[undertow]

Not sure this is listed somewhere I don't see much on it so a few questions:

1- What is the input impedance for XLR & RCA -

2- Will they work well with Passive Preamps?

3- Does the input have an input cap for DC protection from preamps without output caps?

Thanks

[Chris Adams]

http://www.hypex.nl/docs/NC400_datasheet.pdf

[undertow]

Sorry,
I don't see the input impedance after flipping thru that manual, nor do I see if it has a dc input blocking cap.

[TomS]

Sorry,
I don't see the input impedance after flipping thru that manual, nor do I see if it has a dc input blocking cap.

DC passes right through it.

[*Scotty*]

Read the PDF DOC page 2 section 2 Audio Input Characteristics and
also read page 5 section 8.1 Firmware operation. The amplifier's behavior when DC fault conditions are detected is explained.
Scotty

[undertow]

It looks like the input impedance is 104 k ? If so that should be plenty high to run anything.

So in other words I currently have a passive XLR preamp, No dc blocking caps as there are no output caps being its totally wire and transformers, and I have a Phono stage that currently has no output caps running into that so the whole chain is pretty much capless. Its fine now due to the amp I am using has caps at the input so don't need them up the chain.

I just want to make sure this would not be an issue on this little amp module if I build it and set the speakers on fire with no dc blocking caps!
 
Thanks

[Chris Adams]

I believe the transformers will not pass DC. Better check to be sure. If you have a VOM set it to DCV and measure across the + - output of the pre with signal passing through it.

[poseidonsvoice]

DC passes right through it.

8.1 Firmware operation
The microprocessor has three main functions: to provide an interface for controlling the amplifier, to monitor the supply voltages in order to prevent spurious operation during power up/down and to detect error conditions. Most errors clear automatically as soon as the error condition lifts. The exception is a fatal DC fault. When a large DC output is detected, the amplifier first shuts down to be able to differentiate between an actual power stage breakdown and a DC condition caused by DC at the audio input. If the error persists, the FATAL line is asserted (pulled down) to turn the power supply off. If the error goes away the amplifier turns back on.

Best,

Anand.

[undertow]

But the only issue is if it does shutdown, that means I guess I would have to get caps somewhere in the chain then. Probably best adding something right at the XLR input of the new amp build?

I mean hopefully there would be no issue and yes it looks that its protected, but if it keeps shutting down that will not be too fun to listen too so it would have to be corrected somehow?

Thanks

[*Scotty*]

undertow, what brand and model phono stage are you using and does the manufacturer caution you about having protection on your power amp from potential DC output or fault conditions.
Also does your phono stage have any protection built into it to protect downstream components from turn on or turnoff transients.
Scotty

[TomS]

Note that it says "large dc output" for protection. I measured ~0.5vdc on the output before adjusting the offset at the input and output. It wasn't shutting down for that amount.

[poseidonsvoice]

Note that it says "large dc output" for protection. I measured ~0.5vdc on the output before adjusting the offset at the input and output. It wasn't shutting down for that amount.

Do you remember how low you got the offsets for input and output? Indeed making sure that you do the final adjustments prior to plugging them to your speaks is warranted.

Thanks,

Anand.

[TomS]

Do you remember how low you got the offsets for input and output? Indeed making sure that you do the final adjustments prior to plugging them to your speaks is warranted.

Thanks,

Anand.

Less than ~15mv on output I think.

[undertow]

Scotty,
The brand of phono is Aqvox, it has dip switches inside to disable all the caps. I could "Turn them on" I hate to do it due to the incredible transparency without them, and of course I don't want to upgrade them all if I don't need to use them.

Aqvox does warn "Some manufactures" preamps etc... might not like running the phono with no output caps, but again its a passive, and I know I am cutting dc at the input of the amp anyway with no reason to worry about it now. But if I put this amp in, I am not 100% sure what the possible outcome is if there are no caps at the XLR inputs.

NO the amp manufacture does not warn against dc, as a matter of fact its the opposite as an upgrade path available from them they actually completely remove the input caps as part of a whole circuit change. However, my case is obviously a little unique in that I can bypass the caps in the source(phono stage) and also running no caps all the way down thru the passive direct connection into the amp.

So its a crap shoot I think, as many manufactures such as krell that I have spoken with in the past also think you normally will not need any dc coupling caps, but again I don't know that they are accounting for passive preamps, and devices with their own caps lifted in the first place as they think everybody builds their gear mostly with output or input caps so no need to double up putting more in the way on every component.

As stated above, maybe the autoformers in the preamp will block dc from passing anyway, I have a good source to call and find out I believe, but would have to do that on Monday.

Thanks

[ChrisPa]

Undertow

What's your passive preamp?

If it is transformer, as you imply, then there will be no DC link from input to output

Otherwise, as Chris Adams said, simply measure the DC output level at the preamp output of your existing system. The nCore has a 20x gain.

But in general DC coupling throughout seldom is a problem.

[undertow]

ChrisPa,
Right it seems in general I should be fine then, but not sure what you mean at 20x gain? Yes it is an autoformer based preamp from Sonic Euphoria.

Thanks

[ChrisPa]

Your question was about DC coupling
The gain will apply to whatever DC is fed into it.
You have a transformer based passive pre - DC isn't a problem

They really are no-fuss
Simply bolt the amp modules to an aluminium case and you'll be fine
As will be the rest of your concerns

[undertow]

Sounds good.
Thanks

[Occam]

An auto(trans)former will not block dc, unlike a real transformer which provides galvanic isolation. but an autoformer will not be a source of dc offset  in and of itself. If your source components have no dc offset, by capacitive coupling, servo, etc..., the connected autoformer will not have a dc offset, either.  FWIW

[undertow]

If I run a single chassis Dual Mono is there a distance that should be required between the 2 power supplies and or the amp modules?

Also, if hooked in a dual power supply config. in otherwords with 2 of the SMPS600 to a single IEC cord input what size fuse should be used?

Or is each SMPS600 already fused? Then no Main fuse is needed?


Thanks