, I'm confused.

[duck_arse]

you both proved and disproved my theory at the same time. I was thinking there was still a short somewhere, but it shouldn't have changed when you pulled the caps. and having come right, I can't fathom how it's gorn rong agin. lucky, I spose, it was the first cap in. but it doesn't make sense to me, anyway I look at that string and the voltages, unless it's the section we've so far discounted - the power supply. but again, I can't see how adding that cap would upset the supply.

if I squint hard enough I can make those readings look suspicious, but they are the best we've seen, so let's carry on.

what we really need is a passing qualified person to throw in some reasoned ideas, they might suggest the opamp might be oscillating or somehow going unstable. failing that, I'd be removing the chargepump IC and trying a different one if you have one, otherwise I'd get a pair of nine volt batteries and wire thm for 18V, and connect them to the Kathode of D3. then measure voltages around the TL072 again. hopefully there will be a wisp of smoke to show where the problem was.

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Checked all my resistors again everything seemed fine. Caps in circuit seem ok. Checked for bridges and a solder reflow. Nothing changed so I put in a new 1044 and here's what I
1, 9.01v
2, 9
3, 4.5
4,0
5, 8 8
6, 9
7, 9
8, 17.83

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I started replacing caps one at a time measuring voltages each time and the culprit seems to be the 100nf cap going to ground from sustain three the first two caps I put in slightly lowered my pin 1,2,3 voltages but when I put the 100nf cap in, pin1 bounced around from 16v down to .54v to 2 v just all over the place.
1, wandering
2, 12v
3, 16v

[duck_arse]

I started replacing caps one at a time measuring voltages each time and the culprit seems to be the 100nf cap going to ground from sustain three the first two caps I put in slightly lowered my pin 1,2,3 voltages but when I put the 100nf cap in, pin1 bounced around from 16v down to .54v to 2 v just all over the place.
1, wandering
2, 12v
3, 16v

the first two caps? you were supposed to put the 100nF to ground first! something I noticed on you baord, there is a long cut on the top left side where ground and 9V wires join. get your soldering iron and heat the little bits of copper until the glue under melts, and the copper sticks to the iron tip. this works better/quicker with a fresh dob of solder on the tip.

remove any of the caps around the opamp you've fittted. tack in a wire between the bottom of the 22k bottom left of board, across to the pin 5 track, so that resistor is connecting to V/2. now power on and measure voltages. they should [as per usual, should] be rock steady.

people get ready, gonna do the rock steady, uh-huh. uh-huh.

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So I removed the slivers with the iron and ran a jumper wire from 22k resistor over to pin5 track and As usual you are 100% correct.

1, 9.1
2, 8.8
3, 4.4
4, 0
5, 9.1
6, 9.2
7, 9.2
8, 18

I also have a question why is the voltage on pin 3: 4.5v instead of 9v?? From looking at the schematic and based on the things I've read on op amps, this is a inverting amplifier correct? From what I've read op amps try to keep both input voltages the same (closed loop config) and pin 5,6 and 2 are 9v so why 4.5v at pin 3 and the fact that pin 5 is tied to 9v, is that what makes 6 and 7 9v?? I know you explained this already I guess I'm just verifying I fully understand.  Regardless,  pin3 is still a mystery to me.

[duck_arse]

when you apply 9V bias to the (+) input, the output pin will follow, and also sit at 9V. because the output has a feedback connection to the (-) input, it also sits at 9V. so pin 5 MUST always be at 9V, no matter what, cause it is connected to the middle of the two resistors from 18V to ground. pins 6 and 7 MUST follow, should be at 9V.

pin 5 is also connected to the 9V by a resistor, so when you measure the voltage at pin 5, the meter looks like a resistor to ground and adds some load. if the output pin reads 9V, and the (-) pin reads 9V, it doesn't really matter what the reading at pin 5 is cause the opamp is giving the correct results, because/while you aren't probing across that resistor.

so it follows, if yer meter is a 1M input impedance, and you measure across a 1M resistor tied to 9V, the meter red probe is now in the middle of a voltage divider. if you put a second meter to the output pin at the same time, you will see the correct 9V when the input meter is away, and the wrong [yet still correct] 4V5 when the input measuring meter is there.


to your build. there is a capacitor missing from the layout, a 100nF ceramic between the opamp supply pins, shown on the circuit - this is considered a mandatory addition to opamp circuits in general. you want to wire it as close to the pin 8 as you can, preferrably without all the usual vero up and around and along. across the IC pins is good, under the board is fine. this shouldn't cure the problems .......

the input/gain stage is non-inverting, the output/tone stage is inverting. the mpsa stage is also non-inverting for audio.

it is not unknown for opamp circuits to behave wrongly when ground is used as audio ground instead of the Vbias voltage, in this case 9V. the reverse also proves to be the case in some instances. it might be a test to try - take the 22k/100nF cap to the pin 5 voltage instead of the 0V supply ground.

did you go any further after adding that wire? did you add the in or out caps to see if the whole thing held up? I rekon try the 100nF to V/2 first, if the volts appear good then add the input cap and remeasure, etc.

[edit :] are there any documented cases of this circuit built to this layout working correctly? and by correctly, I mean with the correct voltages listed.

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Sorry it's been a busy few days with work and family. I placed the jumper and replaced all caps and my voltages are
1, 9.2
2, 8.6
3, 4.3
4, 0
5, 8.8
6, 9
7, 9v (level pot fully CCW) 12.44v (FULLY CW)
8, 17.8

Still getting unwanted distortion/overdrive sound. At this point I've considered just buying the pcb or rebuilding the Vero from scratch but at this point, this has become quite personal. A pride thing if you will. 😆

[duck_arse]

pin 7 voltage changes w/ pot rotation? what now?

measure at the IN wire for DC voltage - should be none, or 0.0something millivolts. measure at the OUT wire for DC volts, should be about the same reading.

do any of the other pin voltages change when you turn the level pot?

what haven't we done yet? haven't removed the ldr. haven't removed any the pots and replaced with short or resistor. haven't done the power section replacement w/ batteries test. haven't removed the IC socket to have a look at under it.

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Yeah exactly pin 7 voltages changes with the full sweep of the level pot. All the way down 9v all the way up 12.44v. I see on the schematic level 1 is connected to pin7 and Level 2 is pin 6. I'm assuming this shouldn't be happening. I measured my dc voltages on the in and out
In 0.002v
Out 0.004v
I removed all caps from power section, tested and replaced. All were within range. I retested all resistors and all were relatively close (except the two 1M next to the clamping diodes and the *2M2*) I retested my pots all were sweeping accurately. I replaced the vactrol. I've tried different 1044s, Tl072s and even a 4558. So before I take out my charge pump and run these batteries let me verify EXACTLY  what needs to be done. Run two 9v in series for 18v and connect to cathode of D3 and other to ground, correct??

[duck_arse]

that was a plan, yes. but now, see, you have found something. something, somewhere, somehow is pulling pin 7 towards 18V, being as that is your only voltage higher than yer measured 12V44. and we can't see what it is, and I can't understand the mechanism. do any of the other pin voltages change when the pin 7 changes?

measure the resistance of the strip from pin 8 to the right board edge. measure the resistance from pin 7 to the board edge. measure the resistance from pin 7 to the 18V stip mid-board as you turn the level pot. we are interested in the value at either end. measure resistance pin 6 to 18V too.

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Ok I tested my resistances.
Pin 8 to right side  59k
Pin 7 to right side 207k
Pin 7 to 18v .91M - .93M
Pin 6 to 18v 150k-225k

No other pins changed voltage with level pot and Pin 7 is consistent from 9v-12.44v. I used the 18v strip that the mpsa18 collector is on but on the side the "IN" is on before the cut next to 10k and then mpsa18 collector. I'm assuming this is the one you meant.

[duck_arse]

Ok I tested my resistances.

Pin 7 to right side 207k

I'm really hoping you've measured and reported this reading correctly, because, as I look the layout, it should read 0R. there are no cuts showing on the layout on that track, so if your reading is correct, go along the track from hole pair to hole pair and find where that resistance appears.



those areas circled have bothered me for a while, now.

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Ok I tried again and all extremely low or wandering resistance. Idk why or what I did last time. I went around and recut through my traces again and reflowing the area you circled. Still distorted. I've looked this layout and build over so many times. I don't even know how to proceed at this point.

[duck_arse]

wandering? should be, MUST be dead short, constant, from pin 7 out to edge, no wandering allowed. if I had the thing here, I could apply the technique - idly probing and pondering, but I'm not smart enough to point at your numbers and say 'it's a b or c', especially with vero involved. so, all I can advise at this point is to start a new build. take extra special double care with your cuts [show us before soldering], use all different components, and hope it works the second time.

[added :] build a new, yes, but don't strip the current bad one. then, WHEN the second builds fires right up first bloody go, you can compare and contrast the two to play spot the difference. and you end up w/ two working compressors. in theory.

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Ok will do. I report with the new build shortly. Thanks for all the help man. Much appreciated.

[duck_arse]

good luck.