100 watt amp kit step by step
Transcription
100 watt amp kit step by step
I NSTALLAT I ON GUI DE > 1 > 2 > METROPOULOS AMPLIFICATION 1045 ADAMS RD. BURTON, MI 48509 810 614 3905 www.metroamp.com 3 > I NSTA L L ATI ON G UI D E STEP 1 The first step is to take inventory of all the parts in your kit. You will find a packing list included with your documentation. Next, you’ll want to set up a workspace and start assembling. A good way to start is to glue the plexiglass panels in place. Some clamps go a long way for holding them in place. Be sure to give them ample time to dry before continuing. You might even cover them with masking tape to avoid scratching them during assembly of your amp. I NSTA L L ATI ON GU I DE STEP 2 With your panels in place,you can start installing the transformers and choke. The mounting holes should line up and wires should only pass through holes that have rubber gromets installed. A Power and output trannies are secured using the large brass bolts with lock nuts. And the choke uses the medium brass hardware. Be sure to mount the OT rotated 90 degrees to the PT for hum cancellation. B Once installed I use small spring clamps to hold the wires together and out of my way. A B I N STAL L ATI O N GU I DE STEP 3 Next, the tube sockets get installed. The output tube sockets each get a ground lug on the bolt closest to the rear of the chassis. Be sure that the notch near pin 1 points towards the the rear, as well. Don’t forget to install the tube retainers on top of the chassis. The output tube sockets use the medium brass bolts and the preamp sockets use the small brass bolts. I N STAL L ATI O N GU I DE STEP 4 A Next, install the filter caps into their mounting brackets. Be sure the negative terminal is in line with a mounting tab on the bracket as several of them will attatch to ground lugs. B The caps mount with medium brass bolts and all but two get ground lugs. Those two are shown below and are mounted closest to holes for the switches and indicator lamp. The cap nearest the fuse holders (top right) will get an extra double hole ground lug for transformer wires. C Two of the caps also have a 56K 2 watt resistor mounted between their two positive terminals and ground terminal (shown below). These resistors and the ground connections should be soldered now. Grounds are made with 18 gauge buss wire. B A C I NSTAL L ATI ON GUI DE STEP 5 A 1 ohm resistors mounted on the output tube sockets are an easy way to measure and adjust bias. One should be wired on each socket between pins 8 and 1. The extra lead from pin 1 shouldgo to the ground lug. B Next locate and twist tightly the two black wires from the PT. These are the heater wires. They attatch to pins 2 and 7 of the output tube socket farthest from the preamp tube sockets. The green wire is the center tap for the heater winding which attatches to the ground lug on the nearby filter cap. C A second green wire is the bias winding common tap, It should also be grounded on a lug. The 220V and 240V taps aren’t being used in this amp so they’ve been cut short and had shrink tube applied as an insulator. They are neatly cable tied with the other remaining wires. B C A I NSTAL L ATI ON GUI DE STEP 6 This is one of the most tedius parts of the whole job: wiring the heater connections. But it’s worth doing well for better hum rejection. Not to mention looking pro. The wires (red and black) should be twisted tightly and only as long as necessary. A The output sockets will be wired in parallel to pins 2 and 7. B The preamp sockets will be wired in parallel to pins (4 and 5 together) and 9. A Take your time, twist tight and remember that doing a good job will reduce noise in your amp significantly. B I NSTAL L ATI ON GUI DE STEP 7 A Next you can mount and wire the impedance selector switch. It mounts with the small brass bolts. You’ll want to add a purple wire to the wires from the OT and cable tie them. FOR 100 WATTS THE COLOR CODE IS: Brown – common Yellow – 8 ohms Black – 4 ohms Green – 16 ohms. The purple wire is the negative feedback wire and normally attatches to the 8 ohm tap in amps with EL-34’s. You can try it on any of the taps. B Now, using the yellow wire, connect pins 6 of the output sockets to each other. Also connect a length of wire to the socket closest to the preamp sockets. This will go to the circuit board. B C Locate two 1.5k resistors (brown-green-red) and extend one of each of their leads with buss wire and cover them with the insulating material. One of these will go between pins 5 of each pair of output sockets. The left two and the right two. C A I NSTAL L ATI ON GUI DE STEP 8 A Locate the (4) 1K 5 watt resistors. They mount on the output tube sockets, between pins 4 and 6. B Next, mount the speaker output jacks. The brown wire from the OT attatches to the terminal closest to the chassis. So does the black wire (red arrow) which connects to a ground lug on an output tube socket mounting bolt. C The terminals on the jacks all get connected with 18 gauge buss wire. I also extend the buss wire from the terminals farthest from the chassis, over to the impedence selector switch. Some insulation here is a nice touch. A C B B I NSTAL L ATI ON GUI DE STEP 9 A Now, install the (2) toggle switches. The red wire from the PT attatches to the lower two terminals of the power switch. The yellow wire from the PT attatches to, and connects together, the positive terminlas of the filter cap closest to it. The orange wire attatches to the mains fuse holder (4 amp fuse). B The blue and grey wires get twisted together and attatch to the lower two terminals of the standby switch. At this point all then PT wires should be attatched except the white bias tap wire which connects to the circuit board. A B A C Next, using red wire, make jumpers bewteen the filter caps as shown. Also, run red wire from the filter cap nearest the power switch, to the 1 amp fuse holder. And run a red wire over to where the circuit board will mount. Make sure to leave some extra wire. C You’ll need to run a length of yellow wire from the filter cap with the 56K resistor, too. Cable tie these together. I N S TAL L AT I O N GU I DE STEP 10 A A Attatch red and black wires to the indicator lamp and install it. Check to see if you have a 120VAC or 6.3VAC lamp. The 120V lamp will be wired as in the pics. The 6.3V lamp is wired to the heater connections on the last output tube socket. Twist the wires tightly. One wire attatches to the lower power awitch terminals with the red wire from the PT. The other wire attatches to the mains fuse holder with the orange PT wire. Cut two lengths of blue wire and solder them to the upper terminals of the standby switch. Twist them and run them over to where they will later be wired to the circuit board. Solder a length of blue wire to the filter cap near the fuse holders. Run it over towards where the circuit board will mount and, like the other wires, leave plenty of extra. B Attatch a length of red wire to the high voltage (HT, 1 amp) fuse holder and run it over with the blue wire. Cable tie these wires where ever necessary. They should now look like a wiring harness, as in the pictures. B A I N S TAL L AT I O N GU I DE STEP 11 Now locate the 6 pots. Each one should be installed with a lock washer on the inside of the chassis and a flat washer and nut on the outside. Their values from left to right are: PRESENCE BASS MIDDLE TREBLE VOL1 VOL2 5K linear 1 meg audio 25k linear 250k linear 1 meg audio 1 meg audio The bodies of the pots should be connected with a piece of 18 gauge buss wire. A buss wire should also connect terminal 3 (farthest left on each pot) to the ground buss for the volume controls and middle tone pot. A .1uf 100V cap is mounted on the presence pot, with one lead connecting to pin 2 (center terminal) and the other lead conneting to the ground buss and terminal 3. A black ground wire attatches from the ground buss to the ground lug on the filter cap near the output tube sockets. Another connects the ground buss to the ground lug on the filter cap near the preamp tubes sockets. You could also attatch a 500pf “bright” cap across pins 1 and 2 of the ch 1 vol. control at this time. I prefer to wait so I can tweak the amp with the perfect value cap, which usually ends up between 100-500 pico farads (pf). I N S TAL L AT I O N GU I DE STEP 12 A A You should assemble the pairs of input jacks before mounting them. Follow the diagram (above left) and install the 1meg resistor, ground buss wire and crossover wire. Green wires will also attatch to the terminals I’ve labled as “high input” and “low input”. This coresponds to the high and low sesitivty inputs for each channel. The jack with the 1 meg resistor is the high input. This can get confusing when the chassis is turned upside down. B Ground wires should be attatched to the lower right terminal (with the 1 meg and buss wire) of each input assembly and ran to the ground buss on the pots. C Next, red wires need to be soldered to the positive terminals of the filter cap near the preamp tubes. They need to be left approx. 8 inches long for installation to the circuit board later. B C A HI I NPUT L OW I NPUT I N S TAL L AT I O N GU I DE STEP 13 A Next, install the circuit board mounting bolts, there are six. You should check their alignment with the circuit board before tightening them. When the fit is right, you can start on the fun part…loading the board, right? Actually…it’s easier to wire the board before loading it. But don’t worry, you’re getting close. Included with these instructions will be a full page diagram. You’ll want to refer to it for the wiring of the buss wire and insulation. They should go on the board before anything else. B Once installed, your board should look like the one below. B A I N S TAL L AT I O N GU I DE STEP 14 A A Now you can start wiring the board into the amp according to the diagram. It’s easiest to start with the wires you ran in the power supply section. From there you can work your way to the left. I prefer to wire the power supply wires, followed by the wires on the input side of the board and finally the wires to the preamp sockets. This step is the most time consuming, and it’s worth taking your time and making nice solid connections between the wires and terminals. A helpfull tip for wrapping the wire around the terminal is to strip about a 1/4” of insulation, then apply a small amount of solder to the end so the bare wires stay together. Now bend the wire around the terminal with needle-nose pliers and apply solder. B I also find it easier to connect the wire to the terminal before feeding it through the hole in the board. It’s a pain to do right, but nicely wrapped connections make for a great looking amp. Don’t be afraid to clip off the end and start over on a wire just won’t cooperate. B A I N S TAL L AT I O N GU I DE STEP 15 Now, finally, comes the fun part. Installing the components on the board. Just like the wiring, attention to detail here makes all the difference. It’s worth taking the time to straighten all the component leads with needle-nose pliers. Next, hold the component in position over the terminals it attatches to, with the pliers grab one of the leads where a bend should go. Bend the lead and cut it off so about an 1/8” is left to go in the terminal. Put the component back in place and repeat the bending and cutting. It should now fit perfectly with straight leads going to each mounting point. Be sure to observe the polarity of the diodes and electrolytic caps (10uf bias caps and 250uf cathode cap). The positive side of the bias caps actually go to ground near the bias pot. Don’t forget to install a bright cap on the channel II volume pot, between pins 1 and 2. A You also need to install a 100K resistor on the second preamp tube socket. One lead should connect pins 1 and 7, and the other end should attatch to pin 6. When you’ve gotten this far, take a break and congratulate yourself however you see fit. You’re so close to firing up your amp that your neighbors are getting nervous. A I N S TAL L AT I O N GU I DE STEP 16 The final thing to install is the AC cord and strain relief. Strip 6-8 inches of insulation from the end of the cord and run in through the hole in the chassis. Make sure there’s anough wire inside to reach the poswer switch. Wrap the strain relief around the cable and compress it using pliers. You should be able to push it into the hole. The white wire attatches to the open terminal on the mains fuse holder. The green wire gets a ground lug and needs to be bolted to the chassis with it’s own bolt to meet code. Finally, the black wire runs to the power switch and attatches to the the top two terminals. Install the fuses (4A main and 1A HT) and look over your work. Take some time to double check any components or wiring you’re not sure about. It’s better to catch something before powering up the amp. If you’re satisfied and with no tubes installed, plug in the AC cord, cross your fingers (just kidding) and turn on just the power switch. Assuming there’s no explosions, you can take some voltage readings. Set your meter to AC volts on the 10 volts or higher range. Put the black lead in one of the chassis mounting holes and touch the red lead to pins 2 and 7 of each of the output tube sockets. You should read approx 3.25 VAC. You should get the same reading on pins 4, 5 and 9 of the preamp tube sockets. If all is well, set you meter to DC volts on the 100 volts or higher range. Touch the red lead to pin 5 of each of the output tube sockets, you should read anywhere between -30 and -50 VDC. Adjusting the bias pot should change this reading. If you don’t get these readings, check the black wires from the PT for the heater voltage and the white wire from the PT for the negaitve bias voltage. Make sure these are right before moving on. I N S TAL L AT I O N GU I DE STEP 17 I like put my meter in the extra space in the chassis. Notice the black lead in the mounting hole. This allows you to put only one hand in the amp at a time. The other hand should go in your pocket to avoid touching any part of the amp that might use your body to complete a circuit. With no tubes installed yet, and if your readings are correct so far, turn on the standby switch. With your meter set to the highest DC volts setting, measure the voltage on pin 3 of each output socket and on each side of the 1k 5 watt resistor. Be extremely carefull as these are the highest voltages in the amp. Your readings should be in the 450-500 volt range. If so, turn the amp off and install the preamp tubes. Turn on the power switch with the standby off and watch to see that the 12ax7’s light up. When they do, flip the standby on. You can now reference your readings to the included voltage chart. Keep in mind that your readings may vary from the chart by 1020%. The important thing is that the readings are proportionate to those listed. For example, if your highest voltage reading is 20 volts less than the listed voltage, that may be a 5% difference. All of your readings should be approx 5% less than those on the list. When you’re happy with your maesurements, turn the power switch off but leave the standby switch on. This will allow the filter caps to drain their stored voltage. Now install the EL-34’s, turn the bias pot all the way towards the front of the amp, plug in a speaker and turn the standby switch to off. Flip the power switch on and let the EL-34’s heat up. I N S TAL L AT I O N GU I DE STEP 18 Now turn the standby on. Slowly bring up the volume control and listen for any squealing, humming or otherwise unnatural sounds. If there are none, turn the volume back down. Set your meter to DC millivolts and touch the red lead to pin 8 (with the 1 ohm resistor) of any of the output sockets. This will tell you your bias current, which should be quite low. Next turn the bias pot up about half way and measure on pin 8 again. The reading should be much higher. Continue this process until you read 35mV. That indicates that the tube in that socket is properly biased at 35mA. Check the other tubes in the same way. They should vary by a few mV’s, but normally not more than 5mV’s. You should be able to find a setting that puts all the tubes between 30 and 40ma’s. Take some time to play the amp now, test each input, make sure the controls all do what they’re supposed to. Watch the ouput tubes to make sure they don’t ever glow red. If they do, increase the bias voltage. After playing the amp for a while, recheck the bias as it will drift. If all is well, CONGRATULATIONS! Next, you can start to tweak the amp to your liking. Please visit the forums at: www.metroamp.com/forum to share your experience and for tech support and mod suggestions.