How To Build a Great Audiophile Phono Preamp
Vinyl Records are still interesting . . .
After upgrading a Dynaco Stereo-80 and restoring a Stereo-120 power amp, I starting thinking about the old days — when all that was needed was a turntable, a stereo amplifier and some speakers to enjoy a record. It had been years since I had done any serious listening to my vinyl collection. Then I began having conversations with a friend who had a very extensive Jazz and Classical vinyl collection. As we talked, the old desire was re-kindled and, with his encouragement, I began to haunt flea markets and old book and record stores looking for vinyl treasures. I still had a decent turntable, and had recently upgraded the cartridge, but my phono preamp was at least 10 years old and not the best to begin with. It sounded ok, but the next logical upgrade was a more serious audiophile phono preamp.
The Hunt for an Audiophile Phono Preamp
As I looked around, it became clear that it’s easy to spend a lot of money on a phono preamp. I really wanted a tube model, but the choices were either way more than I wanted to spend, or very inexpensive models from China. They might be fun to try, but maybe not this time. Then I remembered: the same company that had sold me replacement parts for the Dynaco stereo amplifiers also sold kits. Their online store, Akitika.com listed power amplifier and preamplifier kits. They looked promising and a kit would be fun to build.
Akitika sells a complete, stand-alone, phono preamp kit that includes the preamp, power supply and case (about $250 + shipping), but I wanted to make a custom version, and thought I could build the case and power supply myself. The phono preamp board was $80 (including shipping) so I bought one. It arrived in just a couple of days, but with the holidays and preparing a course I was teaching in January, the project had to wait. I opened the box to look at parts and instructions, and they looked great — I was really looking forward to it.
Assembling the Preamp Circuit Board
By early February, I was ready to start. The assembly order made sense, with the smallest parts added first and gradually working through larger ones. This really helped, since it is a crowded board and the larger parts would have made the smaller parts harder to install. The instructions were excellent, with check boxes to account for each group of parts as they were installed. The tiny capacitors were the biggest challenge for my aging eyes, and magnifying glasses and a capacitor checker were helpful to identify them. Working carefully, I had the board finished in about 6 hours.
Now we need a power supply
The preamp requires regulated plus and minus 12-volt power supplies. The assembly manual for the complete phono preamp kit showed a recommended schematic, and it was similar to analog supplies I’ve built before. One new wrinkle: the use of a toroidal transformer. Compact and self-shielding, they are clearly better than the standard open-frame transformers I’ve used before. But where was I going to get one of those? As I looked around the Internet, I finally checked on Amazon, and, to my amazement, they had the perfect transformer. Not too expensive at about $26, I had one on order in no time.
Being an avid electronics experimenter, I had many of the other parts on hand. Compared to the 1970’s when I first began building projects, parts have gotten relatively cheap — especially when bought in assortments. Kits I already had provided most of the parts needed for the power supply:
- Blank PC Board Kit with Headers and Terminal Blocks
- Three-terminal Positive and Negative Voltage Regulator Kit
- Electrolytic Capacitor Assortment
- Monolithic Ceramic Capacitor Assortment
I also needed a few other parts:
It’s worth pointing out that all of the Amazon links provide larger quantities than are needed for the power supply build. I view it as building my parts stock. With only a few parts used out of each assortment, the cost for the power supply board is less than $6. A well-stocked junk box may yield many of the same parts.
A Few Parts for the Chassis
The PR-101 assembly manual also provided a layout. I decided to build the preamp in an aluminum chassis with a lid on top. This would make it easy to adjust the cartridge loading, frequency response and gain jumpers on the preamp board. Using the PR-101 assembly manual as a guide, I would need a few more parts:
- Aluminum Chassis – 10-inch by 8-inch by 2 1/2-inch
- Aluminum Chassis Cover
- Brass Hex Standoffs
- Switch, Fuse and Power Socket
- 10K Audio Taper Stereo Pot
- Gold-Plated Phono Jacks
- Blue 3 MM LED and Holder
Total cost for the chassis and hardware: $55.45. Again, some of the purchases, like the standoffs, LED and LED Holder, and Phono Jacks came in assortments. More back-stock. All together, the total cost of the project was under $150.
Building the Chassis
Careful layout goes a long way towards making a neat finished project. Metal work has never been my strong suit, and I was determined to take my time. Back in the day, I lacked many useful tools like an automatic center punch, a drill press and burr removers, so this time, I thought I could do it well. Leaving the plastic coating on the chassis while laying out and drilling holes minimized scratches and dirt on the chassis surface. A metal nibbling tool and some metal files made short work of the irregular hole needed for the power switch/fuse/power cord jack. I think the finished project looks pretty good, and I plan to dress up the chassis with some paint or vinyl covering after I’ve tested it a while.
But How Does the Audiophile Phono Preamp Sound?
I couldn’t remember when or where I got my old phono preamp — I had had it for years. The Technolink TC-750 sounded fine for an under-$50 device, but I hoped that the new preamp would be noticeably better. The Akitika documentation said it would be dead silent with no signal, and it was. Was it even working? I started a record, turned up the volume control and the music began to play. I was playing a London recording of the Vienna Phil playing a Schubert Symphony (CS6772). I sat down in the “sweet spot” to listen and noticed immediately that individual soloists were more precisely located in the stereo field and the overall placement of the orchestral sections was clearer. I was noticing musical details that I hadn’t heard before. The top registers were more crystalline and the percussion was more crisp. A very good first impression. One final touch: I noticed that the voltage regulators were getting a little warm, so I added couple of homemade aluminum heat sinks. Complete with silicone grease.
I’ve got a little more tweaking to do with the various preamp settings, but I would have to say I’m pleased. Getting to know this new sound is going to be fun!
Jim – This is smart money! The phono pre-amp (source) is the best place to put your money to upgrade the fidelity your Hi-Fi system, unless of course, you prefer the sound of digital streaming.
May well follow up and build . One point the lack of earth bonding to the metal case. ! 240volt fault path thru the turntable earth
Glad to hear you enjoyed the post. This preamp was built for use in the US, and has a 120-volt, three-wire power cord jack that includes hot, neutral and safety ground connections. The safety ground is bonded to the aluminum case. It is visible (the green wire) in the “Detail of Complete Power Supply” photo. I see what you mean regarding the turntable connections, I believe they are floating to prevent hum loops. This might be a good question for Akitika. The turntable I use has an insulated base and controls, and the motor power is isolated from the signal path. You may need to do something different for UK use.
Hello Mr. Kerkhoff, I’m in the process of building the power supply for the preamp using the same toroidal transformer that you used. Some of the wire colors match those of the Akitika schematic, but some are different. I have the data sheet for this transformer, but I couldn’t find a diagram for the one that Akitika used. I spoke with Mr. Joffe at Akitika and he helpfully described the connections.
If you still have your notes, would you mind checking my wire color substitutions?
On the primary side, I’m replacing the white wire on the Akitika schematic with the violet wire on the transformer. The other three primary wire colors match (blue, grey and brown).
On the secondary side, I’m replacing the orange wire on the schematic (+V out) with the yellow wire from the transformer. I’m replacing the green wire on the schematic (-V out) with the black wire on the transformer. And I’m connecting both the yellow and red wires from the transformer together as the ground lead.
Thanks for any help!
Scott – I don’t have a direct reference that specifies the wire colors with respect to the Akitika kit because I built my own power supply using the Amazon-sourced transformer mentioned in the blog post. I’ll do my best to talk you through my process though. Rather than using the Akitika transformer colors as a starting point, I would verify the Amazon transformer connections. I would start by finding each pair of transformer windings with an ohmmeter. You should find two separate primary windings (in my case: brown, blue, violet, grey) and two separate secondary windings (black, red, orange, yellow). The primary wiring might be easiest to understand from the blog post pictures. I omitted the 120/240 switch to simplify the wiring since I won’t ever use my preamp on anything but 120 VAC. I also used a device that integrates the power cord socket, fuse and power switch.
In my preamp, The blue and violet transformer wires connect to one 120 VAC leg, and the brown and grey wires connect to the other. It is important to get the primary windings paralleled correctly for 120 VAC, because the transformer won’t have any output if the phasing is backwards. The same is true if you intend to connect the primary windings in series for 240 VAC supply. They must be phased correctly to work. You can test this by connecting only the primary wires, applying power (through a suitable current limiting device like a 100 watt incandescent light bulb) and then measuring the output on the secondary wires. Be careful — there are lethal voltages present! The two secondary windings are separate and each pair should have the same voltage. If that is true, then you’re got the primary wiring correct. Next, connect two secondary windings in series to create a combined, center-tapped AC voltage. In my case, the orange and red transformer wires go to the power supply board connection marked “purple” on the Akitika schematic while the black and yellow wires go to the board connections marked “green” and “orange.” Be sure to test the power supply for the correct plus/minus DC voltages before connecting it to the preamp board.
These connections are a little different than you suggested in your comment, so I hope this will help you determine what is correct for the transformer you actually have. – Jim
Thanks Jim! Comparing your notes to mine, I think that I have the wiring set up correctly, but it is the complete reverse of yours (phase dot on secondary going to +Vout instead of -Vout). Thanks for describing the test setup, I will definitely confirm the connections before building it out. Many thanks, Scott C.