“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.