Hi to All ! My first post ,,,
I have a stock Nap160 CB ( was recap ) . If I take the standing current measurement I read 100ma and 95ma for 36.9vdc . At 0r22 resistor 7.5mv both rails . The power transistors are naim 002 . I take my measurement at the +40v rail using an digital ammeter.
Other then a recap ( value for value ) the amp is in stock condition . offset voltages are 10mv and 20mv .
Comparing to the traditional 33-35ma, 100ma seem very high .
What can cause those NAPA pcb to have such high values ?
thanks for any help ! Nicolas.
Posted on: 11 March 2017 by Huge
I'm not sure of your measurement technique (adding resistors into the power rails can destabilise some amps), but superficially 100mA does seem very high, particularly as Naim traditionally used a quasi-complementary output pair with a particularly low quiescent current setting.
For a definitive answer, you need the service manual, or someone who knows the service procedure for this particular type of amp.
Posted on: 11 March 2017 by stutgart
Thanks ! After the recap I was scared by those figures so I lower them to 50ma .. I will put back to were they where ! the amp sound fine to my ear but !!!! it is very old .
About measurement technic I have only done an ampere measurement , so opened the +40vdv put the ammeter in series . the other measurement was made at the emitter resistor or22 .
Posted on: 11 March 2017 by stutgart
Hmm there is a lag of response in the forum ,, is all message filtered first ??
Hey Huge thanks , yes 100ma seem high , I have just opened the +40vdc rail and put an ammeter to read the current ( no load no input ) 20 minute warming time . I have used the same technic for my Nap250 those were normal reading of 33ma both channel .
Maybe the 160 is different .. will keep it like that .. cannot get to 35ma using the trimmer .. strange ,, it is a standard NAPA pcb .
Posted on: 11 March 2017 by Darke Bear
100mA is very high - it should be around 25-30mA quiescent current biasing each output stage on the NAP160.
But I don't think this sort of thing is meant to be done by the customer. Too much and thermal runaway, too little and it sounds harsh - I used to tweak until it sounded best and that turned-out to be 25mA or thereabouts.
DB.
