Paralooper problems

[343 Salty Beans]

I built the bass paralooper, from the UPDATED version of the layout on moosapotamus's site (scroll down, there's two versions on his site):

http://moosapotamus.net/THINGS/paraloop.htm

I made no parts substitutions, and followed the PCB and schem to a T. I've compared the schem and the PCB, and they look as if they're the same. Here's pictures of the way I did the PCB (a point-to-point PCB, commonsound.org style):

http://www.diystompboxes.com/smfforum/index.php?topic=50061.0

I'm only using a 9V DC power jack, not battery power.

Bypassed, the signal is fine. I did my wiring right, I'm 99% sure. there's only two things. First, moosapotamus didn't include a pad for wiring the circuitboard to ground, so I grounded it to the input jack's sleeve. Second, Is it okay if I wired the circuit and LED in parallel to the 9V+ on the power jack (2 9V+ wires from power jack, one to circuit, one to LED power lug on the 3PDT) instead of series as I've seen in most diagrams (a 9V+ wire from the jack to the circuit and then to the LED power lug)?

I put the whole thing in a sweet cherrywood box basicaudio made for me (thanks again, John) and tried it out. The first time, no sound came out. After checking some stuff, I realized I hadn't isolated the power jack from the aluminum shielding  . I isolated it and tried again. This time, I got the signal, but also an unpleasant, not-even-close-to-unity-gain farty and pretty distorted signal. I figured I probably burned out the ICs when the power jack wasn't isolated and I had 9 volts or more flowing to ground. I took the TL072s out of the sockets and put 4558s in their place. Now, when I turn on the effect, I get a massive switch pop, which was not there before. Right after the pop, there's a fizzing signal that fades quickly in about half a second. After a few times of on-and-off and that fizzing noise, it no longer makes the fizzing noise. It's just the pop.

I'm powering the whole thing from a 9V wall wart that actually puts out 13 volts (yes, it is the correct polarity on the barrel and pin). Here's the IC voltages:

IC1 (JRC4558D):
1: 4.11v
2: 4.11v
3: 2.62v
4: 0v
5: 4.08v
6: 4.08v
7: 4.08v
8: 13.34v

IC2 (JRC4558D):
1: 6.61v
2: 6.61v
3: 3.25v
4: 0v
5: 3.27v
6: 6.5v
7: 5.74v
8: 13.31v

IC pins like so:
1       8
2       7
3       6
4       5

One guess: It looks as though R6 on the layout could be shorted or a bad resistor. I'll check it again, but it measured 2.2K when I put my meter to it. I'll check around it for shorts.

Anyone else have any ideas? I'd really appreciate it. Thanks  343SB

[boogietube]

The only thing that I noticed was on the pcb layout upper right hand corner next to r13 - this outside trace appears to be the ground point. I haven't completed mine yet, but this is the point that I chose for ground when I crossed referenced with the schem.
Hope this helps.

[343 Salty Beans]

I actually just soldered my ground wire to the "lower" lead of R2, but it's the same thing.

[nosamiam]

I had the same prob with the original layout on PCB.  Farty noise that cuts out after about half a second.  I tried to get it working and gave up after maybe 4 or 5 hours over a week or so.  A couple months later I tried it again on perf.  Same prob.  I gave up and decided to go with the ROG Splitter-Blender.  Haven't gotten around to it yet, though.

[343 Salty Beans]

hmm...anyone else have this problem? It's odd that two of us would have the same issue...maybe it's something easy to screw up. I know the ICs are in the right way though...maybe there's an electrolytic reversed that shouldn't be, mislabeled part on the schem, or somesuch?

[343 Salty Beans]

After much audio probing, DMMing, and replacement...

I've discovered the problem lies in a single area of the circuit...

http://moosapotamus.net/THINGS/paraloop/paralooperSCH.gif

That is the link to the schem. I'd post the image for easier reference but I don't want to post moose's work.

ANYHOO, moosapotamus, your schematic is mislabeled. First, U2-B and U1-B are switched as opposed to the layout. the way you've got the layout set up, U2-B is the one that has the 10K and 100K setting the gain...

Secondly, I traced the problem down to the two gain-setting resistors on U2. Only between pins 6 and 7 of the opamp am I getting no signal...thus, I have a problem...Which I believe I've figured out. Moosapotamus, you've labeled R12 100K. This sets the gain of the opamp too high...at 11. I think you meant to label R12 10K, which sets the gain at 2.. The original schem confirms this:

http://www8.plala.or.jp/KandR/cir_bassthru.html

I have learned quite a bit about debugging, even though this circuit has been an enormous pain in the ass and I've used up my last opamps ....

Can anyone experienced confirm my theory before I unsolder this?

[slacker]

ANYHOO, moosapotamus, your schematic is mislabeled. First, U2-B and U1-B are switched as opposed to the layout. the way you've got the layout set up, U2-B is the one that has the 10K and 100K setting the gain...

yeah you're right the the U1B and U2B are switched round on the layout. That shouldn't cause any problems though, might confuse people if they're comparing the schematic to the layout that's all.

Secondly, I traced the problem down to the two gain-setting resistors on U2. Only between pins 6 and 7 of the opamp am I getting no signal...thus, I have a problem...Which I believe I've figured out. Moosapotamus, you've labeled R12 100K. This sets the gain of the opamp too high...at 11. I think you meant to label R12 10K, which sets the gain at 2..

That shouldn't  cause the problems you've had, a gain on 11 is not very much and shouldn't cause the op amp to distort unless you fed it a really hot signal from send/return loop.

I think the problem is that C9 is the wrong way round on the schematic and layout. The positive side should be towards pin 5 of the opamp and the negative side towards VR2-2. That would cause the problems people have mentioned.

[343 Salty Beans]

Well, I'd think that if pin 5 wasn't working right. But pin 5 is getting good signal...pins 6 and 7 are the problems. I checked the voltages and they seem to be all over the place, but kind of close to each other. I'll reverse it to see if it's my problem...if not, anyone else have any ideas?

Update: Slacker, you were right. Once I reversed that electrolytic, I got signal. Now I've got another problem though:  distortion. I think it's the opamps, but they introduce quite a bit of overdrive. If I pluck really hard, I get a super buzzy distortion for a split second and then back to the typical overdrive. I think it has something to  Here's my new opamp voltages:

IC1 (4558)
1: 3.95v
2: 3.95v
3: 2.56v
4: 0.00v
5: 3.92v
6: 3.92v
7: 3.92v
8: 12.93v

IC2 (TL072)
1: 6.43v
2: 6.43v
3: 3.21v
4: 0.00v
5: 3.21v
6: 6.43v
7: 6.43v
8: 12.93v

In addition, I'm getting a buttload of noise...it seems like it might be power supply noise, but I've tried several power supplies, regulated and unregulated, and the noise won't go away. I also tried putting on the bottom cover to shield....no luck. I'm gonna try it with a 9v in a bit, but I hope I don't have to power it that way :/

Do you guys think I've got a bad IC? All the voltages look okay to me...should the + inputs of IC2 be half of the - inputs and outputs? Does pin 3 of IC1 look fishy to you?

PS: I'm using a passive bass, not an active one, so I don't think there's a super-hot signal going in.

[slacker]

I've just had another look at the schematic and C6 and C1 are the wrong way round as well, flip them round and hopefully everything will work as it should.

[343 Salty Beans]

I redid em, and now the circuit only overdrives a wee bit, when the level's high up and I really jam on the strings. That seems normal enough...

Thanks for the help, slacker. I've got to learn about those gorram caps...I don't know how they work too well  .

My last problem is my power supply hum, which is confounding me to no end. Actually, I'm pretty sure it has something to do with R7...it's definitely the same hum that comes off the power supply (i used my audio probe to check). If you look at the schem, R4 and R7 look as if they're doing the same thing (what that is eludes me  ). They both lead up to pin 3 of their opamps (That would be the + input). IC1 has no problem with the hum...it stops right after R4. However after R7, the hum continues. It's from the power section for sure...it exists at C2, R1, R2, the anode of the diode, and up through R10 as well. Could someone explain why it's going through R7 and R10, but not through R4? And could they also explain what those resistors do? They all seem to have same circuit placement. All of these are directly after their BIAS points on the schem, if that helps.

Thanks very much for the help so far 

PS: one more question : I've discovered that the 4558 as IC1 is what's overdriving the output. When I turn the blend knob clockwise (which means less original signal), The overdriving goes away. When the blend knob is all the way counterclockwise is when it overdrives. I think it's just the fact that I'm using a JRC4558, which can get a little dirty as far as ICs go, which is not my cup of tea which means I'll be ordering none of them and more of TL072s and NE5532s in my new opamp cache. Do you think that'll help?

[343 Salty Beans]

After experimenting quite a bit, I've decided to try to get around this unbearable power supply noise. Batteries mean no noise, but limited life. I don't want to waste money on batteries all the time, so I've decided to try a 9v regulator (L7809). I was going to build a spyder, but I never got around to it  and I don't feel like getting zapped by a transformer.

Anyhoo, I had the idea of just splicing out the latter half of my power supply circuit. a 220uF cap across the power line and ground, followed by a L7809. The output of the L7809 would hit a 100uF cap to ground, and then I'd lead the power and ground lines off that cap.

Would it work to eliminate all the 60Hz hum I'm getting?

[slacker]

Thanks for the help, slacker. I've got to learn about those gorram caps...I don't know how they work too well  .

Basically with polarized caps like electros the + side needs to be at a higher DC voltage than the - side. So if you look at C1 the side facing R3 will have about the same voltage on it as pin3 of U1 and the end facing the input jack will have 0 volts DC on it. So the + side goes towards R3.

I don't really know whats causing the hum except that have you made sure all the jack sleeves are grounded and the circuitboard ground is attached to the signal ground.

PS: one more question : I've discovered that the 4558 as IC1 is what's overdriving the output.

There shouldn't be any overdrive coming from IC1 because it's just being used as a buffer with no gain added. The only place you might get some overdrive is from the second half of IC2 where you've got some gain, but even then you'd have to hit it with quite a hot signal.
If you've socketed the opamps what happens if you swap them over?
The only other thing is that your voltages look a bit low on IC1, I'd expect them to be more like IC2.
If you don't mind could you remove the opamps and then measure the voltages on the empty sockets and also measure the bias voltage where R1 joins R2. This might narrow it down to a problem with the opamp or possibly a wrong value resistor somewhere.

[343 Salty Beans]

"
Basically with polarized caps like electros the + side needs to be at a higher DC voltage than the - side. So if you look at C1 the side facing R3 will have about the same voltage on it as pin3 of U1 and the end facing the input jack will have 0 volts DC on it. So the + side goes towards R3."

I know why they need to be oriented, but I just never know their function. I really should look at caps a little more closely...once you said that, it made perfect sense. Thanks.

"I don't really know whats causing the hum except that have you made sure all the jack sleeves are grounded and the circuitboard ground is attached to the signal ground."

I'll resolder the jacks and check for continuity from the jack to the enclosure just to be sure...but I'm 99% sure it's just a power hum issue. I know cuz I used a battery to power the circuit and the hum disappeared. It's in the circuit at 9v+ wire with the probe (which makes sense, there's no signal there), and continues down through C2 and all through the BIAS section (R1, C2, C3, R2). However, when you measure the end of R4 (a 1M resistor) that's pin 3 of IC1, the hum disappears completely. I'm assuming that's what the 1M is for. That's why there's a 1M resistor for pins  5 and 7 of IC2 as well. However, the hum is present in both opamp sections of IC2. I'll check, but I think it's present in all the inputs and outputs, not just one or the other. Just a wild guess, and I'm not sure how I would do it, but could placement of an electrolytic capacitor in both of IC2's opamp input paths block the DC hum? Why is the hum getting blocked at R4, but not at R7 or R10? 

"There shouldn't be any overdrive coming from IC1 because it's just being used as a buffer with no gain added. The only place you might get some overdrive is from the second half of IC2 where you've got some gain, but even then you'd have to hit it with quite a hot signal.
If you've socketed the opamps what happens if you swap them over?
The only other thing is that your voltages look a bit low on IC1, I'd expect them to be more like IC2.
If you don't mind could you remove the opamps and then measure the voltages on the empty sockets and also measure the bias voltage where R1 joins R2. This might narrow it down to a problem with the opamp or possibly a wrong value resistor somewhere"



I'll use the audio probe in a bit, but I've got a Sociology paper to finish. I don't tihnk it's a wrong value resistor on my part, because I checked all of them with my multimeter when the circuit first had problems. Maybe it's another schematic error? I'll update once I've got the voltages and a source of the overdrive.

Thanks a load for all your help.

[343 Salty Beans]

Got it all fixed. Removed most of the hum with a 220uf across ground and power to a L7809 to a 100uF cap across the L7809 output and ground. In any case, it's working well enough to play with. The overdrive is only present when I've got the blend knob cranked at least 80% towards the dry signal, which I generally don't do. I'm assuming I'm just overdriving the 4558 when all the signal is running through only one of its sides. There's still a little bit of hum, but it's managable now and it's only there when the pedal isn't bypassed (I'm going to eventually shield the input and output wires, because that's probably what it's from).

Thanks a load for the help, slacker.

If anyone could answer my questions about the 1M resistors and what they do (see the post above) so I can understand a little more about electronics, I'd be grateful. If not, oh well, i'll learn it eventually. 

[$uperpuma]

Have you e-mailed Charlie? I had a question about the circuit and me mailed me back in a few days with an answer...

[moosapotamus]

Been away... I just spent all of last week in the hospital, but I'm all set now. Sorry for any confusion. Glad you guys got this sorted out. Another thing that may be contributing to the disto is those 1uF caps. You can probably easily go down to 0.047, like in the bass-thru, with no loss of low (bass) freq, and it might help to tame the gain structure a bit. You also won't have to worry about polarity, and some like the sound of film caps better than electros, too. I don't know technically what the 1M bias resistors are doing, but there are plenty of searchable resources on power supplies, bias circuits, opamp gain setting, and so on..., out there. 

Best...
~ Charlie

[343 Salty Beans]

Sorry 'bout the hospital, charlie  hope you're feeling better. In any case, I don't use the blend that high, but if it ever gets too irritating I'll try your lowering suggestions. Thanks a load, man!