Chipamp Dual Mono LM3886 Gainclone Speaker Amp

I'll be dipping my feet in the chip amp waters again. I enjoyed the results of my previous Chipamp.com LM3886 build, so I decided to build another, more serious version. You can visit that post to read a little bit about the history of the chipamp, also known as the Gainclone, based on 47Labs Gaincard topology.

As you are likely aware, DIYers have created chip-based builds using a variety of power opamp or audio opamp chips including National Semiconductor LM1875, LM3875, LM3886, and LM4780. The most popular chips being the LM3886 and LM3875. You'll find a number of these designs at Chipamp Electronics.

This more serious build features a pair of Antek 300VA torroids, each with their own shield, integrated amp functionality with an Alps Blue Velvet and multiple selectable inputs, film capacitors on the driver board, and higher end parts like Nichicon Gold Tune power caps, Cardas binding posts, and Cardas RCA connectors.

Cardas wire, RCA connectors and binding posts

Other nice additions to the build include a 6 position Grayhill selector switch and the Alps Blue Velvet RK27 (100K) volume potentiometer, both with the corresponding ChipAmp BrianGT PCBs. The RK27 board is handy as you don't have to discern which pin is which (the white screen tells you which wire goes where). It's also a little easier that soldering to the little pins. The Grayhill switch's pins are so minuscule that you really have to use the board, it's not like an Elma or Goldpoint with larger gold solder lugs. The nice thing is the combo is a fraction of the price of the fancier selector switches.

  

Chipamp's PCBs for pre-amps / integrated amps

This project would require a larger box than the Bud 7" x 12" x 3" aluminum box I used previously. Rather than build my own gravity mount chassis, I wanted something a little different this time. I turned to Horace Atkinson of www.iagaudio.com for a robust 17.5" W x 10"D x 3.75"H chassis. I stumbled upon his chassis work on eBay: it's a nice combination of aluminum and wood panels for sides, as well as attractive wood accents on the bottom. The metal used in these chassis is a thicker gauge, one piece .125" aluminum tubing, so it can support heavy transformers without any bend or flex. (FYI IAG offers thicknesses up to .188"). The bottom features perforated sheet metal for adequate air ventilation reaching the heatsinks cooling the LM3886. A unique feature is the wood side panels actually act as feet, holding the aluminum portion up higher to allow for ventilation, very cool!

IAG Audio aluminum and wood chassis 

A view of the bottom with the perforated sheet metal removed. Note the bottom of the chassis is not completely open due to the rigid, tubular design, however underneath the wood side panels, there are removable metal panels that can be removed by unscrewing two flush mounted screws to give you adequate access for drilling, etc.

Chassis interior

As noted, the wood panels are all easily removable if you decide you want to access the sides of the chassis interior or change the wood stain, etc. Horace found some beautiful figured maple for me, as you can see below:

Figured maple side panels and accents

After much internal debate, I decided the chassis would be colored to match some of my other equipment with a red and cream color combo, so the wood was stripped down and stained a deep red hue, then given a number of generous coats of MinWax Satin Clear Urethane.  

Red stain and urethane on Maple

Now that the wood is my a nice shiny red, it's time to drill the chassis. After planning out the layout in Photoshop, the chassis is prepped with a ruler and sharpie and taken to the drill press. Many of the holes will be countersunk for this project. The others will be deburred using a Skaviv deburring tool with Cobalt bits. The IEC hole is trimmed using the typical combo of drilling four holes in the corners and using a Dremel cutting wheel to remove the rest. 

Chassis prep

For the heatsinks, I found some reasonably priced ones on eBay that had mounting holes for screws. The instruction manual from Chipamp says you can also use a 3"x3"x1/2" piece of aluminum in free air in certain applications. I installed 1" aluminum standoffs on the heatsinks so I could mount them to the chassis. Small drilled venting holes will be above them so when heat rises it can escape the chassis. 

Below is the chassis after a nice cream colored powdercoat. 

Since the amp is dual mono, it gets not one, but two chunky toroids. The transformers are always what weigh down an amp (big magnets with large quantities of copper wire spun around them aren't the lightest of materials). The pair, with steel cases, weigh in at a healthy 22 pounds. These are 300VA rated units from Antek.

Below is one of the toroids in a steel case. I had these powdercoated brick red as it makes a nice accent color for the cream. Typically the steel cases are used as a shield within a chassis, however I'm using them as both a shield and external transformer covers. I don't think I've ever seen a solid state amp with external transformers (usually they're just hulking boxes) so this will be a unique design choice.  

I'm adding the Power Supply Soft Start Board (or SSB for short) from DIYAudio for this build, this allows a gentle inflow of power on startup, which protects the power caps and should offer a more reliable service life for the amp. 

With everything ready, the chassis can start to get filled in. Shiny Cardas RCAs adorn the back of the unit, the binding posts would have been a bit tight on the back, so they were mounted to the top of the chassis right behind the transformers. Four large film caps will be residing in this chassis as well, so you'll notice some zip ties within the chassis as well.

Getting everything in place was a tricky predicament, as the sides of the chassis which held the heatsinks were screwed in place, then the wood panels were screwed to them, but the capacitors would have to be slid in to be held and secured, so order of operations took precedent. 

The power capacitors were a bit tall, so I had to use some minuscule PCB standoffs so they wouldn't come in contact with the chassis. The film caps, as you can see, were a perfect fit. I made a few small turret boards to keep the wiring neat. Cardas wiring handles all the signal work and thicker power wires as well. If you look carefully you'll notice one of the blue wires exists after the potentiometer to the RCAs to handle subwoofer duty. 

And the final product, see what you think:

Final weight was about 40 lbs. thanks to the hefty transformers and very solid tubular chassis. It's a unique take on a solid state amp, not the typical big black box with heatsinks on the side, but a more vintage tube-amp looking chassis. The sound is excellent, will be looking forward to putting it through the burn-in process and most more impressions.

The Fine Print:

Please remember that building/modifying circuits can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind. 

DIYTube Budgie SE 3W Single Ended Amplifier

Our good friend Shannon Parks over at DIYTube has designed another great tube-based amplifier, this one using a pair of EL84 power tubes and a single 12AX7 driver tube.The Budgie has been designed from the ground up to be an affordable build, the power and output transformers (sourced from Edcor) run a measly ~$100 or so dollars for all three! Throw in the parts ($35), tubes ($35), PCB ($39), and build your own chassis ($20), and you should be able to scrape by under $250. Granted, this would be a bare bones build, but it just goes to show you that this is an affordable design. You can go hog wild and add Shannon's top custom printed top plate and a Hammond chassis with walnut sides, and maybe some boutique coupling capacitors, and we're still looking at a reasonable price tag for a single ended tube amplifier.

Budgie SE with custom printed top plate and walnut sides

The DIYTube Budgie SE Schematic

I chose to skip the top plate as I enjoy building my own chassis (it prolongs the whole building process which I find inherently enjoyable anyway). I had a scrap piece of copper which I trimmed to 7" x 12", which is a little larger than the custom printed PCB and will allow a little more air between the components. The base would be an intricate mitered wood frame made from chair rail molding from the hardware store. 

The copper plate was cut, punched, drilled, Dremeled, etc. to hold all the parts in place. The layout used to plan the initial plate size was used to determine where each hole would fall. Small holes were drilled using the drill press, larger holes for tubes and the Neutrik locking plug were punched using GreenLee punches, the extra-large holes for the capacitors were cut using hole saws on the drill press, and square holes, like for the transformer and IEC inlet were cut using a Dremel metal cutting disc. The copper is a little denser than aluminum and requires a bit more effort to cut through.

Once the chassis plate had all the holes necessary to accommodate the parts for the build, it was sanded down, starting with 80 grit sandpaper and ending with 600 grit. Next, a coat of clear satin finish was sprayed on each side to protect the copper, otherwise it tends to pick up fingerprints and oxidize. I've had good luck with the clear satin enamel from Krylon. I tried the Valspar outdoor clear satin and it clouded up and flaked off, so I won't be using that again. Gloves needed to be used after the sanding process so my fingers wouldn’t leave any oil on the copper. Once the clear coat was dry, parts could finally be fastened onto the plate.

Copper Plate with myriad holes

First the various connectors and jacks could be installed. The RCA females are nice quality Philmore gold plated units with a Teflon dielectric. The binding posts are generic heavy duty gold plated brass with clear plastic on top, made to look like WBT's early binding posts I assume. Also installed is the ubiquitous Neutrik 1/4" TRS locking jack, which I elected to install with the release up front for ease of use, the IEC inlet with built in fuse, and a small toggle switch for power.

The Budgie gets some cost effective connectors

Populating the PCB were a number of parts I had lying in the parts bin, some Koa Speers resistors (green) from Mouser, and some spiffy Elna RFS Silmic II electrolytic capacitors from Digikey. Both the Koa Speers and Elna Silmics are considered to be "warm" sounding parts (the opposite of bright or harsh), which is usually what I'm going for. The big blue caps are 150uF Cornell Dubiliers that have good ripple current ratings, which will help smooth the power supply a bit in addition to the Triad choke called for in the design. In addition, I added some surplus Nichicon 0.1uF film caps bypassing the power caps, which would help ripple to some minor degree as well. I also found some oddly shaped Mundorf EVO Aluminum 1uF film caps that I installed on the side of the board. These were relatively low cost and a bit more interesting to look at than a standard film cap.

Top of the PCB with Tube Sockets, Film Caps

Bottom of the PCB

The PCB could now be fastened to the copper plate with short aluminum standoffs.

Directly beside it would sit the 1H Triad choke which I pulled from an ST70 when I upgraded that choke to Classic Valve's heavier duty model.

Sitting directly beneath the output transformers are a pair of matched vintage Russian silver mica capacitors. If a manufacturer was making these today, I'm sure they'd be pricey, but given that they are old military surplus, they're downright affordable. Some audiophiles feel these sound comparable to the Russian Teflons, so I figured I'd give them a shot. They are certainly interesting looking little metal brown boxes.

Check out those Russian silver mica caps!

With all the small parts in place, I could secure the Edcor power and output transformers. I purchased some unpainted bells from Edcor (I'd imagine these are popular products on their page for anyone who doesn't want blue) and had them powdercoated with an antique copper color, then replaced the nylon washers and the nickel hardware with brass for a more uniform look. These were secured to the copper chassis with rubber washers to dampen a bit of the vibration they produce.

You can always hide a depth mounted screw under an xformer

Since a copper plate cannot sit on its own, a wooden base was fashioned out of some decorative molding from the hardware store, the edges rabbited with a router so the plate could sit on top via "gravity mount", and then mitered to be a perfect fit for the plate. Once the four pieces of molding were secured together with woodglue and allowed to dry, I went through the process of copper leafing and antiquing the wood. If you'd like to see more details on this process, please check out my Bottlehead Crack Coppermine project.

Completely wired up

And the photos of the finished unit:

Front

Rear

I had a listen with a pair of Sennheisers and really enjoyed the quality of the headphone output. I'll be testing the unit with some speakers shortly. Looks like Shannon has another winner on his hands!

The Fine Print:

Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind. 

Custom RCA Switch Box for Audio

So in any given audio setup there may be multiple amplifiers (e.g. a headphone amp, speaker amp, etc.) or possibly multiple sources (e.g. a record player, CD player, DAC from a computer, etc.). A switch box keeps it simple so one doesn't have to reach in the back of the rack and manually switch interconnects to listen to particular equipment. They will commonly have multiple RCA jacks (or in some cases XLR jacks) for both input and output and a switch which is commonly 2 pole (stereo with common ground) or 4 pole (stereo with isolated grounds).

They may be handy, but not all switch boxes are created equally; audio enthusiast know that using a generic one can potentially degrade the audio quality, a situation which just isn't worth the added convenience. All the ingredients need to be of high quality to ensure there is no notable degradation of the signal.

This post will be detailing a simple 6-to-1 switch box making use of high quality parts to ensure transparency. Parts include a Swiss-made Elma 04-1264 switch, EAR isolation feet, Philmore Teflon insulated gold plated RCAs, Neotech UP-OCC sold-core copper wire in Teflon and a lovely custom-made chassis from Keith (ebay seller po1019).

The first task was to take the chassis and drill holes for the switch, feet, and RCA connectors. It may be easy to use a ruler and mark where each hole is going to be, but drilling the holes perfectly in line *probably* won't happen, even on a drill press. When there are multiple items lined up, the eye can very easily identify any slight aberrations to a straight line. I was able to get them pretty close in this case. The chassis was then powder-coated a nice cream color.

Chassis prepped for the build process

The next process is installing the RCAs. Because the powdercoat insulates the aluminum, the back of the holes were filed so the RCAs would ground to the chassis so the chassis would act as a shield. You might be gawking at the Philmore RCA blister pack and thinking "wow, that looks like dollar store garbage"... Looks can be deceiving; under the homely packaging are a pair of very nice quality gold RCAs with Teflon insulation. I like to use Cardas RCAs in many of my builds, but when one is using seven pair, like in this case, that would be quite costly; that's where the Philmores come into play. Each one is cranked on using a socket wrench and the ground washer bent at 90 degrees. 

The chassis populated with Philmore RCAs

Each of the ground washers is then tweaked together with a pair of pliers and a ground wire is run through them, then soldered in place. This particular wire is silver but any bus wire would be fine. This ensures that there is a common ground between all inputs and outputs. 

Ground wire connected to each RCA

Now comes the fun part; wiring up each RCA to the Elma switch. Seeing which solder lug corresponds to each switch position is relatively straight forward, simply look through the transparent plastic at the location of the gold contacts. Each wire is soldered in place and a small amount of heatshrink is placed over the connection. 

Beginning the wiring process

The Neotech wire was kept nice and short for each connection. On the bottom, EAR isolation feet were fitted with a screw, lock washer and nut.

Wiring complete

The box could now be assembled and the nicely finished wood panels placed on the sides. Below are a few photos of the finished product.

Switchbox complete!

Switchbox Front

Switchbox Rear

Switchbox Bottom

Some nice points about this design are the short signal paths thanks to the small chassis, the Teflon insulated wire and RCAs, the gold contacts on the switch and the point to point wiring with no circuit board for the signal to run through. This box could either be used to allow 6 inputs and 1 output, or 1 input and 6 outputs. With a larger box and a second switch, there could be both multiple inputs *and* outputs. Or there could be two of these boxes daisy-chained, allowing for 6 inputs and 6 outputs. Tons of options!

Update: I created a nice little logo "iO" standing for input output and had it custom engraved on a brass plate for the top panel. Looks rather sharp I think :) Some additional photographs with the plate are below.

Need a great sounding passive audio switchbox to tie your system together? Please contact Zynsonix Audio for details. 

The Fine Print:
The above steps detailing the building of a switch box are for entertainment purposes only and not to be performed under any circumstances. The owner of this blog and all associated parties can not / will not be held responsible if you attempt the process posted and cause physical harm to yourself, your surroundings or your property. Please keep this in mind.