"Calibre 834" - tube phono MM preamp

Esoteric, some years back, sold a tube phono preamp called the EAR 834p. It got excellent reviews. The schematic is available and kits based on the original schematic are plentiful. This is one of the cheaper ones by not providing tubes. I have three pairs of match 12AX7s - Mullard, Sovtek and Tung-Sol. Time to put them to use. I used the Sovteks as they had the smallest plates which is good for microphonic control. The third tube is a cathode follower for driving the next stage. GNFB is used.

The kit comes with top shelf components;- Vishay resistors and capacitors, Dales and other quality parts. The brd. is silk screened and double sided plated through. A trick I have used in the past (and used here) is to mount the passives on the bottom of the brd. and not on top. This allows the tubes to poke through the top of the preamp. The brd. is easy to assemble. Also mounting it in yet another Hammond wood cheeked light Al chassis was easy. Once more an XLR plug and socket bring in the HT and heater voltage from a choked external PS. The PS itself runs from a 24VAC 1A wall wart.

WBT silver solder was used and silver plated wire-warp wire used in the signal path. A light multi-stand hooks up the HT and heaters. The brd. is designed to utilise two separate PSs but I joined them to one. Excellent sounding preamp and well worth the cost of parts.

"Overture" - LM4780 chip power amp

Built two Audio Sector LM4780 based amp modules. Each module is a stereo amp. They can be bridged and paralleled. On a request I finally put these compact modules into a finished amp. The enclosure is a 2U 19" rack mount which gave me plenty of space to work. The buyer was happy to spend money on better parts. These included Panasonic caps on the board, 2X 22000uf Mundorf MLytic audio grade filter caps. copper, palladium and Teflon RCAs and extra heavy duty speaker posts.

The signal wiring was with fine silver plated copper wire and heavier wiring is twisted pairs of solid core cat5. All caps are snubbed and the amps is absolutely dead quiet. Should produce near 60Wpc.

Excellent sounding amp and well worth employing these compact "Overture" modules. 

"Icon" - CV-181Z (6SN7) preamp

After a very successful build of three similar preamps I wanted to make another using some excellent and less expensive Shuguang CV-181Z (6SN7) 50 Year Treasure tubes. I bought these some years back and it was wrong not to use them. Staying with external DC supplies and using similar construction methods I used in the past "Icon" was born. But this build had to stand out, be different and not just another Grace or Elite (see earlier posts). There are some similarities; same chassis, ceramic sockets and the use of an XLR socket to bring in the two DC voltages to power the preamp.

Where the big changes occurred were mainly in the passives (of course the tubes are very different). Firstly all wiring was with twisted pair or single strand solid core Cat5. I retrained the use of WBT 4% silver solder. The output caps are Mundorf EVO Al and oil types and the resisors are metal film instead of 1W carbon film. A single 4uf PIO cap (snubbed) was used on the HT at the plate instead of one cap for each tube.

I never use a cathode resistor bypass cap (Ck) because I want some local NFB and to supress 2nd harmonic. This time Ck was employed but not with the electrolytic suggested,\ - NP caps. This raised the gain a little but has produced a much fuller and even deeper bass. Also here three inputs instead of two and the selection switch at the front and not the rear. A cheaper stepper attenuator was used rather than the premium version used in Elite. Caps, tubes and stepper were cheaper in this build.

The preamp sounds glorious. It is rich and deep in tone and bass. A big full sound with real depth. Is it better than Elite? That gets down to personal taste, regardless it is an excellent and less expensive build.

"najah" raw 180W Class D amp.

Yet another Class D but this time using the onboard PS. It comprises a diode bridge with ultra fast soft recovery diodes and 10,000uf Nichicon cap. All quality parts. I added a 500VA tranni and a 0.1uf poly snubber to the Nichicon. Amp sounds very good. I've called the amp "najah". These boards are packed with quality parts; Jantzen and wima are some and comes with speaker crow bar protection.

Bass sounds heavier than my T3 expensive monoblocks. So easy and cheap to make a 180Wpc amp which is true hifi due to extremely low distortion figures. I know ultra low distortion doesn't always mean it sounds good but it does mean it is true high fidelity.

180W Tripath Class D amp

Yet another Class D Tripath amp using the hifimediy Class D 180W module V1.3. This one is setup for a 4ohm load. Lower PS voltage but higher current - 13A. I added 16000uf of smoothing caps and 40A rec bridge. Bipass caps keep the bridge and electros quiet. Four rear inputs with very heavy duty speaker terminals. All switches up front with a small power switch for each input. A Cat5 solid core cable brings the input to the selection switches. The pot is a 24 step stepper and with 4oz brass, gold plated knob.

An IEC socket has a power filter and the enclosure is earthed and fused. The enclosure is a 19" 2U rack mount in a black stipple. Really heavy bass with a very smooth sound, feels effortless. Dead quiet operation. The module has much current and voltage protection plus crowbar speaker protection. This was a commission job.

"retro-6J6Pro" -Oatley tube headphone amp with OPTs

Once more another tube headphone amp from Oatley. The last two have been mounted on bread boards to show off the "pretty" and extensive PCB. This time into a pro 2U 19" rack mount enclosure. There are two inputs on the rear which are auto exclusive. If there is an input in the phone jack the RCAs are switched out and if there is no phone connection the RCAs are active. This ensures only one source is active at anyone time. Tubes are GE NOS, socket ceramic and caps Polies.

To help keep costs down a basic stereo pot is used but to ensure clean quiet power a RFI/EMI filter is on the mains. The enclosure is earthed and fused. The power cable fixed. The output phone jack is on the front. Not often included here is an inside image.

The sound, as with the others, is enjoyable, quiet with moderate gain. I listen extensively with Sennheiser 700s and enjoyed the experience.

"Elite" - 6SN7-SE preamp with low noise tubes

Another preamp based on the expensive limited edition SE Psvane globes. There are two grades of these tubes; Grade "A" and Grade "B". Grace was has the Grade "B" tubes but in this build the even more expensive Grade "A" low noise tubes are used. Grace and Elite share the same schematic (active load - totem pole) and all of the same parts. Even in the first few minutes of pay I could hear the better tubes shining through. The sound is even more clearer and precise than the earlier build. 

As in Grace Jensen copper foil, paper in oil caps are used in the output. These caps are rated 630V and are quite large. They also have pure silver leads. There is only three carbon film resistors and the output caps in the signal path. EIZZ 24 step gold contact attenuator once more controls output level and is on the output. WBT silver solder and silver plated fine copper wire is used for hookup. There are two selectable inputs on the rear and an earthing point. The external PS floats.

Twisted Cat5 carries the heavier currents for filament (which is DC) and HT voltage. Russian military PIO 4uf caps sit at the plates to hold HT. These are further snubbed with 0.1uf polies. The Jensen caps are also snubbed with 0.01uf polies to provide a clearer HF path and trap any noise in the caps. 

The PS is a little beefier than Grace's but in other respects is very similar. It uses a double Pi filtering configuration and is choked. A total of 400uf (400V caps) ensures a quiet HT. Snubbing caps are placed across the two diode bridges to supply HT and DC filament voltages. The filter\storage caps for both voltages are also snubbed. A 24VAC wall wart supplies the initial power.