Hypex Ncore

[diyaudnut]

can someone clarify a basic question:

say a DAC's balanced output produces +4dBu at full digital scale. This is 1.23v

Is the differential input voltage at say Ncore input 2.46v or 1.23v

As i understand Ncore will produce peak power at 2V input level. Again is this +2,-2v on the differential input (4V) or +1,-1v (2V) ???

 

[Julf]

say a DAC's balanced output produces +4dBu at full digital scale. This is 1.23v

+4 dBu is 1.23 VRMS (root mean square). The peak-to-peak value of a 1.23 VRMS sine wave is 3.44 V, or +1.722/-1.722 if you reference it to some arbitrary middle point, but that is the wrong way to think about it.

As i understand Ncore will produce peak power at 2V input level. Again is this +2,-2v on the differential input (4V) or +1,-1v (2V) ???

A fully differential input doesn't know anything about "ground" or "earth", so when you say "+1,-1", the logical question is "referred to what". The right way to think about a differential amplifier is that it amplifies the difference between the non-inverting and the inverting input - in the case of the Ncore, a 2 V voltage between those inputs will cause full output.

 

[Julf]

The choise is between NC-400 without U-pad attenuator or NC500 with attenuator (but better specs?) What would you guys choose?

I wouldn't lose any sleep over either the small differences in specs or an attenuator. The main question is really "do you want to buy a ready-made amp or do you want to do some lightweight DIY?". If you want to do DIY, then NC400 is the only choice.

 

[DonJunker]

I wouldn't lose any sleep over either the small differences in specs or an attenuator. The main question is really "do you want to buy a ready-made amp or do you want to do some lightweight DIY?". If you want to do DIY, then NC400 is the only choice.

I did arise to the same conclusion and has ordered the NC400 kit as it gives me more control of the gain.

 

[Boggit]

There are some hefty white papers on the Hypex site covering the subject in full.

 

[Julf]

There are some hefty white papers on the Hypex site covering the subject in full.

Which subject? Voltage levels or choosing between nc400 and nc500?

 

[SGK]

Oh that one cracked me up... (Sorry Boggit)

 

[Boggit]

Voltage levels etc connecting DAC's directly, came across it last night could not find it again today to post the link, its there somewhere!

 

[Julf]

Voltage levels etc connecting DAC's directly, came across it last night could not find it again today to post the link, its there somewhere!

If it is a hypex white paper, it ought to be one of the 8 papers at Hypex Electronics BV - White papers (or the equivalent page on hypexpro.com). Any recollection of which one it was?

 

[pos]

in the case of the Ncore, a 2 V voltage between those inputs will cause full output.

Are you sure?
I thought the 2V rating was RMS (8dBu) !
Gotta rethink my gain structure

 

[Julf]

Are you sure?
I thought the 2V rating was RMS (8dBu) !
Gotta rethink my gain structure

My bad - I should have stated "2 VRMS".

The nc400 has a voltage gain of 26 dB, so a factor of 20. For a 400W output into 4 ohm (or 200W into 8 ohm), you need an output voltage swing of 40 V, so an input signal of 2 VRMS.

 

[diyaudnut]

+4 dBu is 1.23 VRMS (root mean square). The peak-to-peak value of a 1.23 VRMS sine wave is 3.44 V, or +1.722/-1.722 if you reference it to some arbitrary middle point, but that is the wrong way to think about it.

A fully differential input doesn't know anything about "ground" or "earth", so when you say "+1,-1", the logical question is "referred to what". The right way to think about a differential amplifier is that it amplifies the difference between the non-inverting and the inverting input - in the case of the Ncore, a 2 V voltage between those inputs will cause full output.

missed saying thanks. That totally makes sense, disuse has made me forget a lot of things. Thanks

 

[BBLV]

So does anyone have a "simplified" diagram of the circuit I can add to trigger the SMPS from the 12v of my A/V pre?

P.S. I'm slightly circuit illiterate I can read 'em, but I can't write 'em!

 

[DonJunker]

Now the NC-400s are up and running. Stunning details and control of the speakers. Next step is to play with room correction/equalization at frequencies < 250Hz

What are you guys recommmending (may be a little off topic). I'm looking at https://www.minidsp.com/dirac-series/ddrc-22d

 

[Omholt]

What's the best way to reduce the gain of NC400 down to approximately 20.6 dB?

 

[Julf]

What's the best way to reduce the gain of NC400 down to approximately 20.6 dB?

Change or remove R141 (in the feedback network).

 

[Omholt]

Can't seem to find R141. Where's it placed on the board?

 

[Omholt]

Ok. I found it. Wow, it's a tiny!

1. How do you remove it?
2. Does it take soldering to replace it by a new one?
3. Where and what do I buy to get the desired gain?

 

[ds23man]

If you don't have any experience with smd, do not touch it!!!!!! Find someone who can do it.

 

[Julf]

Ok. I found it. Wow, it's a tiny!

Welcome to the world of SMD devices

1. How do you remove it?
2. Does it take soldering to replace it by a new one?

There are pretty good guides to SMD desoldering on the net. This one is not too bad.

3. Where and what do I buy to get the desired gain?

Gain is 4.5 x (1 + 2*Rf/Rg). Rf is 2.2K, Rg (R141) is normally 1.2K, giving a gain of 21 (26 dB). To get 20 dB, you need to drop the gain to 10, so Rg needs to be 3.6K. You can buy SMD resistors from an electronics component supplier such as Farnell or RS Components.