ACA Mini — stock build
The standard kit build. One afternoon, five watts of Class A, and a very good reason to build your next amp.
Hi-Fi · Studio · DIY · Fresno, CA
Audio is better when you understand what you're hearing.
Equipment notes, DIY builds, and system advice. What worked, what didn't, and how to hear the difference for yourself.
15+ years listening40+ builds∞ rabbit holes
Recently
Article · Aug 2026
WiiM Mini vs WiiM Ultra
Two streamers, a 6× price gap, and an honest answer about where the money actually goes.
Read → Build · Jul 2026Sparkos op-amps in the Fosi ZA3
A twenty-minute swap on a $100 amp. What changed, what didn't, and whether it was worth it.
Read → Equipment · Jun 2026JBL 305P MkII on the desk
Powered monitors after years of passive speakers and separate amps. A few surprises.
Read →
What RSD Audio is
A place to talk about audio.
Equipment notes, DIY builds, and system advice from someone who's been deep in this hobby a long time. The goal isn't to tell you what to think — it's to share what's worked, what hasn't, and help you find what sounds good to you.
Currently in the system
WiiM Ultra
Fosi ZA3 · Sparkos SS3602
Klipsch RB-2
ACA Redux
Fosi ZA3 · Sparkos SS3602
Klipsch RB-2
ACA Redux
01 · Read & watch
Articles & Video
Circuit notes, system matching, listening observations, and whatever rabbit hole is currently open.
Articles → 02 · Owned & usedEquipment
Streamers, amps, monitors, and studio gear I've actually spent time with — plus where each one falls short.
Browse gear → 03 · Soldering iron onDIY
Class A kits, op-amp swaps, tube swaps. Parts lists, bias procedures, and the mistakes already made for you.
Start building →
Knowledge
Articles & Video
Writing and video on audio topics worth the time. If it's useful to you too, great.
Featured · DAC · May 2026
ESS vs AKM — two chips, two flavors, one interesting box
The Douk Audio Q11 does something you don't see often: an ESS9038Q2M and an AKM AK4493 in the same box, switchable while music is playing. Using it alongside the Moondrop Dawn Pro taught me a lot about what chip character actually means in practice, versus what people say about it online.
Read the article
More writing
Streaming
WiiM Mini vs WiiM Ultra — where the money goes
One is a hockey puck that does AirPlay. The other has an ES9038Q2M, a phono stage, room correction and a screen. Whether the gap is worth 6× depends entirely on what's downstream.
Aug 2026
Speakers
Powered or passive — JBL 305P MkII against the Klipsch RB-2
An active monitor with its own amps versus an efficient horn-loaded bookshelf on 5 watts of Class A. Two completely different philosophies, and both are right for something.
Jul 2026
Amplification · DIY
What makes the ACA Mini worth building
A $25 board, matched transistors, and 5 watts of Class A. The circuit topology, why it sounds the way it does, and what Nelson Pass was going for.
Apr 2026
System design
Matching an amp to your speakers
Impedance and sensitivity together tell you more than either one alone. A practical guide, not a textbook — with real numbers from the speakers on this page.
Mar 2026
Gear
Equipment
Things I own or have spent real time with. What each one does well, and where it falls short.
Ratings are five segments, filled. They mean "how much I reach for it," not lab performance.
Build it
DIY Projects
Parts lists, build guides, upgrade paths, and bias procedures — written by someone who already made the mistakes.
Featured build · Nelson Pass design · May 2026
ACA Mini — full board rebuild with upgrades
Complete rebuild after a blown channel. New matched transistors from the diyAudio essentials kit, upgraded Nichicon KG output caps, RL8 polymer rail bypass, and a full re-bias walkthrough. Includes the complete Mouser parts list with upgrade notes on every cap and resistor.
Build specs
- Design
- ACA Mini
- Topology
- Class A push-pull CFA
- Output
- 5 W @ 8 Ω · 8 W @ 4 Ω
- Supply
- 24 V DC switching
- Devices
- LSK170 / LSJ74 · IRF520 / 9520
- Upgrades
- Nichicon KG · RL8 · RNL
- Cost
- ≈ $85 all-in
- Difficulty
- Beginner–intermediate
ACA Redux — single-ended build
The revised Amp Camp Amp. Single-ended Class A, more output than the Mini, and the same forgiving build process. Heatsinking and bias set-up matter more here.
Fosi ZA3 — Sparkos op-amp swap
The ZA3 sockets its op-amp, so the upgrade is genuinely plug-in. Pull the stock part, note the orientation dot, seat the Sparkos SS3602. Check clearance before the lid goes back on.
Vox VT20X — JJ preamp tube swap
The stock 12AX7 comes out from the back panel. A JJ ECC83S goes in. Let it cool first, seat it fully, and give it an hour before judging anything.
Get in touch
Contact & About
R
Robbie
Founder · RSD AudioI've been into audio a long time — hi-fi, home studio recording, and a fair amount of DIY amp building. I've owned gear across a wide range and built more kits than I can keep track of.
RSD Audio is where I put what I've picked up along the way. It's not a business and I'm not trying to tell anyone what to think. I just love this hobby, and writing about it helps me enjoy it more. If it's useful to you too, great.
Send a message
System advice, build questions, general audio talk — all welcome.