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Modified Naim NAP140 Schematic
Modified Naim NAP140 Schematic
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Old 22nd February 2012, 04:50 AM   #11
jazzclassics is offline jazzclassics
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removed C5 from on channel (refer to the above schematic). The sound becomes cristally clear. I can hear much more fine tunes of very high notes. Sadly, later, I found that the head sink becomes very hot. Cannot touch it with bear hand. Power off, Cool down, and power on again, the quiscent current seems not stable. It could jump from a few mA to hendreds of mA in few second, which seemed to be triggered by the input signal.
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Old 22nd February 2012, 01:47 PM   #12
carlmart is offline carlmart  Brazil
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I don't think you can remove that capacitor. You can change the value, but not zero it.

Or you can do what Douglas Self suggests on this book, using two transistors, but there will a capacitor there anyway.
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Old 22nd February 2012, 02:05 PM   #13
east electronics is offline east electronics  Greece
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your are on a very wrong road my friend ....

miller caps provide stability and determine the usable frequency expand for a transistor...removing the capacitor will let free the circuit to oscillate....ideally you could locate the source of oscillation and eliminate it ... but this will only happen in a an ideal world with ideal transistors ,loads and so on

this can also be pcb related issue ...
then again removing it or lowering the value is a thing that can only be verified by instruments and someone that knows also how to use them

obviously simulators will also not tell you much about your pcb or load or cables and so on
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Old 23rd February 2012, 04:57 AM   #14
jazzclassics is offline jazzclassics
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Yes. The capacitor is critical to maintain the stability. However in some design, JLH class A for example, this cap is non-exist. That means some circuit is inheritantly stable.
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Old 23rd February 2012, 05:04 AM   #15
jazzclassics is offline jazzclassics
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I later on tried 4.7pF for C5, but that seemed worse than having C5 off circuit. It sometime gave audiable resonance noise from the speaker. According to the simulation, the C5 is a bottle neck that slow the amp down, ie. lead to low slew rate. Any idea how to modify the circuit and make it faster? The Naim design seems good for the turn table era, but not so good for the modern digital music sources. This is only my own opinion...
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Old 23rd February 2012, 11:47 AM   #16
homemodder is offline homemodder  Portugal
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Increase the LTP tail current to around 5 or 6 ma. Next increase the value of the degeneration resistors to 100 ohm and use correct value of compensation where the amp is stable.
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Old 23rd February 2012, 12:41 PM   #17
carlmart is offline carlmart  Brazil
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I think you could try the two-transistor correction Douglas Self applies to stages like that on the Naim.

Basically you would have to add a transistor and cut some pcb tracks, but it shouldn't be too hard.

Be noted that this doesn't eliminate the Cdom capacitor, which as Sakis said provide stability.

Perhaps you could try this mod on the simulation first and see what you get.
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Old 21st March 2012, 02:05 PM   #18
jeffreyrow is offline jeffreyrow
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Anyone has the schematic for the nac 72 switch on relay board, 325/7.....much appreciated
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Old 21st February 2016, 06:34 PM   #19
windchimeman is offline windchimeman  United States
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Default Hi

Hi everybody

This is my first post in such a great place . The reason that i am posting here is that i just received two NAP-140 clones that i bought .And i am thinking to connect them to a switching power supply +-36V . adjustable to 40V like the one here:SMPS300RE 36V Dual Voltage 300W 230V Power Supply Connexelectronic | eBay

Has anybody used similar PS in AB class Audio amps?
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Old 6th February 2019, 10:23 AM   #20
domenico80 is offline domenico80  Italy
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the 140 is an honest amplifier without any ideas for wanting to excel between the audio amplifiers.
But it lends itself to several rather simple interventions.
I was thinking of modifying the input stage using a dual j fet cascode-loaded
a trimmer on the junction of the input torque emitters to better control the offset
delete the cap IN
use two pairs of power final transistors per channel
feed everything at 50 volts
change drivers with MJE 15000 series
if you want you could also use power transistors P and N instead of only N

Last edited by domenico80; 6th February 2019 at 10:25 AM.
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