NAD 216 THX - Make it sound better?

Hi there,
I own a NAD216 amp, it's been playing in my stereo system for almost 13 years now.
about 5 years ago it start making some problems - taking it for service resulted in two things:
1. amp was fixed
2. service guy removed several components / changed several components - making the amp sound way better than stock

three months ago the amp went off again, this time it was due to electrical problem from the AC network.

took it again to service -
this time the service guy (a different one) used the amp original electrical schemes and just went over them and made sure all working properly.

now the situation is simple - i had an improved amp (i do not know exactly by what measuers), i sent it to service and now i got a stock amp again.

i need assistance in reviewing the amp electrical schemes and noting there what places can be "Improved" by manners of:
1. remove / bypass redundant / unnecessary protections
2. remove / bypass circuits that are in no use (bridge channels part / soft clipping)
3. remove filters applied in the amp which are not necessary

i found the schematics of the amp here:
Index of /~jga/nad216thx

link is taken from a thread located here:
http://www.diyaudio.com/forums/solid-state/148986-help-noisy-nad-216-a.html

i could not locate and electrical schemes for any Silverline amps from NAD for comparison, so if any1 has some assistance about that as well, this may also help


would appreciate any kind of help

BR


Ron.
 
In "Stock" mode the response between 20 and 20kHZ is + or- 0.8DB worst case!
That is pretty flat so removing any filter/clipping/protection bits and pieces will make the amplifier non linear and possibly dangerous.
Can you be specific as to the difference in sound reproduction?
Any "Professional Engineer" that removes components or indeed changes the values without the authorisation by way of an official update from the manufacturer, requires re-training in my view.
 
Hi Jon,
regarding the sound -
after the modding, amp sound had improved dramatically on the lower end (very low to be specific) -
it sounded like a complete spectrum wad added to the amp the lower end, more of a feel rather than hear frequencies.
in addition, highs had become more sharp / crisp.
Somewhat like an expanded headroom was added to the amp original sound

regarding the note about removing / modifying components -
when designing a product for mass production you make a lot of compromises - for matters of manufactureability , regulatory, safety etc. this means that more often that one would like, he needs to move from its optimum design towards alternatives and other routes.
as an individual, i care less of those aspects and more about the sound of the product i want to tweak.
i practice my own words in the field of cars handling / engine tuning for motorsports, where im more experienced than in the world of audio electronics...
 
Some people say that removing the Dc protection relay makes an amp sound better. Well you can bypass it but should anything goes wrong you will have to buy new speakers, not worth trying that. Maybe you must just check if the main power supply caps is Ok. I have a Nad 214 which is basically the same, got a 240mv dc offset on one channel, turns out to be be a leaking cap. I have replaced all elcos and never had problems again, sound better than new.
 
thanks for the suggestion - after latest fix amp returned to me in new like-stock condition - all caps renewed (plus - the third couple of caps replaced from 4700uF/80v to pair of 15000uF/100v pair)

what about the signal path of the inputs?
is there any play in that direction?
 
Inputs of this amp are single pair of RCA plugs - they go through certain route -
via bridge / not bridged switch and via soft clipping circuits (you can see that in the attached file)
in addition - i want to make sure if there are any other filters along the way...



you can see the electric scheme of the amp in the link at the first post of this thread.
from a quick glance that i took - the amp has a single pair of inputs.
 

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It is funny that you mention this -
after the tuning of the amplifier, i had a problem in my pre-amp, it was this exact thing - something went wrong inside it, and it sent out DC to the amp.
this resulted in fried up tweeter's of my B&W CDM1NT...

i never thought this could be it - but now it makes a perfect sense.

will i go over this again, taking this chance?
if this was the change that added so much headroom in the lower spectrum of the amp, think i would do it again...

Do you think i can recalculate the cap's value to cut the frequency at a lower stage, keeping the DC protection along with expanding the lower end headroom?
 
Check this, Sakis gave me some info, he has seen this all. This is a great amp. Fix it, you will be a happy chappy. http://www.diyaudio.com/forums/solid-state/220173-nad-214-dc-output.html



thanks for the link - very useful information.
some expressions are not clear to me: (taken from the original link)

--- muting transistors in the input is something i disapprove and normally remove to all units - any chance to mark those on the schematics?
---Given the chance you may upgrade the main power banks to something bigger since the pcb may accommodate more but only thin and tall as far as i remember - i replaced two pairs of the original big caps (4700uF/80v) and replaced third pair with two 15000uF/100v
---Inspect IC 201 for soldering issues verify proper voltage there - just had it re soldered

---Input caps are also low quality .... some better and may be bigger cap there may be some improvement - any chance to mark those on the schematics?

---Tackle the protection relay to see for interrupt while in very low power mode if needed replace - how do i do that?

---Inspect input plugs often there you have soldering issues especially if input plugs/cables are big or heavy - inspected, they're fine

--last verify bias of the amplifier since the manufacturer of the amp ( depending on the serial number ) decided to decrease the bias on production to preserve some safety more while the designer on the service manual share some other opinion . Tune according to the schematic expect overall temperature to increase but just a bit .remember to warm up tune and verify more than once or twice if needed . - on my check list, will probably do it by end of tomorrow
 
I think you imagined the improvement in sound, because they guy said he had improved it.

I think you are imagining another change now, that the guy said he turned it back to normal.

In reality, the amp most likely sounded exactly the same, all along. You can't make a few tweaks to improve the sound of an amplifier - you have to go with a different design altogether.
 
I think you imagined the improvement in sound, because they guy said he had improved it.

I think you are imagining another change now, that the guy said he turned it back to normal.

In reality, the amp most likely sounded exactly the same, all along. You can't make a few tweaks to improve the sound of an amplifier - you have to go with a different design altogether.

of course you can change the sound of an amp by performing a few tweaks, otherwise you'd be dropping the ground from under 99% of the discussions here
 
In "Stock" mode the response between 20 and 20kHZ is + or- 0.8DB worst case!
That is pretty flat so removing any filter/clipping/protection bits and pieces will make the amplifier non linear and possibly dangerous.
Can you be specific as to the difference in sound reproduction?
Any "Professional Engineer" that removes components or indeed changes the values without the authorisation by way of an official update from the manufacturer, requires re-training in my view.


Come on John this is so WRONG !!!

Removing filter/clipping/protection bits and pieces cannot and will not change the linearity of the amplifier .... On the other side one capacitor in the feedback chain will do that ( for example )

Removing filter/clipping/protection bits and pieces can and will change the safety margins of the amplifier ...only !

@ Ron
What you ask me to do is not easy since i have no idea what happened inside your amp anyway

As a generalization
--Higher capacitance on the power supply
--Higher capacitance on the secondary power supply better quality elkos there is a must
Bypass will also help in both stages need to be careful there and verify results with a scope
For the input stage :
Remove :
R101,R103,Q101,C103 R102,R104C102,Q102 these are the parts that mute the input Need to replace though C103-104 with 2.2ufd /63volt quite hard to find and i wouldn't recommend higher voltage than that ( exotic parts often behave as microphones due to physical size )
Then add 100pf in parallel with R105-106 do something like styroflex there anything but not ceramics
hardwire the input directly to C103 /104

Removing D101-103 and R109 110 will not only disable the soft clipping function but disconnect completely from the signal line

These are easy to do ... do it and listen and tell us what do you think ....

Kind regards
Sakis
 
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ok,
so reports from today -
i check the bias -
it what pretty out of tune -
left was 22mV but right channel was 6mV
i tuned them both to 21mV (after i let the amp seat for 15 min while it was on)

but than the down side occur -
i tried to disconnect the soft clipping section:
i disconnected D101, D102, D103, D104 and also disconnected R109 and R110 (i did not took them out, but disconnect only one of the leg's each)

when i try to connect the amp again to check the bias - it will turn on now, but will only lit the red LED (like it has turned on, but will not come come out of protection or something)
should i expect this to happen?
did i get something wrong?
 
another update and further question:

1. working with bias level of 21mV led to a lot of heat while amplifier was on (practically -always) so bias rechecked and adjusted to 18mV

2. Any idea why removing the above components from the board caused the amp not to exit protection mode?
 
I have bought recently a couple of this amps. 216 THX and open one of them for checking the caps since this is a simple way of making improvments. I was surprise to find out quite good Nichicon all the way on the power supply part of the amp.
I have measured them with quite good results. ERS = 0.11 and with good values close to what it should be originally. However I have found better caps (for replacing 4700 uF caps only) at Mouser electronics for incresing the capacitanse to 22 mF and decreasing ESR to. 0.03. No bad Elcos at all were found in these amps. Any one who knows if it was any improvement from early modells?