retro-34UL power amp

In an effort to use-up so many spare parts I have I put together another EL34/KT88 amp. Part of the inspiration to build the amp came about when I was given four 1996 NOS Svetlana EL34s. These bare the old Svatlana logo. Also I had dismantled a bread board amp which had a large power tranni and choke which were perfect for this build.

The base is Australian Spotted Gum and the power tranni and choke are Hammond. The OPTs are Edcor 15W open frame types, reside in the base and are shock mounted. The feet are filled with lead sinkers for resonance control. A CLCRC filter network ensures the amp performs dead quietly and has an extremely high head room. Frequency response is to 40Khz and power is 5W RMS into 8ohms. Russian paper in oil caps are used in the inter-stage and bipolar caps and low ESR caps are used in the cathode bypass. Silver plated wire-wrap wire hooks up the gold plated RCAs to the nearby 6N1P and connects  the secondary of the OPTs to the binding post.

The paint work is epoxy enamel on 2mm high grade Al plate. Silver solder is use in the driver stage. Component-2-componet wiring is used to ensure signal path length is kept to a minimum. There is no shielded wire or PCBs to degrade the sound. This is a fast amp with a huge sound stage and a rich lush EL34 sound.

This amp has been built to sell.

Fostex FE206En drivers in dual bass chamber box

I had the boxes made some years back with no idea what I was to do with them. When I went back to 2 Channel theater with a 3.5W 6EM7 integrated amp (Paris) I knew they would be perfect around my new 46" LED TV and Oppo BDP-93 blue ray player. The finish is satin black stipple and the grills are held in place with four rare earth button magnets. Easy to pop on and off. The stipple effect was produced with a roller going over the fresh paint a number of times as it dried. The drivers huge magnets have bitumanised Al foil dampening attached and the internal wiring is two stands of lightly twisted wire wrap wire to each binding post.

The top chamber is lined (but not stuffed) with Dacron but the bottom chamber is empty. There is no Xover in these full range speakers. Efficiency is 96db at 8ohms impedance so they work well with flea power tube amps. Sitting higher than the tweeter (wizzer cone) the sound is quite natural with just a touch of forwardness in the mid-range. The speakers not only look stunning they sound excellent for a $500 spend.

"Luciano" - 807 SE Power Amp

I managed to purchase a couple of 807/ATS25 tubes for $7 each and were giving two in excellent condition. Both pairs of tubes test 85% emissions. Matt, an American electronics engineer, volunteered to design an amp around the tubes. Though this project stagnated for years finally it has come to completion.

The bases are made by a local amp builder and are from Australian Spotted Gum. The top and bottom plates are 2mm Al and the colour "Red Delicious". Edcor 30W OPTs and power tranni grace this smart looking amp. The design is SE with no feed back apart from Ultra-linear. The driver tube is 6SN7 and the rectifier tube is a 5Y3. I have a few different 6SN7s and rectifier tubes to roll this amp and another pair of JAN 807s.

The sound appears natural with a little forwardness in the upper-mid and excellent head room. Loud and dynamic passages are handled with no compression or strain. Voice clear, stands out and is natural. Instruments are individually defined. A pleasing sound and a well performing amp.

"Paris Duo" - 6EM7 monoblock power amplifier

Building on the success of the Paris amplifier (dual mono construction) I was asked to build a pair of monoblocks. Paris Duo has a two stage power supply filter using a small choke and resistive network with large electrolytic capacitors. Tightly twisted wire-wrap wire feeds the signal to the first triode and the same wire connects to the speaker binding posts.

The power transformer is rubber mounted to reduce resonance on the cast Al chassis. The finish is epoxy enamel paint with an acid etch primer. The tube compliment is a 5Y3 rectifier and Sylvania (NOS USA) 6EM7. A small Hammond choke and Edcore 10W output transformer are inside the heavy chassis. There is also a EMI mains power filter in the chassis and a choke on the power lead. The bottom of the chassis is drilled for cooling with a layer of bitumanised heavy Al foil to control resonance. Soft silicon feet secure the amplifier and also help provide resonance and vibration control.

The sound is similar to the original Paris amp with an ultra clear mid-range, heavy in detail and good bass extension. In room testing proves a low 40hz tone with only a modicum of attenuation. Treble is on the sweet side rather then bright and is extended. An excellent sounding amp providing a touch over 2W of delivery.

Two Stage Tube Phono Preamp

Tubecad, in a tutorial article, described a number of tube phono preamps. This is one of the simpler Tubecad designs and uses two 12AX7s in a two stage, passive RIAA equalisation, configuration. Golden Dragon tubes and quality tube rings are used here. The preamp employs a 24VAC wall wart which is step up to 260V and then well filtered. The HT filter is in two stages using a C-R-C-R-C network. The heater voltage is also rectified and filtered. There is a MM/MC switch to switch between 47K and 100 ohm loading. Gain is high.

All construction is on veroboard (strip board) and silver soldered. The four coupling capacitors are the Russian paper-in-oil (PIO) and the RIAA equalisation circuit uses Sprague “orange drops”. The enclosures are Hammond anodized Al cases. A separate power supply and substantial filtering helps keep noise out of the sensitive preamp cct. The sound is bright and very liquid. The preamp appears to work extremely well with pop, rock and jazz and most classical music.

"Paris" - 6EM7 Dual Mono 2W Integrated amp.

In this construction, "Paris", is a dual mono build. The preamp tube at the front of the amp is the only shared tube. Each channel has its own power transformer, 5Y3 rectifier tube, choke and 6EM7 tube. The transformers are rubber mounted, sockets are ceramic and an Alps Blue Velvet pot attenuates the output from the preamp section. A power filter and Edcor 15W OPTs in the base. A black chrome 4oz brass knob adds to the look and feel of the amp. The colour is called Sungold but some may say yellow. Paris contains two signal caps sets which can be switched between.

Two selectable inputs grace the back plate. This is a true integrated amp with a 4S Universal preamp section. Any 12A?? tube can be used for the preamp allowing the user to customise the "tone" of the amp. Sprague poly caps are used in the signal path. Power output is about 2.5W. Only sensitive speakers should be used. It has the best mid-range detail I have ever heard in any amp.

Universal - 4S preamp MKIV

This is the forth of these Super Simple Single Stage (4S) valve preamps. This was not designed by me but for me and has come after building three others and posting results on the diyaudioprojects forum. The others (see earlier posts) were specifically designed for the 12AU7 dual troide. This breaks away from that theme and will work with any of 12Axx available. This includes: 12AX7, 12AU7, 12AT7 and 12AY7.

Once more there is only one cct. brd. (this time strip board or veraboard) and holds both the PS and the amp itself. Expensive Solen caps were used in The Black but in this build MKP caps were used and less expensive parst and construction all round. With the right tube in place its sound is very close to The Black.

Housed in a Hammond Al case and quite sleek looking it is powered by the same 24VAC wall wart power pack the others are. It is quiet and has extensive gain. After some listening and comparing its performance across a number of different valves the Universal delivers a detailed sound with solid bass and airy mids and highs. The best valve tested with it so far is the 12AU7 Golden Dragon. Very easy to listen to all day!