"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.

"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 own 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)

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.

retroPi - dedicated, high performnace, inexpesnive, compact music servers.

A Tri-Pi or a Trio of Raspberry Pi(s). retro-thermionic has moved into the Pi business. Computer or laptop based music was never really convenient, always noisy and rarely worked that well. You had to have drivers loaded and purchase software to organise and play your music files.The Pi, dedicated, high performance credit card size computer, makes the modern music server a reality. Controlled from the browser on any smart phone, iPad or laptop and music stored as files on any drive type, listening to high quality music never got easier or cheaper.

The Pis being credit card size can be fitted with credit card size, DACs, Optical and digital interface or just connect via HDMI to any DAC or amplifier. DSD DAC cards can be purchased inexpensively. For a few hundred dollars you can have a very high performance music server player anything from MP3s to DSD files.

Above are three very different looking and configured Pis. Two Pi2Bs and one Pi3B. The Pi3B is use with a USB DSD XMOS DAC whose quality exceeds the Sabre32 DAC in my Oppo 95! One of the Pi2Bs is fitted with a Optical and Digital interface card to work with current DACs with digital interfaces.

The Pi3B have a quad core, 64bit 1.1GHz processor and when paired with a suitable DAC and supported by Volumio or Runeaudo free (Linux based) software bring file based audio to the fore. A must of any hardcore music lover.

"Mimic - S" - custom built phono preamp

"Mimic - S" combines a lot of the SE upgrades with better RCAs and better internal poly caps. As usual silver plated copper wire is used for hookup and WBT silver solder. For this custom build the customer wanted two inputs and the ability to switch from MM to MC on the fly. This build does all of that. The top switch selects the different inputs and the bottom MM/MC.

Once more this simple OPAMP based phono stage sounds very good. It sounded especially good with my direct drive TT and MM Garrett Brothers K2 cart. Running on 3 X 9V batteries ensures dead quiet operation with about 100hours operation between charges.

Crackatowoa - Bottle Heads Grand headphone amp!

Once more I have assembled a Bottlehead headphone amp for someone else. I really don't mind, no outlay only my time. This has to be the top of the range. Others I have assembled are of a smaller kits. Two big cct. brds. and two valve regulators.  The overall sound is absolutely excellent. If you intend to purchase a Bottlehead amp, get this one.

Bottlehead tube headphone amplifier #2

Yet another Bottlehead headphone amp for someone else. I'm not complaining it helps support my hobby. Apart from stronger colours than I usually work with this was a standard build. On request of the owner I added a few small poly caps to improve top end and reduce noise in the PS. It does have the Speedball upgrade.

The colours are a copper top plate and a dark timber stain base. The base has also had four coats of polyurethane. The amp sounds great and the owner was very pleased with the work.

"VoXGrandious" - Beyma, High efficiency, 15" speakers

The specification of the 15" drivers promised much deeper bass then the 12" versions, and that's what I got. In 170ltr braced enclosures these large speakers produce effective bass down to 31Hz. The bass is very tuneful and transparent, not something I have heard in other speakers.

With just a little more efficiency at 99db\m\w my flea power amps really roar. I have also teamed these speakers up with power Class D amps with excellent results. The woofer section is crossed at 1600Hz and the 2" titanium tweeter is padded down by 6db. The woofer is on a 2nd order roll-off where the tweeter is a 3rd order roll-off.

The completed speakers weigh 40kg and are well dampened inside with two 14cm X 8cm long ports on the rear. Crossovers are external with separate woofer and tweeter brass binding posts on the rear for flexibility.The finish has been rolled on and teased out to produce an acoustically dead and soft stippled finish. An expensive but very pleasing build.