“Rococo” - 5961/6V6 two stage power amp

“Rococo” ;- 5961/6V6 amp complete and playing very nicely. Tubes, as I mentioned, RCA 5961 red base and currently Tung-Sol 6V6GT (matched - 2009) ). I have other classy 6V6s but Ill listen to these a while. All tubes new.

Asian OPTs and blue CDC coupling caps. I have noticed these caps in some very expensive high-end power amps. PS is two 3A Fast diodes and double Pi filtering. HT feed to the driver is split into two single feeds with each a 22uf LESR electro for better separation and sound stage. Noise with RCAs open is 1.4mV. Thats quiet.

Big clear, very dynamic sound leaning toward the bright side emphasising voice. Tubes need 50 hours to burn in from new. Worked at first on. I played the new amp over the afternoon and into the very late evening. Watched a movie with it providing the sound and up in volume.

A few more details for those interested;- the timbre base is the last I purchased from my amp building octogenarian Don. He doesn’t make amps or bases any more. So a fitting tribute to his skill. The finish is a spray lacquer which went on well getting three coats all at once with no runs. 

The power tranni, as usual, is Hammond, ceramic sockets and all wiring is solid core Cat5. No shielded wire and noise is 1.4mV. 306V on the 6V6 plate and 160V on the 5961. Bias is 1.4V and 18V, all as the schematic. CDC interstage caps Ive had for years and sound excellent, WBT silver base solder used. The double Pi filtering adds upto 350uF of 400V caps and snubbed - 0.1uf poly. 

Mostly 1W film carbon film and 5W wire wound Rs throughout with a few metal films. Quality gold plated RCAs and heavy solid brass speaker posts also gold flashed. Ck(s) are all NP 100V types. 

Beautifully clear transparent midrange from the tube compliment and well presented through my horns. Bass sounds well extended and balanced against the other frequencies. Still smiling. Love the look

“Automony” - small signal preamplifier

 

Completed the cct. brds. thirty years ago and they have sat around until recently. There is no pcb but just a pad brd. There is no hookup wire on the brds. Each component is wired to the next directly with no other connection between. This I call component-2-component wiring, better the point-2-point wiring which uses hookup wire. To add to this there is six very expensive Jensen copper foil, paper and oil caps. Also two Solen caps plus a mix of carbon and metal film resistors.

Recently I discovered high voltage SMPS which I have successfully powered other preamps with. Here it also powers this preamp, the same “Universal” PS. The brds. plus a remote control Alps blue velvet pot fit snuggly into the Hammond wood cheek chassis. The preamp was designed for 12AX7s but here Im using LinLai 12AU7s. 

The finish colour is Ironstone and a heavy sculptured brass gold plated knob finishes the look. There is two inputs selected by a switch at the back. The sound is smooth and romantic. This maybe due to the both local and global negative feedback. This is old school design and has a lot to do with the smooth, creamy audio presentation. A fitting completion to what started thirty years go.

“Dadirri” - 71a power amp.

 

Every now and then you build an amp which stands out from all the other builds you have done in the past. Of the 71a amps I have built there is one for me and now two for others. Though there is a list of standard parts used in this build for some reason it sounds way better than it should. I did use new driver tubes - Tung-Sol 6SN7 - but the other tubes, 71a Cunningham and RCA 80 rectifier tube are vintage and I have used them before. I guess just accept it, listen and enjoy and don’t over think it. I know the new owner will be very pleased. He is using his own tubes. 

The timber chassis I am now buying from Aliexpress and though pricey they are solid and very good. In this build I left the top plate natural low sheen Al. It would be a shame to paint this one. An oversize Hammond power tranni and Asian OPTs round out the iron. Carbon film 1W Rs, wire wounds and a few metal film Rs were used. Interstage caps are Russian PIO in glass and metal envelope. I wired 4 and 8ohm speaker connections in this build. 

The 5V DC heater voltage for the 71a tubes is provided by a 3A bridge and two 4700uf caps and taps off from the 6.3V AC filament voltage for the 6SN7s. All wiring is with solid core Cat5 and no shielded wire is used. Noise is less than 1mV. HT is rectified by the 80 tube and a double Pi filter cleans up the 220V DC reaching the 71a tubes. There is 247uf of storage and smoothing caps. The HT feeding the driver tubes is split in two and 2X 10uf 450V caps hold a fast and individual power storage. The stereo imaging of this amp is extremely good and it may be due to this HT split to the drivers. 

I’m extremely pleased with the overall appearance of this amp. Matching the good looks is the most beguiling sound I have heard from a tube amp which only supplies about 300mW of power but in my system plays quite loud with my 93db efficient speakers. This one should have been a keeper.

50W Class A Holton based power amp

 

For a long time friend, who already has two of my power amps, one SS and one tube, I was requested to build this Class A power amp. Holton Precision of Tasmania had developed some new Class A 50W modules. That’s 50W pure Class A before sliding across to B. Amp should produce 90W in Class B. 

The PS consisted of a 300W tranni and 132,000uf of Mundorf Mlytic audio grade caps. Dual 35A rectifier bridges round out the PS. The caps were heavily snubbed with high voltage polies. With a result the amp has near zero AC noise. But better than that, the amp produces beguiling music like I’d not heard before. Its ability to dig out inner detail and bring it to the front was uncanny. The new owner liked it also. 

The amp runs extremely hot and to help control the heat two silent running fans were installed. The fans sat on rubber grommets for isolation and were run on low voltages. With a result they could not be heard. Though this build produced many challenges, over months of construction, it was worth it. 

“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.