I just built this MI Audio Crunch Box today. Here's the vero
(http://4.bp.blogspot.com/-oGGcx4FqypQ/T9nM7A2EjPI/AAAAAAAABpo/Gkn7VN69iN8/s1600/MI+Audio+Crunch+Box+-+V2+with+external+presence.png)
I think this is the correct schematic:
https://dl.dropbox.com/u/54382528/miaudiodistv2rx7.jpg
The layout is from IVIark's blog and is verified.
The problem I'm having is that when I turn it on the sound is kinda gated. After playing for a few minutes it just fuzzes out to nothing eventually.
After leaving it alone for a while it works again.
Here are my voltage readings:
My power adaptor is supposed to be 9v but it's putting out 11.2
IC
1. 4.93
2. 4.96
3. 5.30
4. 0
5. 5.30
6.constantly changing between 1.90-3.10
7. 11.02
8. 11.24
D1
+ 1.43
- 0
D2
+1.51
- 0
I'm gonna guess this is a capacitor problem but I really don't know.
Thanks for any help or pointers. If you've experienced this "gated, then quits, then works again" problem, please share what solutions you've found...
I would say you have to recheck all the connections/solder joints around the right part of the opamp.
Also, take a multimeter and check (circuit being not powered) that resistance between pin 7 and ground/V+ is huge, then that resistance between pin 6 and ground/V+ is huge. Also check that you really have 1M of resistance between pin 6 and 7 and not infinite.
If the above is not true, then it may be the cause of the problem and you have to track were there can be a mistake/short-cut.
Also, I check that all your cuts are of perfect quality with a magnifier (especially for the cut under C3, 100n). Sometimes very small pieces of copper can go unnoticed.
Thanks,
With my meter set to the 2000's range here's what I read.
Pin 7: 305
Pin 6: 354
Between 6 & 7: 143
I checked the track cuts again and they are all in the correct places and cut completely. The jumpers are also correct.
I'm wondering if a component is going out of spec as it receives power. I was hoping someone would be able to tell me what would have to be the wrong value in order to get a gated sound. I know jfets are biased with a resistor/trim pot, so by misbiasing it you can end up with a gated or splatty sound. I'm not sure what would cause that in this situation.
Also there's a lot of crackling and noise before it cuts out. It also sounds a lot more like a fuzz than a "marshall in a box"
the wrong value is full voltage on pin 7,it should be around those on pin 5 and 6.
recheck every trace especially around pin 7 and 8.maybe under the ic socket?
i never liked stripboards,i always ended up with problems,i use them for little circuits with no more than 10 components
"It should be around those on pin 5 and 6".
Do you mean pin 7 should get a reading similar to 5 and 6? Or that 5 and 6 should be around full voltage?
Quote from: mikestahlme on November 19, 2012, 12:01:21 PM
"It should be around those on pin 5 and 6".
Do you mean pin 7 should get a reading similar to 5 and 6? Or that 5 and 6 should be around full voltage?
the only place where you have to read full voltage is pin 8.
on pins 5,6,7 you have to read similar values like pin 1,2,3.
the theory is that your AC signal rides on top of that half voltage and when it gets to the top it fuzzes out.
Now you are costantly having a 5.3V on pin 5 and 11V on pin 7,there is a mismatch,hence the gated sound.
I am not sure I understand the results of your measurements at pins 6 and 7:
1) Remove the IC to make these measurements
2) Resistance from pin 6 to ground and/or V+ should be infinite
3) Resistance from pin 7 to ground and/or V+ should be infinite
4) Resistance from pin 6 to pin 7 should be around 1 mega-ohms
Any other result says you have a vero mistake.
Okay, I have to clear that up before : Did your try another IC? I assume you did, any double opamp will do. Once I chased a problem for hours and the opamp was at fault, I was just assuming it was working because why would it be faulty after all (it was a brand new opamp, still wrapped) ? I was wrong... It happens.
In operation, pins 5 and 6 should read the same, just like pins 2 and 3. If an opamp has its 2 inputs being apart, there is only 2 solutions:
1) The opamp is faulty
2) It is not working in normal operation (problem in the feedback loop)
Let me know what you get.
Removed IC
Pin 6 & V+: Infinite
Pin 7 & V+: Infinite
Pins 6 & 7: 118 when set to the 200k range, 151 when set to the 2000k range.
I haven't tried another IC yet, I made the same assumption. I have a TL072 I can put in.
With those readings between 6 & 7, it looks like you might have R5 wrong. Are you sure it's a 1M resistor ?
Photos of the top and bottom of your board, please!
For sure check that R5 is really 1M (mistake or blown up resistor)! It could also be a faulty C6!
With only 150 between pins 5 and 6 you have a negative gain: divided by 66. 6 which is the number of the beast, hence the devilish failure of your circuit! :icon_twisted:
More seriously, opamp don't really work as expected below unity gain, so on the top of killing your distorted sound, it will just behave erratically and may have a DC drift, which explains why it takes some time to fail. Basically I think the output starts in the middle and the DC drift slowly takes it to the V+ rail where it gets stuck.
I had accidentally placed a 10k for R1, But R5 was a 1M. I replaced it anyway though.
I changed C6 from 100p to 47p to try and get more gain.
after making these changes it is still the same. Next I will try the TL072, when I'm home from work.
I'll try to have some pictures up as well.
If you've socketed the opamp, remove it and with the circuit powered measure the voltages on the socket pins 5 to 7, you should get about 5 volts on pin 5 and nothing on pins 6 and 7. If you get any voltage on pins 6 and 7 then you have a short or a misplaced component connecting them to one of the voltage rails.
I think it is not a shortcut of pin 6 or 7 to the rails, but a shortcut between pins 6 and 7 since mikestahlme posted the following:
"Removed IC
Pin 6 & V+: Infinite
Pin 7 & V+: Infinite"
Once again:
If you really measure 120/150 ohms between pins 6 and 7 (while having the IC removed, R5 being 1M, and C6 being not being fried), there is a short cut somewhere! It is the only solution electrically speaking!
What about removing the IC and desoldering one leg of R5 and one leg of C6 and measuring the resistance between pins 6 and 7? It should be infinite then. If you have 150 (or anything else for that matter), then you have a to chase a shortcut, again.
By the way, changing C6 to 47p from 100p should just give you a little more sizzle, but not more perceptible gain. It is of course not the cause of your problem (unless you fried C6, which is pretty common with small ceramics because they are fragile). It is a matter of taste.
I really hope you will get that one to work, it is really good sounding!
True, but if the problem was only a short or partial short between pins 6 and 7 you would expect them to have the same voltage, and you would just get no or little output. Given his voltages and what you just said it's probably a bad opamp. I just always do the voltage check as a matter of course.
Slacker,
As measured, 150 ohms would be a partial short, making a gain lesser than unity and an opamp that could behave randomly and get stuck to one rail. It is possible.
Of course a full short would have 6 and 7 identical.
Thanks for the explanation, I knew some opamps don't like a less than unity configuration, but I didn't know it could could cause them to get stuck like that.
I haven't had the time yet to sit down and test this thing, hopefully tonight. But I've seen you mention the opamp "getting stuck" acouple of times. What do you mean by that?
Hello,
By "get stuck", I mean that sometimes under non-standard conditions, opamps that are unstable can manifest that unstableness by having their output (pin 7 here) going to one power rail or the other. It would explain why pin 7 is almost at V+, but not quite because the LM833 is not a rail-to-rail opamp so a small voltage drop is expected at full positive excursion.
If there was a real short of pin 7 to V+, voltages would be mainly identical. This small voltage drop at pin 7 basically gives away that the higher than expected voltage comes probably from the opamp and not a shortcut. Electronics is all in subtleties... But I may be totally wrong on this one anyway, it is just a theory.
A good way of seeing that an opamp is not in standard conditions is to check if there is a difference between the 2 inputs (pins 5 and 6). Under standard linear conditions they HAVE TO BE identical in term of DC and AC.
It is part of the opamp Golden Rules, and the most important rule even:
I. The output attempts to do whatever is necessary to make the voltage difference between the inputs zero.
II. The inputs draw no current (or at least it is negligible enough).
So the 2 different voltages you reported for pins 5 and 6 tell me your opamp is not operating in standard conditions, hence the possibility of unstableness and erratic behavior. Obviously, another reason for erratic behavior is a defective unit.
Thanks for the explanations guys! Sorry for the delay, this was kinda put on hold because of the holiday.
I pulled out one lead from R5 and C6 and measured infinite resistance between pins 6 and 7 like you said.
This opamp did come from China, but I ordered it through Tayda who I thought was pretty reputable. Maybe it's defective like you said?
I guess my next step would be to put in a TL072 (also from Tayda) and see what happens.
Not a big fan of vero board... can get confusing! Ever etch a board? :icon_wink:
Hey Jok3r, good to see you.
Mikestahlme,
I would desolder C6 and check it has infinite resistance in DC with a meter; then if it is not C6, desolder R5 out of the board and check it is really 1 Meg with a meter,. Then change the IC if R5 and C6 you are 100% sure that R5 and C6 are not damaged. It is quite common for ceramic caps to fail by short-cutting while resistors would more likely fail by becoming non-conductive at all. Because of that I would check C6 in priority.
If you have eliminated that and want to swap the IC, a TL072 will be fine, but any double opamp will do for the purpose of testing. I hope your IC is socketed. It is better to socket them, less risk of frying them when soldering, and easy swap if they fry for any other reason.
Jok3r, I haven't etched my own board yet, but I have a friend who has and it doesn't seem to be too hard. :)
Jymaze,
Thanks for all your help.
I checked both components and they tested fine. I ordered some sockets a couple of weeks ago when I realized how much I'd be messing around with this one. (lesson learned!) Unfortunately they won't be here until ~ December 26. I'll have to look around and see where I can find one.
If you live in North America, they have decent DIP-8 sockets at Radioshack.
Ok, I replaced the IC with a TL072 and a JRC4580D and got the same gated fuzz sound. I think I may have fried the LM833 earlier because when I put it back in it is considerably quieter than the others.
Any tips from here? I was thinking maybe I should start replacing caps that I haven't already replaced.
Are your voltages still wrong for pins 6 and 7? What voltages do you get if you measure those pins with the opamp removed and the circuit powered?
I really don't understand what is wrong with your circuit.
Can you do one more round of voltages at all pins while powered, and measure resistances between 5-6 and 6-7 while unpowered, all of the previous with the IC on and the IC off. With that much info, we should be able to fully characterize the problem hopefully.
Changing other caps is probably not needed now as long as you are sure that C3 and C7 are fine. I remember you checked C3, so you can check C7. Value of C7 is not critical as long as it is at least 2.2u so you can change it with anything you have that is at least that value.
OK, here we go
Powered, IC OFF:
Note: The longer it is powered, the LEDs go from being very dim to moderately bright. They start out flashing and eventually stop.
1. 0.80
2. 0.98
3. 1.08
4. 0
5. 5.5
6. 2.2 (not steady, fluctuating between 2.1 & 3.0)
7. (fluctuating between 0.1 & 0.9)
8. 12.1
Resistance between...with IC OFF
Pins 5 & 6: -1.5 (negative?)
Pins 6 & 7: (fluctuating between 125 & 128)
Powered, IC ON:
Note: At this point the LEDs are moderately bright and steady as soon as I plug it in.
1. 1.4
2. 1.2
3. 1.07
4. 0
5. 4.0
6. 2.5
7. 2.7
8. 11.9
Resistances...with IC ON:
Pins 5 & 6: 88 and climbing into the 90s. Checked again, this time reading infinite on the 200k range and 777 when set to the 2000k range.
Pins 6 & 7: 97
I have replaced the 2.2u once already.
I hope this helps, thank you for your time.
Bad news, your readings are totally messed up. Besides the power supply readings, not even one of them makes sense! Not even one!
There is just so much that is wrong that I don't even know where to start. For example, the LEDs should not light up in any case without signal, IC being on or not! The rest is in the same vein, with discrepancies in every kind of ways.
At this point, I think the only thing left is to take pictures of both sides of you board (put your IC on too), as clear a possible, and post them here.
I am confident it will help.
Hold on!
Quote from: jymaze on December 01, 2012, 04:51:59 PM
Bad news, your readings are totally messed up. Besides the power supply readings, not even one of them makes sense! Not even one!
There is just so much that is wrong that I don't even know where to start. For example, the LEDs should not light up in any case without signal, IC being on or not! The rest is in the same vein, with discrepancies in every kind of ways.
At this point, I think the only thing left is to take pictures of both sides of you board (put your IC on too), as clear a possible, and post them here.
I am confident it will help.
Hold on!
+1 :icon_wink: What he said!
Here are pics of the front and back.
The top of the back side picture corresponds with the top of the front side.
https://dl.dropbox.com/u/54382528/DSC_1973.JPG
https://dl.dropbox.com/u/54382528/DSC_1972.JPG
In case you can't tell from the picture: Because of the size of the electroyltics, the 10k coming off the top track has its lead bent around the side of the 100uf elect cap. That same cap's negative lead is in fact going to the ground rail right next to D1.
Are you using lead-free solder by any chance? It does look like the solder may not have wetted onto some of the component leads on the pcb. The red wire soldered to the LED is similar in the way that the solder has not flowed enough to properly bond the LED leg and the red wire. Just a thought. It's going to be a nice looking build once/when you get it going.
I see a couple of places where you might have a short between traces, I've shown them below. Either go over those with your iron to remove the unwanted solder or use a sharp knife to scrape it away.
(http://www.eskimo.plus.com/fxstuff/DSC_1972.JPG)
If it still doesn't work after doing that, please could you do the measurements with the opamp removed like you did before.
Probably not the problem but you never know?
Why don't you leave the stomp/foot switch off until you are done trouble shooting in case you may have wired it wrong? Just wire it straight without a switch/ always on...
Also, I don't know if you checked this and I am not going back through and re-read the past posts but make sure you have the polarity wired right...
Thanks for the pictures. I cannot find anything suspicious right now, but I'll look better.
Some more measurements request:
1) The resistance you measure between pins is with the circuit being unplugged right? I feel like you measured it with the power being on, it is not how it should be (it would explain the wacky values, like a negative resistance). Also, check that your multimeter is reading correctly on some spare resistors in your stock and/or check the battery: Sometimes it can get crazy when the batteries are getting low. Please remeasure if any of the above was causing a problem, I really would like to have accurate measurements.
2) Can you measure the DC across the LEDs, with power being on this time: It should be 0 volt. Actually you should check that DC across all pots is about 0 volt.
3) The bias should be 4.5V both on pins 3 and 5. I have no idea how it could be anything different. What is th resistance from the bias point (pin5) to V+ and then to ground (power being off)?
Hey, while double checking my polarity I noticed I'm not even getting infinite resistance between the positive and negative wires at the power supply! Instead it reads 145k what's with that?
Slacker, the spots you circled are just longer leads that appear to be crossing over because of the angle. No shorts there.
The resistance I measured between the pins was with the circuit unplugged.
I see how my measurements are wrong, when I test resistance between V+ and pin 5 I'm getting -7 BUT that's because I have my black probe on the V+ and my red probe on pin 5! I didn't think this would make a difference when just measuring resistance without power but apparently it does. With my red probe on V+ and black on pin 5 I'm reading 58.5k
Sorry! I'll have to re do my original measurements tonight when I have time. :-\
It should not make a difference for the resistance measurements with the IC off the socket at least. You just don't want to inadvertently counter-polarize C5 and C7 by having the red lead on the ground.
I was thinking about something too: Make sure that the tracks on the left and right edges of the vero are not short-cutting to the case. Usually I add a good bevel so the tracks don't reach the border of the board.
You know, your vero looks good, but the measurements are all whacky, I really have no idea why. As Jok3rx said, check your off-board wiring again, and maybe pull the whole thing off and try to have the pedal work with minimal wiring in the open at first with foolproof wiring (one battery, the 2 jacks, no switching, with the pots just hanging there).
It is easier to debug that way, and you can take great pictures for us to see. Then when it is all fixed (hopefully we will get there), you can rebox it.
Some of those solder joints don't look solid especially on the RHS. Could possibly have a dry/cold joint or two. The solder should be coming up the component legs, try re-soldering them and make sure you heat the component legs so that the solder wicks up them.
I pulled it all out of the box and it's still doing the same thing. I'll try going over all the solder joints again and post some pictures.
I'm still trying to figure out the neatest way to wire this into the box, using the least amount of wire possible. I wired this with all the parts already in the box. Is it better to just wire it up outside the box?
Usually I wire with everything already in the box, giving just enough slack to be able to bundle the wires together with some zip-ties so it looks less messy in the end.
OK! I think we're getting really close! ;D
I went through a bunch of the solder joints that looked like the the solder wasn't wicking up the lead, tested it and it worked great! Except for one thing, when I turn down the gain pot to almost zero it cuts out and starts getting slightly gated again.
Even when I turn it back up it's not the same. I'm hoping it's just more cold joints that need to be fixed.
I re did all of the solder joints and it seems to be working perfectly! thanks guys for all your help and time!
;D
Awesome!
For the record, I always remelt my solder joints right after making them, when the component I am putting in is soldered on both sides so it is not moving anymore. I never had a cold joint following that procedure.