Once this cures in 24-36 hours I can finally vanish and assemble these beasts!

Two-channel valve microphone preamplifier, takes a mic or instrument on a combo XLR/jack, runs it through an input transformer and three valve stages, and puts it back out balanced through an output transformer — into a screw terminal for the main output plus two JST headers that feed an ADAT converter board and a gain meter. I'd like a second set of eyes on it before I order boards.

**Signal flow (per channel):**

Combo XLR/TRS in → P48 phantom feed (2 × 6.8k, switched) → −20 dB pad (820R / 182R / 820R, switched) → polarity reverse switch

→ input transformer (Neutrik nte10-3) → 12AY7 gain stage (68 k plate, bypassed cathode) → coupling cap → 100 k gain trimmer → 12AY7 second stage (150 k plate) → DC-coupled → 12AU7 White cathode follower → output transformer (off-board) → balanced out ×3

The jack tip is normalled through the connector, so with nothing plugged into the 1/4" side the grid sees the mic transformer, and inserting a plug swaps it over to a high-impedance instrument input. Roughly 60 dB of gain in the valve stages on top of whatever the input transformer contributes. The White cathode follower is there specifically so the output transformer gets driven with real current capability rather than a plain follower.

**Power:**
both rails come in from external supplies on screw terminals, nothing rectifies on this board. B+ is 225 V DC regulated, with 2 × 22 µF / 400 V of bulk on-board and a 4.99 k / 10 µF RC per channel for the gain stages. Heaters run on 50.4 V DC with all four valves in series (4 × 12.6 V @ 150 mA); the chain is ordered so both cathode-follower valves sit at the top of the string, which keeps the worst-case heater-to-cathode voltage around 98 V.

**Main components:**

- U1 / U3 — 12AY7 / 6072A, input and second gain stage (one per channel)

- U2 / U4 — 12AU7 / ECC82, White cathode follower output stage

- J1 / J11 — Neutrik NCJ10FI-H, combo XLR + 6.35 mm switching jack input

- SW1 / SW4 — +48 V phantom, Alps SPUJ190900 latching DPDT

- SW2 / SW5 — −20 dB pad, same switch type

- SW3 / SW6 — polarity reverse, same switch type

- R12 / R31 — PT01-B120D-A104, 100 k gain trimmer

- C17 / C18 — 22 µF / 400 V, B+ reservoir

- J4 / J14 and J3 / J13 — input transformer (NTE 10/3), off-board on JST

- J6 / J16 and J5 / J15 — output transformer (UTM3510), off-board on JST

- J8 / J18 — balanced main output, screw terminal

- J10 / J20 and J17 / J23 — balanced output to ADAT converter and to gain meter

- J21 — B+ 225 V in, screw terminal

- J22 — heater 50.4 V in, screw terminal

**Board:**
180 × 200 mm, 2-layer (top signal + ground pour / bottom signal + ground pour), 1.6 mm FR4, 35 µm copper, through-hole only, single-sided assembly. Ground pour on both layers with 161 stitching vias. Custom clearance rules for the high-voltage nets: 1.25 mm for everything at or above ~167 V, per IPC-2221 table 6-1 case B2. DRC is clean — no errors, no unconnected nets.

Any feedback welcome — layout, grounding, the high-voltage side, component choices, anything I've missed.

Good evening,

Today, I am presenting my latest project: a pair of compact active speakers. The objective was to design speakers capable of operating standalone with solid bass performance, while also pairing seamlessly with a dedicated subwoofer.

This project also served as a proof of concept to validate two key technologies:

• An acoustic lens for the tweeter (inspired by Bang & Olufsen), offering controlled 120° horizontal dispersion and high precision in the highs.
• Side-firing force-canceling bass drivers (inspired by Barefoot and Devialet) to minimize vibration transmission to the tweeter.

Enclosure Design & Structure

• Materials and structure: 3D-printed chassis made of glass-fiber reinforced PETG (11 kg for the pair) for optimal damping.
• Force-canceling system: The woofers press against a custom washer creating a direct mechanical link between both drivers, maximizing vibration cancellation.
• Inertia & Weighting: The front baffle, side panels, and tweeter module are weighted with mortar/concrete to block any stray resonances.
• Finish & Design: Style inspired by the Sonus Faber Concertino, featuring a black central section, wood-finished side panels, and gold accents (screws, midrange front plate, rear binding posts).

Driver Selection

(Components repurposed from previous projects)

• Bass: 2× Peerless SDS-P830657 (Norstone W250 wiring)
• Midrange: 1× Monacor SPH-60X (Atohm ZEF Mini wiring)
• Tweeter: 1× SB Acoustics SB26STC-C000-4 (MHP CA1 wiring)

Technical Specifications

• Architecture: 3-way sealed enclosure with Linkwitz Transform.
• Dimensions: 23 × 33.4 × 36.1 cm (W × H × D).
• Weight: Approximately 10 kg per speaker.
• DSP Crossover (24 dB/oct Linkwitz-Riley):
  
  • Standalone Mode: Crossover points at 135 Hz and 2,600 Hz.
  • Subwoofer Mode: Crossover points at 80 Hz, 135 Hz, and 2,600 Hz.
• Protection: Subsonic high-pass filter at 45 Hz to protect the woofers at high volumes.

Sound Performance & Listening Configurations

• Acoustic lens performance: High frequencies are projected cleanly toward the listener with a controlled 120° horizontal dispersion. There is virtually no perceptible shift in frequency response when moving around the room. Measurements taken at random off-axis angles show that the tweeter curve retains its original response without losing energy, fully validating the effectiveness of the lens.
• Dual-mode operation:
  
  • Subwoofer Mode (80 Hz crossover, 24 dB LR): This configuration offers the highest headroom and overall dynamics.
  • Standalone Mode (Speaker alone): The speaker performs remarkably well on its own. At high listening volumes (1 m), distortion below 100 Hz barely exceeds 2%.
• Room gain: Positioned in a small room, placing the speakers closer to the rear wall provides a significant boost in the low bass, placing less strain on the built-in woofers while maintaining a rich low end.

Hey all! I wanted to get your thoughts about an extended range 2-way desktop speaker.

I've done some reading recently about using small full range drivers in lieu of tweeters on 2-way speakers, and the 2" Tectonic TEBM35C10 seems like a perfect candidate for this. It has extremely wide dispersion to avoid beaming problems typical to these designs.

As the woofer, I'm looking at a W3-2053S. It has an impressively low predicted F3, and is usable up to 600hz.

I'd like to cross it over as low as practical, maybe 400hz, to keep the mids as out of the woofer as possible.

Anyone have any thoughts about this idea?

I'll likely 3D print a ~1.5L box with a sealed portion for the tweeter, and as much passive radiator as I can manage to fit.

Hi there! :)

Goal:
I'm feeding a Raspberry Pi 3.5mm into the PU input of a 1956 Philips B2X60U tube radio. Signal chain: Pi 3.5mm out → passive stereo-to-mono summing (2×470Ω + 10kΩ to ground) → 10kΩ level pot → Monacor FGA-35 audio isolation transformer (1:1, for galvanic isolation) → banana plugs → PU input. Power side: radio is run through a 100VA mains isolation transformer for safety (verified with a multimeter, chassis reads ~0V to true earth).

Problem:
Constant 50Hz hum/rumble on the speaker, only when the setup is actually connected. Behavior:

• Signal wire disconnected, ground wire connected: ~10% hum (baseline)
• Nothing connected at all: ~10% hum (same baseline)
• Both signal and ground connected: hum jumps to 100%, loud, constant, unaffected by the pot position (turning the pot all the way down does nothing)

What I've ruled out:

• Speaker itself is clean: tested the exact same passive summing + pot + FGA-35 chain directly into a normal external speaker, completely clean, no hum.
• Normal radio reception (AM/LW) is clean, no hum, so the amp/PSU/speaker chain in the radio is healthy on its own.
• Not a wiring/cold joint issue in my build, continuity-tested every stage individually, and the "external speaker" test above confirms the whole chain up to the banana plugs works.
• Not proximity/orientation of the isolation transformer to the radio — moved it from 1.5m to 15cm away, no change.
• Not shielding of the last cable run, added shielding on the last segment (isolation transformer output to banana plugs), no change.
• Not the exposed tip of the banana plugs picking up interference — pulled heat-shrink as far forward as possible, no change.

Question Does this pattern (fine until both signal+ground are connected together, external cabling changes make zero difference) sound consistent with a coupling cap or grid-leak resistor issue at the PU input to you? Any other internal culprits I should check before I start pulling the chassis apart? Tube lineup is UCH81/UF89/UBC81/UL84/UY42, in case that's relevant to which stage is involved.

Pics of cable and power (cant upload video and pics): https://drive.proton.me/urls/2QQSR6N8BC#YOw5wVxslCQ6

It works pretty much exactly like a normal sixth order. Though I couldn't get the subwoofer to have a nice seal so the radiators would slowly move one way while playing heavy bass.

Before anyone says i wasted time and money: The passive radiators are from a different build. I did not buy them for this! and the wood is just scraps from a shed building place near me.

There are two Chambers of unknown volumes, the smaller one has two weights 150 g on the passive radiator and the bigger one has all the weights (5) 375 G which gives roughly 25 Hertz tuning on the low and 45 HZ tuning on the high.

The weights are 75 grams each.

I’m restoring a pair of Fostex PM-2 active 2-way monitors. One factory 8-inch woofer has a broken voice coil, and since original Fostex replacement woofers (#379013) are long discontinued, I am fitting a matching pair of aftermarket 8-inch woofers. Have looked everywhere, the only option is hoping for a donor/oem replacement to show up second hand, so in the meantime i have began looking for aftermarket woofers

I’d love some input from anyone with active speaker building/modding, here is an ai overview of the info i have gathered plus the drivers im looking at:

System & Cabinet Specs

• Enclosure Type: Ported / Vented (Dual front-firing ports, tuned to ~40 Hz)
• Measured Internal Dimensions: 22.5 cm × 23 cm × 37 cm
• Internal Volume: ~19.1L gross ~16.5L–17L net (after accounting for active plate amp, ports, and driver displacement)
• Damping: Factory hybrid lining (1" polyfill on walls + light stuffing behind driver cavity)
• Electronics: Bi-amplified active system (120W woofer amp / 40W tweeter amp)
• Electronic Crossover: 2 kHz crossover point
• Cabinet Cutout: 184 mm inner cutout diameter (willing to drill new pilot holes / use T-nuts)
• Use Case: Desktop near-field listening (Dub / DnB / Movies / Casual listening)

Current Shortlisted Drivers

1. Peerless SLS-P830667 (8-ohm, Paper Composite)
   • Specs: 86.5 dB (1W/1m), 11.1 mm extension, 120W RMS.
   • Pros: Heavy excursion capability for low sub-bass; smooth paper cone transition at the 2 kHz crossover.
   • Cons: Lower sensitivity (can compensate via active rear trim knob).
2. Dayton Audio DA215-8 (8-ohm, Aluminum Cone)
   • Specs: 88.0 dB (1W/1m), 5.5 mm extension, 80W RMS.
   • Pros: Stiff cone, fast transient response, tight bass.
   • Cons: Aluminum cone breakup spike around 5.5 kHz (plan to apply a software PEQ notch via Equalizer APO if needed).
3. Dayton Audio DS215-8 (8-ohm, Paper Cone)
   • Specs: Smooth response, 5.5 mm extension, 80W RMS.
   • Pros: Smooth non-fatiguing midrange, no top-end breakup.
4. Budget Alternative: QTX QXW8 (8-ohm, Woven Kevlar)
   • Pros: Very cheap (~£24 each), high power handling.
   • Cons: Limited excursion, punchy upper-bass focus, requires software EQ boost for 40 Hz extension.

Here's the first post/video that showed the project.

https://www.reddit.com/r/diyaudio/s/LWIR50xvtM

I wasn't able to include audio/music, but here's a video showing the audio quality of the speakers.

I have a JBL 305P MkII with a dead mainboard and want to restore it using a replacement amplifier.
I’ve already started designing the original 4th-order active crossover, which will go before the amplifier.
The LF and HF drivers are each rated around 41 W.
I’m currently looking at TPA3116D2-based amp boards and trying to figure out if they’re suitable for driving the two drivers.
Would a TPA3116D2 be a good choice, or is there a better amp/module I should consider?

No sound going to my Lil 8 inch bass in my truck, recently ran new rca cables, I dont really know what im doing just trying to replicate how my setup was before hand. Any ideas based on the picture?

Hey everyone, I’m planning to build a set of speakers for my dad and could use some input. He only listens to vinyl and mostly listens to Rock, Metal, Jazz and Blues, and lately he’s gotten into Hip Hop too, mainly MF DOOM.

I was thinking about going with Klipsch La Scala clones with the low extension mod or maybe something with Fostex drivers, but honestly I’m open to pretty much anything at this point. Budget isn’t fixed yet so I’ve got some flexibility there.

What would you build for a listener like that? Looking for something that can handle the punch and energy of rock and metal but still sound good and detailed on jazz and blues, and hold up on hip hop bass too. Any recommendations you’d point me toward would be awesome. Thanks in advance!

Hi,

Recently bought a 12v Bluetooth amplifier. I wanted to put inside a Phillips speaker my dad had lying around, then make it so it plugs into my 12v canopy setup to play music on it while camping.

I wired it all up, music was playing great. I had loose wires connected to a car battery just to test it out before making plugs etc. I then turned up the knob on the amplifier. And turned it down from my phone. So I can turn it up to max from my phone.

Then I started hearing a strange tick in the background happening rhythmically but it would go away once phone disconnected.

Then out of nowhere it just started blasting static noise and now, everyone i power it up, the power up noise starts, then the connection noise starts and stops repeatedly while playing static Im between. And my phone won’t connect to the amplifier at all. All the connections to the amplifier look the exact same as when I soldered it.

Need help Im not very good with this stuff.

Kind regards, Raphael

Does anyone recognize this exact OEM spec sheet? Are these pulled from a specific Samsung, LG, or JBL soundbar? I am trying to find the exact cutout diameter for an enclosure, the recommended box volume, and the power handling (RMS watts) so I can safely use them in a custom build.

Bought this cheapo Samsung driver for 10€ in mint condition (for a party sub build) and it ended up getting damaged due to poor packaging.

Should i return it and miss out on the fairly decent price or is there a good way to straighten it out?

None of the surround has peeled off or anything it's just the mounting right that's a little bent. And its a nice even bend too, nothing crumpled or pinched

This is an update to my last post here in this sub:

What’s new:

I change the tweeter from the monacor dt300 with the wg 300 waveguide to a seas 27tdfc.
I did that mostly because the dt300 did not really integrate well.. and I would have needed to cut the waveguide to be able to push the tweeter back to adjust the phase alignment. Also I was not satisfied with the resolution and performance above 10khz..

Secondly I modified the enclosure to push the tweeter closer to the woofer. I also cut the bottom of the speaker at an angle in order to angle the speaker a bit upwards. This also created a tappered reflex port at the bottom.

The crossover:

After about 20 iterations I was able to integrate a full first order crossover with the crossover point being at about 2 kHz.
I personally found that first order crossovers sound best if you can integrate them properly.

In this case I had to combine the first order crossovers with a rcl circuit for both the woofer ( membrane breakups which bled into tweeter response) and the tweeter ( to linearize the impedance peak ).

Now I’m working on some quarter wave and Helmholtz absorption to get rid of as much damping material as possible.

Hello everyone!

I wanted to share a deep dive into my custom-built Digital-to-Analog Converter, which I have named the "MilleDAC". I originally started this project in 2013. Bringing it to life took about 6 months of development and required writing approximately 2000 lines of custom code.

The goal was to build a no-compromise DAC that not only sounds incredible but also offers a great user experience through a modern touchscreen interface. Here is a breakdown of the design and hardware:

🎛️ Core Audio Processing & Inputs:

• The heart of the system is the highly regarded ESS ES9018 DAC chip running in 8-channel stereo mode.
• To maximize performance, four of the DAC's channels are wired in parallel for each stereo side.
• It handles extremely high-resolution audio, supporting up to DSD512 and PCM 384kHz.
• Input options are highly versatile, including an Amanero COMBO384 USB module, as well as optical (Toslink) and digital coaxial (S/PDIF) inputs.
• Master timing is controlled by an ultra-low noise Crystek CCHD-575-100 quartz oscillator, which boasts an incredibly low 82 femtoseconds of jitter and ±20ppm accuracy.

🔌 Analog Stage & Outputs:

• The ES9018 is configured in current-output mode to help suppress 2nd and 3rd harmonic distortion.
• The active I/V (current-to-voltage) conversion stage is built around precise LME49990 operational amplifiers.
• The analog signal path is populated exclusively with premium components, including ±0.01% tolerance metal film resistors (with a temperature coefficient of ±2ppm/°C) and ±1% NP0 capacitors.
• For outputs, the board provides a standard RCA line-out alongside a 3.5mm headphone jack.
• The headphone output is properly buffered using an LME49600 high-performance audio buffer, providing enough current to easily drive demanding 600-Ohm headphones.

⚡ Power Supply & PCB Layout:

• The whole project sits on a custom 160x100mm 4-layer PCB.
• The board design utilizes dedicated, fully separated ground and power planes, alongside two layers for signal routing.
• To prevent noise interference, there is complete galvanic isolation between the digital and analog circuit branches.
• Clean power is critical, so the board features 8 independent power phases utilizing high-end ultra-low noise regulators (six TPS7A4701, one TPS7A3301, and one LP5907).

🖥️ Microcontroller & Touch UI:

• The brains of the operation is a 32-bit Atmel AT32UC3L064 microcontroller.
• The user interface is driven by an FTDI VM800 controller connected to a 3.5" Touch-Display (VM800B35A) with a 320x240 pixel resolution.
• The custom on-screen menu allows for source selection, muting, and 0-100% volume control, while also displaying incoming signal information like the sample rate.
• The microcontroller saves user preferences to a serial EEPROM, so everything is exactly how you left it when you power it back on.

I put a massive amount of time into calculating the I/V stage values in PSpice and ensuring the ground planes were perfect.

Let me know what you guys think of the build!

I have been designing this class A, push/pull tube amp in ltspice. Curious if anyone would like to comment on the design. The amplifier uses a cathode follower input stage, a differential push/pull gain stage, and a push/pull output stage. The amp uses transformers for phase splitting and for coupling the gain stage to the power stage. Preamp tubes are 6SN7s and the power tubes are KT88s or KT120s. I have also designed a digital board to go with this amp that measures and displays the current to aid in setting the bias, as well as providing for source selection using latching signal relays, if anyone is interested. The digital board is designed around a pic 8 bit microcontroller and was designed in KiCad. Cheers. Martin.

Hello. I am an avid wood worker and enjoy good hifi so i thought I'd do my tires into building my own 3way speakers. Looking for something that i don't have to use a subwoofer. I like the epique speaker line on parts Express, but to build a three way from that line, it wouldn't be very efficient. Anyone have any ideas? Could also use some help with the crossover... is what I'm looking to do even possible?