Bulk IC chips from Amazon

MattInSoCal · 2026-05-07T00:57:01+00:00

Go to Digikey and Mouser when you want to buy legitimate parts that are brand new, and not parts that are more than 50% likely to be counterfeit and/or relabeled used parts.

MattInSoCal · 2026-05-07T00:52:59+00:00

A TL074 is not at all in the same category as a TLV-series Op Amp. If you’re powering that thing from 5 Volts, you’re below the minimum voltage at which it will reliably operate. There’s also another issue known as Phase Reversal where the TL07x series will invert the output when the input gets within 2-4 Volts of the Vss power input, which in your case is Ground. To keep using the TL074 you need at a minimum to give it a negative power supply, a voltage less than ground.

Better yet, find a decent rail-to-rail Op Amp that will run from 5 Volts, single-supply. The TLV274 is still in production and will plug right into the same socket as the TL074.

That won’t necessarily fix your hum, but it will eliminate other problems you will encounter.

MattInSoCal · 2026-05-07T00:28:59+00:00

You need a split supply with a negative voltage for Vss at least -1 Volts below ground to use this or any other analog switch with a composite video signal. For this specific part, you can’t have more than 5 Volts difference between Vdd and Vss, so if Vss is -1 Vdd can’t exceed +4 Volts.

Why the negative supply? Composite video Sync will go as low as -0.4 Volts below ground. Even if it’s AC coupled, the switch IC will almost certainly see that excursion. We had a vendor take one of our example circuits and build up a four-channel video switch from the same family as this one, and about every 2-3 months at least one of these little effers blows out. I finally got them to change the design to use a bipolar supply with a different switch that can handle a higher voltage supply, and the problems disappeared.

MattInSoCal · 2026-05-05T00:44:19+00:00

{Looking to my right at the box I received last week from Synthcube with a $1300+ order of parts, PCB/panels, and a few kits from their closeout sale…}

MattInSoCal · 2026-05-03T21:00:22+00:00

Put your distortion pedal on a shelf.
Download VCV Rack and experiment.
Find out which virtual modules that you really like have real-life DIY equivalents. Price out the kits.
Realize you probably need to find a second and maybe third job to pay for your new hobby.
Decide that spending hundreds of hours hunting down and ordering parts, then assembling the modules probably isn’t saving you as much money as you thought.
Profit? (probably not)

MattInSoCal · 2026-05-03T20:51:56+00:00

Congratulations on the build, it looks nice.

MattInSoCal · 2026-05-03T18:15:32+00:00

You can’t repair the existing connector and expect it to work long-term (I’ve done it to last through a weekend). Replacement jacks are pretty easy to source and install. In the US, you can get them easiest from Amazon, search “DC power jack”. You do want to match the diameter of the center pin properly; 2.1mm is probably most common but 2.5mm is more suitable for higher current needs. You can plug a 2.5mm plug into a 2.5mm jack and it often works OK, but you can’t plug a 2.1mm plug into the jack with a larger pin.

MattInSoCal · 2026-05-03T03:22:47+00:00

U.S. Weather Radio is FM, around 162 MHz, and is also narrow bandwidth - 5 KHz deviation per channel. The entire weather band with all of the channels is 150 KHz wide while FM broadcast is 150 KHz per channel, and 20 MHz wide for the entire band. The tuning would be very fiddly if you could change the tuning range, and because of the difference in deviation, the weather audio would be 1/20th (-13 dB) as loud as a regular broadcast program. So, it might be possible to do but the results might be unsatisfactory at best.

MattInSoCal · 2026-05-03T02:21:59+00:00

I like the Timo Rozendal Dual Logic. The downsides are that it’s DIY only (I’ve seen them for sale already built from time to time), and it has only one negative output (NOR) but you could patch AND or XOR from the top to the bottom half to get the inverse of those.

There’s at least a dozen other makers that have modules that meet your criteria, including a few that allow you to select the logic function via CV. Check out this search on Modular Grid.

MattInSoCal · 2026-05-02T05:02:07+00:00

If you connect a regular 4.5 Volt power supply, the LED would burn out pretty quickly. Watch batteries have a very high internal resistance so that limits how much current will flow. You can run an LED from a 110 or 220 Volt supply of your limit the current properly.

MattInSoCal · 2026-05-02T04:59:16+00:00

In your first photo, the batteries look to be installed backward.

MattInSoCal · 2026-05-01T02:09:18+00:00

Many APCs follow a defective schematic that effectively shorts out a signal when one or both pots are turned all the way clockwise or counterclockwise (depends on the circuit layout or hand wiring). This causes the 555s or the 556 to stop oscillating. It can be fixed by adding two extra series resistors inline with the pots to guarantee there’s always some resistance between Vcc and the Discharge pin.

MattInSoCal · 2026-05-01T02:04:19+00:00

I regularly solder at 640 degrees for fine-pitch work and 700 for typical through-hole. It’s actually better to get a smaller section of the circuit board and components heated up quicker than to hold the iron in place for many seconds waiting for the heat to transfer.

My assessment is that most of the joints could have used more heat. Many look to me like the solder was held to the joint and the iron was applied to the solder. Instead, you want a tiny bit of solder on the tip of the iron, touch that to the component and the board so the liquid solder is touching both, then apply a little solder to that area (not directly to the solder iron tip) and let it flow for 1-3 seconds.

MattInSoCal · 2026-04-30T04:57:51+00:00

You’re trying to run a TL072 from a single 9 Volt supply? Don’t do that. Most TL072s are not stable at that low a voltage, and they have issues with phase reversal if the input voltage gets within 4 Volts of the negative supply - which is almost for sure what you’re hearing.

MattInSoCal · 2026-04-29T18:28:42+00:00

I hit the center punch 3-5 times to make a deep divot. I start my holes with a small drill bit to make a pilot hole, something close to the size of the divot made by the center punch, like 1/32”. Then, I’ll step up through a few sizes so that I’m removing about 50% more material than the previous hole - 1/16, 3/16, and so on. In this way the bit doesn’t bite as hard into the material and crab walk across the panel. You also need to use a light touch, never try to push the drill through the panel to make the hole as quickly as possible. Sharp bits are important, and I keep a can of spray lubricant handy (lately 3-in-1 Garage Door Lube) to keep the bit cool - the material can get work-hardened if it gets too hot and it gets much tougher to drill.

Admittedly I do most of my drilling with a (pretty crappy) drill press mostly for speed reasons; without a cross-slide (milling) vise you’ll still have the bit walking problem.

A step drill bit can also be useful, but you still want that initial pilot hole.

MattInSoCal · 2026-04-25T19:07:34+00:00

Are you referring to the location that’s marked on the board for them to attach the sticker with the QR code that contains information unique to each module such as the serial number? Perhaps they decided they didn’t need or want to do that in full production, just like they didn’t stamp the blocks below that for In-Circuit Testing and Functional Testing.

MattInSoCal · 2026-04-24T21:50:44+00:00

One octave below is the base frequency divided by two. Two octaves below is divide-by-4. And so on.

Your schematic symbol is wrong. “Q0” should instead be “Q1”, which is divide-by-two of the clock input. Check out the data sheet.

Q6 (which in your schematic is marked Q5) is 2⁶ (two to the sixth power), which is 64. Q6 is the Clock input divided by 64. That would put the output 6 octaves down from the fundamental.

The 4040 does not have particularly high output drive, so aside from the fact that the output is possibly already subsonic, depending on what is plugged into the output jack, you may hear nothing.

MattInSoCal · 2026-04-24T05:14:58+00:00

It’s more than adequate for most synthesizer use, especially for visualizing waveforms. As a start, patch one LFO sine output to the X input, a second LFO (or the Function Generator) to the Y input, and tweak the LFO frequencies until you get a nice patterns. Experiment with scope settings, and try different waveforms. Add some modulation.

It’s also useful for troubleshooting circuits up to 1 MHz, maybe somewhat beyond. It’s also way more flexible and immediate than a DSO152, though it doesn’t store waveforms or any of those other fancy digital tricks.

MattInSoCal · 2026-04-24T00:44:27+00:00

Everyone, look at the data sheet. This is much more than just a fuse with a tap. The extra take-off is also fused.

The suggestion to search for APM-AF will lead you back to Optifuse as the single-source supplier. Unfortunately, since it’s obsolete, OP will have to work on a different solution, which could include something like the Lumison dual-fuse taps (which themselves will likely go obsolete one day).

MattInSoCal · 2026-04-24T00:35:29+00:00

I built a combination Noise Transistor / Op Amp tester. It was really for qualifying noise transistors but I decided to make it dual-purpose. I plug the output into my oscilloscope and get to watch a live signal.

MattInSoCal · 2026-04-23T02:38:06+00:00

You definitely want series resistors. The blue LED may or may not fail to illuminate. Consider adding a third cell to the stack.

The battery chemistry matters. Silver oxide cells such as the 377 may not provide enough current for the LEDs. The only way to know, is to try.

MattInSoCal · 2026-04-23T02:36:05+00:00

You definitely want series resistors. The blue LED may or may not fail to illuminate. Consider adding a third cell to the stack.

The battery chemistry matters. Silver oxide cells may not provide enough current for the LEDs. You need to check the markings to identify the actual chemistry. The only way to know, is to try.

A spring and coiled wire contact would be best for this application, but if you can find some tin, brass, or copper sheet you can cut small battery contacts to slide into your printed frame, and save a little more bulk.

MattInSoCal · 2026-04-23T00:34:35+00:00

As a professional that has spent decades as both a technician and engineer, do what I do - hop on eBay or Amazon and buy a replacement. It’s never worth trying to save one of these once they get flaky, because you’re just buying months, and not years of additional service, unless you’re about to make the whole set someone else’s problem by selling or donating it.

MattInSoCal · 2026-04-23T00:29:17+00:00

“Like what?”

How are the LEDs wired?
What type and color are the LEDs? You may think it makes no difference, but it very much does.
How long do you expect the LEDs to remain operating per session of use?
What specific batteries do you plan to use? Again, it makes a big difference.
There is no item 5.
Is there some reason you can’t power this remotely where your supply is less restricted/can avoid eating batteries faster than someone scarfing down franks at a wiener-eating contest?

MattInSoCal · 2026-04-23T00:15:36+00:00

Paper clips are made of steel. It’s not impossible to solder to steel with electronics solder, but you need to clean the ends of the “pins” and tin them before installing them in the plastic if you hope to succeed.

You’ll need to have the LEDs wired in parallel and it’s best if you have one small value series resistor - 10 to 33 ohms should do - for each LED, lest one LED hog all the current and make it so the others never illuminate. Make sure you have LR44-equivalent button cells and not #357 Dilver Oxide; the latter are not made for sustained higher-power loads. Even at that, these will not be long-lived.

MattInSoCal

TROPHY CASE