EQUIPMENT HISTORY:
Everything I am describing below is IMPORTANT, read it please!
This amplifier is part of my "collection" of all things audio, both professional and consumer gear. I personally don't mind a decent NAD piece of gear and this particular unit was a "to be looked at" as it is NOT WORKING - see the FULL details below.
These 3140 amplifiers are often praised for their audio qualities and the ability to handle "peaks" with a dynamic range that often surprises many. They use a design which results in an amplifier that easily produces far greater audio output than the listener could be expecting.
This amplifier is designed to supply 40W Audio power (RMS) per channel into a "normal" 8 Ohm loudspeaker system but on loud passages/peaks, this amplifier easily delivers 80W output on each channel - the idea being that when listening to music with a wide (demanding) dynamic range, this amplifier will sound great no matter if the audio is of a low level or suddenly jumps up in level considerably, the 3140 takes it all in its stride. Other amplifiers, when pushed hard, will spit the dummy and sound absolutely horrible (distortion).
I have over the years collected together a LOT of quality audio equipment due to my business activities in pro audio post production and general electronics but the day has finally arrived when it must be shown the door!
My wife says (quite rightly) "for goodness sake, get rid of that mountain of gear" so them's my orders ... out goes all the equipment.
This NAD 3140 does have issues, and it is extremely important that the complete description is read in full.
THE CONDITION OF THIS EQUIPMENT IS CLEARLY STATED BELOW, BOTH COSMETICALLY AND ELECTRICALLY
There is no warranty, there are no returns - but I am very thorough in my descriptions and do not "gloss over" any issues I might discover!
Even if the new owner doesn't feel up to repairing or having this equipment restored, it is still a great source of some very hard to find parts - a component "farm".
NAD 3140 Stereo Amplifier
Model: 3140
Made in Taiwan
Serial # 3425108
Released to market 1988~1989
Frequency response: 20Hz ~ 35Khz
Power Output (8 Ohm) 40W RMS per channel or 80W RMS per channel 4 Ohm
+3 dB of dynamic headroom is available, which means the 3140 is capable of delivering over 80 watts per channel (8 ohms)
THD (at full power): 0.02%
Damping Factor: 50
Signal/Noise Ratio: Phono 76dB Aux 95dB
Inputs provided:
2x PHONO
Phono 1 has a fixed input impedance 47K/100pF
Phono 2 has a user selectable input capacitance (100/200/320pF)
Both Phono inputs are designed for commonly used MM cartridges (Moving Magnet) and there is NO user switch for MC cartridges (unlike other NAD amplifiers)
TUNER
AUX
2x TAPE
Dual speaker outputs (A & B)
The power amplifier has 2 different inputs, to which you can connect the Preamp output directly or via external audio processing equipment
Power amplifier input LAB is wide band and quite specialised in that it is designed for use when undertaking laboratory test measurements
Power amplifier input NORMAL has some "out of audio band" filtering to reduce the possibility of intermodulation distortion.
FRONT PANEL:
Speaker select: A,B,OFF or A+B
Bass
Treble
Speaker EQ (User selectable 45 or 70Hz 12dB BOOST!)
SPECIAL NOTE: This speaker EQ can be useful if your system uses long-throw woofers (generally larger than 8" diameter) but BEWARE if using this feature on smaller loudspeaker systems, it is easy to overdrive the woofers in particular - read the User Manual about this.
Mono (ON or OFF)
Tape Monitor (ON or OFF)
Input select switch
Loudness (ON or OFF)
Volume & Balance (Concentric control)
LED's indicate POWER ON & SOFT CLIPPING & SLC
SLC is a circuit designed to compensate for excessive resistance in your speaker leads i.e using loudspeaker cable with thin conductors.
Dimensions: 420 x 110 x 320mm
Weight: 9Kg (packed weight closer to 10Kg)
COSMETIC CONDITION:
ISSUE #1
I cannot find the top cover! Yeah, this is pretty basic stuff but for the life of me it is missing in action so at this stage, the amplifier is supplied WITHOUT THE TOP HALF OF THE CASE
ISSUE #2
I noticed the AC lead (fixed) sheath has a couple of nicks in it - the wires are not exposed but this really means (for safety sake) that the lead be either replaced or shortened, cutting out the small length which has the "nicked" sheath.
First glance, the overall front and rear panels are not too bad at all.
The colouring used in this model is that NAD weird grey/greenish colour with slightly yellow screen printed labelling - not it's not dirty, it really is a yellowish colour.
Front panel all labelling is clearly readable, not partially rubbed off at all.
All knobs are present and undamaged EXCEPT the first knob (Speaker selector) which has a little mark on the front, near the knob white pointer.
One small mark in the panel paintwork right next to the NAD logo on the left hand side.
Power output meter window is clean and not scratched
Rear panel is very similar, meaning the labelling is clearly visiable with no rubbing to the screen printing.
All connectors are clean and shiny, including the preamp-power amp U links.
Speaker output connectors are the spring loaded "push the wires in" type, all are clean and working fine.
Slide switches at the rear are all fine physically.
NO signs of a "drop" in other words, the steel frame is not bent or dented.
NO chassis screws are missing.
All feet are present
Base panel is fine, although I can see signs that water must have been present once (before I got it I believe although I did have issues with water while it was in storage but this amplifier was placed up fairly high anyway)
This amplifier was in every day use until about 10 years ago (!) when it suddenly stopped working. As I had many many amplifiers we could use in our business (general audio monitoring purposes) this NAD 3140 was put to one side "I will look at that later" Hmmmm, at least 10 years on and still I didn't get to look into the issue!
Next I take a look inside ...
Overall, the assembly of components on the PCB is a bit dear I say it "Taiwanese like" with components leaning this way and that and not so neat and orderly as I have seen from other manufacturers of this period although it is better than 7150/7155's I have seen!
Dust levels are low but it is not pristine clean. I also removed some dust so I can undertake my evaluation more easily.
I especially was on the look out for any tell-tale signs of water or dampness (rust) as I noticed this on the base plate. No rust or board substrate damage observed at all, if anything, the input selector switch has a little rust on the topside only.
No electrolytics are bulging or showing signs of stress.
No substrate (single sided board) burn marks and no component shows signs of excessive heating.
I also notice that the board has been worked on previously by 'someone", certainly not me or a member of my staff but there has been work around the power output transistors and the power supply regulator. The work looks to have been performed to a reasonably professional standard.
Read more about this work further down ...
Extensive fusing inside the case, NO fuses are "blown"
TESTING:
Yeah, this is what everyone wants to know! What does it sound like?
This amplifier has the preamplifier and power amplifier linked via a U link on each channel, nice and easy to split the audio system for testing.
I used a separate NAD 7150 as my test power amplifier when checking the preamp and conversely, used my test 7150 to provide line level test signals for the power amplifier of this 3140.
HERE WE GO...
Plugged it in, on comes the Red front panel LED - all good.
Also the SLC and Soft Clipping LED's come on, I had activated these at the rear panel so all good once again
You won't hear that reassuring "click" from a protection relay, there isn't one! The protection system is totally electronic and silent.
PRE-AMPLFIER TESTING
ISSUE 3:
There isn't any audio at the Preamp output connectors! Doesn't matter which input was selected, zilch nada zero! So there is an issue with the Preamplifier.
Let's move onto the ....
POWER AMPLIFIER:
First up I checked both loudspeaker outputs for any dreaded DC voltage being present, none at all thank goodness! Never should you see DC voltages at your amplifier speaker outputs because if you connect your prized speakers to such an amplifier, your speaker voice coils suddenly turn into little heaters and then go POOF! This is something you must prevent at all costs - ALWAYS check an unknown amplifier for DC at the speaker outputs before connecting your speakers.
ISSUE 4:
Next I sent test audio into the NORMAL input for the power amplifier, yeah! I have audio, well don't celebrate yet ... one channel is good, the other is not so good (distorted when driven hard)
Ok, although I am not supposed to spend a lot of time faulting finding this equipment, I decided it wouldn't take long to check and adjust the DC offset and Idle currents, using the Service manual as my guide.
DC OFFSET
Left measured at 90mV - adjusted back to 0V as per the service manual
Right measured at 95mV - adjusted back to 0V as per the service manual (tricky as the trimpot track seems a little dirty)
IDLE CURRENT
Both channels were much too high (above 100mV) at the test points, readjusted the trimpots to as close to 6mV as I could achieve
So both adjustments were performed without any drama's, then I noticed a couple of things ...
The output transistors (both channels) are NOT originals, they should be MJ15003/MJ15004 but instead are SANKEN 2SA1215/2SC2821 pairs! So at some time in the past someone has decided the original output transistors needed changing to a different type.
I then fired up the amplifier again and double checked the power amplifier audio output quality...same as before, one channel is fine but the other becomes distinctly distorted, especially when driven to higher power output.
So at this stage we have an amplifier with no preamp audio signal and just one channel working fine - not a great start!
Back to basics, look around the power rails. I took a sniff around the DC power supply, starting from the bridge rectifiers/filter capacitors and then the regulators (discrete transistors not prepackaged 78 or 79 series regulators)
Primary DC supply (power output supply) measurements: 44V +/- which is a little lower than the design 50V +/- but shouldn't be an issue
ISSUE 5:
Next I took at look at the 25V + & - rails and here is an issue, NO DC at all on either rail - no wonder the Preamplifier is dead, there is no DC supply. For example, at the Q804 collector & emitter I have 0V
The active devices are all BC556/BC546, BD139/BD140 all "ordinary" commonly available devices
At this time I also can see signs of previous work being undertaken around the DC regulator area and Q808 has been changed for some reason.
Q808 should be a BD140 but instead is now a 2SB536 (Why is beyond me, the BD140 is as common as muck)
Q804 remains a BD139
The past work around this regulator area on the PCB is easy to see but it is not messy, so they did a good job but why were the components changed to different types?
I am not suggesting that Q804/Q808 are faulty but simply that although I have raw DC going into the regulator circuit, I measure no 25V DC at the outputs and something is definitely amiss around Q808, with that transistor type change and it becoming quite hot in a short time of operation.
I have included a schematic "snapshot" of the relevant area, with the two transistors highlighted in red.
A full (readable) Service manual is readily available for this NAD 3140 online or I can supply on a CDr if the new owner prefers (35 pages, a bit much to print as a hard copy)
SUMMARY:
So here we have a 3140 with a dead preamplifier as a result of no supply voltage to this section.
The output section is only providing one good channel, usual (but not always) suspect is the output pair - DC rail looks fine to the Power Output section.
AC lead input cable needs a minor repair or replacement.
Top case is missing! Yes this is quite a drawback but if the new owner has a "spare" top case then all is good OR just use the 3140 as a parts "farm" for other NAD amplifiers.
If being restored or even having parts removed, this must ONLY be undertaken by a capable professional technician, personal safety is of paramount concern and the voltages present inside can cause death if not treated with knowledgeable respect!
