Cool new product! ‘Add-A-Buffer’ adapter boards (Your op-amp + TI BUF634A in a DIP-8 socket)

This board fits any single SO08 op-amp and a TI BUF634A buffer IC into a single DIP-8 socket!

Useful wherever increased current drive and immunity to capacitive load is desired. (Headphone amplifiers, line drivers, active filters, equalizers, etc.)

Buy them here.

The TI BUF634A adds a fast and powerful output stage to any op-amp. It is inserted into the feedback loop, essentially becoming a part of the op-amp itself.

Here’s one installed in a phono preamp I built for a friend. This particular design benefited greatly from the BUF634A, as the output drives a 464 ohm load on its feedback loop, which is a heavy load for most op-amps, but a breeze for the BUF634A.

New Product! Earth-Loop Breaker Boards

Earth-Loop Breaker

How’s this for procrastination? I’ve had these boards ready to sell since 2017, and have been using them in my own projects, but only now got them up in the store! Buy them here…

An earth-loop breaker works to reduce noise in a system, by inserting a buffering impedance between a device’s signal ground, and its earthed chassis, to reduce currents circulating between them.

Earth-Loop Breaker Schematic

The metal-oxide resistor provides the buffered impedance at low frequencies, and the polypropylene capacitor—in parallel—gives a low impedance at RF. A bi-directional diode clamp—also in parallel with the resistor and capacitor—does nothing in normal operation, as there is 0VDC across it. In case of a fault, such as a DC power rail coming in contact with the chassis, or AC power being shorted into the device’s signal ground, the voltage across the diodes will rise above 0.6V, it will clamp, and the fuse should blow.

Recommended reading: Rod Elliot has a terrific article on the subject of “Earthing your Hi-Fi” where he describes the use of earth-loop breaker circuits, and gives invaluable advice on the subject of making electrically safe, and quiet audio equipment.

New policy at Hoppe’s Brain: I’m going to start actually billing for my time. :)

Real talk y’all. Hoppe’s Brain has been in business since 2016, yet I am constantly BROKE. I barely have enough money to keep parts in stock, and my partner has been paying more than their fair share of household expenses. I feel guilty when I spend money on fun things. I haven’t had a real vacation in 8 years. 🙁 It cannot go on like this. I am stressed out, working my ass off, and yet constantly struggling financially.

So what’s the problem? Profit margins on my products are good, and I’m working about 50-60 hours per week! It’s not because I’m not working hard!

I’ve realized it’s because I’m not getting paid for my time, doing tech support for customers, and teaching people electronics in the course of doing so.

I spend hours every day, answering tech support emails and taking phone calls, helping people troubleshoot their amplifiers for free. I really love helping people fix their stuff. It’s why I’m in business. But I can’t do it for free anymore.

Electronics is hard, amplifiers are complex, and there is so much that can go wrong with them. It takes years of training and practice to get proficient at fixing amplifiers. Most of my customers are hobbyists with real jobs, so they cannot be expected to be expert electronics technicians, and that’s great! It’s a fun hobby! But when people get stuck on their repairs, or the magic smoke escapes from their amplifier, and they’ve already spent lots of money with me already, I feel obligated to help them get it up and running. I really want them to succeed! Sometimes I worry that the customer’s problem might actually be something that’s my fault, or that maybe the board is bad, or maybe I got a bad part from a supplier… etc etc etc…

But you know what? It doesn’t even matter if it’s my fault, I still need to bill for my time. My products are superb, and I work super hard to make sure they are as flawless as humanly possible. But I am human, and I do make mistakes, and that risk is part of the price of doing business with me.

New policy: My products come with 30 minutes free tech support, and that includes writing emails, phone calls, and researching your issue. Time beyond 30 minutes is billed at $75/hr. If you anticipate needing help getting your amp running, I am happy to do that, but please consider my time as part of the price.

Thanks for reading, and for all the support I get, it’s much appreciated.


Parts shortages :(

Parts shortages are stressing me out! And threatening my business. :( I’m worried that the Central Semiconductor CMXSTB400 is about to go extinct. Mouser is the only supplier, with 371 in stock and none on order.

The only other stabistor that I’m aware of, is the Nexperia BAS17, a single stabistor diode in SOT23.


So I’ve added SOT23 footprints to the bottoms of my BFA-565 boards, so the boards can accept all three kinds; the original through-hole stabistors, the CMXSTB400 or the BAS17. It works out pretty well, and some people may find these SOT23 packages easier to solder than the SOT26.


Top-side accepts original through-hole stabistors, or SOT26 CMXSTB400.


Also LT1012’s and OP97’s in DIP-8 are currently nowhere to be found, and I’m running out of stock.
So I’ve added dual DIP-8/SO08 footprints.


I’m also starting to have trouble finding film and electrolytic capacitors, transistors… Even these little JST board connectors are getting hard to find! I had to order quantity 2000 from Utmel in China.


These JST connectors are far from obsolete; they’re used in everything!

Anyways, I’m trying to buy things in bulk so I’ll have them in the future. More work-arounds are in my future though.

New Product! Binding Post Adapters for 3/4″ binding posts.

The Problem:

You want to replace the binding posts in your amplifier, but the holes in the chassis are too large for most binding posts on the market, which are designed to fit chassis cut-outs of 10mm or 11.5mm in diameter.

The Solution:

Hoppe’s Brain Binding Post Adapter Plates.

Two fiberglass plates sandwich the sheet metal, and the binding posts fit into the plates, which are firmly attached with four M3 screws and locknuts. Simple, secure, and easy to install and service.

Get them here:

New product! Cable assemblies for GFA-585.

The board header connectors and cables inside GFA-585’s are often corroded, from leaked capacitor spittle and time. These types of “JST connectors” are meant to be machine-crimped, but they can be soldered manually, but that’s a real pain.

So I am offering a complete set of new cables and board headers for $40. They’ll be up in the store soon!

Cables for GFA-565 and GFA-555 MKII continue to be available.

Finally! I’ve written better documentation for the GFA-535 MK1 Power supply boards.

After much procrastination, here is is! Thorough, complete installation documentation with lots of pictures.

I’ll get to the GFA-535 MK2 and GFA-545 documentation soon, but it’s pretty much the same, so if you’re installing one of those model boards, this is for you too.