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. 

Modifying the MHDT Paradisea NOS DAC

The MHDT Paradisea is an excellent sounding example of a NOS (non over-sampling) tube DAC. If you're not already familiar with MHDT's offerings or the concept of a NOS DAC, I encourage you to read through my post regarding the modification of the MHDT Constantine DAC. Both of the units make use of a Philips TDA 1545A DAC chip and come in a handsome translucent dark acrylic.

The main difference between the two units is the 5670 tube buffer, which is directly coupled to the op-amp. Per the Enjoy the Music review of the Paradisea, various tube equivalents can be substituted, such as the 2C51, Western Electric 396A, 6N3Pi (6H3pi), or the 6CC42. I have yet to experiment much with tube rolling on the unit, but the example here came with a Western Electric 396A. Visibly, there are quite a few more parts in the Paradisea, and MHDT appears to have used mostly Nichicon MUSE electrolytics versus the Elna Silmics in the Constantine. The Paradisea also contains a torroid rather than a flat-pack transformer, it appears that MHDT has switched their entire line to torroids now, so I'd imagine this difference is indicative of the vintage of the unit. 


Of course the unit was going to be going under the knife, but I wanted to identify my purpose for doing so. When I first plugged in the Paradisea, I immediately noticed a more crisp and detailed presentation as compared to the Constantine. While the added detail is nice, the treble energy may be just a tad much for those of us with sensitive ears. Taking a look at the parts inside, every resistor was blue, which in nearly all cases means that they are metal film. Carbon film resistors typically are a tan color, of course when it comes to boutique resistors, vendors color them whatever they like (pink Takmans, green Kiwames, red PRPs, etc.).

The reason this makes a difference is that carbon films generally have a slightly warmer and more natural sound compared to the more detailed sound of metal film. The vast majority of new equipment makes use of metal film as it's very easy and cheap to get values within 1%. Carbon film is more typically found in vintage equipment, along with the slightly sweeter sounding carbon comp resistors. People tend to stray away from carbon composition these days (except for grid stoppers) as they pick up a little more noise and can drift over time, but they do have a nice sound and can be used as long as you are mindful of their shortcomings. Because I'm more fond of the sound characteristics of carbon film versus metal film, I decided that I wanted to replace as many metal film resistors as I could from the Paradisea. 

The original MHDT Paradisea with the top off

Resistors cannot be measured reliably when within a circuit, they need to be removed to be measured or you can read the color stripes on the resistor, although this can sometimes be difficult to determine a color (orange versus red, white versus gray) on a minuscule resistor. In most cases, I removed the resistor to measure it, wrote down the value and position, and only if it was a strange 1% value I put it back. Any other resistors that visibly matched these values were not removed. Common values were replaced with a combination of Kiwame (Koa Spears) and Takman resistors, the Kiwame leads needing a little bit of filing to fit. Some 1% uncommon values were replaced with generic 5% carbon films; I basically purchased large amounts of close values and measured them, picking out the ones that measured within 1% of the color code on the original resistor. It's a very slow and regimented process, but is enjoyable if you like working on electronics ;) 

Modifications in progress

The MHDT units come with some very nice parts for sure, but there can always be room for minor improvements. I opted to replace the stock film caps, which are relatively small compared to other caps of the same value. Based on dimensions, Auricaps, Obbligatos or ClarityCaps would be the closest match, all being a little bit larger. I selected Obbligatos as they tend to be fairly neutral and are a nice price for what you get. The problem with Obbligatos is their attractive gold shell is conductive, so when the leads are bent around the bottom or the cap is sitting on solder eyelets, the shell will short them. I usually put some 3:1 clear heatshrink over top to prevent this from happening. 

Clear heatshrink over top of the Obbligato cap

Heatshrink shrunk to fit

For the output caps, which is a very audible position for capacitors, I selected a matched pair of 2.2uF Mundorf Silver in Oil. These are quite large, with thick leads, so some creative mounting was required. The solder eyelets for the capacitor leads had to be enlarged with a 1/16 drill bit, and one of the caps actually sits outside of the unit for a very hot rodded look :) When solder eyelets are drilled, it effectively separates the conductivity from the top and the bottom of the board, so in some circumstances, depending on whether the copper traces on the PCB run along the top or the bottom, you have to solder not only to the bottom but the top of the board as well. 

Finished PCB - front view

Finished PCB - rear view

I opted to cover the leads of the right channel Mundorf capacitor with teflon, then sleeve them with black nylon as they would be visible from outside of the unit and needed to look nice. 

Finished mod, PCB in case with top off

Completed Modified Paradisea

The Paradisea now has a more warm, natural sound with slightly more bass quantity (while still being very controlled). Midrange seems to be more liquid and smooth. Overall, I'm very happy with the presentation. Now for some tube and opamp rolling! :) 


UPDATE (6/11/11): The Paradisea is made for op-amp rolling (pulling out the stock operational amplifier and putting a similarly spec'd one into the gold 8 pin socket). I dropped in a vintage NOS Tung Sol 2C51 tube and a Texas Instruments OPA2107AP op-amp in the unit. Immediately noticeable was a big bump in upper-end clarity and detail. I'll need to spend some time with the unit to see if this is preferable to the stock op-amp with Western Electric 396A or not (verify if this new-found detail is fatiguing at all over long periods).

The Fine Print:

Please remember that 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 posted modification 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.