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 actually had a number of these 7150 series receivers, this particular unit was a "to be looked at" as it was NOT WORKING CORRECTLY - see the FULL details below.
Like many NAD amplifiers, these 7155 receivers surprise many. They use a design which results in an amplifier that easily produces far greater audio output than the listener could be expecting.
But the 7155 is not just an audio amplifier but has a very competent tuner and a widely acclaimed Phono system for your turntable, which user loading and capacitance settings and it will handle Moving Magnet (most common cartridges) AND Moving Coil.
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!
My wife says "for goodness sake, get rid of that mountain of gear" so them's my orders ... out they all go.
This equipment does have a couple of 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 and do not "gloss over" any issues I might discover!
I love details, lots of them, but it has been suggested I summarise the equipment condition FIRST and then go into the details later .... so...
NAD 7155 SUMMARY:
Overall, electronically the 7155 Receiver is in really good condition.
Power Amplifier is great
Preamplifier is great albiet with a noisy Volume/Balance concentric control
Tuner PCB has a problem on FM only - no tuning! Great display but the Tuner is not changing frequencies
I can easily ship this equipment anywhere around Australia (INCLUDED in the asking price)
NAD Stereo Receiver
Model: 7155 (B1 Australia)
Made in Japan
Released 1984 ~ 1985
Serial #209490
Dimensions: 435mm x 106mm height x 390mm
Weight (unpacked): 9Kg (packed in a box) 11Kg
Fitted with a standard Australian GPO plug (2 pin NO earth) - I have checked the AC input lead and this does indeed appear to be a non-power earthed system as the lead, wiring and solder joints to the front switch are original and have not been tampered with.
BASIC SPECIFICATIONS:
These manufacturer specifications have been obtained from the Service Manual. I found some of the information online to be confusing, with many different figures thrown into the air by some users.
Power output 55W RMS per channel into 8 Ohms
Now this can be very deceiving when it comes to NAD equipment! These amplifiers have very high dynamic-headroom ratings and are able to drive very low load impedances (such as 2 ohms) at surprisingly high power levels without clipping or other distortion.
The "real life" clipping-output ratings (across the audio spectrum 20Hz ~ 20Khz) are:
65 watts into 8 ohms continuous
These are all your industry standard RMS ratings but if you look at the dynamic power ratings, they are:
100 Watts into an 8 or 4 Ohm load
130 watts into a 2 Ohm load
In real life this means that if your music has a wide dynamic range and at times a heavy demand is placed on the audio output section to delivery much greater power, the 7155 easily takes it in it's stride without falling into a horrible distorted mess.
But wait! there's more ...
This 7155 has bridging capabilities (switch on the rear panel which allows you to create a HIGH OUTPUT MONO amplifier)
When bridged you can expect 125 Watts RMS OR 250W Dynamic power into a standard 8 Ohm load.
OFF, A or B or A+B speaker switching at the front panel
Speaker outputs are all screw down type and will NOT work with a banana plug (all plastic at the back)
Frequency response (3dB points) 20Hz ~ 20Khz
Damping factor: 100
Maximum Total Harmonic Distortion (THD) at full power into 8 Ohm load: 0.03%
Preamplifier ~ Power Amplifer U linking (you can use just one section or splice in some external equipment if that is your desire)
Inputs: AUX, PHONO, TAPE 1, TAPE 2
Separate switching for audio feed to an external tape machine (I used this with a Revox A77 at one time)
Sensitivity (these figures are the input required to achieve FULL power output):
Phono (MM) 2.5mV
Phono (MC) 0.15mV
AUX 150mV
Bass & Treble rotary controls provide +/- 7dB adjustment with centre frequencies of 100Hz and 10Khz
Infrasonic filter switch provides -3dB cut at 15Hz
Audio mute control kills your audio output level by -20dB
COSMETIC CONDITION:
In a nutshell, Wow factor is 9/10!!!
I used this 7155 until about 15 years ago, then it had an issue (see below for details) and I put it back in workshop "must look at one day" area! Never went back there until today!
Never abused, always used carefully but nothing lasts forever!
I still use another 7155 series receiver everyday here in my little workshop/office and they are usually wonderfully reliable systems, I am always testing other gear using my own 7155 and it simply doesn't miss a beat.
The case is straight and true, no dropping has occurred (although it is fairly heavy, carry with care!)
The sides have one light scratch on each side, which does NOT break through the outer coating - it is not a serious blemish.
The top of the case is wonderfully clean and clear of any marks.
Front panel is in very good condition with no damage to the labelling (none have rubbed off partially or completely)
On the front panel there is a serious scratch right in the centre, up on the top edge (see the photograph) which was caused by putting it away in the backroom not carefully enough!
Rear panel is substantially clean but there is an engraved ID of a previous owner (before me). The ID is just a Drivers Licence number with no name). The location of this engraving is on the rear, top left corner near the AM antenna.
Base panel is clean sheet steel, no corrosion signs at all (always look underneath an amp to get clues as to how it has been treated)
All knobs and buttons are correct and accounted for - none are missing!
All rear panel sockets/switches are clean and shiny, particularly the Phono RCA's - it is extremely important to keep these very clean due to low level audio here.
Front panel display is clean, clear and unscratched.
Display is the standard blue/green fluorescent type and the brightness of the display is very good.
I took a look inside and it is very clean, substantially dust free and with no signs of component distress (see more about this in the testing section below)
Dare I say it, cosmetically this 7155 is in very good condition considering it is approaching 40 years old - just that scratching on the front centre area (up the top) that spoils it from getting a 9/10
TESTING:
Ah this is the part that really matters....
Gathered together some nice audio sources, Marantz CD player and a Technics turntable running with a SHURE VI cartridge. Multimeter at the ready!
Both the top and base covers are off, I want to look at the condition of the boards, any mods or repairs and watch out for failed or failing components.
Two large PCB's, the upper being the Tuner/Display etc and the lower is the preamplifier/power amplifier and masses of switching!
The two AC power transformers both sit tucked away on the left hand side of the amplifier chassis. Top of the primary AC transformer and the Tuner RF shielded section over on the far right have oxidisation. I don't know why because my other 7150 series receivers have exactly the same thing and yet they have not "seen" water or high humidity - strange.
The boards (topside) that I can see look clean, substantially dust free although I cannot see a large part of the power amplifier board as it is covered by the tuner/display board.
Underneath I can only view the preamplifier/power amplifier board and this is clean and doesn't look to have been worked on at all. The output transistors look like originals with that nice even (old) white silicon grease being undisturbed. Devices fitted are 4x 2SB863 & 4x 2SD1148 (T is the manufacturers logo) - none show any external signs of stress. If these needed replacement in the future, they appear to be readily available online for around A$25/pair of 2SB863/2SD1148's
The main filter capacitors (10,000uF 50V 85C MARCON) look good, no bulging or leakage (just that horrible glue they used to secure them to the board!)
Actually while looking very closely at these (and its not easy due to the location of them) I did see some dust collected on that lower board - a good "blow" might be in order or if you are very adventurous, lift off the top board and give it a decent clean up.
Time for power up!
Power ON-OFF switch operates correctly and locks in place as it should.
Fluorescent display comes alive! This is normal, no matter which input source is selected this display should light up - it is like your ON-OFF lamp (which there isn't one anyway)
Protection relay operates as normal after 1 ~ 2 seconds (always good to hear that little "click" just after turn on.
Prior to connecting my precious Tannoy loudspeakers, I checked both outputs for the dreaded DC voltage being present, none at all thank goodness! Never ever 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.
No issues at all on either channel (no AC or DC of any significance), so I confidently connected my 8 Ohm test loudspeaker system.
I have removed the U links between the preamplifier and power amplifier to check just the preamp first.
TUNER (AM-FM)
All controls functions as they should (scanning up/down, auto lock to signal, AM-FM selection and the memory selection buttons)
AM stations are loud and clear, just using the built in "loop antenna" at the rear.
The display is showing the correct frequencies and signal strength
FM though is NOT working correctly!
The display does show the changes in frequency selection and on auto it just scans looking for a signal FOREVER!
The audio output is just "white noise" or FM "hiss" with no stations being heard and nothing indicating on the display regarding signal strength.
I had the cover off and although I didn't intend to diagnose further, curiousity got the better of me! Following the Service Manual, I checked the tuning voltage - Yikes! no good at all. Sitting on 1.3V no matter which frequency is "dialled up". This tuning voltage comes from the TC9147 chip via a 4558 Op amp. I have not followed the tuning voltage back to the chip but instead checked the Vdd of the chip - 4.95V, great! So at least the digital tuning chip is getting the correct supply voltage.
As I am under "time pressure" I have not gone further with this but that TC9147 would be a good starting point, see what it is putting out to those Op amps and go from there.
So there you have the tuner, AM sounds great (as good as AM can be) but FM is just a lot of hiss!
INPUTS (AUX, TAPE, PHONO)
Using my CD audio source I checked the higher level inputs, AUX and TAPE - NO issues at all, great sound!
I also checked the preamp with no audio input at all, dead as, no background noise at all and you wouldn't even know it is turned on!
I also operated the various filters/controls such as Bass, Treble, Loudness, Mute and they all perform as they should - without rotational noise.
The concentric Volume and Balance control also operates fine BUT it is a bit noisy in places - this needs a clean (switch cleaner spray) if it is not sealed (I don't actually know and I cannot see it as it is buried inside!) otherwise just put up with it or replace the pot. This noise only occurs when you are moving the control, not when you have selected the setting you wish to use.
Now this pot is well buried behind the front panel and I am not about to dismantle the whole front section to get to this pot so I have made no attempt to clean it.
Phono input uses a special "plug in" card (72-2153-0-2). I have always found these to be a pain! They fit onto a main PCB molex style connector and are not locked in place except for the clip on the motherboard connector. In my view this is really poor design by NAD - such low level signals with great potential for noise introduction. I am talking about the physical setup, the design on the other hand is very good and is based on all discrete active devices. Many NAD (and other) users praise the sweet quality of the phono inputs in these 7155's.
Played a bit of vinyl using a MM cartridge, great great great! Nice sound as expected. I don't have an MC cartridge to hand so I was unable to check this except I did change the setting on the rear and used the same MM cartridge, audio loses a lot of "highs" but more surprising, the level doesn't change very much at all - I was expected it to be much lower louder as this is the most sensitive input for the amplifier - but then it was loaded very poorly so perhaps this is normal, perhaps not. If you just stick with MM cartridges (most do) then everything is fine anyway.
I physically "wiggled" the Phono board while playing music and no hints of bad connections at all - Phew! However the noise of the volume control becomes really obvious when using the Phono input, due to the low level signals - if you are into your vinyl then it is probably a must to get this pot sorted out.
In summary, the preamplifier is looking damn fine with the exception of the FM Tuner having issues. Any other issues I have noted are pretty minor.
Now for the Power Amplifier (lets Get Together and join the preamp with the power amplifier with the U links)
Again, the techie side got the better of me and I measured the main supply rails to the amplifier - 48.1V across each filter capacitor. In my opinion that is a bit close for comfort with a 50V electrolytic and while sorting out the Tuner issue on FM and that noisy pot, it might be a good idea to upgrade those capacitors to a higher working voltage if they will fit (its pretty tight around those caps). This is only a suggestion, AT THE MOMENT THERE IS NOTHING WRONG BUT ...
Fantastico! I have full power, clean audio on both channels of the power amplifier! At risk of really annoying the neighbours I turned it way up in volume and no signs of issues at all - just great punchy NAD audio - yes, Guns n Roses again because I am checked a lot of their music at the moment!
I will be running this 7155 continously each day until it has found a new home, I want to check the heatsink from time to time and the overall medium term sound.
I then switched to a non audio input and checked for background hum, damn this amp is very quiet with just the very faintest of 50Hz hum way way way in the background with the Volume turned fully clockwise.
Market prices for a used NAD 7155 range from A$230 ~ A$400 and keeping in mind the two issues above (NO FM & Noisy Volume/Balance) plus the fact I will ship this equipment anywhere around Australia FREE OF SHIPPING COSTS (tracked and fully insured), I believe this asking price is fair and reasonable.
