Author Topic: NAD S300 Amp Question  (Read 184 times)

0 Members and 1 Guest are viewing this topic.

Offline uslrsTopic starter

  • Contributor
  • Posts: 37
  • Country: gb
NAD S300 Amp Question
« on: January 23, 2025, 11:23:12 am »
Hi All, I've been doing some repair work on a NAD S300 amplifier and am struggling to understand the function of the plus and minus drive lines with respect to the operation of the gain stage and power amp - J315/J321 on the gain stage and J515/J521 on the power amp.
 I'd really appreciate a basic explanation of how the circuit functions in relation to these signals and how they relate to/influence the input signal. Many thanks.
« Last Edit: January 23, 2025, 11:28:45 am by uslrs »
 

Online coromonadalix

  • Super Contributor
  • ***
  • Posts: 7113
  • Country: ca
Re: NAD S300 Amp Question
« Reply #1 on: January 23, 2025, 01:10:25 pm »
on one page  you have the power amplifier section,  drives lines are just a name to the driver section of the second page


there was not enough place to put all the schematic,  drive line could be called pre-driver section etc ...

the "output" line is returned to the op amp  TL074, who provide output feedback to the pre-driver section, and another op amp section  for the error detection ...

q501 is your Bias transistor,  it should be placed on the heatsink ?  or at least be in contact with
« Last Edit: January 23, 2025, 01:16:53 pm by coromonadalix »
 

Offline uslrsTopic starter

  • Contributor
  • Posts: 37
  • Country: gb
Re: NAD S300 Amp Question
« Reply #2 on: January 23, 2025, 02:46:22 pm »
Thanks coromonadalix, the gain stage is on the main board with the power amp separate, hence the connector identification. This pair is duplicated for the other (right) channel.  I think I understand your point to mean these 'drive signals' are simply interconnections between the main and power amp boards and the title 'drive' is simply an identifier.  That makes more sense now although I'd like to understand the circuit operation better before the complimentary driver pairs (Q507/509, Q511/513, Q515/517, Q519/521).  Am I right in thinking the primary purpose of the op-amps is to reduce inherent noise (i.e. to improve THD)?
« Last Edit: January 23, 2025, 02:49:40 pm by uslrs »
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf