This is a project developed by Douglas Self and published in the Elektor in October and November 2010.

The idea is rather unusual: "An interesting power amplifier can be made by connecting enough 5532s in parallel, how about 32 for a start? This may sound like a radical course of action, but it actually works very well, making it possible to build a very simple amplifier that retains not only the excellent linearity but also the power-supply rejection and the inbuilt overload protection of the 5532, which reduces the external circuitry required to a minimum."

Elektor used to sell PCBs for this project, which I used. I modified the circuit slightly to incorporate an active volume control along the lines of Douglas Self's preamplifiers.

Here is the result:

My first solid state amplifier build, in 2009, was The Penultimate Zen, aka Zen Variations Part 4, aka ZV4. It was built with the parts I could find back then, without knowing where to look. It ended up big, heavy with two 400VA toroidal transformers, ugly inside with some electrical tape here and there, without proper grounding, etc., etc. I was as disappointed with the sound as my wife was disappointed with that heavy black metal brick gathering dust.

My first mod on ZV4 came after I turned my disappointment into finding better part suppliers. I returned to my ZV4 and replaced the output caps with something marginally more decent from eBay. The sound improved a notch. Aha!

My second mod was to rebuild the power supply. I threw away one of the toroids, added a softstart circuit from Hypex, and put in a CRC filter with some Mundorf HC caps. One power supply for two single ended channels forced me to learn about grounding and add input transformers and balanced...

I built this one a while ago but could not find time to post.

This is a Class B power amplifier that follows the Ultra-LD Mk.3 amplifier design published by the Australian Silicon Chip magazine in 2011, which in turn draws heavily from the concept of a Blameless amplifier devised by Douglas Self. I used a different power supply and speaker protection, and changed the grounding scheme vs what was published.

The distortion at 1 kHz is below my measurement capabilities, and the amplifier does sound very nice, although it seems to give more sibilance than my Class A amplifiers.

The acid test I use is the dual CD "The Very Best of Placido Domingo" album published by EMI Classics. Many amplifiers I have heard cannot deal well with Domingo's tenor, esp. on louder and higher tones. Class A amps, particularly those using simple internal structure like the Zen series, perform well in this test. This amplifier seems to do better than any other...

Big, hot, and heavy! Just completed it and adjusted for distortion, have not had yet a real chance to listen to it. (Update: I have listened to this amp for some time, and it seems to be a keeper, at least for now.) The discussion is here.

The build is in a 4U/400 case from modushop; each side has two 200mm heatsinks, each holding six MOSFETs (three complementary pairs) and a biasing circuit.

The construction is dual mono (separate transformers for each channel) with CRC filtered +/- 18V rails, quiescent current is 3A per channel. Eight Mundorf MLytic® HC High Current Power Caps and two 300VA toroids occupy the most of the chassis, while the actual electronics is mounted on the sides.

Now I need a balanced preamp. I contemplate building some variant of BoSoZ, but am also thinking about a SuperSymmetric balanced preamp using JFETs or tubes...

UPDATE: No- and low-feedback amplifiers have no (or little) control over output errors...

I build myself a Millett's Hybrid Headphone amp, originally published in AudioXpress issue 11, 2001.

The amp uses low-voltage 12AE6A tubes for voltage amplification and BUF634 solid state buffers to drive the load. Each tube houses two diodes (unused) and a triode, here loaded with a CCS. The whole thing runs off a 24VDC power brick and consumes maybe 150mA after the tubes heat up.

The DC operating point of the triode can be adjusted with a multiturn trimpot. The original AudioXpress article talks about the influence of the operating point on the sound and suggests to trim for symmetrical clipping, then adjust for the subjectively best sound.

The aha! moment came when I connected the amp to my sound card and looked at the distortion spectrum. On small signals (~300mV output into 300 ohm) the distortion is 2nd harmonic only. The operation point can be trimmed to the point where the the 2nd harmonic goes into the noise floor! I've read about this but...

I added a TentLabs XO2.2 low jitter clock and a separate power supply for it to my exposure 2010S CD player. The process was very straightforward - see the pictures.

The exposure 2010S CD player has an easy internal layout, where most of the components sit on a large PCB.

The original clock is based on the 74HC04N chip located in the middle of the PCB, to the left from the three white power connectors connecting the toroidal transformer. A close-up picture shows the crystal resonator wrapped in a black heat-shrink tube, two 33pF capacitors on each side of the resonator (those with black dots on top), and a resistor R75, which also serves in the circuit. The oscillator is built on the single invertor (pins 13 and 12 of the IC).

The original clock is generating 16.9344 MHz at 5V CMOS levels.

To install XO2.2, I removed the resonator and the capacitors, leaving the resistor in place. I connected the signal cable from XO2.2 to the...

Just finished fine tuning my First Watt F5 clone.

I built it about a year ago out of parts that I had on hand back then, including a power supply reused from another project. The resulting sound was rather disappointing. Now I spent time matching transistors and tuning the feedback network. The amplifier now is very close to the performance described in the original service manual.

I am listening to F5 (the music is Tchaikovsky performed by Wiener Philharmoniker and von Karajan) and realizing that it is so good that if this was my first amplifier, I might not be interested in building anything else.

Update: after a year, this is still the best amplifier.

Update: I purchased the official F5 PCBs from the diyAudio store. I will rebuild the amplifier, hopefully with better FETs and other parts.

Bruno Putzeys posted:

About power ratings, well... Normal "critical listening" levels hover around a long-term average of 85db SPL at the listening position. If we're assuming uncorrelated signals (rather inaccurate assumption but it'll do for the purpose) that is 82dB SPL for each speaker alone. Crudely calculating back from a 2m listening distance to the 1m standard measuring distance that's 88dBSPL, one speaker, one meter. It's not unusual for speakers to have an efficiency of 88dB/1w/1m so 1W is roughly the required amplifier power.

The current crop of unlistenable hypersquashed pop music has a peak to average range of around 4dB. So all it takes to reproduce pop at a reasonable level without clipping is a 4dBW (2.5W) rated amp.
Before the loudness war got into swing (say until the early 90's) peak-to-average ranges up to 14dB could be found in mainstream music. To play Sultans of Swing at the same average level requires an amp rated at 14dBW

...

Now that Nelson Pass published the details of the JFET upgrade to First Watt F2 and that Newark sells power JFETs from Semisouth, there was no excuse not to upgrade my Zen V4 with the new active device.

I replaced Q1 (see the original schematic) with SJEP120R100A; increased R5 to 130 kohm to bias the JFET correctly with Vgs of approx. 1.5V; and reduced R8 to 22 ohm.

The measured result is a nice reduction in THD+N; attached are the graphs for THD+N @ 1W into 8 ohm vs frequency, before and after the upgrade. With IRFP044 as Q1, the distortion was mostly 2nd harmonic (at -65dB), plus some traces of the 3rd harmonic. With the JFET, it is still mostly 2nd harmonic, which is now at -80..85dB, with the 3rd below my measurement floor.

Subjectively, the improvement is remarkable! There is additional detail and depth of the scene.

In 2009, Penultimate Zen aka Zen V4 was my first solid state build. I used the parts that were available, did not know much about making it work well, and did not have test instruments beyond a cheap multimeter. Also, I did not have a preamplifier to work with it or speakers sensitive enough to enjoy its 25W. As a result, the amplifier turned out not quite satisfactory and for two years has been gathering dust and my wife's complaints. I was thinking about scrapping it and reusing the enclosure for something more useful. Instead, I reworked it.

I removed one of the two power transformers (moving from dual mono to stereo configuration), replaced my original dodgy Chinese PSU filter caps with Mundorf M-Lytic HC, replaced internal low voltage wiring with thick speaker wire, reconfigured grounding (so it is finally safe!) and installed balanced inputs with input transformers. What a change in sound! With my Exposure CD player, B1 clone preamp and Heresy III speakers, the amp...