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Old 21st February 2012, 01:35 PM   #1
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Join Date: Jun 2010
Default New amp build

Ok its done well the first half is done anyway.. Started this a few weeks ago and just got around to finishing it up this weekend..

One more to go and ill have stereo...

The AC power cord is temp.

Let me know what you think...

for those interested the build is linked below titled first-post build

First post/build

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Old 21st February 2012, 04:21 PM   #2
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Location: Canby, Oregon
Hello Jbryant, I see from your comments that the AC power cord is temporary. When you put the permenant one in place, you should route the black wire to the line switch and connect the white wire to the power transformer. As it is shown in the picture it is reversed and this will not provide the proper fusing line protection. In the event you use a line cord that contains the international coloring of the conductors when you replace it, connect the brown wire to the switch and the blue wire to the transformer. You should also install a dedicated ground screw for the safety ground power cord wire connection rather than using a shared screw as is shown. Obviously, all my comments are in quest of improving the safety. Very clean nice wiring job on your project! Mickeystan

Last edited by Mickeystan; 21st February 2012 at 04:23 PM.
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Old 21st February 2012, 04:42 PM   #3
kevinkr is offline kevinkr  United States
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Connect the black wire in your line cord directly to the fuse, and the white wire to the cold end of the transformer primary. Do this now as it is safer in the event of an insulation failure or winding short in the power transformer primary winding. (Only the relatively low current permitted by the fuse can flow as opposed to the 15 - 20A rating of the typical branch circuit as it is now wired. The fault current flows through the ground wire and currently will bypass the fuse completely as it is in the neutral lead.)

Ground the ground buss to chassis at one point only.

I think you have grounded the first cap and HV center tap to another point on the chassis - lift this and connect to one end of your ground buss - preferably at the end where the buss is grounded to chassis.

The RCA jack appears to be directly connected to chassis, isolate it and run a wire back to the point where the ground buss connects to chassis.

As implemented it is probably going to hum when connected to other components in the audio system due to multiple ground loops. If you still have hum after you do the above you can try adding a ground lift network between the circuit signal ground and the chassis. (Essentially a 1 - 10 ohm resistor and a pair of anti-parallel diodes all in parallel. Use high current silicon diodes. Search here - there is further discussion on this subject.)

The safety ground using a ring eyelet should be connected directly, and permanently to the chassis with its own dedicated hardware which should include a lock washer or two to prevent it from loosening up and to provide a good connection to chassis.
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
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Old 22nd February 2012, 12:41 PM   #4
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Ok I went ahead and made the repairs to the AC cord. Good looking out thanks for the heads up....

I also wanted to say anyone reading this post might belive the amp hums from the replys... It does NOT hum and is dead quite... I have two large horn systems and you would never know they were on.

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