“Immerse” - headphone amplifier using 5W chip amps.

I had two 5W chip amps (TDA1905) in my collection for many years but did not need just another low wattage power amp to drive speakers. The end result is a headphone amp. With the chips capable of driving eight ohm speakers to 5W driving 32 ohm head phones to just part of a watt should be easy. The manufacture of the chips claim 0.1% THD at 3W. That means the distortion levels into phones will be very low. And plenty of good drive power.

Using a similar enclosure I have used many times I hoped the amp would work with batteries but it drew too match current. Batteries were out. I have a few DC wall warts and a 12VDC 880mA unit was perfect for the job. I added another 1500uf of filtering in the amp some snubbing caps to keep noise low. Noise is less than 1uV. A mix of carbon and metal film Rs used throughout.

The headphone amp is dead quiet, sounds distortion free on both 250and 32ohm HPs and is clear and very detailed. The amp was constructed on a piece of vero-brd and solid Cat 5 wire used for hookup. And because I had a well preserved antique bakerlight knob on hand this dressed the front. Apart from a little too much gain the amp works perfectly and I have enjoyed many hours of music driven by it. A good outcome.

“Five” - Pass inspired F5 Class A power amp with SMPS.

 

For some reason, still unknown, I had chronic hum issues with this build. I tried two different F5 cct. bds. and one Class AB module. Even modding the PS with an additional rec. bridge didn’t fix the problem. With large tranni and 132,000uf of high grade Mundorf caps there should be no hum. The other seven or so F5s I built were dead quiet. 

Replacing the PS, tranni, caps, diodes etc with a SMPS of suitable power fixed the hum. But the SMPS would overheat and shut down. By adding a larger heatsink and a 12V silent fan running on 9V fixed the problem. The fan cannot be heard and now with large tranni removed the amp is much lighter. 

The amp stays a Pass F5 build and does sound very, very good with good power, dynamics and bass extension. Usually I use it with one of my many tube preamps. A great combination and has given me many hours of enjoyment. It took many months of trial and error to get to this point but glad I persisted. 

The enclosure I engineered from scratch around two very large heatsinks I had had for many years. My local metal supplier did all the plate cutting then I did a hell of a lot of drilling and assembling and re-assembling to get things right. The finished amp looks good and sounds better, once again, glad I persisted.

“Mimic Classic” - MM RIAA phono stage

 As you will see by earlier posts I have made a number of these. While building the earlier couple I realised I still had parts on hand for one more. The only part I was missing was a decent enclosure. These compact cast Al enclosures are perfect for this type of build. The finish this time is Gum Metal. Parts inside are similar to earlier builds including big polies on the output. Looks good sounds just as good. 

ArmaDillo - 600W Sure Class D power amp

Complete apart from decal - all18kg of it. Two 600W 12A transformers, two 47,000uf Mundorf MLytic high current caps in a sturdy 3U enclosure. The Sure Class D module is rated 1500W but here should deliver 600Wpc. Heavy duty speaker posts and RCAs and all 10A wiring and 20A switch. Differential voltage is +/-68V. Excellent bass depth and very clear mid-range. 

“Mimic - Classic and Pro”

 

I required for my own use another MM RIAA phono preamp. I had these two compact enclosures on hand and most of the parts. I only had to purchase a subminiature power switch, cheap RCAs and two metal 9V battery holders. All the passives and chips (OPA2134) I had on hand. "Pro" uses 1/4W carbon film Rs and "Classic" all 1/2W metal film. There is a mix of better and standard caps in "Pro" and just polyester caps in "Classic". 

Both run on a couple of 9V batteries which use a resistive network and a couple of low ESR caps to provide +/-9V and a virtual earth. the entire cct. including the PS section is built on a tiny bit of strip board smaller than a matchbox. Inexpensive gold RCAs were purchased as I wanted to keep cost down. Having so many parts on hand made these builds easy and cheap. Hookup wire is silver plated fine copper wire. 

How do they sound. Good in a word. Bass is solid and the overall sound clear to transparent. No hum or buzz due to battery operation which should give me about 50 hours of play on fresh batteries. There is a battery test point at the front and battery replacement takes only a few minutes. The chip can be changed to any equivalent.  

“MC - Loader”

 

I had a request to build a loading box for MC cartridges. Happy to have this cast Al enclosure on hand and it worked out to be a perfect fit. Not much inside other than six resistors and some fine copper silver plated wire. Solder was WBT silver solder and heavy duty gold RCAs on back. 

The switch is center off and in this position, loading is 330 ohms. Switch to the left, according to the name plate on top, provides 100 ohms and to the right 50 ohms. All Rs were metal film and the Al box is double bitumanised heavy Al foil lined adding weight and resonance control.

“Retro-EAR834p” - an EAR834p tube MM phono stage

This is the third of these MM phono stages I have built and all for commission jobs. As an addition here a MC step-up stage was also built. The MC stage is the La Pacific single FET, battery driven stage and is seperate from the MM stage. The PS is external and uses a Hammond tranni. The EAR kits come with a PS board with HT and filament DC rectification and filtering. The HT is smoothed by a high voltage power FET. Works well. 

Looks smart on the stippled Hammond wood cheek chassis. With Tung-Sol and LinLai tubes sounds detailed and transparent and the new owner reports excellent bass. We are both happy with the result.

“ZeroOne-A” - 100 year old globe DHT tubes preamp.

 

Inspired by my 71a tube amp I thought I would try another DHT preamp but with a 01a tube. Again Cunningham tubes used as with the 71a but with the 71a I also have RCA tubes. These globes are from the mid 1920s. Where the 71a preamp - “MWH” - has mainly carbon film resistors in the signal path and a Russian PIO output cap this build has all metal film resistors and a Mundorf EVO oil output cap. 

To enhance the performance of both preamps I built a new much beefier external PS on a repurposed cast AL chassis which already had a RFI/EMI power filter added. The 5V DC on the heaters is regulated and balanced. The 01a preamp has a remote Alps volume control and two inputs. Hookup wiring is via fine silver plated copper wire and high quality heavy duty RCAs ate  used. Not a lot of gain but a very revealing, detailed sound with extended reverb. Love the colour - Iron Stone.

A 6N7 preamp with remote

The now converted 01a preamp is now a RCA - NOS NIB - 6N7. The tube is metal (No!) so not much of a glow and is a dual triode with single cathode. The tubes are wired as a single triode with grids and plates paralleled. 
 

This preamp was designed for me many years back and was originally built into a timber box as “Heavy Metal”. It had heat issues. In the better and classier chassis looks retro and business like. With Alps Blue Velvet remote pot. 
 

I required 0.68uf output caps but had none of that value. But did have four 0.33uf Sprague orange drops. Doubled them up for a near enough 0.66uf. Had them for decades, as the tubes, so time to use them. Most 1W carbon film resistors and some metal film and wire wound. Double Pi HT filtration - 300uf total. 
 

DC on heaters, 260V HT and 2.55V bias. All on point. Gain should be 20db with Rk un-bypassed. 

 

Tubes are run in but the rest new so some complete burn in time required. Sounding relaxed and midrangy with voice a standout from the sound stage. Dead quiet operation with retro-Zen EL34 amp but hummed with my latest EL34 amp. Very happy so far. 

“Perspective” - EL34 Single End Ultra-linear power amp

 

This amp is based on a pair of new Mullard reissue matched EL34s with a universal driver tube. Any 12A*7 can be used as a driver. OPTs are Asian 3.5K 10W with 4 and 8 ohm taps. I have used the 5W 5K versions in other amps with outstanding results. The OPTs and power trannies are shock mounted on split rubber grommets to reduce resonance.  The PS is external with over specced Hammond power tranni. A Sylvania 5U4GB handles rectification. 357uf of filter caps smooth and store 366V of HT. Further filtering feeds the driver tube with a 4uf PIO cap and 2.5K 2W resistor. The amp is very, very quiet. 

Filament current is rectified with a 10A bridge and single Pi filtering - 9400uf of filtration. HT and filament caps are snubbed with 0.1uf polies to reduce noise. The chassis is a Hammond wood cheek and is made of steel for strength. The finish is black stipple. The chassis for the PS is cast Al with a black epoxy enamel finish. The PS is fused and earthed. 

RCAs are Paladium plated and speaker posts solid brass with gold plate. Audio path wiring is fine silver plated copper wire. All wiring is point-2-point, no cct. brds. and no shielded wire. Not required. Sockets are ceramic and power is brought to the amp via three pin large XLR connection. The driver tube being used here is a Tung-Sol ECC803S gold pin. 6L6 and KT88 can be rolled here and any 12AX7 equiv. can also be rolled. 

Amp presents full bass and a complex warm soundstage with smooth highs. It is a pure Class A amp. Not only good looking but excellent sounding and definitely worth the weeks of work. The EL34s I’ve had for twenty years so now they get to entertain as they are designed to do. 

“retro-Zen” Decware inspired 6BQ5/EL84 triode strapped amp

 

A Decware inspired 6BQ5/EL84 (Zen) triode strapped amp with attenuator. Driver is 6N1P. And of course chicken beak knob with AWV 6BQ5.

OPTs are 5W Asian sourced which I and others have used and find excellent. They are shock mounted on split rubber grommets for HF/resonance suppression. Sockets are ceramic and gold plated with Visheys MKP interstage caps. Hookup wire is Cat5 solid core. 

External PS has a Sylvania 5U4GB and works with two other power amps saving me $400 each amp. But if I sell one ill have to make another PS. Power tranni is Hammond. Chassis is a cast Al with Epoxy Enamel paint. This is meant to be a fun amp, single input and just 2.5W. Good den amp or desktop amp. For good level music listening you need speakers with better the 90db sensitivity.

“Hegemony” - 6L6 monoblocks.

 

I was asked to build 6L6 monoblocks for a very keen tube collector. He would provide the tubes and I would build the amps. Monoblocks are almost double the work with two power trannies and filtering circuits. The requirements were also to use Silk OPTs from Thailand. I chose 20W models for a 5W amp. Interstage caps are Mundorf Evo oils. RCAs are Palladium.

These austere looking smart amps produce deep articulated bass, grounded detailed and rich midrange and crisp highs. Chassis are Hammond steel with wood cheeks and are difficult to drill but worth the effort. Hammond power trannies and 300uf of filtering in a double Pi config produce a very low noise (1.5mV) amp which plays plenty loud. Definitely one of my better and more expensive builds. You are rewarded, though, with an exceptional audio experience. 

“Rhetoric” - EAR834p MM phono stage

EAR834p MM phono stage in a Hammond wood cheek. External PS with Hammond tranni. DC on the heaters and the HT is electronically smoothed. Palladium and copper RCAs, and fine copper silver plated hookup wire. Im not supplying tubes but here Ratheon 12AU7 and two Mullard 12AX7 re-issues. 

“Elements” - 12AX7 SRPP preamp with remote

 

Built mainly from parts on hand including tubes (Gold Lion), enclosures, output caps and power tranni. The power tranni I got free because the filament windings were open. I had a 12V tranni on hand and was used here for heater voltage. 

Three inputs and Alps remote volume control with RFI/EMI filter in the external PS. Russian military metal clad output caps in a Hammond extruded anodised Al enclosure with a big gold knob make this a smart looking build. Brilliant sounding as well as smart looking, a great use for so many parts which had remained unused.