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fitzfish 15th March 2012 09:03 PM

F5X -- the EUVL Approach - The Build Thread
This thread will document build details for EUVL's F5X amplifier. The main thread is here: F5X -- the EUVL Approach

I'll start off the thread with the official BOM and schematics, Circuit board assembly, amplifier initial biasing and bring up. There will be some related articles thrown to help as well. Measurements will be posted as soon as I have time to compile them and there will be information about final wiring and the amplifier case along the way.

Thank you for your patience and feel free to post assembly related comments or questions here. Let's keep this thread focused on assembly or similar issues and maintain other discussions on the main thread.


EUVL 15th March 2012 09:13 PM

At long last.

My most sincere thanks for your endless efforts with the PCB layout and the build and test.
I am sure your effort would be most appreciated by all.


fitzfish 15th March 2012 09:27 PM

Hi Patrick.
My pleasure. I did not expect to be this involved in the beginning but have enjoyed it all.

fitzfish 15th March 2012 10:28 PM

EUVL F5X Amplifier Schematics and BOM
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Here are the official Schematics and BOM for the EUVL F5X amplifier. These are for the standard version, non-cascoded front end. I will post the cascade schematics and BOM details a little later for those interested.

fitzfish 15th March 2012 10:35 PM

Build Notes - Assembling EUVLs F5X
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This is the first in a series intended to detail assembly steps necessary to get your F5X amplifier circuit boards up and running. It is written with the average DIY audio builder in mind and therefore may have more information than necessary for many readers. The steps and suggestions herein are just that. Feel free to use whatever method and materials will work best for you. You will also see some words of warning. Nothing different here than any other DIY project but please be careful when dealing with HIGH VOLTAGES, HEAT, SOLDER, CUTTING, DRILLING, SPACE TRAVEL, BRAIN SURGERY, NEGLECTED SPOUSES, etc… You have been warned.


Bills of materials, schematics, and wiring references are included as separate files for revision management purposes. Please refer to these for component procurement and stuffing locations. You will also need matched input JFET and output MOSFET devices. It will be discussed separately to highlight some simple multi-point matching techniques that do not require a curve tracer. This is a well covered subject elsewhere and any questions can be posted in the thread.

The PCB sets will arrive panelized. That is multiple boards are manufactured as a unit and scored/routed so that they can be easily parted once you are ready to assemble them. All the boards necessary to build one mono amplifier channel are combined into a single panel. If you ordered the F5X case and PCBs from the group buy you will also have the power supply circuit board panels that include the filter and regulator PCBs specific to the GB case. These are similarly combined into a single panel and each builds into one mono channel.

fitzfish 15th March 2012 10:38 PM

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While the PCBs can be assembled while still panelized I chose to part then into individual boards for the prototype build. The boards must be flexed at the score lines to separate them from the panels. Be aware that the routed edges of fiberglass PCBs CAN AND WILL CUT YOU given the right moment of carelessness. Once separated, the area of the score lines will also likely have some fiberglass splinters or hairs that can be a real nuisance if they inadvertently become inserted under the skin. A piece of sandpaper or a fine file can smooth down any rough edges after separation.

Another consideration is the little “ear” that will be left in the corner of the boards near the slots cut in them. Since the tool is round that cuts these slots, the edges here cannot be square. Simply remove it with a file or hobby knife blade.

You might be contemplating “why panelize the boards? Why not simply make them all separately?” There are three boards for each amplifier channel plus five power supply boards per channel if you bought a case. To tool and build each of the eight PCBs separately instead of just two in panels invites errors and increases costs. Most importantly, it makes logistics simple. One panel per channel in a box and you get everything you need to build your amp the first time!

There is a protection PCB that is not yet available. It will be documented separately alongside the case assembly and wiring in the near future.

fitzfish 15th March 2012 10:41 PM

Power Supply Assembly:
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This is pretty straight forward but included for those who desire a reference. If you are not using these boards you can skip directly to the amplifier assembly. Start with the filters by inserting and soldering the screw terminals if you intend to use these. Capacitors come next. Make sure to observe the polarity of the capacitors when assembling these. You will end up with 4 each of +VE and –VE boards for one stereo amplifier.

Next, install all of the diodes and resistors in the regulator boards per the bill of material list. Observe polarity for the diodes and capacitors. Follow with the relay, terminal blocks, and capacitors. Do not solder the power FETs in yet as that will be done once assembled to the heatsink. You will need two of these once complete.

fitzfish 15th March 2012 10:48 PM

Amplifier Assembly:
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Like the power supplies, amplifier assembly is straight forward. First solder the surface mount devices on the bottom of the PCB. It is easier to do this with no components on the top. There is a separate post comming that can help with SMT assembly suggestions.

I begin through-hole assembly with all of the ¼ watt resistors. Insert them and bend the leads slightly outward on bottom to hold them in place. Flip the board over and solder. To make the next step easier I go ahead and clip the leads after each solder step. Keep in mind that the 33R resistors R18, R19, R24 and R25 are from matched sets and should be inserted into the correct locations as sets of three. Install the resistors for the optional cascades now if you intend to use them. If you are not using cascades or intend to use add them later solder jumpers in place of Q7A and Q10A pins 1 to 2. Solder a jumper in place of Q11A, and Q14A pins 1 to 3. I use leftover leads but check them with a magnetic because those from capacitors are often steel and less desirable than copper.

Next, install the 220R 1W resistors on the board. Be careful not to mix up R21 and R22 into the matched 220R resistors sets in locations R17, R20, R23 and R26. You can elevate any of the resistors a little if you like. I chose not to.

If you are contemplating using the optional cascodes I suggest you install the capacitors C1 and C2 now. Install the pots and transistors. Be aware that static can damage the transistors. Last, install the source resistors. It is beneficial to install these spaced above the board so that the leads are accessible. This will help with probing when you initially bias the amplifier. Around 0.080" (2mm) is a recommended minimum.

fitzfish 15th March 2012 10:51 PM

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For the initial bias setting it is necessary to configure the board as “grounded X”. This essentially separates the two halves of the amplifier into two individual amplifiers for adjustments. To do this, cut 4 small loops out of leads left over from assembly and insert them from the bottom of the board.

The little loops will help later when you need to remove them to reconfigure for floating X. It is necessary to install them from the bottom because the input board will cover this area shortly. Solder them in place and trim the top side leads. Two jumpers are also necessary at location J14 and J15. I used mil spec solid 16 AWG (1.5mm) Teflon insulated wire. Make the jumpers as shown and use spacers to elevate them from the surface of the PCB to prevent shorts. The Teflon jacket conveniently worked for spacers in my case.

fitzfish 15th March 2012 10:55 PM

Input Board Assembly:
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Solder the input board components and trim the leads. If you are using the mute relay board, also assemble it at this time.

I used a copper standoff I made for the center ground conductor. EUVL specifies a brass standoff. Assemble the input board onto the standoff and center it over the matching holes on the main board.

The BOM calls for wire to connect the input board to the main amplifier board. Insert the wire through the input board and amplifier board one at a time and solder on both boards. Three wires are necessary on each end, two 20 AWG (0.8 mm) and one 16 AWG (1.5 mm). These will extend through the mute board on the end opposite the input pads if you are using it. Just leave some distance between the mute and input boards.

Don’t forget to install the source resistors and make sure to keep them as sets if yours are matched. For ease of setup when we bias the amplifier I suggest you install these elevated off of the board by at least 2mm. This will allow us to probe them with clip leads during biasing to measure the actual current across each half of the amplifier.

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