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Old 11th December 2013, 05:33 PM   #1
6L6 is offline 6L6  United States
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Default ACA illustrated build guide

An illustrated guide to building the Nelson Pass 'Amp Camp Amp'.

First read Nelson Pass’ article on Amp Camp Amp #1 if you haven’t already:
Amp Camp Amp #1

Another great guide can be found here - Amp Camp Amp #1 A Pictorial Build Guide


Click into any photo for full-size.

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The Chassis shipping box. Not very large, but quite interesting…

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Careful packing is always a good sign.

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They just seem to be the perfect size.

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The chassis pieces exploded.

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Chassis hardware.

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The heatsinks are pre-drilled and tapped. Everything just screws together.

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Parts kit contents - Left to right, wire, chassis connections, resistors and capacitors, transistors (in protective mylar bag), circuit boards and insulators.

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Circuit boards and the insulators for the power transistors.

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Enough wire to make all the connections necessary.

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Resistors, capacitors, potentiometers.

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Power switches, chassis connections (power, RCA input, speaker output), hardware.

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ZTX transistors, MOSFET power transistors (the big ones), LEDs

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LSK170 transistor. Don't confuse it with the ZTX transistor.

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Time to get some tools. Digital Multi-Meter (DMM), screwdrivers, pliers, dikes (flush-cut is best), wire stripper, zip-ties. Also a soldering iron and solder of course.

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Time to stuff the PCB.

AT THE MINIMUM you need to have the schematic in front of you, and your DMM out and ready to measure the resistors.

Measure the value of every resistor with your meter before stuffing/soldering into the PCB. This will save headaches later.

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I strongly suggest aligning the resistors in one direction, with the value showing out. This will assist in troubleshooting later if there is any problem. Start inserting the small items first.

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The small resistors have the value marked on them - here you can see the other markings and the value of 100 Ohm.

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Again, the various markings and the value of 1K ohm. A common mistake is to overlook the "K" if it's in the value. Since "K" means "x1000" this is very important!

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The large 3 Watt resistors also have the value printed on them - here 0.68ohm

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Bend the component leads out a little before soldering to hold them in place.

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Placement of the large resistors.

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Capacitors that are used in this amp are "polar". In other words they have plus and minus leads. This polarity is shown in 2 ways - the negative lead is shorter and the heatshrink on the can next to this lead has minus signs. (---). The positive lead is longer.

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Parts placement. Don't install or solder the Power Mosfets Q1 and Q2 yet

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Please note On this photo you can see that the printed pads on the PSB for the small transistors (Q3 and Q4) have a shape to them - there is a flat side and a rounded side - The transistors also have a flat side and a rounded side and must be inserted to correspond with the printed pad, as it's essential that they not be installed backwards. In this amp the flat side of the transistors should face the big capacitor.

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Now it’s time to bend the leads of the power Mosfets. If you bend the legs up right close to the point where the pins narrow, it should fit perfectly.

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Use the screw and washer to mount the Mosfets to the heatsink with the Keratherm insulators between them. Keratherm insulators have exceptional heat transfer characteristics but must not be used with thermal grease.

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Also mount the brass standoffs as shown. Don't over-tighten them.

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The PC mounts to the standoffs with the screw and a washer on each side of the PCB.
Slide the PCB down over the leads of Mosfets Q1 and Q2

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Now solder the Mosfet leads to the PCB.

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If you decided to solder the wires inserted from the top, which is a fine way to do it, make sure to check that the wires do not touch the heatsink or anything else under the PCB.

Put the heatsink/PCB assembly aside for a moment and turn to the rest of the chassis.

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This is all the parts to the RCA jack. Notice that one of the washers has a shoulder - this needs to go inside the chassis hole to keep the metal of the jack from touching the chassis.

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Also note that the ground tab goes outside the washer but under the nut.

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The speaker terminals - to isolate them from the chassis the plastic washers go on either side of the chassis wall. The 2 nuts go inside, one on top of the other, to lock them in place.

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The connections installed, as seen from the interior.

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The power connector. Note it has 3 prongs, but we'll only use 2.

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This is the proper wiring for the power jack. The red wire is positive, connected to the pin that touches the center. The black wire is negative and attached to the “middle” tab. The leftmost tab (in this photo) is unused. Make sure the wires don’t touch anything other than their tabs.

To be sure your jack is wired correctly, before installing the power jack in the chassis leave the PSU unplugged from the wall receptacle and insert the plug from the PSU into the power jack. Now plug the PSU into the wall receptacle and use your voltmeter to identify the +19v connection tab and negative tab as discussed above. Now you can install the power jack into chassis

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Last edited by 6L6; 13th December 2013 at 12:10 PM.
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Old 11th December 2013, 05:34 PM   #2
6L6 is offline 6L6  United States
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Modification instructions -

The current PCB have been found to be needing one extra resistor added to get the bias set to a range where the amp will make it’s full designed power and lowest distortion. This is a minor compensation for the particular small-signal transistor (ZTX450) and will be integrated into new revisions of the PCB. In the meantime, you will need to add this resistor above the PCB.

It is going to be very helpful to have a 2nd person to help you hold things in place as you solder.

The end result should look like this -

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First take the 2.2K resistor and bend the lead around a small screwdriver.

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The resistor will go here - don’t cut anything yet, but try to bend the leads so they go in the approximate correct location.

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Trim and solder

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Be sure that the resistor lead touches only the first leg of the transistor.

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With one end attached to the transistor, bend and trim the opposite lead.

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Solder. Repeat on other amp channel PCB.


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Power switch. The switch mounts from the outside with the tabs aligned center and down.

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Inside switch. The middle tab attached to the PCB and the lower tab to the power jack.

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This little widget is the LED holder for the front panel.

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The LED holder inserts from the front into the hole above the switch.

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Slide the LED in from the interior (rear).

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It’s worth noting that the chassis is designed so it can be mirror-imaged for the left and right monoblocks. The heatsinks, PCBs, connectors, front panel, etc. all can be mounted to create left or right amp orientation,
but you must get the wiring correct and with the MOSFETs oriented towards the bottom of the heatsink.

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Wiring. The Blue/White pair are to the speaker Jacks, Blue positive, White negative. The red will go forward to the center tab of the power switch, and the black to the power jack.

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Again, the red from the PCB ‘V+’ goes to the switch center, the switch lower goes to the power jack. PCB ‘GND’ goes to the power jack.

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Similar shot, but this is the other, mirrored chassis.

Please note - It doesn’t hurt anything to keep your wires a little long - you will need to do all the wiring and soldering with the chassis and heatsinks in this position and then do the final assembly later. 2 inches too long is ok, but 2MM too short is no good at all.


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Rear panel interior -
PSU jack Red to power switch lower tab: Black to PCB ground.
Speaker terminal: positive Blue, negative White.
Input RCA: Thinner wires, positive Purple, negative Yellow. Twist these wires tightly as shown to minimize hum.

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Front Panel power switch -
Center tab to PCB
Other tab to Power Supply jack Red


Some more photos showing the wired interior -

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Attach the heatsink to the chassis with the silver machine screws.

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Now install the top and bottom chassis covers with the black self tapping screws.
Peel the backing off the rubber feet and install one on each corner.
Completed front.

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Completed rear


Bias procedure

First, let the amp warm up - plug it in and turn it on for about a 1/2 hour.

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With your meter set to DC volts connect as shown - black on ground (and the open hole is signal and power ground) red on pin 2 ( the middle pin) of the output transistor Q1.

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The adjustment point is the blue potentiometer in the upper left corner.

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Adjust the pot until you read 10V on the meter. (A few 10ths of a volt off in either direction is fine.)
This is a finicky adjustment and things happen in slow motion, so make a small adjustment and wait for it to ‘catch up’. Repeat until the bias is set.

Last edited by Variac; 11th December 2013 at 10:21 PM.
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Old 11th December 2013, 05:36 PM   #3
6L6 is offline 6L6  United States
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Placeholder post.
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Old 11th December 2013, 06:44 PM   #4
NYCOne is offline NYCOne  United States
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Great post. I added my "extra" bias resistor to the underside of the board. It's cleaner looking, and there's plenty of clearance between the heat sink.
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Old 13th December 2013, 08:10 PM   #5
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hi,
I'm just about to begin with my aca (waiting for the boards)
and I keep asking myself if it would be a good idea to replace c1 with a
foilcap?
i've got some nice little mks2 10F/50V from my local dealer.
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Old 13th December 2013, 08:35 PM   #6
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mistake! sorry, I ment c3 of course.
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Old 20th December 2013, 08:52 PM   #7
tooppy is offline tooppy  France
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Is the power lead connector of american type, two flat pins? Is it possible to have it for EU two round pins ?
Thanks
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Old 20th December 2013, 09:11 PM   #8
Zen Mod is offline Zen Mod  Serbia
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is that trick question ?

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Old 21st December 2013, 09:29 AM   #9
tooppy is offline tooppy  France
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Quote:
Originally Posted by Zen Mod View Post
is that trick question ?

I don't quite understand what you mean, nothing tricky here, except your reply.
As the power lead goes to a AC low voltage transformer, it has better have the proper socket to plug to the main.
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Old 21st December 2013, 11:45 PM   #10
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Quote:
Originally Posted by tooppy View Post
As the power lead goes to a AC low voltage transformer
Please take a good series of photos, when you plug in your amp and AC low voltage transformer for the first time--and post them in an ACA tread here.
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