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What's a rough practical footprint (and height) for an uncrowded dual mono build? (stereo with separate power supplies)
I noticed in Steidl Guitars's build here http://www.audiocircle.com/index.php?topic=106187.20 bolted connections are being made to the inner side of the rear plate of the chassis without going fully through the plate. How is this done? (A short tapped hole plus a threaded insert or more basic?)
Where do you source the cable tie down anchors I see attached to the interior of some of the chassis and how are they affixed?
Those are all through holes -- bolts through the outside, nuts on the inside. You could drill and tap them if you preferred. Any of the usual general suppliers such as Mouser, etc.
What are they properly called? (To help me search)
BTW I think your build is superb!
I notice people generally seem to be using a switched IEC inlet with a fuse. Why not use a circuit breaker to avoid the fuse (and use as a main power switch)?
Would a 3 channel setup require a high current inlet?
Would there be any heat issues having 3 PSUs and 3 amp modules in the one enclosure of circa 450W x 300D x 80H (mm)?
like looking for a needle in a haystack.
BTW did you ever sort out the wiring for your front switch so that the light turned off when the amp was muted?
The SMPS has a fuse built in so another isn't needed or required.
BTW I noticed some people splashing out on rhodium plated connections.
I'm a bit confused as to what specific things need to be adhered to in order to comply with Class II and hence not need to link the chassis to mains supply ground? Double insulated wire for the internal AC wiring?
If it's relevant, I would be using balanced XLR input (from the rear of the chassis connector: left pin 1 to cable shield, right pin 2 to +ve, bottom pin 3 to -ve and top pin to chassis. I also understand from reading here that the nAmpon "thin black wire" needs to be connected to the chassis although I do not yet understand the wiring if nAmpon and a front panel mute switch.
Steve,While Class II is usually involves double insulation (not just of the wiring, but everything that carries a voltage), the real guiding principle is "no single failure should result in dangerous voltage becoming exposed so that it might cause an electric shock". Class I accomplishes this by having the chassis connected to safety earth, so that a failure will be shorted to earth and causes the fuse(s) to blow. In Class II you have to accomplish the safety function without grounding the chassis to safety earth, so insulation requirements are much stricter.If you have a metal case, you need to make sure the electronics are well enough insulated from the case, and that nothing can be inserted into any hole in the case so that it makes contact with any of the electrical circuits. There are formal requirements for Class II, but they shouldn't apply to a hobbyist making something for their own use - but do understand that I can not recommend anything else than conforming to the formal Class II safety requirements and standards.
nAmpon needs to be connected to ground (the cable shield).
Ground (the cable shield) might or might not be connected to the chassis (the Hypex recommended connection is to connect both the cable shield and pin 1 of the XLR to the chassis). If you have a metal shell XLR connector, the top (shell) pin will be connected to the chassis anyway through the metal contact between the XLR shell and chassis.
using something like Cardas 15.5AWG litz wire for internal AC wiring would not technically conform to Class II due to the lack of double shielding?
Where are the instructions for connecting nAmpon? (Or is that it?)
I would want to have a front switch mute the amp in very much the way Steidl Guitars did (with the switch light off when the amp is muted). I don't yet understand how to achieve this.
Ok so cable shield (and nAmpon) to pin 1 and pin 1 to chassis. Leave the top pin alone. Keep it simple.
Because I'm a bit of a Cardas fan I may use these:http://www.thecableco.com/Product/CM-XLR-F-Chassis (despite the rhodium)
As long as you can ensure the litz wire doesn't make contact with the metal case you should be OK. You could use spacers, or a separate, insulated sub-chassis. Independent of the Class II issue, I am not sure litz wire is such a good idea. Litz wire has a higher inductance than ordinary stranded wire, and for something like the nc400/smps600 you probably want the lowest possible inductance. Litz wire is good for conducting frequencies in the 1 MHz range - but with the nc400/smps600, you want to attenuate, not accentuate, anything above 50/60 Hz.
Pretty much, yes. Formally I guess it is specified in the NC400 data sheet, under 8.3 "Pulling nAMPON low enables the amplifier" and table 3 specifying logical high as 2.65-3.6V and logical low as -0.3-0.5V, with a 27K pull-up to 3.3V. Thus grounding the nAMPON enables the amplifier. Ground is different from safety earth.
I suggest using a double pole changeover (DPDT) switch, with one pole for the nAMPON signal and another for the light. Another possibility is using a relay.
Any particular recommendations for a quality build? (I live in the UK)
Presumably a mute switch simply lifts this ground for disable?
I very much like the look of what Steidl deployed with the light part of the switch itself. He used a part similar to the Bulgin MP0045/1E2BL012. http://www.mouser.com/ds/2/57/Bulgin_2010_p193-15602.pdf It's a DPCO switch which I believe is similar in practice (?). (I note his point about needing a resistor because of the higher voltage.)
I assume you would use the switch as a mute switch, rather than to switch the AC - in the latter case I would be concerned about the 3A rating of the switch.Yes, a DPCO is perfect fr your use - one pole for the mute, the other for the light.
