Hello team MBP,
I'm in the middle of testing out my voltages on the ICs before I rock my box. I stated off with the 4558 ICs since there were so many of them. I'm not even sure I am taking these readings correctly. What I've been doing is putting my red probe on pin 4 and using my black probe to read across each pin. I.e., Pin 1 connected to Pin 4 gives me Xvdc.
My voltages seem to be all over the place on some of these ICs. IC1, IC4, IC5 all appear to be okay. IC3, IC9 are wozzed up.
IC3 P1: -9.3vdc
IC3 P2: -12.6vdc
IC3 P3: -12.8vdc
IC3 P4: -14.8vdc
5,6,7 all fine. pin 8 reads 0vdc to ground.
IC9 P1: Varies
IC9 P2: 7-8.6vdc
IC9 P3: varies
IC9 P4: -15vdc
IC9 P5: varies (7-9)
IC9 P6: varies (8-9)
IC9 P7: 8-9vdc
I could totally be doing these readings incorrectly. But any help would be appreciated. I did try to google the heck out of how to measure and test 4558s but all of the videos are in Hindi ...
Welcome! To measure 4558s or any other passive, put the black prone on any ground point and measure with the red probe.
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As said, you want the black probe at ground level. I use the input jack ground for readings.
Your readings are strange indeed, if you did if from pin 4 to pin x, why is IC3P4 -14,8vdc? Shouldn't it be p4 to p4=0vdc?
The 4558 is a normal dual opamp, so the readings are done as for a normal OpAmp.
Check a video of how to read circuit voltages and it will be the same. I guess the extra load of the voltmeter is negligible here.
I measured the voltages again this time grounding my black probe to the ground lug of the jack. Now I have verified all of my voltages are within 5% of what's on the spec sheet provided by MadBean.
I tried hooking up my oscilliscope (Rigol 1052E, hacked to 100Mhz) but I have no idea what I'm looking for on the screen to measure the BBDs and timing chips. So I tried to just plug the pedal into my amp and all it produces is a loud hum, no signal. I may have hooked up the jacks wrong as they are stereo jacks and I always get the wiring backwards.
You want to look at the signal after the BBD and see if the BBD is correctly biased (there is signal coming through, and the signal is symmetrical, and not distorted on one side).
You will need a signal generator, that produces a sine wave or strum your guitar while measuring. With a sine wave it is easier, because the wave is symmetric and periodic. Try 0.25V at 600Hz.
Ground probe of the oscilloscope should go on ground and the other probe goes at the first BBD input. If you get signal at the input, it is working until this point. Then, check if there is signal at the output of the BBD. It will have lots of clock noise. If there is no signal adjust the bias trimmer until the signal is visible. You will have to do the same for the next stage.
The gain trimmer is used to get unity gain between stages.
Ahhhh! Okay so I don't have a signal generator (yet) so I'll have to use my guitar. Here's to hoping it works! Will report back.
There are app based signal generators that work well. I use Function Generator PRO on my phone. You can build a 1/8 stereo to 1/4 mono converter out of an old set of headphones. If you have kids, you defiantly have a broken set somewhere ;D
Yes, I like to use audacity (pc).
You can define the kind of noise or signal, freq., intensity and so on. You just need a cable that goes from your computer's audio output to the pedal input.
Great idea! What would be a good signal generator to purchase for pedal and amp work like this? I have a Rigol 1052e hacked to 100Mhz.
Ditto looper works fantastic.
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I dunno if my scope is jacked or the pedal is jacked? When I put a signal from the looper across the input of the pedal and measure at pin 1 of IC6 I get nothing but junk on the scope. Any suggestions for what I'm doing wrong?
I have tried it set on AC and DC. I have 10x prob on. I'm using Channel 1. I've tried auto and manual capture. I messed with horizontal and vertical and trigger. I've adjusted the bias to max or min and I'm getting squat.
Also, maybe I wired my jacks incorrectly? Could someone take a peek?
Ok, pin 1 of IC6 (BBD) is ground=0V.
The input of the BBD is pin 7, while the outputs are pins 3 and 4 (take a look at the schematic).
I am guessing here, that you already checked the voltages and the problem is with the continuity of the signal path.
If you are not sure how to use the oscilloscope, try using an audio probe first, you can easily build one yourself:
(http://diy-fever.com/wordpress/wp-content/uploads/2010/07/audio_probe_socket1.gif)
In my opinion, you need to know at which frequency you are looking at when using the oscilloscope, otherwise you could be checking it at a wrong configuration and it will be barely visible. The audio probe will give you an easy way to assess if the signal reaching the ICs.
Then play some music or use your looper at the input of the pedal and touch some points along the signal chain to check if you have signal, it will play through your amp if there is something. That will also help sorting out any problem with the wiring.
The input is the left jack shown in the drawing (j1, orange or green wires). Check the signal at every IC input and output:
IC input output
IC1A: 2 1
IC1B: 5 7
IC2A: 6 7
IC3A: 3 1
IC6: 7 3 or 4
IC4B: 5 7
IC7: 7 3 or 4
IC4A: 2 1
IC3B: 5 7
IC5A: 3 1
IC2B:14/15 10/11
IC5B: 5 7
And check at both sides of the blend pot. With music or the looper playing, if there is signal you will hear it and you can move to the next point. The second half of the compander has 2 inputs and outputs. Check both of them. Let me know where the signal vanishes and look around that point if you can find a wrong resistor/capacitor or a large solder blob (colder joint). You can check for colder joints with your multimeter (continuity or diode mode).
If there is no signal at the output of your IC it could be a bad IC or a problem with one of the resistors/capacitors that sets the gain of the stage.
Looks like the jacks are wired wrong. Use you DMM to fund out which is the sleeve and which is the tip.
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I've built an audio probe but am putting this one on the shelf for a week or two. I had a back log of pedals that were were ready be boxed up and decided I needed some time away from the DMM. I just finished a King of Tone clone with original MA858 and 1S1588 diodes and it sounds great. And I'm in the process of finishing a Univibe clone.
Once I get those two done I'll put a pin on building anything new so I can focus on the DMM and I'll resurrect this thread in a week or two if I run into trouble. Thank you for all of your help! :)
I think for scope work, you want to get the app based signal generator or a computer based one. A sine wave is much more informative than a guitar signal on the scope, and as Thomas said, you will want to set the frequency. The "Function Generator PRO" I recommended, is a few dollars and IMO well worth it.
To set up your scope, first thing is always to dial in on the input signal, right at the tip of your input patch cable. I believe the Rigol will have an AUTO button. When you press that it should put the scope in a good freq and voltage ballpark, then you can fine tune from there.
I'll for sure get the app!
So, after getting my king of tone rolling, and almost done with a shin-ei Univibe clone, I've had a chance to poke around with the memory man again.
I plugged it into the amp tonight and I'm definitely getting bypass signal, though it's real low output (true bypass wiring) and when I engage the pedal I hear the delay working!
What isn't working is a nasty ass hum that overtakes the entire signal, whether bypass or engaged. Maybe pots touching the solder blobs. Dunno yet but I put down some electrical tape. I'll test it tomorrow and see what it looks like.
I also created a voltage testing spreadsheet with all of the references values, so ill do a full measurement run and post on google docs.
That sounds like a good plan.
First, low signal in bypass mode means there is something wrong.
In true bypass, and with a 3PDT, the signal should go directly from the input to the output jack. You can check the layout from Brian's PDF and brown wires are grounded, while orange wire connects to jack's blue wire when the 3PDT connects the lower pins. At the same time, input of the board (green) is grounded by brown wire on the 3PDT. You can check this with a multimeter. Just check if you have a good continuity. If you abused your 3PDT it can also introduce some resistance, so try measuring the resistance between jack tips. It should be almost 0.
This test should be done with the pedal unplugged (no power), since in true bypass the pedal is just part of the cable. So there should be no hum in the signal.
If there is some short between the back of the pots and the board it could create some problems. Tape might be too thin. I had cases where the tip of the solder blob just perforated the tape. Since then I use a thick plastic sheet (0.5 mm? It is thicker than an overhead projector sheet).
If you can lift the board, so that the pots won't touch it, it would be better. If we can roll out a short with the pots you can check the rest of the circuit. Most likely a lack of grounding somewhere(cold solder joint?).
In this wiring diagram for true bypass switching are lugs 4,5 and 9 supposed to be wired together as shown? Or 4 and 9 to input tip and 5 to board?
Hello folks! Wife out of town and kids in bed. So, I had time to do a full measurement on the board.
Audio-wise -- the hum in bypass or effect mode is still full on. It's even worse than before.
Included here is a link to my voltage tests with all ICs in, powered with an EHX 24v adapter. As far as I can tell, all of the voltages are pretty damn close.
If you have a moment to review I'd really appreciate the confidence check.
https://docs.google.com/spreadsheets/d/1_148Y8SX5kXWO9-Wrv2Y6N1t137AuvCW/edit?usp=sharing&ouid=115840715864376621355&rtpof=true&sd=true
Have you given the audio probe a try, to identify where the noise begins? Sometimes correct voltages at the ICs is not enough.
Anyway, looking at your table I would check everywhere where there is a difference of almost 1V. For example, IC3A, pins 1 to 3. But it makes sense, since pin 7 of the NE570 is also different.
IC4B is also lower than expected. Weird, because its bias comes from IC4A, where the voltages seem OK. They both should have similar voltages on the signal pins of around -7.5 (VB). You can check for shorts, or wrong parts.
My mistake, IC3B comes after IC4A in the signal chain. IC4A is biased by the trimmer and matches the BBD input.
I'm guessing differences in IC6 and 7 (BBDs) are caused by the bias of the BBDs, which can vary.
PS. Some suggestions to rule out some common problems:
1. Bad Jacks or 3PDP: Test the pedal without the power supply. If the true bypass signal is strong and loud there is not problem here.
2. Dry signal with power supply, aka clean booster: The dry signal only goes through IC1A and the blend pot. With the blend on 100% dry and feedback/repeats on 0% check the output with the pedal engaged. You should hear the clean signal only, without delay, and the output can be controlled by the level pot. There should be no noise, since there is no feedback and no wet signal. If it still hums check all components that are nearby and go to ground.
3. Identify where in the wet signal the noise starts: Remove the BBDs from their sockets. If there is still noise it must be introduced after the second BBD. If it stopped, insert the 2nd BBD in its socket. If there is noise, it comes either from the BBD or from the previous gain stage (IC4B). If there is no noise, it comes from a stage previous to IC4.
4. With the audio probe you could just check different positions of the circuit without having to remove the BBDs to see if there is Hum or not. If all of them have some hum, it is probably something like a missing ground of the power circuit.
5. Every time I had a loud hum in a circuit it was a cold solder joint on a ground pin. Check the continuity between the ICs/resistors/capacitors ground pin and the jack ground. If there is continuity move to the next one. Do not measure it directly on the solder blob, sometimes the solder makes contact, but the pin of the component don't.
Hope it helps you in some way.
Hello! I haven't had time to use the audio probe yet. I did do all of these tests below. Here are my results:
1) Bypass mode w/ no power -- dead silent, no hum, pure signal goodness. Sounds amazing.
2) Dry only -- lots of hum
3) No noise/output with the BBDs removed. Insert one, hum. Insert two, lots of hum. On power or not.
It really seems like when using the blend pot to bring in more wet signal, obviously, the hum gets way worse.
Seems like the wet circuit is totally jacked though I'm not sure why. I have gone over every blob 2x at this point.
I haven't done the continuity checks yet but I will do those when I have some time and report back. I appreciate all of your patience. I'm definitely swimming in the deep end here, but just from your last post I have learned so much!
**When pulling an MN3005 out of the socket I accidentally broke off the small/thin part of the leg. Can I just solder a good lead onto that to fix it?
You can do that with the 3005, you might want to replace it eventually.
We definitely need voltages and very clear well lit close up photos of both sides of the board and off board wiring, please.
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As requested!
Well, without the BBDs the dry side should work at least...
It seems the second BBD might be creating a problem here(if you added it first)?
I made a mistake here, now I see that after IC4A comes IC3B and not IC4B. IC4B comes before the second BBD and is biased by the trimmer. It also matches IC7 pin 7, so no problem here, my bad.
Thanks for the pictures, there are some suspicious solder points. Look for the ones that look like a large round drop or where it looks like there is a separation between the component leg and the solder. I would test all with a multimeter, cause sometimes even good looking solder blobs are can be bad...
You forgot the Jacks, but I guess they are right, since it works without power.
Check the continuity of the small black wire from xs to xr too. I guess they are good, otherwise there would be no repeats at all.
Face palm moment of the day. I didn't test with the second BBD in first. I did first BBD and then second BBD. Will re-run that test and report back!
News! I tried the step again where I removed the BBDs. I put the second BBD in first and VOILA! I have relatively clear dry and wet signal. The hum I'm getting now appears to largely just be from running the pedal un-shielded and outside of a box.
Then I plop the first BBD in and BOOM! Nasty hum is back!
Wait, what?
If you remove one of the BBDs there should be no or very weak wet signal. The wet signal path is broken. Unless there is some power line that is not correctly decoupled (VB?, which could work as a path for the signal).
Try bypassing the first BBD: With only the second BBD in the socket, put a capacitor in the socket of the first BBD(between pin 7 and pin 3, any value that you have on hand higher than 100nF). That will create a path that jumps over the first BBD.
If the noise is there, it probably enters the circuit before the first BBD stage and the BBD only allows it to pass. If there is no noise, you should check connections around the first BBD, because it might be causing the problem.
With the signal probe, it would be much faster to identify where the noise is introduced, because you would be able to check the signal at the input of every IC.
I only get very loud and strong hum when there is a missing reference (resistor to ground), for example when you turn on a high gain amp and the cable is still not connected to the guitar and you touch it.
What I mean is that I am getting good dry signal and when I click on the pedal, I am getting very low output, barely audible, but no crazy hum.
Does the polarity of the cap matter? I'll test tonight.
Ideally you would use a film cap, without polarity. Otherwise I would have to check where the voltage is higher in the circuit...
Nasty hum is still present with a 220nf film cap jumped between 7 and 3 on BBD1.
So the hum must be coming in before the BBD. I'll start poking around. I'm going to order a honey tone amp to put on my bench for the audio probe work.
Yes, that sounds the case. You can play with the cap and bypass other parts of the circuit to pin 3.
Stick one pin in the socket and solder a wire to the other and voila, you can now connect it anywhere where there is signal, even the input jack. The Cap will protect anything that comes after pin 3.