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"NuHybrid" Solid-State Headphone Amplifier
Assembly instructions
What you need:
The bare PCB plus Korg Nutube 6P1 (from pmillett.com via eBay)
The parts (from Mouser)
A soldering iron and solder (Tin/Lead 63/37 is the easiest to work with - lead-free
solder is more difficult)
Wire cutters ("diagonal cutters")
DMM (Digital Multimeter)
The following are optional, but recommended:
Needle-nose pliers
To order the parts from Mouser, go to
http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=b68a30231c, or go to the
http://www.mouser.com/Tools/Tools.aspx
"Tools" page at
Sharing" towards the bottom of the page:
The Mouser BOM includes all of the parts needed to build the NuHybrid except for the PCB
and the Korg Nutube, which are available from http://stores.ebay.com/pmillett. You can also
refer to the bill of materials at the end of this document for additional info.
Occasionally one of the parts on the BOM may be out of stock. The BOM has some
suggestions for alternate parts that can be used instead, as well as alternate parts that are
available from Digi-Key. Note that the Mouser BOM may be updated from time to time as
parts become difficult to source.
When assembling, keep the BOM and schematic handy, in case you have any questions
about what parts go where.
It is assumed that the builder has some basic electronics knowledge, like knowing which end
of the soldering iron to hold in the hand, and hopefully some experience building electronics.
However, this is a very easy project and is suitable for a first-time builder.
If you are new to soldering, it's highly recommended that you review one or more of the
excellent on-line soldering tutorials. Just search "soldering tutorial" on the web and/or
YouTube.
There is nothing sacred about the order that is listed for assembly. It can be convenient to
build starting with low-profile components, and work your way up to taller parts, so it's easier
to solder on the board backside. That is the way the instructions read. But you can install
parts in any order you want.
and enter this access code in "Cart
b68a30231c
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Summary of Contents for Millett NuHybrid
- Page 1 Sharing" towards the bottom of the page: b68a30231c The Mouser BOM includes all of the parts needed to build the NuHybrid except for the PCB and the Korg Nutube, which are available from http://stores.ebay.com/pmillett. You can also refer to the bill of materials at the end of this document for additional info.
- Page 2 PCB Assembly Step 1. Introduction Start with familiarizing yourself with the bare PC board: You'll see that each part has an outline silkscreened on the board, and a reference designator (name) next to it. Parts are numbered starting at the lower left, so you can expect to find resistor R1 somewhere near the lower left corner.
- Page 3 2. Install resistors Each bag of parts from Mouser looks like this: Match the Mouser part number or the description with the parts on the BOM. In this case, you will see that 33.2k resistors are installed at R12 and R15.
- Page 4 Note that the resistors may be different colors. In no particular order, install the resistors. After you remove them from the bag, you'll need to bend the leads (you can just use your fingers) so they look like this: Next, insert them into the PCB in the appropriate spots: Push them down flush with the board:...
- Page 5 And bend the leads on the backside slightly: Next, solder the leads. Touch the soldering iron tip to both the pad and the lead, and apply a little solder:...
- Page 7 Next, using wire cutters ("diagonal cutters"), trim the excess wire leads: It should wind up looking like this: Now, repeat this process for all of the resistors.
- Page 8 When you’re done, the board should look like this:...
- Page 9 2. Install diodes The diodes are installed the same way as the resistors. Diodes need to be installed in the correct orientation, so be careful and double-check to make sure they are pointed the right way before soldering. Note the diodes have a band on one end that matches with the band on the PCB silkscreen, and the PCB also has a dot near that end.
- Page 10 3. Install IC sockets Two IC sockets are installed for the opamps, so you can change them to different ones if desired. Note the orientation of the sockets - there is a small notch to indicate pin 1, which is aligned with the PCB silkscreen:...
- Page 11 The IC sockets are soldered in as before, but since they have short pins that cannot be bent, they somehow need to be held in place while you solder the pins. If you are dexterous you can hold them with one finger while soldering, or just use a piece of tape:...
- Page 12 Flip the board over and solder the pins as before. No trimming is needed. It should look like this when you're done: By the way, don't worry about the flux that gets splattered on the board when soldering. It's harmless...
- Page 13 4. Install film capacitors Next, install the film capacitors. (Note that the parts provided might be slightly different sizes or colors than those shown). These are small parts with the two lead wires sticking out one side, so you don't have to bend the leads before inserting them into the PCB: Bend the leads over a bit to hold them in the board, solder, and trim the excess.
- Page 14 5. Install the small electrolytic capacitors Install the smaller electrolytic capacitors. Be VERY careful that they are installed the correct way - the PCB has a dot marking the positive terminal of the capacitors. The longer lead wire is the positive terminal. Note that on the capacitor body, only the negative side is labeled – so the other side is positive.
- Page 15 6. Install large electrolytic capacitors Install the four larger electrolytic capacitors, the same way as the smaller:...
- Page 16 7. Install the bias adjust trim pots, transistors and voltage regulator Install the bias adjust pots (R17 & R18), three small transistors (Q1, Q2, and Q3) and a voltage regulator IC (U3). Note that Q1 is a 2N7000 MOSFET, and Q2 & Q3 are 2N3904 NPN transistors –...
- Page 17 8. Install the test points There are three small test points installed near the opamps. Insert them and solder.
- Page 18 9. Install the relay K1 and common mode inductor L1 Just place them – the relay will only go in one way, and the inductor works either direction – bend the leads a bit, solder, and trim the excess leads. Note that the relay may be a different color…...
- Page 19 10. Install volume control RV1, headphone jack J3, and switch S1 These parts are simply inserted into the PCB and soldered. Some may snap into the PCB and stay put, and some you may need to use tape or your fingers to hold it in place while you solder them in: Make sure you have the parts seated all the way down on the PCB before fully soldering them in.
- Page 20 11. Install power jack J1, input jack J4, and line out jack J2 Install the jacks on the rear edge of the PCB. J2 and J4 snap into the PCB, but J1 may need to be held in with tape (or your fingers) when you solder it in. As before, make sure the parts are fully seated on the PCB before completely soldering them 12.
- Page 21 13. Install the Nutube Last part! First, peel the backing off of the two squares of double-stick foam tape (these are supplied with the PCB and Nutube), and apply them to the PCB in the area indicated on the silkscreen: The foam tape holds the Nutube in place.
- Page 22 Next, remove the backing from the top of the tape to expose the adhesive. CAREFULLY insert the Nutube into the PCB and press it onto the tape. The pins are very soft and fragile, so go slow, and be careful not to bend the pins. Solder the pins.
- Page 23 12. Inspection Before you plug the opamps into their sockets, first do a thorough visual inspection of the PCB. Make sure all the parts are soldered in, and all are oriented correctly. Match it to the photo below:...
- Page 24 13. Install the opamps U1 and U2 into the sockets Now, plug the opamp ICs into their sockets. You may need to gently bend the leads together so they are parallel to fit the socket: Then press them into the sockets. Make sure you align pin 1 with the notch on the sockets, and the notch on the PCB silkscreen! Be careful that the leads don't get bent! If they do, pull the IC out of the socket and straighten the leads, and try again.
- Page 25 14. Power-on test Verify that your power adapter is 24V DC (check the label). Connect it to the power jack on the board, and plug it in. Flip the power switch on (on is up). The power LED should light, and you should see a bluish-white glow from the Nutube triodes –...
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Page 26: Output Bias Adjustment
15. Output bias adjustment Set the DMM to measure DC volts, and position the leads of the DMM on TP1 and TP3 as shown in the photo below. Adjust R18, the “L Bias” potentiometer, to get a reading of about 11V. - Page 27 23. Listen! At this point, all checks out. Plug the amp into a music source, headphones into the output, and listen. Note that the power-on mute circuit will not turn on the headphones for about 5-10 seconds after power is turned on. This avoids a big “thump” as the amp powers up. 24.
- Page 28 Troubleshooting If the amp doesn't work, there is a 95% chance that there is a solder problem, either an open joint or shorted leads. Go back and inspect all of the solder joints one by one. If any look suspect, re-heat them with the soldering iron.
- Page 29 Appendix 1: Bill of Materials (Parts List, or BOM) You can also download this in .XLS or .PDF form from www.pmillett.com. 1 K1 NEC-Tokin KEMET EC2-24NJ 551-EC2-24NJ 655-V23079A1005B301 399-11037-5-ND PCB Low Signal Relays - PCB 24VDC NON-LATCH 2.43 2.43 1 L1 Kemet SU9V-05020 80-SU9V-05020...
- Page 30 Appendix 2: Schematic You can also download this in .PDF form from www.pmillett.com...
- Page 31 Appendix 3: Mechanical Drawing You can also download a .DXF or .PDF file at www.pmillett.com.
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