Elliot P101 humming

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I finished my P101 a while back and was concerned about the output voltage . Now, I have another concern. The amp is dead silent until I connect the input RCA cables to a source. It doesn't matter what the source is it will hum. I'm wondering if this is a grounding issue of some sort or the fact that every input device I've connected has been on a polarized plug while the amplifier uses a grounded IEC plug and there might be a possible ground reference issue between the neutral and ground (earth) in my house wiring. Any thoughts on this?
 
Install a ground loop breaker between chassis earth and 0V on your power supply. Ensure your RCA connections are isolated from the chassis.

If it's possible you have an earth leakage issue, get an electrician to do an earth leakage and EFLI test on your house.
 
I've been doing some more reading about ground loops and I'm tempted just to cut the ground pole off a cord to see if the hum goes away (testing purposes only). It stands to reason that this might make it worse (allowing it to pick up noises elsewhere) because then it would be floating. Anyway, I measured between the neutral and ground with the breaker off and I only see a couple tenths of an ohm of difference.
 
I concur with the above, as I have finally got rid of, to paraphrase Rod Elliot, "the @£$%ing hum."

ISOLATE EVERYTHING from the casing. In particular the RCA jacks, AND the transformer. Then earth/ground your box at one point (only) via a 10 ohm 2 watt resistor, to kill off any hum. (You will need to scrape away paint and use a tight bolt).

An alternative to isolating RCA jacks is to use balanced XLR connectors, (without necesary using balanced circuits). They have the metal body, which shouldn't be electronically connected (but they will be bolted to the chasis, and therefore earthed via the 10ohm resistor). Of the 3 pins, one can be used for the screen (usually pin 1).
 

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I purchased the chassis and transformer from Antek on Ebay. The rest of the machining and metal work I did myself. I'm running about 36k uf per rail in capacitance and the transformer is 1kVA. I am now using an Omron Zen "smart relay" (it's a baby PLC) to start the amp, provide soft start, and control the fan. On startup, the indicator in the power switch blinks for 10 seconds while everything charges before switching the relay. I am a controls engineer by trade, so that's why it looks rather industrial.
 
Looks Great! I bought one of my 800VA 50-0-50 toroidals from Antek/Par-metal and both of the rackmount cases from Par-metal. I am running 44,600 uf per rail. Plc controlled is novel. I am a maint.mechanic for a veterinary Pharm/Bio manufacturing ,filling and packaging company ( Wyeth) most of our machines are controlled by AB SLC500 PLC's. Anyway hopefully we can get rid of your hum problem. Did you try swapping your source inputs around to eliminate that potential noise source? It sounds to me from your previous post that the problem is pretty much narrowed down to one channel. You could power it up with the hum present and with a non-metallic tool tap around on the suspect pc board and associated wiring to locate/isolate source of noise which sounds to me like a faulty connection ie cold solder joint. :)
 
I used a plastic rod and pressed on the offending unit. Pressed on it in various places, slapped it around a bit and the sound didn't change. I've been meaning to swap out the heat sinks for some bigger ones, so I'll probably use it as a chance to check the solder joints as well. As I'm sure you've noticed, once you use a preamp, this thing really sings! My previous amp was an old Mitsubishi DA110 that supposedly made 110W/channel. This amp blows it away. I made the mistake of thinking the gain was high enough to not need a preamp. I picked up an Audiosource preamp for the time being while I design my own. As soon as I get this thing figured out, I'm going to reroute most of the wiring. It's a bit messy right now. The bug has bitten!
 
Yep these amps sound great. I'm using and old refurbished Yamaha C-2a preamp with dual preamp outs to drive 2 pair of Yamaha NS-1000's. I had to replace all of the electrolytics & bi-polars(used all nichicon caps) clean corrosion from the rca jacks and thoroughly deoxit all of the switches and potentiometers, adjust the + and - rail voltage and basically give the whole thing a good thorough cleaning ie dust,cigarette residue etc. She sings like a canary now.:D
 
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