The Person:
Hi to you, my new masters!
I've had an interest in HiFi for a lot of years, but the money have been prioritized elsewhere.
Not new to electronics in general and have a basic understanding in how all this works.
This is my first tear down however, and attempt to repair an amplifier so I need someone to hold my hand through this.
I'm from Sweden and lives in Gothenburg, which can be good to know when recommending components.
The Problem:
My NAD C372 have been in my possession for its last 7 years.
When I bought it it made a low noise, like tearing cloth slowly, when cold.
After like 5 minutes it was completely gone.
Now it never goes away. Always there, lurking in the silence.
The Mission:
I hope to get some guidance not only to fix this amp, but to upgrade it too.
Budget is hard to say when I don´t know what to change and to what yet, but let's say 150€-200€.
I´ll try to take pictures on things as I go, not only to make it easier for others to follow but because it's a lot more fun to read posts with pictures in them.
With a good help from you this can serve as a guide for future DIYers, with my lack of skill it can serve as a warning.
Let's hit it and see how it turns out!
We'll start with the Main Board and the PSU. Later on I want to have a look at the Amplifier boards.
My first approach was to open it up and look for leaking or bulging caps.
I found a lot of brown gunk around 4 bigger caps (bulk caps for rail B and C: C734, C735, C748, C749).
Since the noise is in both channels, the PSU seems like a plausible source of the noise in my noob head.
This is where it all started. Sourcing caps and info on what kind of caps I needed, aka opening Pandoras box...
I had a lot of problem with the small footprints and the 105C rating. The C372 is known for running hot so no 85C for me please.
Most HiFi-caps were too big since rail B and C clearly was designed by some engineer sharing closet with his wife,
while the main rail A was designed by previous mentioned wife.
After 3 days and 2 nights without sleep I ordered the best I've found:
2 x Vishay 2200uf 50V 105C with 7,5mm pitch (part# 2222 048 61222)
2 x Nippon Chemi-Con 1000uf 160V 105C with 10mm pitch (part# EKMQ161VSN102MP40S)
Cost: 20€
This is where I couldn´t help myself. I took another look into that box and soon realized that it's more fun to upgrade something than to repair it.
Invest money instead of just spending it so to speak.
I have no idea if these caps will solve my problem since it could be more bad caps.
I've also learned that not all caps bulge when they're bad, and that the brown stuff might be glue.
My idea here is to change most/all of the electrolyte caps (all branded Jinghai) to newer and better ones since they're all old.
(Are Jinghai good btw? In the computer world Chinese caps are not that welcome...)
We'll take a break here for some questions before looking at what to do with the main rail.
Any idea if I'm on the right path to solve the main issue, or do you think it´s something else?
Is it a good idea to spend money on upgrades, or should I first try to fix it first to be sure if it´s worth it?
Do I need to change other caps than the electrolytes, or does the film-types age better?
Should I change the film-types anyway for better sound?
Piggyback small somewhat high-end caps to cheaper filtering caps to keep cost down or get smoother power, like a 0,220uF in parallel to C746 and C747 in C for example?
Hope you will join me in this one!
/F
Hi to you, my new masters!
I've had an interest in HiFi for a lot of years, but the money have been prioritized elsewhere.
Not new to electronics in general and have a basic understanding in how all this works.
This is my first tear down however, and attempt to repair an amplifier so I need someone to hold my hand through this.
I'm from Sweden and lives in Gothenburg, which can be good to know when recommending components.
The Problem:
My NAD C372 have been in my possession for its last 7 years.
When I bought it it made a low noise, like tearing cloth slowly, when cold.
After like 5 minutes it was completely gone.
Now it never goes away. Always there, lurking in the silence.
The Mission:
I hope to get some guidance not only to fix this amp, but to upgrade it too.
Budget is hard to say when I don´t know what to change and to what yet, but let's say 150€-200€.
I´ll try to take pictures on things as I go, not only to make it easier for others to follow but because it's a lot more fun to read posts with pictures in them.
With a good help from you this can serve as a guide for future DIYers, with my lack of skill it can serve as a warning.
Let's hit it and see how it turns out!
We'll start with the Main Board and the PSU. Later on I want to have a look at the Amplifier boards.
My first approach was to open it up and look for leaking or bulging caps.
I found a lot of brown gunk around 4 bigger caps (bulk caps for rail B and C: C734, C735, C748, C749).
Since the noise is in both channels, the PSU seems like a plausible source of the noise in my noob head.
This is where it all started. Sourcing caps and info on what kind of caps I needed, aka opening Pandoras box...
I had a lot of problem with the small footprints and the 105C rating. The C372 is known for running hot so no 85C for me please.
Most HiFi-caps were too big since rail B and C clearly was designed by some engineer sharing closet with his wife,
while the main rail A was designed by previous mentioned wife.
After 3 days and 2 nights without sleep I ordered the best I've found:
2 x Vishay 2200uf 50V 105C with 7,5mm pitch (part# 2222 048 61222)
2 x Nippon Chemi-Con 1000uf 160V 105C with 10mm pitch (part# EKMQ161VSN102MP40S)
Cost: 20€
This is where I couldn´t help myself. I took another look into that box and soon realized that it's more fun to upgrade something than to repair it.
Invest money instead of just spending it so to speak.
I have no idea if these caps will solve my problem since it could be more bad caps.
I've also learned that not all caps bulge when they're bad, and that the brown stuff might be glue.
My idea here is to change most/all of the electrolyte caps (all branded Jinghai) to newer and better ones since they're all old.
(Are Jinghai good btw? In the computer world Chinese caps are not that welcome...)
We'll take a break here for some questions before looking at what to do with the main rail.
Any idea if I'm on the right path to solve the main issue, or do you think it´s something else?
Is it a good idea to spend money on upgrades, or should I first try to fix it first to be sure if it´s worth it?
Do I need to change other caps than the electrolytes, or does the film-types age better?
Should I change the film-types anyway for better sound?
Piggyback small somewhat high-end caps to cheaper filtering caps to keep cost down or get smoother power, like a 0,220uF in parallel to C746 and C747 in C for example?
Hope you will join me in this one!
/F
Funny, I saw one of these for sale as a non working 'project' (blowing fuses) in Gothenburg not long ago, so I downloaded the service manual and did some googling, but decided it was not interesting enough to pay the asked price. There seems to be many things going wrong with them, and I'm personally not a fan of CFP outputs either.
Anyway, I would say definitely get it to work properly first, before sinking money in it. Seems they are not in demand, and second hand prices are low. I remember reading something about a common problems with the standby supply, regulated voltage supply, main transformer, and bad quality electrolytic caps in general.
Maybe check soldering first, common places for it to crack is around output transistors, supply caps etc, where there is more mechanical and thermal stress on the solder connections. Check for leaking caps, and caps in hot places.
Anyway, I would say definitely get it to work properly first, before sinking money in it. Seems they are not in demand, and second hand prices are low. I remember reading something about a common problems with the standby supply, regulated voltage supply, main transformer, and bad quality electrolytic caps in general.
Maybe check soldering first, common places for it to crack is around output transistors, supply caps etc, where there is more mechanical and thermal stress on the solder connections. Check for leaking caps, and caps in hot places.
Problem with PSU due to old caps was what first popped up in my head.
Or actually, the first time I heard it I thought cracked soldering, getting tighter as it warms up.
It´s just that it has been getting worse quite drastically lately.
The noise is consistent when I turn up the volume from 0% to about 80%, then it starts increasing quite fast.
It doesn't react to the balance from right to left, and is at the same level in both channels.
I've tried looking for bad soldering, but haven't found any yet.
The caps arrived today btw.
Didn't help though...
I think you are right. I need to get it in order before I start upgrading anything.
Just thought I could kill two birds with one stone by replacing all caps.
I have attached a Photo of a NAD C370 main board, this is before the Amplifier was recapped and repaired.
The issues with the electrolytics failing over time is common, and if you de-solder the large power supply capacitors you will most likely find one or more of the pins fall off and if you shake them they will rattle confirming they have completely dried out
Also many of the capacitors are mounted close to the heat sinks of power components, so again they will have dried out.
Its the same for the left and right channel Audio output modules.
NAD fitted J&H capacitors and still use the same brand for more recent Amplifiers.
As you have identified if you order Audio grade capacitors they are physically larger than those installed, also the cost will be very high for the large capacitors.
So there's a compromise you can still fit brand named capacitors for example Nichicon, Panasonic etc.,
You need to get the Amplifier to a known state before further fault finding, and in this case all the electrolytics ideally should be replaced.
starting with the power sections.
If your plan is to repair and keep it then maybe you can justify the cost and time, but if your repairing it for resale then you may spend more money on parts than the unit is worth.
The issues with the electrolytics failing over time is common, and if you de-solder the large power supply capacitors you will most likely find one or more of the pins fall off and if you shake them they will rattle confirming they have completely dried out
Also many of the capacitors are mounted close to the heat sinks of power components, so again they will have dried out.
Its the same for the left and right channel Audio output modules.
NAD fitted J&H capacitors and still use the same brand for more recent Amplifiers.
As you have identified if you order Audio grade capacitors they are physically larger than those installed, also the cost will be very high for the large capacitors.
So there's a compromise you can still fit brand named capacitors for example Nichicon, Panasonic etc.,
You need to get the Amplifier to a known state before further fault finding, and in this case all the electrolytics ideally should be replaced.
starting with the power sections.
If your plan is to repair and keep it then maybe you can justify the cost and time, but if your repairing it for resale then you may spend more money on parts than the unit is worth.
Attachments
Thanx for the advice!
It feels a bit like a catch 22 to recap it to know if it's worth recaping it.
I've ordered an cheap LCR meter to check the caps, but even if I find faulty ones changing them might not solve the problem.
Would be great to know where the problem most likely is, and try to recap that part, and if it doesn't help make a decision whether it's wort continue or replace it.
I'm not doing it for a resale, but I don't want to spend more for a repair than it's worth, which I believe is somewhere around 250€.
I'm ok with spending time though, as I learn a lot doing this.
The noise you describe is heard through both channels so it points to a common cause.
The power supply sections would be the first thing to check as if the capacitors are open circuit then you would hear 100hz noise.
The issue here is all the capacitors will be at some level of deteriation, the large power supply capacitor have a hard life as do any that are mounted next to the heat sinks or voltage regulators, power resistors etc.
The ESR meter will confirm bad caps and an ESR meter can be used to check electrolytic CAPS in circuit but only to a point, removing them and testing out of circuit is the only way to confirm 100%. So while your removing them for testing you might as well just replace them.
The smaller CAPs will not be expensive the large power supply capacitor will be approx €14 Euros each.
The power supply sections would be the first thing to check as if the capacitors are open circuit then you would hear 100hz noise.
The issue here is all the capacitors will be at some level of deteriation, the large power supply capacitor have a hard life as do any that are mounted next to the heat sinks or voltage regulators, power resistors etc.
The ESR meter will confirm bad caps and an ESR meter can be used to check electrolytic CAPS in circuit but only to a point, removing them and testing out of circuit is the only way to confirm 100%. So while your removing them for testing you might as well just replace them.
The smaller CAPs will not be expensive the large power supply capacitor will be approx €14 Euros each.
With some help from the user PerStromgren at the Swedish forum faktiskt.io I tried remove the bridge between preamp and power amps. No noise.
Tried to connect audio directly to the amplifiers without all the other fuzz, and no noise!
If I'm understanding this correctly, then my problem is between the mains and the pre-out.
This means that those expensive 10.000uF 100V bulk caps isn't faulty (Might be worth changing anyways, but not critical ATM.)
But most of all, this means I can use it as an amplifier even if I can't fix the problem with the preamp.
@Audio Service: 100Hz ripple seems right, and the 34V rail is a compact one!
I guess my next step is to fix all caps from the rectifier in rail C all the way to pre-out.
Good thing that I already changed the most expensive by far along that road!
As you say @Rallyfinnen, the shipping is the expensive part, if we are talking about the small caps anyways.
Now I need to source as many caps as possible from the same store.
What should I get?
On my hot list right now I have:
Panasonic FM, FC
Nichicon KZ, Muse KG
Elna Silmic RFS, Cerafine
Mundorf
I guess this list can get quite long, but are there any brand/series I missed that I really should consider?
Tried to connect audio directly to the amplifiers without all the other fuzz, and no noise!
If I'm understanding this correctly, then my problem is between the mains and the pre-out.
This means that those expensive 10.000uF 100V bulk caps isn't faulty (Might be worth changing anyways, but not critical ATM.)
But most of all, this means I can use it as an amplifier even if I can't fix the problem with the preamp.
@Audio Service: 100Hz ripple seems right, and the 34V rail is a compact one!
I guess my next step is to fix all caps from the rectifier in rail C all the way to pre-out.
Good thing that I already changed the most expensive by far along that road!
As you say @Rallyfinnen, the shipping is the expensive part, if we are talking about the small caps anyways.
Now I need to source as many caps as possible from the same store.
What should I get?
On my hot list right now I have:
Panasonic FM, FC
Nichicon KZ, Muse KG
Elna Silmic RFS, Cerafine
Mundorf
I guess this list can get quite long, but are there any brand/series I missed that I really should consider?
For small caps and quick and cheap delivery in Sweden I normally use Electrokit.com. I would not worry so much about what type of cap for the supplies to the preamp, no high currents etc. Just use some decent quality caps that won't die quickly again. I would probably get high temp type, and especially if they are anywhere near something warm.
When it comes to big main PS caps, I usually ended up buying from Mouser or Digikey to get the caps I want, and then there is high shipping costs (from US) and customs fees etc.. so they get really expensive. I have not found a company shipping from EU that has 'everything' (including decent prices) when it comes to PS caps.
When it comes to big main PS caps, I usually ended up buying from Mouser or Digikey to get the caps I want, and then there is high shipping costs (from US) and customs fees etc.. so they get really expensive. I have not found a company shipping from EU that has 'everything' (including decent prices) when it comes to PS caps.
Been spending some hours with Excel building a spread sheet to see what the big vendors got to offer.
ElectroKit got a lot of caps I need, and that at reasonable price too.
Not all of them however, so I need to make at least one international order, but that's ok.
The big bulk caps are four-pin, but the main board is prepared to take two-pins with a 10mm pitch too.
Are there any advantages except build stability to use four-pins?
Now we got the PSU part covered (hopefully), let's look at the Amplifiers.
The red caps are basically the same smothering caps that rail B and C have locally if I understands this correctly.
My plan is to get the ones mentioned above for exchange and maybe add another higher grade small decoupling cap too in parallell.
The others are a bit of a mystery to me however.
I think that the violet is doing the same thing as the red ones and that the blue is a buffer of some kind, but that's just guesses.
Are there any of these I should chip up some extra money for?
I would say the blue (DC) and green(over current) protection circuits. Whatever works.
Red ones for rail decoupling to prevent oscillation. Low ESR is good for that.
Violet is input cap (some people are very specific with the quality/type here)
I would think the yellow ones to the right are bootstrap caps..
Basically I would replace all the electrolytic caps, and maybe put some audio grade on the input cap. Poly cap or bipolar electrolytic.
BUT: get the amp working first, before you start spending.. especially on the big PS caps.
Red ones for rail decoupling to prevent oscillation. Low ESR is good for that.
Violet is input cap (some people are very specific with the quality/type here)
I would think the yellow ones to the right are bootstrap caps..
Basically I would replace all the electrolytic caps, and maybe put some audio grade on the input cap. Poly cap or bipolar electrolytic.
BUT: get the amp working first, before you start spending.. especially on the big PS caps.
You are absolutely right, this would be the sound thing to do and I too recommend everyone to get it in working order first.
But since the power amp works as it should, and I only use one line in, I really have no absolute need for the integrated parts that don't work.
It will work as I use it now, and I can use it as an amplifier for my surround system that is in a dire need of an upgrade, later on if I decide to replace this in my living room.
Would still kind of suck knowing it will be hard to sell and get my money back, but it will save me some shipping costs.
I do this at least 50% for the fun of it and to learn things, so it's a risk I'm willing to take.
I can answer my earlier question about the shorted pins.
Those are, like me, dummies.
It's not recommended to connect them to any power though according to Nichicon (IIRC) since it will add to the power leakage of the cap.
Will opt for two-pins instead.
When it comes to the input cap there are quite a big lack of space there.
The cap sitting there is ~5mm, and I can replace it with a cap up to the 8mm of Elna Silmic II for example , but how do I fit something like a 30mm film cap?
Is it ok to connect it to wires and glue it some place else, or how should I mount it?
So, this is what I found.
The big boys is only 80V, as the first version of the C372 had, but six of them instead of just four and that of better quality so I hope it's ok.
Bold prices are what I'm planing to go for.
The price difference from non audio grade to audio grade in the smaller caps are close to nothing.
80% of the cost are those 10.000uF.
I still kept it under the 150-200€ budget.
The big boys is only 80V, as the first version of the C372 had, but six of them instead of just four and that of better quality so I hope it's ok.
Bold prices are what I'm planing to go for.
The price difference from non audio grade to audio grade in the smaller caps are close to nothing.
80% of the cost are those 10.000uF.
I still kept it under the 150-200€ budget.
Of course I didn't!
I just read this thread: https://www.diyaudio.com/community/threads/nad-c372-to-restore-or-not.248323/page-2#post-5199342
along with the assumption that it would be ok since 64V is 80% of 80V.
But we all know who's mother assumption is...
I'm gonna make this in two steps then.
First I'll order everything I need from Electro-kit. Among those caps are the ones I need for the 34V-rail (missed them in my last post).
I'll try fixing the problem with the amp, and resolder the main bulk caps after I checked them. Then I'll make sure that the 64V-rail indeed is 64V.
Then I order the rest of the stuff from Digi-key, just like you told me to in the first place.
I have some doubts about adding the two extra big bulk caps too.
I don't think it will do that much extra for the sound and just stress the PSU for no good.
How about adding two smaller caps with lower ESR instead.
Will that do any good?
Yes. Mine is one of the upgraded units with 100V caps instead of the bad 80Vs.
While waiting for new caps for the 34V rail I removed and meassured the old ones.
The 1uFs seems ok but the 22uFs were not that great.
Checked the big ones too.
They're not perfect but not terrible either.
Soldered them back to be able to test the amp with new caps in 34V rail.
They should show up today.
The 1uFs seems ok but the 22uFs were not that great.
Checked the big ones too.
They're not perfect but not terrible either.
Soldered them back to be able to test the amp with new caps in 34V rail.
They should show up today.