Derailer issues (feedback and distortion)

[arficus]

First build.
Works ok at low gain. About a third into the gain squealing feedback and static-like distortion is introduced. The "bright" switch being flipped to high or low also introduces high pitched feedback as well. I used tantalums for the three 22uf (instead of electrolytic) and TL072 (instead OPA2134).
Any hints/tips what to focus my attention on?

 

[eh là bas ma]

Check the solder joints, reflow all suspicious pads. Hunt for shorts. Use the multimeter on continuity mode to make sure.

Check the ground network with a multimeter set on continuity mode, all ground points should be connected.

Check all polarized parts orientations, caps, ICs, diodes.

Stick the IN and OUT wires with tape along the sides of the enclosure, away from the pcb.

If all of that fails, post clear pictures of both sides of the board, showing your soldering joints, and voltage readings on both ICs.

Using A50K potentiometers for Gain and Volume on this pleasant and refined circuit is a popular modification on this forum. Helps opening up their usable range of action.

R

Thread 'Derailer gain mods'

Jan 21, 2021

Has anyone built the Derailer? I've just got mine working and am gobsmacked by the amount of gain and volume early in the knob rotation. It was also built using a TL072 instead of the OPA2134.
Would the OPA2134 have a noticeably different gain structure? Everything I've read suggests little difference in practice but practical experience may show something else.
Would I be better off using log/audio pots for Volume and Gain? And what of the HiCut?

• rickn2112
• Replies: 18
• Forum: Modifications

Using OPA2134 doesn't do an obvious difference compared to TL72, in this case.

 

[arficus]

If all of that fails, post clear pictures of both sides of the board, showing your soldering joints, and voltage readings on both ICs.

What looks like solder shorting switch terminals is just flux. I'll follow up with V readings later....

 

[DailyDovetails]

Some of the solder joints look either cold or starved. I would reflow them and make sure your soldering iron is hot and make sure the tip is wet with solder.

I would also clean the board with a toothbrush and some isopropyl alcohol after you are done it will make it easier to inspect your work.

Beyond that check between op amps and the board for any solder drops or loose component legs and double check the values or all the components.

If you haven’t been already it’s a good idea to check your components before installing them. A TC-1 tester is inexpensive and makes it pretty easy.

 

[jcpst]

cleaning the board might help. I circled some spots that looks suspicious to me

 

[eh là bas ma]

Are you sure that's only some flux?

Toggleswitches are easily melting and malfunctioning if we heat them too much or too long. Just pressing on a lug when the toggleswitch's plastic is hot may break the mechanism. With a multimeter on continuity mode you can make sure they work as they should. The middle lug is supposed to be connected with the upper one or the lower one, depending on the toggle position.

We can see some excess of solder under the switch, this could create some short. I would use a desoldering pump to suck off the solder from the other side of the pcb. Take your time, let it cool off between attempts, to avoid overheating the toggleswitch.

 

[arficus]

Upper op-amp
1: -4.4
2: -4.4
3: -3.5
(rapidly changes to -2.2
4: 0
5: -4.4
6: -4.4
7: -4.4
8: -8.9
lower op-amp
1: -4.6
2: -4.6
3: -4.2
4: 0
5 -8.9
6: -4.4
7: -4.5
8: -4.4

 

[arficus]

The relatively different V on pin 3 that also changes with probe applied--I'm guessing that's relevant and that I should look upstream from there?

 

[arficus]

Are you sure that's only some flux?

Yes, cleaned it off.

We can see some excess of solder under the switch, this could create some short. I would use a desoldering pump to suck off the solder from the other side of the pcb. Take your time, let it cool off between attempts, to avoid overheating the toggleswitch.

Checked all the switches with meter.

 

[eh là bas ma]

Upper op-amp
1: -4.4
2: -4.4
3: -3.5
(rapidly changes to -2.2
4: 0
5: -4.4
6: -4.4
7: -4.4
8: -8.9
lower op-amp
1: -4.6
2: -4.6
3: -4.2
4: 0
5 -8.9
6: -4.4
7: -4.5
8: -4.4

Using this pinout :

On the lower IC you should have around 4.5V on pin 5, 9V on pin 8. I guess you made a mistake with the pinout ?

And yes The upper IC pin 3 should be at 4.5V too. Other than that the other readings are ok.

You can try your luck and reflow all soldering pads around this location. See if that restore 4.5V at pin 3. If it fails you 'll have to investigate the components related to this pin 3.

It's not clear which chip is IC1 and which is IC2 in the instructions. You will need a multimeter and check the connections to make sure, following the schematics. If you enlarge the circuit diagram, the IC pins are designated.

Once you've found the various parts connected to pin3, reflow them, check their values.

An alternative would be to use an audioprobe, following the signal path around pin3, to make sure that's where the noises are generated, and find precisely the location where it starts.

Misc > Audio Probe : DIY Fever – Building my own guitars, amps and pedals

[DIY Fever] Audio Probe - very simple contraption that helps with debugging audio circuits

diy-fever.com

To follow the signal path, you just follow the quickest way from IN to OUT on the schematics. There are other part of the schematics where there is audio, but the quickest way from IN to OUT is a good start. Once you've found where the issue appears in the signal path, then you can probe the rest of the aera, to pin-point the origin.

Your tantalum caps... are you sure they are oriented correctly ? they also have a + and -.

 

[arficus]

On the lower IC you should have around 4.5V on pin 5, 9V on pin 8. I guess you made a mistake with the pinout ?

Yes, I reversed order of pins 4-8.

And yes The upper IC pin 3 should be at 4.5V too. Other than that the other readings are ok.

I changed cap upstream and got V right.

You can try your luck and reflow all soldering pads around this location. See if that restore 4.5V at pin 3. If it fails you 'll have to investigate the components related to this pin 3.

I reflowed all solder joints, checked orientation of caps, checked all component values, still has same issue.

 

[eh là bas ma]

I'd suggest to remove the excess of solder under the toggleswitch (see reply #6). Remember to be quick because the plastic is heat sensitive, if you heat the toggle's legs too long it can melt the plastic inside and break the mechanism.

Then, if reflowing the suspicious soldering joints, fixing the voltage readings and removing the excess of solder under the toggle didn't work, i'd suggest to use an audioprobe. Set the controls so you can hear the noise issue, then probe the signal path until you find a point in the circuit where the noise starts.

That's the signal path.
Power up and activate the Derailer, send some signal into the circuit, and use the audioprobe here and there along this path.
Once you hear some suspicious noise, probe the components connected before that point, untill you find the origin of the noise. Then inspect carefully that location and the components connected to it, reflow, check the values, orientations, check the connections with your multimeter set on continuity mode, looking at the schematics to make sure these parts are connected as they should be.

The audioprobe is probably the best tool to locate the origin of an issue in an audio circuit. See reply #10, i posted a link showing how to build this tool.
Just ask if you have some issues using an audioprobe.

I would also add some solder on your 3PDT pads :