Hi, I have a nad 2400 amplifier that I use with a tube preamp that I built. The preamp has output capacitors.
I enter the nad via the LAB input which bypasses the first operational amplifier. The first thing the signal encounters is the 33uf c401 electrolytic capacitor. Do you think I can delete it? I don't use other amplifier inputs.
If I remove the c401 do I have to leave the resistors r402 and r402?
Thank you
I attach the schematic
I enter the nad via the LAB input which bypasses the first operational amplifier. The first thing the signal encounters is the 33uf c401 electrolytic capacitor. Do you think I can delete it? I don't use other amplifier inputs.
If I remove the c401 do I have to leave the resistors r402 and r402?
Thank you
I attach the schematic
Attachments
The NAD needs R402, the 22k to ground resistor at all times to preserve low DC offset. It must only ever see that value at its input.
If you remove C401 then R401 should also be removed but you must then guarantee that the preamp output is 100% AC coupled and that any resistors the preamp has after its coupling cap to ground (which it will have if it is a proper reputable design) must be removed. The preamp can then not be safely used with anything other than the modified NAD without putting those resistors back.
Having said all that I would not advise you do any of this. There is just no need.
If you remove C401 then R401 should also be removed but you must then guarantee that the preamp output is 100% AC coupled and that any resistors the preamp has after its coupling cap to ground (which it will have if it is a proper reputable design) must be removed. The preamp can then not be safely used with anything other than the modified NAD without putting those resistors back.
Having said all that I would not advise you do any of this. There is just no need.
THANKS, when you use the word "preamp" are you referring to the tube preamp I use before the nad? Thank you
ok, I understood this. What I don't understand is why I should have two capacitors in series, the one for the tube pre and the one for the nad. I hardly understand. the only thing in between is a meter of signal cable. 🙁
The input circuitry of the NAD would have to be redesigned to make that electrically possible,
although it still would not be a good idea.
In other words, if you just short out C401, the NAD will malfunction.
although it still would not be a good idea.
In other words, if you just short out C401, the NAD will malfunction.
It is common and good design practice and ensures the NAD is safely compatible with any similarly and competently designed preamp.
nad, like everyone else, puts a cap on the input because it is sure that there are no problems, but if one is sure that he uses a preamp with a cap on the output, can't he remove the cap on the nad? Thank you