Thursday, December 26, 2019

"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. 





Sunday, December 1, 2019

"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!




Thursday, September 5, 2019

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.






Sunday, August 25, 2019

"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.




Tuesday, July 30, 2019

"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. 




Friday, June 14, 2019

"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. 

Thursday, May 23, 2019

"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.