the amp works well but when powering up, the delay before the relay kicks on is only about 1 second as opposed to other my other amp (a NAD 2600A) which takes about 3 seconds. My question is, what determines this timing? Is it supplied by IC 803? Here's a screen shot of the protection circuit.
Have to ask, how do you feel the difference is in soundquality and power between these two amps?
No, not using the original value 22uf. I replaced it with a 33uf and it did lengthen the delay a bit. I'm suspecting there's an issue with the protection IC so I have a replacement at the ready in case it fails. The amp is working ok otherwise especially since it's never had any work done to it except protection relay replacements.
Since they are basically the same amp except for power output, they sound very similar. Maybe a little light in the bass area but overall clean and open and capable of prodigious power output with the Power Envelope circuitry.
Have you replaced relays, checked for coldsolder joints, hot spots.. heard there was som resistors (fusible) near the output that could run really hot and cracks in the joints. Worth to check perhaps.
Relay is the classical 1237 right?
Ok, as i suspected very identical amps🙂
Relay is the classical 1237 right?
Ok, as i suspected very identical amps🙂
I have replaced relays in both amps (along with the coil load resistors) but haven't dived into checking for cold/bad solder joints although I have read that can be an issue with these late '80s early '90s NADs (laziness on my part). Both amps are working fine and I use them every day all day long as I'm an old retired guy😀
While there is a delay introduced by the RC on pin 7 (per the data sheet, with 56K/22 uF, that works out to be 1.15 seconds) The actual delay until the relay clicks in also depends on how fast the amplifier outputs settle. Quite possible the outputs of the 2400 may settle much faster than the outputs of the 2600A.
That's an interesting fact. I just assumed there might be an issue because I've never owned a piece of gear that came out of protection so quickly.