A treasure trove of feasible experiences, all of which are also transferable to other devices;-)
I also have a few ideas regarding this NAD that I want to try.
When replacing transistors: the aluminum of these heat sinks is very soft, the screws are very long. They have eaten away at the aluminum in my NAD. One screw also broke off when loosening. Somehow loosen it with feeling using a suitable screwdriver. And use new, shorter screws for the new transistors. And maybe put minimal grease on the threads.
I also have a few ideas regarding this NAD that I want to try.
When replacing transistors: the aluminum of these heat sinks is very soft, the screws are very long. They have eaten away at the aluminum in my NAD. One screw also broke off when loosening. Somehow loosen it with feeling using a suitable screwdriver. And use new, shorter screws for the new transistors. And maybe put minimal grease on the threads.
Roughly equalizing the two paths made no discernable difference nor could I remember it if it did for it would have been too small. Switching between double twisted wire and a single wire made no difference whatsoever even while listening to it live.
Sounds very noticeably better with potentiometer turned all the way up and using digital volume control on my Topping DAC (it upsamples before adjusting the level). I think potentiometer needs to go. Although shorting the contacts does exactly nothing, so I guess all the way turned up will be fine.
For me this amp shines with certain female vocals that are less about the ambience / harmonic content and more about the elements of speech and pronunciation, the cracles, the consonants, more macro kind of stuff. Sustained notes or the richness and nuance of voice don't sound magical, at least not yet.
Also electric guitar like Buckethead - Soothsayer goes crazy. Tandberg was softer there in the electric guitar even if it had more info in most ways especially up top where it shimmered and sparkled despite being somewhat veiled.
There is much to be desired in bass, but it's not completely bad - it's somewhat defined, just no weight. Ofc I hardly changed anything yet, so I shouldn't expect miracles, but I did remove the little board on speaker terminals and create a common ground while cutting out the headphone part.
Why does it seem like preamp is turned on when the power switch is first turned on/off? Can I disable it completely to have more safety with the tweeter? Although the tweeter I have should be able to handle pretty bad abuse. JBL JT025TI1-4
I'm excited to short the fuses. But everything step by step.
Sounds very noticeably better with potentiometer turned all the way up and using digital volume control on my Topping DAC (it upsamples before adjusting the level). I think potentiometer needs to go. Although shorting the contacts does exactly nothing, so I guess all the way turned up will be fine.
For me this amp shines with certain female vocals that are less about the ambience / harmonic content and more about the elements of speech and pronunciation, the cracles, the consonants, more macro kind of stuff. Sustained notes or the richness and nuance of voice don't sound magical, at least not yet.
Also electric guitar like Buckethead - Soothsayer goes crazy. Tandberg was softer there in the electric guitar even if it had more info in most ways especially up top where it shimmered and sparkled despite being somewhat veiled.
There is much to be desired in bass, but it's not completely bad - it's somewhat defined, just no weight. Ofc I hardly changed anything yet, so I shouldn't expect miracles, but I did remove the little board on speaker terminals and create a common ground while cutting out the headphone part.
Why does it seem like preamp is turned on when the power switch is first turned on/off? Can I disable it completely to have more safety with the tweeter? Although the tweeter I have should be able to handle pretty bad abuse. JBL JT025TI1-4
I'm excited to short the fuses. But everything step by step.
Attachments
If I'm not mistaken, I did everything here
Attachments
This part I don't understand, but I'll do my best to figure it out.
I'll replace the C429 and C430 with 100uF once I figure out the polarity. But I don't know where to disconnect the connections to 38V PSU. This is probably basic stuff, but I lack the understanding of the circuit. Pictures are very helpful.
Edit: C 429, C 430 replaced with 100uF and what I'm hearing is a more powerful sound, more powerful low end as far as I can tell.
The components to remove will be removed 🙂 and I'll try to listen for differences.
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Removing C 427, C 428 seem to have improved the sound quite drastically, making it smoother, prettier, more detailed. This could all be placebo though since it takes a second to do the job and I'm not too familiar with the sound of the amp, but I think this one was quite audible.
Removing C 409, C 410. Suddenly a lot more high frequency information seems to have come into picture. High hats are suddenly in my face.
The other ones I don't recall hearing anything specific.
But no this isn't placebo, this is a completely different amp now. And my high frequencies are here! Yay!
Something strange happened a few times though - the volume level rose and dropped like upon turning the power switch but this was during normal operation. Haven't had any complaints with the mains, but I'm in the countryside so anything is possible. And it did that a few times more now.
Removing C 409, C 410. Suddenly a lot more high frequency information seems to have come into picture. High hats are suddenly in my face.
The other ones I don't recall hearing anything specific.
But no this isn't placebo, this is a completely different amp now. And my high frequencies are here! Yay!
Something strange happened a few times though - the volume level rose and dropped like upon turning the power switch but this was during normal operation. Haven't had any complaints with the mains, but I'm in the countryside so anything is possible. And it did that a few times more now.
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;-)
I am happy too;-)
Disconnect the 38 V:
I have marked the 38 V strand in red. I have cut through the copper strand at one channel (arrow) and removed a bridge at the other channel (arrow). I then replaced C 437 and C 438 on the top with a wire - an example: Yellow wire image. These Cs are located between the 28 V and 38 V voltages.
I am happy too;-)
Disconnect the 38 V:
I have marked the 38 V strand in red. I have cut through the copper strand at one channel (arrow) and removed a bridge at the other channel (arrow). I then replaced C 437 and C 438 on the top with a wire - an example: Yellow wire image. These Cs are located between the 28 V and 38 V voltages.
Attachments
C427, C 428 are called "bootstrap".
C 409, C 410: "soft clipping" circuit.
C 407 and C 408 do not remove, at moment:
This amplifier is extremely sensitive to oscillation. They didn't pay attention: they put 2 x 100 nF in series at the output, which only short-circuits above 300,000 kHz: C433, 435, and 434, 436 preferably in parallel, then it is safe. (in my case the big red WIMAs - these WIMAs are no good for anything else;-) And they also have an RC element in the feedback that only short-circuits at > 1 MHz (R 431 - C 421, R 432 - C 422; 1.8 kOhm - 47 pF each). So also nonsense. I assume they didn't even notice this, and because they had a lot of oscillation, the thing was perhaps even constantly breaking down, they put their "Miller" and whatever else in at every conceivable point. That also seems to be a product of inattention or ignorance.
It should not be the case that the volume jumps. But this can have several causes, e.g. solder joints or volume control (dirty). And also oscillation. As described above. I am in the process of reworking the NAD in this respect. But it will take some time. Let's see;-)
C 409, C 410: "soft clipping" circuit.
C 407 and C 408 do not remove, at moment:
This amplifier is extremely sensitive to oscillation. They didn't pay attention: they put 2 x 100 nF in series at the output, which only short-circuits above 300,000 kHz: C433, 435, and 434, 436 preferably in parallel, then it is safe. (in my case the big red WIMAs - these WIMAs are no good for anything else;-) And they also have an RC element in the feedback that only short-circuits at > 1 MHz (R 431 - C 421, R 432 - C 422; 1.8 kOhm - 47 pF each). So also nonsense. I assume they didn't even notice this, and because they had a lot of oscillation, the thing was perhaps even constantly breaking down, they put their "Miller" and whatever else in at every conceivable point. That also seems to be a product of inattention or ignorance.
It should not be the case that the volume jumps. But this can have several causes, e.g. solder joints or volume control (dirty). And also oscillation. As described above. I am in the process of reworking the NAD in this respect. But it will take some time. Let's see;-)
I'm playing with potentiometer always on the fully on position. The soldering job I think I did all right. I'll try to remove the higher voltage PSU as you showed and see if it happens again. Could it be that for whatever reason my power transistors are getting the higher voltage temporary upon turning on and off... but also for some other factors, perhaps oscillation 🙂 I have no idea. Indeed pretty interesting.
Done
It can also be the classic switch-on plop. If there is nothing to switch it or the signal off.
Or a minimal stabilization phase until both half-waves of each amplifier are stable and the offset voltage at the output is zero. I think that's when it's louder when you switching on and off.
It is normal that the NAD is quieter without a preamp. You could increase the amplification factor on the output stage later. And the tuning in general will gradually make the amplifier sound cleaner and therefore more dynamic. At least that's my experience.
And remove all the input resistors. This also adds a little volume and cleanliness. Step by step;-)
Or a minimal stabilization phase until both half-waves of each amplifier are stable and the offset voltage at the output is zero. I think that's when it's louder when you switching on and off.
It is normal that the NAD is quieter without a preamp. You could increase the amplification factor on the output stage later. And the tuning in general will gradually make the amplifier sound cleaner and therefore more dynamic. At least that's my experience.
And remove all the input resistors. This also adds a little volume and cleanliness. Step by step;-)
Well, that's what I did, removed the input resistors and capacitors on Video inputs and now the volume is higher and stays the same regardless if it's in normal operation or being switched on/off. However at this higher volume it starts distorting pretty bad. I think my power caps are bad, because 1. They're inflated and 2. When turned off and the amp is still playing it quickly starts crackling and doing weird things even though the caps are still powered (not completely discharged) and playing for a good few seconds.
I was previously playing through CD inputs and when I switch back to them the volume loss of 15 dB still occurs when the amp power LED turns on, but it doesn't play loud enough to hear any bad distortion.
I was previously playing through CD inputs and when I switch back to them the volume loss of 15 dB still occurs when the amp power LED turns on, but it doesn't play loud enough to hear any bad distortion.
It is normal for the devices to go into distortion when the electrolytic capacitors discharge.
Many amplifiers have the CD input highly damped: higher resistances and capacitances than the normal line inputs. Because many CD players spit out an enormously loud signal. That was normal 30 years ago. Today too? This may also be the case with this NAD. I haven't checked yet. Remove;-)
Many amplifiers have the CD input highly damped: higher resistances and capacitances than the normal line inputs. Because many CD players spit out an enormously loud signal. That was normal 30 years ago. Today too? This may also be the case with this NAD. I haven't checked yet. Remove;-)
All inputs seem to cut 15dB off upon turn on, except the video input now after the modification. Still some work to do, but I already prefer this amp to my Tandberg in almost every aspect. It's cleaner and clearer. Also decays seem to be faster. Which makes it just a little bit less alluring and full and rich in the upper treble so although cleaner and clearer it seems to have less body, maybe the decays are faster. Darker perhaps as you called it. But even the bass is more defined and more fun than the Tandberg now. I payed 50 euros for this amp while Tandberg was 750 and that was already a great deal for one of them.
Now the high volume distortion is a bit of an issue, but I rarely ever play high volume anyway, so I can live with that, although it would be nice to solve. BTW the heavy distortion on high level was present even before modification, maybe part of the reason why I got it so cheap, they aren't supposed to do that, are they?
Now the high volume distortion is a bit of an issue, but I rarely ever play high volume anyway, so I can live with that, although it would be nice to solve. BTW the heavy distortion on high level was present even before modification, maybe part of the reason why I got it so cheap, they aren't supposed to do that, are they?
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I wish to do this, but I don't understand what was done and I will only probably get to do it only after 9 days or so, but I should have the transistors in my hands then, so I imagine it's gonna be really fun to get back to this.
Which capacitors would be the coupling ones? Should I buy them? I'm definitely keeping this amp.
Also if you could please point out which caps are the negative feedback ones, I would appreciate as well. You mean 2,200 uF or nF?
Also thank You so much for all of these instructions and recommendations! This is really really useful and appreciated and fun to follow along and listen. And now I have an amp to listen to music with! With more potential still!
That makes me very happy;-)
But I know that there is still a lot more to do and that the sound will get even better. A great toy to learn a lot. Audible distortions are usually not THD or anything like that. It's all the noise that material and transitions and components make. It's a great task to gradually discover all the little disturbers and distractors and remove or improve them;-)
I removed R 401 and R 402 from mine NAD. The volume potentiometer has 100 kOhm. These 220 kOhms are in parallel. Nobody needs them.
I removed R 421, R 423 and also R 422 and R 424 and replaced them with just one 1 kOhm. I have removed C 405, C 406. But C 407, C 408 remain.
Use the potentiometers R 411 and R 412 to set the offset: simply place a voltmeter between the loudspeaker output and ground and then adjust to 0 volts.
Coupling caps remain: C 401, C 402 (input) and C 415, C 416 (feedback). C 417 and C 418, these bridge the 2,200 uF, simply remove.
C 429, C 430 you have replaced already;-)
The 2,200 Kemet are unfortunately sold out at Reichelt. Leave the original ones in for now.
Q 401 and Q 402 later;-)
But I know that there is still a lot more to do and that the sound will get even better. A great toy to learn a lot. Audible distortions are usually not THD or anything like that. It's all the noise that material and transitions and components make. It's a great task to gradually discover all the little disturbers and distractors and remove or improve them;-)
I removed R 401 and R 402 from mine NAD. The volume potentiometer has 100 kOhm. These 220 kOhms are in parallel. Nobody needs them.
I removed R 421, R 423 and also R 422 and R 424 and replaced them with just one 1 kOhm. I have removed C 405, C 406. But C 407, C 408 remain.
Use the potentiometers R 411 and R 412 to set the offset: simply place a voltmeter between the loudspeaker output and ground and then adjust to 0 volts.
Coupling caps remain: C 401, C 402 (input) and C 415, C 416 (feedback). C 417 and C 418, these bridge the 2,200 uF, simply remove.
C 429, C 430 you have replaced already;-)
The 2,200 Kemet are unfortunately sold out at Reichelt. Leave the original ones in for now.
Q 401 and Q 402 later;-)
The high volume distortion I am experiencing is a very bad one. Sometimes, the Tweeter starts doing weird things like maybe reaching excursion, I don't know, but it sounds bad. (No it's not supposed to reach excursion on that level, but it does sound like some kind of crackling I can't find the word, but it's coming from the amp). It would be fine, but I wouldn't want there to be something like that at lower volume, just me never catching it. Somehow I suspect that's the power supply caps. When they are discharging the volume sometimes goes out and then comes in again, they do really weird stuff I don't think they are supposed to just discharge like that - it should sound more consistent. It's not just distortion that they do, they do weird stuff. And again, they are noticeably inflated.
I've removed C 405, C 406, C 417, C 418 and I can't say for sure anything changed, but if it did it only changed for the better. Seems to sound more nuanced and livelier, but the difference is subtle if it's there. I remember audio for like 20 seconds usually unless I lived with it. But this right now sounds more aluring than anything before, or my melatonin is slowly starting to kick in.
So C 441, C 442, C 443, C444 - remove?
I've removed C 405, C 406, C 417, C 418 and I can't say for sure anything changed, but if it did it only changed for the better. Seems to sound more nuanced and livelier, but the difference is subtle if it's there. I remember audio for like 20 seconds usually unless I lived with it. But this right now sounds more aluring than anything before, or my melatonin is slowly starting to kick in.
I've only just read all your posts. It will sound better without the potentiometer. I also listen without. A headphones output from the laptop is enough for me. Simply direct from the RCA sockets to the power amplifier.
Since the preamp is bridged, it should no longer be involved in the sound - at least not directly. It will not make any scratching or cracking noises. I hope;-)
Since the preamp is bridged, it should no longer be involved in the sound - at least not directly. It will not make any scratching or cracking noises. I hope;-)