Tag: outboard

DIY Audio Project #1 | Tube Saturator with Baxandall EQ (Part 4): Fix, Tune, and Refine

Hello, this is Jooyoung Kim, a mixing engineer and music producer.

Lately, I’ve been struggling with a few things like studying English for the TOEFL, preparing class materials, and conducting research. Among all these things, troubleshooting my tube saturator is the most convoluted work.

I wanted to post my article when I finished my build. However, since this continuous refinement makes it hard for me to write it, I’ve decided to document my progress step by step from now on.

Let’s start!

Main Problems

While fixing this machine, too many problems kept popping up. I’ve listed them below in the order they occurred:

  1. The unit wouldn’t power on, even though I flipped the power switch. -> resolved
  2. As soon as I powered it on, the toroidal transformer got so hot that it could fry an egg. -> resolved
  3. No output signals. -> resolved
  4. I found some issues with the meters. -> resolved
  5. One channel was muted, and a persistent white noise appeared. -> unresolved
  6. To fix the problem 5, adding capacitors made things worse. -> unresolved

So far, those are the steps I’ve taken. Therefore, I’ll explain each step chronologically.

The unit wouldn’t power on

It turned out to be just a cold solder joint. However, it was a real struggle to track down. While re-soldering everything, the problem still wasn’t solved. Then, I realized I hadn’t checked the solder joints on the power cord! Once I reflowed them, the power finally came on!

The toroidal transformer got so hot

This problem stemmed from a design mistake. Specifically, the connection between the 0V line and GND caused the transformer to overheat. To fix this, I disconnected the line and insulated it with heat shrink tubing.

No output signals

I figured that if I mounted the THAT1646 (SOP-16) onto an SOP-16 to DIP-8 breakout board, it would work. However, it turned out to be a completely wrong assumption. So, I ended up replacing all of them with DIP-8 standard devices.

Meter problems

Once I finished soldering the entire circuit, I ran into three major issues with the meters:

  • The right meter channel wasn’t working at all.
  • Even though the meter circuit followed VU RMS standards, the ballistic response was way too fast.
  • The audio signals were too hot, causing the needles to peg.

I found that the first problem was just a wiring mistake on my part.

With a little help from Gemini and ChatGPT, I sorted out the second and third issues by feeding them the circuit text. It turns out the meter circuit was designed for -10 dBV (consumer audio level). To fix this, I swapped out a couple of resistors to pad down the input levels for both channels. As for the meter ballistics being too fast, I replaced the damping capacitors with higher-value ones to slow the needles down.

One channel was muted, and a persistent white noise appeared

Yes… and this is the exact problem I’m still trying to sort out. Following ChatGPT’s advice, I added several decoupling capacitors to stabilize the power supply for the THAT1646 and OPA1612 chips.

At first, I misunderstood the advice and connected the capacitors in series with the supply voltage line and the chip pins. However, drawing on my background in physics, I realized that since it’s a DC power rail, connecting a capacitor in series didn’t make any sense. So, I double-checked the circuit configuration and finally realized it was a mistake.

To make matters worse, I totally messed up.

Honestly, I just needed to solder a few capacitors in parallel to the power rails. But instead, cluelessly overcomplicating things, I ended up desoldering all the chips and trying to install sockets.

Since cleanly desoldering an 8-pin chip is an absolute pain, I just lost my patience and clipped the pins with nippers. Then I tried using square-pin headers, which didn’t fit into the sockets at all. So I had to order brand-new OPA chips, re-solder the pins, and wire up the capacitors in series again.

After going through all that self-inflicted hell, I finally tracked down some round-pin headers, re-soldered the chips properly, and got them plugged into the sockets.

But guess what? Now, instead of music with some background noise like before, I’m getting pure, signal-driven noise blasting through. Ugh… hahahahahaha…haha…

hahahahahahahahahahahahahahahah……ahaha..aaaaaa!!!!!!!

So yeah, this is the story of my troubleshooting journey so far.

While writing this post, I tried fixing a few more things last night. However, it turned out that my efforts were completely ineffective.

Juggling multiple things at once makes this feel like it’s dragging on forever, and I just want to wrap it up already. If all else fails, my last resort will be to rip everything out and wire it up on a fresh PCB… ugh. Trying to finish this all during break was definitely too ambitious.

See you in the next post!

DIY Audio Project #1 | Tube Saturator with Baxandall EQ (Part 2): Simulation

Hello, this is Jooyoung Kim — an audio engineer and music producer.

I ended up taking on way more classes than I expected this semester…
and honestly, just preparing for them is killing me. Haha. Every day feels like it disappears while I’m organizing lecture materials… 😢

And somehow, it’s already been almost two weeks…!

Today, following up on my previous post, I’d like to talk about running simulations.

Alright—let’s get started!

To run simulations in KiCad, you need a library file for each component.

The file extension is .lib.
As an example, here’s roughly what the library file looks like for a potentiometer (variable resistor) I created:

* Logarithmic Potentiometer Subcircuit (A-type taper)
.SUBCKT DUAL_POT_10K_LOG 1 2 3 4 5 6 SET=0.5 VALUE=10k
* Unit A (Log curve: 10% resistance at 50% rotation)
Ra1 1 2 {VALUE*(1-pow(10, -SET))+0.001}
Ra2 2 3 {VALUE*pow(10, -SET)+0.001}
* Unit B
Rb1 4 5 {VALUE*(1-pow(10, -SET))+0.001}
Rb2 5 6 {VALUE*pow(10, -SET)+0.001}
.ENDS

For components that are already built into KiCad, these libraries are applied automatically.

But for components that aren’t, you have to double-click the part, go to the component properties, click Simulation Model, and manually add everything… one by one.

Yeah… that part alone ate up a lot of time. 😅

For the audio output stage, you can simply exclude the XLR jack from the simulation. If you connect it to ground through a large resistor, you can still simulate the audio signal at the output.

Simulation isn’t exactly… simple.

You need to supply DC where DC is required, and AC where AC is required. When checking frequency response and phase response, you’ll need to apply an AC sine signal to both the hot and cold sides.

What’s especially annoying is that every single pin must be connected. If even one pin is left floating, KiCad will keep throwing errors.

Personally, once the circuit is mostly finalized, I find it easier to copy it into a separate file and run simulations there.

Yes, you can exclude individual components from simulation, but…
if there’s an oscillator in the schematic, things get messy again when moving on to PCB layout. 😓

Anyway—once all the libraries are properly set up, you can click the oscillator-looking icon in the top-right corner. That will bring up the simulation window.

If you click the play button in the top-left, a settings window appears where you choose what and how you want to analyze.

Since we’ve attached an AC 1 V source to observe frequency and phase response,
we’ll select AC analysis. With just these settings, you can already see the response clearly.

Now, if playback actually works, it feels amazing. But realistically… it probably won’t work on the first try. (It definitely didn’t for me.) If it doesn’t run, something is disconnected, or a library is wrong—and you’re in for a lot of fixing.

One important thing: if you’ve broken out pins separately for XLRs or DC/AC wiring, you must make sure they’re excluded from the simulation.

You can do this by right-clicking, then selecting Attribute → Exclude from Simulation. The same Attribute settings can also exclude things from board or component configurations.

Simulation is critically important—and you shouldn’t only check the final stage. Especially for processors with multiple stages, you need to verify that the signal behaves correctly at each step.

If impedance isn’t handled properly, the signal simply won’t flow the way you expect—and that will happen. Also, if you want to view signals in an oscillator-style analyzer, you’ll need to switch from AC analysis to Transient analysis.

This is also a convenient place to check for phase inversion.

And if you see signals that don’t line up properly here… welcome to modification hell. 😄 While running simulations to write this blog post… I literally just realized a major mistake.

I already ordered the PCB and finished soldering everything… so yeah, I’m screwed. Haha.

Resistor values are easy enough to change, but everything else was fine—until I noticed that bypassing the EQ flips the phase… and I only realized this now. 😭😭

The final THAT chip is a 16-pin device, but I used an 8-pin footprint and bought an adapter socket. Unfortunately, I placed two of them way too close together, so I’ll probably have to desolder and reposition them.

Including the power section, there must be around 180 components total… I’ll likely have to order a separate Ver.2 PCB later and migrate everything over. 😢

Anyway—this is exactly why simulation matters.

One more important thing: in simulations, op-amps are assumed to be ideal. Because of that, in Transient analysis, you won’t see distortion even at maximum dB levels. You need to keep this limitation in mind when interpreting results.

After all that, it’s time to move on to PCB design.

Apparently, this is often called “art” or “artwork.”

And honestly… there’s no grind quite like this kind of grind. If I include PCB layout as well, this post will get way too long, so I’ll wrap things up here for today.

See you again in the next post! 😊

Types and connections of patchbays, configuration of the system

This article was written on July 17, 2023. It is different from my current audio system, but I translated it and wrote it because I thought it would be helpful in planning the patch bay. Good luck!

Hello, I’m Jooyoung Kim, an engineer and music producer.

As musicians and engineers accumulate more hardware equipment, they often consider adding a patch bay to their setup. Today, I’d like to discuss patch bays and their usage. Let’s dive in!

Types of Patch Bays

There are various standards for patch bays, primarily categorized based on connector types:

  1. TRS
  2. XLR
  3. Bantam (TT)

You’re likely familiar with TRS and XLR connectors, but Bantam might be new to you. Due to its smaller size, Bantam connectors are commonly used in 1U patch bays, which can accommodate up to 96 holes.

However, TRS patch bays can have up to 48 holes and XLR patch bays can have up to 16 holes.

TRS and Bantam patch bays are further categorized based on internal connection methods:

  1. Normal (Full-Normal)
  2. Half-Normal
  3. De-Normal (Non-Normal/Thru)

Once you understand these, it becomes straightforward:

Normal (Full-Normal): The rear signal is connected without plugging in a cable at the front. Plugging in a front cable disconnects the rear connection.

Half-Normal: Like Full-Normal, but plugging in a front cable splits the signal for parallel processing.

De-Normal (Non-Normal/Thru): I opted for a patch bay that supports all three modes, even though I primarily use Full-Normal.

I bought Samson S-Patch: It supports all three modes, but labeling can be tricky due to the narrow spacing.

Configuring Your Patch Bay

Knowing the types of patch bays, the next step is planning your setup. Begin by listing the In/Out of your equipment. Here’s an example with my gear:

EquipmentInOut
Orion Studio Synergy Core12Line Out 16 /
Monitor Out 4
Dangerous 2Bus16Main Out 2 /
Monitor Out 2
Heritage Audio HA73EQ
(Mic Pre)		0 (Mic In not considered)1
OZ design OZ-2200
(Mic Pre)		0 (Mic In not considered)2
Bus CompressorLine In 2 / Side Chain 12

Prioritize your connections:

  • Out on top, In on the bottom for signal flow from top to bottom in Full and Half-Normal patch bays.
  • Begin with the equipment with the most Ins and Outs.

Although there are some limitations, like not fully utilizing some of Antelope’s Ins and the mic preamps’ Line Ins, this setup is efficient without wasting patch bay channels. For mic preamp Line Ins, external cable connections can be made as needed.

And label your patch bay accurately. You can find companies that print labels, but they may charge high shipping fees. Alternatively, you can cut paper strips for labeling.

I purchased an 8-pack TRS patch cable bundle from Hosa, available at an affordable price on Amazon.

With this setup, your patch bay-based system configuration is complete. While my setup focuses on mixing hardware, those using hardware synthesizers can also benefit from a patch bay to enhance their workflow and creativity.

I hope this information is helpful to all music enthusiasts. See you in the next post!

I overhauled my studio setup

Hello, this is Jooyoung Kim, an engineer and music producer.

Previously, I mentioned that I had to custom order and repair a toroidal transformer for my Stam Audio SA-2A. After it was fixed and returned, I was quite satisfied. However, I realized I needed more rack space, so I decided to buy a new rack cabinet.

Thinking ahead about the additional equipment I’d be adding, I also bought a patch bay and cable connectors.

I wanted to get a Samson patch bay to match my other gear, but since there were no Samson S-Patch bays available for delivery to Korea on Amazon, I ended up buying the cheapest one that could be set to Normal mode.

The yen was quite weak recently, so I took advantage of that when purchasing cables and connectors via Rakuten. I bought 100 meters of Canare L-2T2S cable and around 20 Neutrik TRS and XLR connectors.

After looking around, I decided to order a custom-made rack cabinet from Shinsun Workshop(Korean: 신선공방), as their products seemed the most suitable. Other ready-made options were either too shallow or too deep for my setup.

I pre-made the cables and installed everything.

Haha… It was quite a task. I started around 4 PM and finished by 11 PM, with breaks for meals. I even had to do some soldering because I forgot something with the multi-cable… haha…

But in the end, everything looked neat and tidy. I forgot to take a photo of the finished setup, though. After repeatedly sitting and standing, my legs were shaking the next day.

I plan to add a 2U tube preamp to the large rack cabinet, and a Behringer 369 to the smaller one. That will leave about 1U of space, which I might use for an API 2500 or a saturator later on.

I recall making a resolution last year not to buy any more equipment, but I’ve completely broken that promise. Despite buying things relatively cheaply, I should be spending money on releasing my songs. It’s quite ironic that I’m spending all my song budget on gear… Equipment addiction is real…

Lately, I’ve been collaborating with a contact I met through a previous project. We’re producing a few tracks together. Additionally, I’ll be recording and mixing a song for a regular client.

I haven’t posted much about my recent work or projects, but these collaborations have been fun, and I plan to share more once they’re finished.

See you in the next post! 🙂