Hi all
I was given an 3140 that did not really work.
I was given an 3140 that did not really work.
- fixed transformer hum with varnish bath
- fixed left channel distortion by actually soldering wire to volume pot
- adjusted DC and bias
- recap (except 4 filter caps, need to source)
- there is one capacitor that is not in the SM (see pictures - it is not in the parts list and not on the diagram). Is is named C690 and the original one is a 3.3 µF, 25V. It is just next to the "normal in" socket. What is this? and do I just replace 1:1 and forget about it?
- there is a low hum in the speakers. Is does not increase with volume. It dissapears when pressing the "low level" button. It is from the pre-amp somewhere (is not there when using an external preamp). The pre-main plugs are sensitive to picking up more hum when touched. Not sure if this i normal. Internet (chatGPT) says that pre-amp hum can be due to degraded main power filter caps. Could this be it? They are old and bulging. Also when only present in pre-amp section?
- the VU meters seem to react relatively little. Is this normal? I can balance them with the trim pots and they respond "normally" to music, but I need to crank volume quite a bit to get them past the first 1-2 leds
- What main filter caps should I use? they are 4700 µF, 50 V. I am in Europe. I have a hard time separating one from the other.
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The cap would be here:
And so I'm guessing it is something added in production and possible to couple two grounds together to overcome some issue or other such as stray pickup or radio breakthrough. Just fit like for like for a replacement.
The hum may or may not be a 'fault'. This is an ancient NAD don't forget and they were far from perfect.
VU meters almost certainly normal as the lowest LED is 0.5 watt, then 5 watt and 25 watt, 50 watt and 100 watt. Most listening is done around the 1 or 2 watt level... yes it really is that low... and that is why they don't light.
When choosing caps replace like for like for uF and voltage and choose appropriate types that physically fit. You will have to measure the size and pin spacing and look at what is available.
And so I'm guessing it is something added in production and possible to couple two grounds together to overcome some issue or other such as stray pickup or radio breakthrough. Just fit like for like for a replacement.
The hum may or may not be a 'fault'. This is an ancient NAD don't forget and they were far from perfect.
VU meters almost certainly normal as the lowest LED is 0.5 watt, then 5 watt and 25 watt, 50 watt and 100 watt. Most listening is done around the 1 or 2 watt level... yes it really is that low... and that is why they don't light.
When choosing caps replace like for like for uF and voltage and choose appropriate types that physically fit. You will have to measure the size and pin spacing and look at what is available.
Noted - I will try and find a proper replacement.
Maybe - but I have never heard it in any NAD. And to start, good to know if it could be secondary to bad filter caps or if there are other obvious potential causes.
Makes sense - great 🙂
Yes - but there are sooo many kinds/brands. I realise that caps are a little like religion in audio circles - but are there someone who can recommend something particular in this case? They are 10mm spacing, and I can of course measure myself if they fit physically. But normally 1:1 replacements are smaller, right?
Standard decent commercial grade from a recognised brand such as Panasonic, Wurth, Kemet, Rubycon or Epcos is all you need and you don't even need look for 105C rated for something like this. Modern 85C ones are just fine.
The only way to know for sure is to use a scope and look where it is coming from. Otherwise it is all guesswork really. Yes it could be cap problems but without objective measurement you just don't know.
Thank you - that should be doable. I might be confused by all the discussions about low ESR, ripple currents etc., and all the cap series discussions going on.
When DOES it matter what type/spec/temp rating capacitor you choose?
Makes sense. I will wee if filter cap changes helps. If not I need help from someone with a scope 🙂
It matters more in switching supplies. Linear supplies like these are not very critical and have an easy time of it because the normal current draw from the supply is low. The caps are never stressed electrically. The originals deteriorate through being old and perhaps not the best quality to begin with.
Thank you for helping me out here 🙂
I get 17 hits on Mouser when I enter the needed specs - I need to pick something - do I go for long "life", high "ripple current" or other parameter?
Mouser search
I get 17 hits on Mouser when I enter the needed specs - I need to pick something - do I go for long "life", high "ripple current" or other parameter?
Mouser search
The simple answer is that any reputable replacement is likely to be far better than the old originals. The NAD won't come close to having to worry over these things.
Having said that, all the things you mention are worthwhile but deciphering how they are measured takes time. The way the numbers are presented and the test conditions often vary between manufacturers. Cap lifetime for example is usually quoted at max temperature and this increases massively with each 10C drop. So a 1000Hr 85C cap might seem poor but in the NAD it will be fine for decades of use.
Having said that, all the things you mention are worthwhile but deciphering how they are measured takes time. The way the numbers are presented and the test conditions often vary between manufacturers. Cap lifetime for example is usually quoted at max temperature and this increases massively with each 10C drop. So a 1000Hr 85C cap might seem poor but in the NAD it will be fine for decades of use.
True. On the other hand, a 105C rated at 5000h will have 20x the lifespan and the additional cost is often very small.
I fixed my humming 3150 some years ago by fitting new main filter caps so chances are good this is your problem. Also replaced quite some resistors in the power amp section as they were unstable and way out of spec, causing intermittend offset problems. I remember a 22k measuring twice that.
I fixed my humming 3150 some years ago by fitting new main filter caps so chances are good this is your problem. Also replaced quite some resistors in the power amp section as they were unstable and way out of spec, causing intermittend offset problems. I remember a 22k measuring twice that.
Update: I took a leap of faith and ordered these: Cornell Dubilier - SLPX series
Hope I am not being an idiot 🤣
Anyway - hum did not go away.
Hum comes to speaker as soon as right channel “pre out” positive terminal is connected to right channel “normal in” positive terminal.
I tried with a shielded cable instead of the steel plug. No change.
It sounds like a ground loop hum, like an amplification of the remaining transformer hum.
Does this info point anywhere? Is there ground connections to check or something?
Hope I am not being an idiot 🤣
Anyway - hum did not go away.
Hum comes to speaker as soon as right channel “pre out” positive terminal is connected to right channel “normal in” positive terminal.
I tried with a shielded cable instead of the steel plug. No change.
It sounds like a ground loop hum, like an amplification of the remaining transformer hum.
Does this info point anywhere? Is there ground connections to check or something?
There seems to be so many NAD's out there that you can buy full Re-cap kits for them. NOPE !
https://80s-hifi-classics.com/en-in...Jfyisd3FjIcYrLOxPzmr3CWFn9srOB3B8NJbaovMSM5d2
What a rip !
50V PS caps ! 63V , at least.
- 63V @ 6800uF would work and fit the NAD. 25mm X 45mm is the target size for 10mm leads.
- all the other electrolytic's , I went up one voltage range if the size was close. All Panasonic/Nichicon caps.
- NP signal caps / DC blocking caps. = Muse (nichicon) , went up one voltage range as the new caps are usually smaller.
-All the Mylar's were perfect , nothing to age. Ceramics were off ..... replace the critical C619,615,613 , I replaced all pF compensation caps
with silver mica ones - no tempco + 2% tolerance.
Re-grease the output trannies , and Vbe.
Hmmmm ... NAD is a bootstrapped VAS with a singleton input stage. The bootstrap cap should be HQ ,,higher voltage - low ESR.
OS
https://80s-hifi-classics.com/en-in...Jfyisd3FjIcYrLOxPzmr3CWFn9srOB3B8NJbaovMSM5d2
What a rip !
50V PS caps ! 63V , at least.
I just re-capped two amps.
- 63V @ 6800uF would work and fit the NAD. 25mm X 45mm is the target size for 10mm leads.
- all the other electrolytic's , I went up one voltage range if the size was close. All Panasonic/Nichicon caps.
- NP signal caps / DC blocking caps. = Muse (nichicon) , went up one voltage range as the new caps are usually smaller.
-All the Mylar's were perfect , nothing to age. Ceramics were off ..... replace the critical C619,615,613 , I replaced all pF compensation caps
with silver mica ones - no tempco + 2% tolerance.
Re-grease the output trannies , and Vbe.
Hmmmm ... NAD is a bootstrapped VAS with a singleton input stage. The bootstrap cap should be HQ ,,higher voltage - low ESR.
OS
Those look fine to me 👍 The data sheet says the ratings are at 'full load' which I take to mean full working volts applied and max ripple current flowing and max temperature.
The life of a cap is a bit like a bulb. If you run a 12v bulb at 12v it might last 1000 hrs. Run it at 13v and it might last 300 hours, at 14 volt perhaps only 60 hours. Going the other way and it might last 2000 hours at 11v and 6000 hours at 9v and 30000 hours at 8 volts.
Do you see? That 3000 hour life at full load and full ripple and at 85C will be many many times more than it sees in the NAD. The temperature will be more like 45C and the ripple current and few hundred milliamps most of the time. They will last for decades, 30 or 40 years at least.
The service manual for 3140 at Elektrotanya shows neither of these terminals.
Could you post a link to the actual schematics of your amp?
That implies the problem is in the preamp section. Check the +/-25V rails for ripple.
I can read that schematic. NAD is a bootstrapped "super-pair" VAS. I wonder if this is why the NAD designs
are so revered - and expensive , (250 to 500$) for old vintage NAD's on eBay. wow !
OS
are so revered - and expensive , (250 to 500$) for old vintage NAD's on eBay. wow !
OS
It is definitely there 🙂
As standard on these integrateds there is a pre-out and a main in, which you plug together to run as an integrated amp (sorry if I am stating the obvious). As mentioned in an early post, hum is not present when using an external pre-amp.
See pic of diagram and link included
https://audiocircuit.dk/downloads/nad/NAD-3140-int-sm.pdf
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What is 25V rails and can I check this with a standard multimeter or do I need a scope?
Sorry - on a steep learning curve here 🙂