Wednesday, May 10, 2017


Yet another phono preamp but this time a dedicated MC preamp only. This one also uses the LM833 all bipolar chip. One reason is I like the sound of this chip over the OPA2134 and also it had the lowest noise audible through my high efficiency speakers. This build uses MKT and NP caps which are know for there accuracy and stability of capacitance. These features are essential in a phono stage.

Only two 9V batteries would fit in this tight enclosure. I wanted to get back to my epoxy enamel painted enclosure being cast Al. It looks extra sexy in real life. WBT silver solder and fine silver plated hook-up wire is use throughout. No shielded wire is used. The cct. brd. is a prototype brd. and not a PCB. The differential PS is built onboard. A mix of Vishay and other metal film resistors are used and a machined chip socket. Heavy duty gold plated RCAs on the rear and battery test point at the front.

Sound is solid and balanced. Imaging appears good and instrument separation is obvious. Happy with the sound which is based on a very pedestrian OPAMP but as stated above I like the sound of the chip and it was the quietest in this situation.

Tuesday, February 14, 2017

"retro-4040" - Chip amplifier

This amp was started years ago but originally didn't work as expected. Two chip amp Jaycar kits have replaced the amp modules and the heat sink and PS have been beefed up. NOW IT WORKS at long last.
40W RMS into 8ohms with the normal chip amp protection all built in. Also power filter and 160VAC tranni. 10A rec. bridge (snubbed) and 2X8,000uf filter caps. Sounding clean, linear and uncluttered and bloody great bass - OMG! Nice WAF too.

Wednesday, February 1, 2017

"Silver Supreme" - 6L6 SE UL amp in a wooden box

Yet another 6L6 SE UL power amp in a gift wine box. This time the blond box has been stained and lacquered. Two layers of staining and three coats of lacquer provide a deep rich looking finish. The component quality has been raised for this build and the power supply (with external tranni box) substantially beefed-up. Why another similar amp - because they just sound so very good.

The external transformer box houses two 160VAC transformers and connects to the amp via a male and female XLR connection. One for the 12VAC for the tube filaments and the other for the 250VAC HT voltage. Internally there is a two stage rectifier and filter network with over 800uf of storage capacitance. Rectification is via a 1A rectifier bridge which produces over 400VDC. This is limited and filtered to 295VDC for the HT for the 6L6s. This is further limited and filtered to 280VDC for the 12AT7. Tube compliment is the same as the first amp - matched JJ 6L6s and Psvane top-of-the range 12AT7 "T" series MKIIs. These tubes and this combination of tubes produces an extremely accurate and tonally rich sound for just a simple two stage amp.

Mundorf MCap Supreme Silver and Oil caps are used for the inter-stage and Edcor 15W OPT UL trannies for the output. Resistors used are both metal film and carbon film. By-pass (Ck) caps are low ESR and NP types. All hookup wire is Cat5 solid core with no shielded wire and WBT silver solder is used in the audio path. All filtering and by-pass caps are snubbed by 0.1uf poly caps. Earthing wire and filament wire is all 10A rated and the amp is hum and noise free. There are no problems producing 40Hz with rock solid bass and mid-range. Voice is earthy and detailed music has excellent rhythm and flow. An astounding 3W, two stage amp.

Sunday, January 15, 2017

6L6 SE UL power amp in a wine bottle box

This JJ 6L6 and 12AT7 top-of-range Psvane tubed power amp has been constructed in (and on) a $9 gift wine box. The box has been finely sanded beeswaxed twice. There is an external 12V transformer and another inside to step-up the HT voltage. Resistors are metal film and inter-stage caps are Solen.

The amps sound is solid, grounded and well rounded. Only a few watts but plays more than loud enough through my 99db efficient 15" Beyma concentric 170ltr speakers.

Friday, December 23, 2016

"retro-833" - an LM833 based 2006 Silicon Chip MM preamp

Here is a blast from the past - a Silicon Chip phono stage kit (2006). Nice part is you can switch between three different EQ stages. Comes with a PCB and all the parts required. It uses the LM833 OPAMP but it can be swapped out for a OPA2134. I really wanted to hear how the LM833 sounded compared to the OPA1234 so far I like it. The LM833 is all bipolar compared to the OPA2134 which has a jFet front end.
The original idea was to have variable gain but a $2 pot in the gain stage seemed a bad idea. It is a two stage preamp where Mimic is a single stage. The second stage is a buffer and high pass filter to cut frequencies below 20Hz (rumble filter). This left the overall sound too thin and lacking body. I changed the roll off point to 10Hz. This improved the performance of the phono stage dramatically.

Solid core hook-up wire was used in a Hammond Al enclosure and WBT silver based solder. Originally to be powered by an AC wall wart now running on batteries. Sound is bright and immediate where my DIY Mimic is more about tone this one is about detail. After extensive listening I think I prefer this preamp over Mimic but then it gets down to taste.

Tuesday, November 15, 2016

"Tutu" - 150W Tripath Class D monoblocks

The Tripath modules are the T3 150W monoblocks. The gate controller chip proudly displays the Tripath name. The modules are quite small and cut down. No mechanical speaker protection, only small electro on board and not a lot of parts. Could be a sign of better things to come. The tranni is a 300VAC 30-0-30 and I paralleled the secondaries. That provides 30VAC @ 10A. Rectification is by a 10A rec. bridge which is soldered directly onto the first cap to ensure maximum current transfer to that cap. The secondaries are soldered directly to the rec, bridge. A 0.1uf poly bypasses the first cap to reduce bridge and cap noise. And as usual it has its onw mains EMI\RFI filter.

The caps are 2X Mundorf MLytic 22,000uf 63V (44,000uf per monoblock). They are ultra low ESR audio grade and cost $60 each a total of four is required. Power wiring is via thick speaker wire and wiring to extra heavy duty speaker binding posts is very thick speaker wire and is quite short. A RFI choke is around the power cord.

Connection to the board is by large brass spades so a board replacement is an easy job. RCAs are solid copper, palladium and Teflon. The enclosure is steel with a nice finish. Only four large screws hold the enclosure together as a lot of it "clicks" together. Speaker binding post are two way, are insulated and solid brass, big and heavy but nice!! The PS will deliver 420W and the amp can deliver 300W into 4ohms or 150W into 8ohm with 300W peaks. I called the monoblocks "Tutu" (think Mola Mola)

Wednesday, November 2, 2016

Tripath 180W Class D power amp with V1.3 EAT boards.

Here is the latest amp boards (V1.3) from Eastern Audio Technologies. The front of the brd. is very different but not the backend. This still has speaker crowbar protection and the great sound of a true Tripath Class D. With 180W RMS into eight ohms, on tap, this amp will drive any load easily. To ensure maximum current transfer into the first 8,000uf cap the 10A bridge is soldered directly onto it. I doubled the thickness of the wiring from the 500VAC tranni to the first cap. A second 8,000uf cap provides all the filtering. There is more (10,000uf) storage onboard. I called this amp "The Ghost" because is so transparent.

I usually tin the heavy multi-strand hook-up wire which brings DC power to the brd. and hooks-up the speakers to the brd. But why pass the power and the audio output through another different laying, this time tin and lead. So bare copper connection are made where required. Result is a cleaner, clearer more transparent sound. So good a friend heard one track with this amp and his AU$22K Harbeth 40.2 speakers and bought the amp on the spot. He already had some expensive SS amps but this bested them all. Good result all round.