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Old 12th October 2010, 10:33 AM   #1
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Default Cable between power supply and amp

Hi!

I'm building my first chip amp (two TDA2050-channels), and even though i'm not new to electronics (i've built various synths and guitar effects and such), this will be the first project with a DIY power supply.

I've done some research and a snubberized design with a toroid tranny looks like the best option. I want to put the power supply in a separate casing to make the amp as small as possible.

My questions: What kind of cable would be wise to use between power supply and amp, and should the separation between chassis ground and signal ground happen in the power supply or in the amp.

Would an xlr4-cable work for this (chassis ground, signal ground, plus and minus)? If the ground separation happens in the amp, a normal xlr would be enough. (The reason i'm thinking xlr is that the cable would be readily available. If you have better options, feel free to tell me!)

Thanks for a great forum, i've had much help from your expertise!

Regards,

Fredde
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Old 12th October 2010, 12:13 PM   #2
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A couple of things you want to make sure of:
1) there is no way you can accidentally plug mains into the DC connector on the amp,
2) the cable you use is rated for more than the maximum current it will carry,
3) the safety earth pin should be longer so it is first connected, last disconnected,
4) ideally, there should not be exposed pins on the amp end of the cable that could be carrying voltage if the cable is plugged into the supply but not the amp.

XLR has the first one covered. What about the other three?

Me personally, I have a single ground connection from my supply to my amp (+,-,gnd). Since IEC-320 C13/C14 connectors are very common for mains here, and I used that for my mains cable, I went with an IEC-320 C19/C20 cable for my power supply to amp cable. They can't be mixed up, it's rated at 16A or so, and one pin is longer than the other two, so I used that for ground. Also, the supply end of the cable is male (no exposed pins on the supply with the cable unplugged) and the amp end is female (no exposed pins on the cable if plugged into the supply).
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Last edited by Redshift187; 12th October 2010 at 12:17 PM.
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Old 12th October 2010, 12:35 PM   #3
AndrewT is offline AndrewT  Scotland
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I like the use of XLR for power umbilical.
The one long receptacle (female) is good for grounding.

I would also use metal shelled plugs and sockets so that the shells can provide a back up grounding link with a 4th core or shield for this dual grounding scheme.

This will be the PSU cable, it has a Zero Volts and (if you agree) a Safety Earth connection.
This PSU cable has nothing to do with audio signals, neither Audio Ground Star nor Signal Ground. They exist only in the amplifier.

Is there a plug & socket that could activate a relay that isolates mains from the PSU when the Plug is removed from the Socket?
Or do we just use a 4pole or 5pole XLR? Then both plugs and both sockets need continuity before the relay signal can pass and "turn on" the mains supply.
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Old 12th October 2010, 12:59 PM   #4
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Thanks for your replies! Hadn't thought of the ground pin having to be connected first!

IEC-320 C19/C20 isn't very commonly available here in Finland, especially exotic female chassis connectors seem to be hard to come by, so I won't give up the XLR-thought just yet.

Quote:
2) the cable you use is rated for more than the maximum current it will carry,
How about PA-speaker rated cable, shouldn't that do the trick?
Quote:
3) the safety earth pin should be longer so it is first connected, last disconnected,
Like AndrewT said, long female receptacle + connector shell.
Quote:
4) ideally, there should not be exposed pins on the amp end of the cable that could be carrying voltage if the cable is plugged into the supply but not the amp.
Shouldn't this be solved by using a female socket in the PSU and a male one in the amp?
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Old 24th March 2013, 08:48 PM   #5
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Sorry to unearth an ancient thread, but I am a newbie and had the same question. Reading the above, why would you need two grounds (when I say newbie, I mean it!). Thanks.
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Old 25th March 2013, 08:59 AM   #6
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Quote:
Originally Posted by jhsjhs99 View Post
Sorry to unearth an ancient thread, but I am a newbie and had the same question. Reading the above, why would you need two grounds (when I say newbie, I mean it!). Thanks.
I ended up using XLR connectors, female on the power side and male on the "receiving ends". I used standard three core power cable (harvested an old computer cable) and soldered the XLR connectors to that. This was in 2010, and my first power supply build (it works great though and I use it daily). Now I might use speakon/powercon connectors instead (they are quite bulky though, and might not fit all bulds).

Really you could use anything as long as 1) all connectors and cables are rated for well above the expected current, 2) no exposed voltage carrying pins and 3) ground is connected first.

You could use a standard IEC receptacle, but then you have to be absolutely sure no one that doesn't know it's not for standard wall power ever uses your amp. Better to use something non standard that cannot be accidentally misused and put a label at the power input stating voltage and pinout.

About grounding, read this: Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
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Old 25th March 2013, 09:03 AM   #7
AndrewT is offline AndrewT  Scotland
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because there are numerous returns and references that all get referred to by the same name.
It's very confusing calling everyone Andrew when Tom, Dick and Harry would help differentiate.

The Big difference is between Safety and Audio.

The Safety Earth is the Chassis connection to Protective Earth (PE). This has nothing to do with Audio. It is there for SAFETY only.

The Main Audio Ground (MAG) is connected to all Audio Circuits that require to be referenced to each other. The equipment will operate perfectly well with a floating MAG. The MAG does not need to be connected to PE, that's the way all battery powered equipment works.

The complication comes when everyone MUST comply with:
All exposed conductive parts of mains powered equipment must be connected to PE. This is a Safety requirement only and has nothing to do with the quality of the Audio.
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