"fiih"- Holton inspired 150W amplifier

This is my fifth Holton (assieamps) build. Riding on the success of two 150W and lately two 300W (500W into 4omhs) I have built another 150W amp. The last two builds (300W) are with Holton's latest amp modules which use dual die lateral FETs. These were specifically designed with hifi in mind. Each FET will handle 250W or 220V or 16A.  In the 300W versions there are eight power devices in this build only two per channel. 

Once more a beefy PS (the absolute heart of any amp) with 300VAC tranni and 80,000uf of filter/storage caps. Snubbers this time are X2s but still with a 47uf first ploy cap. Diode bridge is soldered directly to the first cap to ensure high current delivery. All soldering is with WBT silver solder (4%). Extra heavy speaker binding posts and quality RCAs used. An over-size heatsink and two 80mm silent fans (running low voltage) provide cooling. Enclosure is steel and AL 3U and with the PS mounted on a sub-chassis the whole amp is very stiff but not too heavy. Power switch is rated 16A and the enclosure is earthed and fused.

The overall sound is extremely smooth and natural from top to bottom. Bass again is the signature of a Holton amp. Deep, powerful and articulated bass with a linear delivery of mids and treble make for a very "listenable" amp. At this point, having compared the 300W "Precision" and this amp Precision has the edge when it comes to absolute transparency. Of course it always comes down to total synergy and personal taste. Either amp is a winner. 

"Precision" - Holton 300W Class AB power amp

Over ten years ago I made two stereo power amps for a friend based on the Holton Precision 200W amp modules. I liked the amp so much I bought two of the 300W (500W into 4ohm) amp modules - nxv500. The modules lay dormant until recently where I built them into an amp. The amp was exceptionally good sounding but the PS I had made (as in the image above) was too big to fit into a 3U rack mount enclosure with two heatsinks etc.  

To finish the first build I built a narrower HS with 40,000uf of caps. I only enjoyed this excellent sounding amp for a week then it was sold. Happy customer and a repeat. Now I had this high power PS with 625VAC tranni and 80,000uf of 100V capacitors, 10A bridge and fully snubbed. What to do? Build another amp of course and use this sub-chassis mounted PS.

Anthony Holton's 300W modules have come a long, long way over the last ten years now in release R5. They now support very high performance dual die lateral FETs which can with stand 200V @ 16A EACH! There is eight per channel. The modules are; HPA-NXL500 R5. The power FETs are specifically designed for high-end audio not just power amplications. 

The amp is now complete with heavy duty 3-way speaker binding post and gold plated RCAs. The amp has a built in power filter, a choked power lead, fused and earthed. The 10A rec. bridge is soldered directly to the first cap bank to ensure he 100A pulses are not supressed before reaching that first cap. This technique I have used many times before with only positive benefits. 

Due to the fact I could not get the HS I wanted this amp runs hot without the lid off and a silent fan underneath. To rectify this this amp will receive a new lower voltage PS (but still 80,000d of snubbed caps) and be converted to a Holton 150W amp with the latest HPA-NXL200 R4.1 modules. These also support the high performance power FETs.

The 300W boards and high power PS will go into 300W monoblocks with appropriate HS to stop any other heat issues. In the meantime I am enjoying this high-tech power amp emencely; Bass is deep and very powerful with NO bloat or boom. Precisely articulated. My 12" ploy cone woofers in a 60ltr sealed box are 100% controlled. Even my 180W Class D amp do not give me the bass depth and control this amp does. Mids and treble are dead linear, smooth and extended from my Altec 511B horns with FailtalPro poly compression drivers. For me its good by Class D hello AB!

Lagoon Take 3

Finally finished this JJ12AU7 preamp - SRPP. Finish is blue hammer tone on a Hammond wood cheek chassis. The cct. is constructed on a turret brd. with metal film resistors and Russian PIO caps. Pot is Alps blue velvet with 4oz solid brass gold plated knob. External PS supplies 260V HT and DC filament current. Two selectable inputs. Sound is very fast and snappy with good bass.

"Gothic" - all FET headphone amp

Oatley Electronics Australia had been selling headphone (HP) kits for some years. These were based around the JAN6418 subminiature pentode and PT2308 HP driver chip. I've built and sold quite a few. Branching out from the normal this all FET HP amp has a two jFET input stage then two small power FETs arranged in push-pull to drive the HPs. A unique design but after  a few prototype brds. were produced the amp was dropped.

I got two of the brds, an "A" and "B". The "B" had better layout and LEDs were added. From the brd. I made "Gothic" so named because it is all black and quiet weighty. The compact cast Al enclosure was prepped, etch primed then sprayed Epoxy Enamel black gloss. RCAs on the rear with 6.5mm phone input. Front has volume, on LED phone out and ON/off switch. Quite simple.

There are two external power supplies. A compact SMPS of 24V @1A and a larger linear PS of 20V @ 2A. I woulkd have thought the HP amp to sound better with the linear PS but the SMPS may be the better sounding. Either PS is dead quiet and the amp works extremely well. Though in Class A the amp runs very cool. The small power FETs which do the driving are mounted on small heatsink sections of the cct. brd.

The overall sound is rock solid and weighty. You get the feel the music goes way back into the black background. With my Sennheiser 700 there may be too much detail but with the Technica AIRs there is a better balance. Overall an excellent HP amp.

"Overture" - LM4780 chip power amp

Originally this 1U rack mount enclosure was intended for another chip amp which really didn't work well.  Now with a LM4780 cct. brd. and repurposed this low profile amp really sings. Currently being used around the TV system and controlled by a single stage tube preamp. Lots of power (60W) into high efficiency single driver Mark Audio speakers and backed with a 175W sub-woofer. Pleased wih the outcome and the repurposing of the chassis and robust PS. Under test in the second image. 

"retro-2308" - portable chip headphone amp

I have been using the Oatley K272C kit in a portable HP amp enclosure for years now. It has spent a lot of time on trains, planes and overseas. Also good use when the wife is home on weekends. After building “LeManja” I realised how good the PT2308 dedicated HP driver chip was. Feeling the K272C a little on the large and heavy side for traveling I figured I could build a smaller lighter portable amp. I wanted to retain the high performance I have been use to in the past.

Above is that build which runs on four AAA batteries for over 100hours of play. That is with cheap AAAs. With lithium’s you could double that time. The enclosure is two tone ABS with matching knob. Al lining is used on the bottom and top of the enclosure and is earthed. The amp is built on Vera-board and is extremely compact. I didn't have much room in the enclosure for the cct. brd.

All caps are NP or LESR and all hookup wiring is silver plated fine copper wire. Safe on is provide with a switched input phone socket. If there is no plug in the input socket the amp will not run. There is also an off switch. The chip is the PT2308 (Class AB) with a THD of 0.001%. The sound is solid and crisp and drives both 250ohm and 32ohm HPs with ease. Light, compact, extended battery life and great sounding. Just what I wanted. 

"LeManja" - Hybrid Tube and chip headphone amp

LeManja comprises a tube front-end and a chip backend. The tube section is a 4SU universal design so that any 12A?7 tube can be rolled with no bias adjustments required. The chip, which drives the headphones, is a PT2308. It is a dedicated very low distortion headphone driver. Generally you would require an input cap for the chip but by keeping the Alps blue velvet pot at the front of the tube I could use the tube section's ploy output caps to block DC. This means there is only two caps in the signal path. Two mutually exclusive inputs are on the back with a four pin socket for the three exernal DC volatges and common earth.  

The PS is external and has a choked (Hammond 5H) triple Pi HT filter. The last cap at the ceramic socket for the tube is a 4uf PIO and snubbed. The tube here is a new Tung Sol 12AX7 gold pin. DC is supplied for the filaments and a separate DC 30V source for the chip. The chip max voltage is 7V so a 6V reg. holds the voltage to the chip. All caps on the chip veri-board are LESR types. A 24VAC 1A wall wart provides the initial power from the mains. All audio path wiring is via silver plated fine single strand copper wire.

The amp is absolutely dead quiet. The back ground is completely black causing all music to standout 3D style with amazing dynamics. The chassis is a Hammond Wood Cheek and is sprayed black with Epoxy Enamel paint first, an etching primer for an outstanding finish. The wood cheeks are treated with a ceda oil. 

"Altec-Faital" - Altec 511B horns with Italian FaitalPro drivers

I never really liked horns whether commercial or DIY but after listening to a friends Altecs I thought that if ever a cheap pair of horns only came up for sale I'd buy them. A few months later refurbished Altec 511Bs came up for $500. I always felt horns a bit brittle and to tame this I added Italian FaitalPro HF108R compression drivers. The Faital compression drivers use a polymer 1" diaphragm. I built a Xover to work with the horns and added a 12" woofer in a sealed 60 ltr box to handle 1100hz and down.

The Xover crossed the horns in at 1100hz on a third order and the woofers on 2nd order. Serious padding was need on the horns to balance them against the horns and the system now at about 90db+ efficient. The horns were boxed for better appearance and shock mounted to keep vibrations from them. Also the horns are wrapped in a sound deadening foam an foil to stop ringing. 

Driven by a 180W Class D amp there is plenty of deep bass (down to 30Hz) from the woofer and great clear, very dynamic mids and treble from the horns. The most natural sound I have heard rom any system. Pleased I tried them. I have since bought a second pair with top of the range FaitalPro drivers. 

"Njira" - 180W Tripath Class D in Hammond chassis

After a number very successful builds in these compact Hammond wood cheeked chassis I thought a matching power amp with external PS maybe the perfect compliment. The amp is a hifimediy 180W T4 Tripath Class D. All the PS is on board and all high quality components. The external PS is really just a big heavy 500VAC toroid.

The amp, as with "najah", produces excellent bass is dead quiet and runs cool. I've included some of the other builds just to show my "three of a kind" hand. 

"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.