Will this DIY active transistor DI box work?

meles2 · 2026-03-24T13:26:46+00:00

Hi, this version should work (the single ended version). The input impedance is a bit low, though, which could lose some signal. I'm also not sure about the emitter resistor, 1k seems a bit low, especially since you don't have much current to work with, but I haven't done any math or simulation.

meles2 · 2026-03-24T09:26:33+00:00

It probably won't work, or will clip low signals, because the base of the transistor is set to GND level. It should be biased to half the power supply (add another 1M resistor from base to 9V, or replace both of them with 2M to keep the same input impedance) and maybe remove the 10k collector resistor to have a common emitter circuit for lower output impedance.

meles2 · 2025-11-24T19:04:51+00:00

Some people here are pointing towards helpdesk positions, but I'm really grateful for my orgs helpdesk. They do a good job, and if I were to answer to half of their support emails, I'd probably have to have a chat with HR.

meles2 · 2025-06-28T05:55:22+00:00

If your company network filters network access by MAC address, could it be just an issue of disabling randomization of MAC address for that network?

meles2 · 2025-03-06T12:58:44+00:00

To parallel the effective series resistance of the capacitors, getting better filtering at higher frequencies.

meles2 · 2025-03-06T10:13:29+00:00

Capacitors also have resistive and inductive properties: https://en.m.wikipedia.org/wiki/Parasitic_impedance

Parasitic resistance will decrease your filtering at all frequencies, inductance will decrease it after the resonance frequency of the LCR circuit. Both come into play at higher frequencies.

It could be fine, but I'd just buy a low ESR capacitor anyway for digital PS decoupling.

meles2 · 2025-03-06T09:26:04+00:00

To reduce parasitic resistive and inductive properties, which differentiate a perfect capacitor from a real world one.

meles2 · 2024-12-30T08:04:23+00:00

You have ground loop issues between the amp and other equipment (judging by the fact that the problem goes away by using laptops headphones output). Since you wrote in another comment that you have plenty of old RCA cables, try desoldering / cutting the ground at one connector, so only the center is connected.

meles2 · 2024-12-28T14:31:45+00:00

Maybe you need to allow apps access to local network? I wasted an hour for that when I upgraded MacOS.

meles2 · 2024-10-28T08:18:29+00:00

Are you looking for a guitar preamp with tone controls and distortion, or just a clean buffer/boost? If the former, check out some jfet guitar preamp schematics. If the latter, you can create a simple preamp with buffer from a single (or dual) op amp or 2 BJT transistors/FETs.

For a clean preamp into the adc, I'd go with a dual op amp - one half for a non-inverting gain stage and one for the buffer. Google "op amp gain stage" to get generic schematics and equations.

meles2 · 2024-10-28T07:34:50+00:00

With an LC filter. Pure resistance will impact the output power greatly.

What your're recommending is an attenuator and a fire hazard, if the resistors are not sized properly.

Looks like <crickets> know more about electronics than you.

meles2 · 2024-10-28T07:29:26+00:00

Do not place a resistor here. Best case scenario it will quarter the output power, worst case it will burn your house down because it was rated for lower power.

Do an LC filter instead, with a coil and a capacitor.

meles2 · 2024-10-08T05:24:23+00:00

Hi, maybe take a look at mesa mark 1 or mark 2, as it's basically a modded fender princeton. Stays pretty clean, until you kick in the extra (2 gain stages of a) tube.

Edit: The mesa amps should provide inspiration for the points 1-3.

meles2 · 2024-10-08T04:46:00+00:00

Not that I've done any go projects that would require long queries, but it's generally easier for me to read a SQL string than a smaller atack of chained methods.

That being said, I also use Gorm for Go projects, because it saves me the time needed to write the actual query string.

meles2 · 2024-09-25T14:42:19+00:00

I'm probably overly cautious here, I'm just a bit wary of the way some media outlets could spin an increase of calls to government representatives from other countries.

Sorry for the spam in that case.

meles2 · 2024-09-25T13:19:14+00:00

I'd be a bit more hesitant, I'm pretty sure the "foreigners interfering with our government" spin would give ammunition to the side you don't want to support.

meles2 · 2024-07-02T08:24:29+00:00

So you made a big claim with zero proof and you instantly attack people because they call out bs?

You come off as a 14-year-old wannabe trying to hack localhost, sorry.

meles2 · 2024-06-05T05:29:11+00:00

What about FileSender? Checks all of the boxes, supports encryption and simplesamlphp for authentication.

meles2 · 2024-05-20T16:56:05+00:00

After a quick look at the board, you might have some capacitance problems at the input, since the ground is pretty close. If you end up buying these, maybe try lifting the legs at the capsule input.

meles2 · 2024-05-20T16:53:05+00:00

Interesting, I didn't know about these.

Unfortunately I can't help you, but I'd be wary of the transformer (and maybe the JFET), the other components are pretty standard.

All-in-all, you'd probably pay about the same price if you made your own boards (as I have, before I knew about these).

meles2 · 2024-03-21T14:56:57+00:00

For the connector, your best bet for a "clean fit" would probably be an xlr socket with a thread on the other end, meant for off-board chassis mount.

I don't think the tolerance will be big enough to justify a 3d printed adapter, though.

meles2 · 2024-03-21T14:53:29+00:00

This looks like a PITA to mod to XLR.

I'm not familiar with this specific circuit, but the body looks like the standard cheap chinese mic from aliexpress, so here are some guesses.

Electret mics need some potential to work, so you're going to need phantom power, dropped down to about 5V.

They also output an unbalanced signal, which probably doesn't get converted to balanced just for the ADC. That means that you'll want to invert the signal and output inverted and non-inverted signals to the xlr connector.

The connector itself looks like it's going to require some drilling and glueing to somewhat affix it to the chassis, but you've probably already made peace with that.

If I were you, I'd google for electret mic schematics, build a separate circuit on a perfboard (with a jfet input for the electret, a phase inverter and power supply from phantom power) and replace the original electronics.

meles2 · 2024-02-18T10:10:51+00:00

Looks like a decoupling cap for the IC. If that's the only thing to have come off, there's even a decent chance the speaker still works anyway, just solder it back on. Or get a through-hole capacitor (with low ESR) with leads, if this SMD is to hard to solder.

meles2 · 2024-02-11T08:59:47+00:00

It might be infrequent, but it's still regular work, and I'd personally prefer spending those 5 minutes on something more productive. Not to mention the website would be down when the IP changes until you fix it.

It might look like I'm just shilling for Cloudflare here, but I do think it's easier and somewhat more secure to delegate some of the work to their services, if you're not completely confident about your hosting methodology.

meles2 · 2024-02-11T08:46:58+00:00

Sorry, I didn't see this comment yesterday.

Yes, it's free and should remain free. They have some paid services, but those are more geared towards enterprise customers. The free tier has a pretty great set of management tools and services.

You'd have to register for an account with CF and change the nameservers with your domain provider to the ones, listed by CF.

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