Lads, I thought this issue is better suited to be looked into by the technically well-exposed people here.
I have a streamer preamp(Primare i15) that is connected to the power amp(NAD 208) using an RCA connection. There is no 12v trigger running from the Pre to the Power. Therefore, when I switch on the system, it will be the Pre first and just a few seconds later, the Power. I did the same today and when I switched on the Power amp after the Pre, there was a loud pitched sound from both the speakers- the sort that is often encountered when the pre is switched off before the power. I have no idea what caused this but I immediately switched off the Power amp and the mains.
I waited and switched ON again in sequence and started playing some music. Felt something was not playing as it should and when inspected closely, I heard the mid-woofer producing a distorted sound. Strangely the vocals were clear but when a track that had a double bass was played, I heard distortion. I listened to the tweeter and the lower woofer and found nothing unusual sonically.
I did a quick check with the multimeter for the DC offset numbers. I took the readings an hour after the power amplifier was powered ON. The next day, measurements were taken immediately(2-3 minutes) after it was powered ON to see if there was any difference and/or whether there were any DC fluctuations. They were the same though. Also, the readings on the multimeter took a few seconds to stabilise. But when they did, they remained solid.
The measurements taken at the amplifier's terminals are as follows:
Speaker A's terminals:
Left channel - -1.4 mv
Right channel - -2.8mv
Speaker B's terminals:
Left channel - -1.4 mv
Right channel - -2.8mv
The heatsinks on both sides felt equally warm. However, I made another observation. When the amplifier was switched ON(after a week), it took about 4 minutes for the relay to click in and emit the green light for usage. The last time this happened was when I got it serviced(after 2 years of storage) and put it to use. The next day, it took 10 secs to get ready. I am wondering if this is normal. In the last 3 weeks, I have been using it, it is ready for use almost immediately upon power ON; sometimes within a few seconds.
I hope I have given enough information for you good people to look into and help me out. Do let me know if you need further information of any sort.
I have a streamer preamp(Primare i15) that is connected to the power amp(NAD 208) using an RCA connection. There is no 12v trigger running from the Pre to the Power. Therefore, when I switch on the system, it will be the Pre first and just a few seconds later, the Power. I did the same today and when I switched on the Power amp after the Pre, there was a loud pitched sound from both the speakers- the sort that is often encountered when the pre is switched off before the power. I have no idea what caused this but I immediately switched off the Power amp and the mains.
I waited and switched ON again in sequence and started playing some music. Felt something was not playing as it should and when inspected closely, I heard the mid-woofer producing a distorted sound. Strangely the vocals were clear but when a track that had a double bass was played, I heard distortion. I listened to the tweeter and the lower woofer and found nothing unusual sonically.
I did a quick check with the multimeter for the DC offset numbers. I took the readings an hour after the power amplifier was powered ON. The next day, measurements were taken immediately(2-3 minutes) after it was powered ON to see if there was any difference and/or whether there were any DC fluctuations. They were the same though. Also, the readings on the multimeter took a few seconds to stabilise. But when they did, they remained solid.
The measurements taken at the amplifier's terminals are as follows:
Speaker A's terminals:
Left channel - -1.4 mv
Right channel - -2.8mv
Speaker B's terminals:
Left channel - -1.4 mv
Right channel - -2.8mv
The heatsinks on both sides felt equally warm. However, I made another observation. When the amplifier was switched ON(after a week), it took about 4 minutes for the relay to click in and emit the green light for usage. The last time this happened was when I got it serviced(after 2 years of storage) and put it to use. The next day, it took 10 secs to get ready. I am wondering if this is normal. In the last 3 weeks, I have been using it, it is ready for use almost immediately upon power ON; sometimes within a few seconds.
I hope I have given enough information for you good people to look into and help me out. Do let me know if you need further information of any sort.
The power on delay should be 100% consistent at all times.
My initial thoughts... the DC offset values are perfect at the time you measured them. Even -/+100mv should not cause any issues operationally. I'm going to suggest you should first try another preamp or at the very least try the power amp with 'shorting plugs' fitted to the inputs and check that the 'on' delay is 100% consistent and with no strange noises.
Beyond that it all gets more involved and you would need to look with an oscilloscope at just what is going on and what this noise is. You also could check the DC offset before the speaker relays to determine if the delay issue is caused by some issue causing an offset. Both channels would need to be measured in that initial time period before it works normally again.
My initial thoughts... the DC offset values are perfect at the time you measured them. Even -/+100mv should not cause any issues operationally. I'm going to suggest you should first try another preamp or at the very least try the power amp with 'shorting plugs' fitted to the inputs and check that the 'on' delay is 100% consistent and with no strange noises.
Beyond that it all gets more involved and you would need to look with an oscilloscope at just what is going on and what this noise is. You also could check the DC offset before the speaker relays to determine if the delay issue is caused by some issue causing an offset. Both channels would need to be measured in that initial time period before it works normally again.
Hey Mooly, the amp was sent in for service a few weeks ago and the checks showed no issue with the internals. This is according to the tech who worked on it. When the unit was there with them, they could not recreate the startup delay. Each time they powered ON, the relay clicked in within seconds. When I got back home, it was the same but as weeks passed the delay became longer. At times, it is within a few seconds. The amp works perfectly fine once the relay clicks- no issues with the amp going into protection mode whatsoever during usage. I am wondering if this is a power issue with my mains or whether it is something within the amplifier itself.
I am not going to work on this as I was told that it is a high-powered amp with a lethal dose of current in the circuit. Being not trained in electronics, I am not going to get my hands on the internals. There is a kind gentleman who had worked on this amp for months and managed to get it working it good order. I believe he is in this forum as well. He was gracious enough to offer me guidance on fixing this but it would be a wasteful effort on his part when I am not technically equipped to follow his directions. I may have to take the advice given here to the techs at NAD in the hope that they will be able to narrow down to the root of the problem.
I am not going to work on this as I was told that it is a high-powered amp with a lethal dose of current in the circuit. Being not trained in electronics, I am not going to get my hands on the internals. There is a kind gentleman who had worked on this amp for months and managed to get it working it good order. I believe he is in this forum as well. He was gracious enough to offer me guidance on fixing this but it would be a wasteful effort on his part when I am not technically equipped to follow his directions. I may have to take the advice given here to the techs at NAD in the hope that they will be able to narrow down to the root of the problem.
I doubt it is mains related.
In the first post you mentioned 'distortion' but now you say it all works fine when the relay is engaged. I would concentrate just on the relay not engaging and what I would do is measure (during the time the relay is not engaged) the actual triggers to the protection circuit to see if anything is tripping it. There are numerous interwoven trips and triggers within the whole circuit but ultimately the relay is driven from IC601 and so that is where I would look, at all the inputs to the chip.
The four at the left are DC offset inputs and over current inputs. The two lower ones on the 100k resistor should be at close to zero volts. I think the other two will be 'floating' and so appear 'high' and if there is a trip condition they will go 'low' to zero volts but I recommend checking the status of these when it is working OK as that will be the normal status of them.
Also the two caps circled (particularly the small 1uF) could be favourite. C606 (which provides AC power detection)has a hard time and is exactly the type and location of a part that could fail/deteriorate. That is well worth just swapping before you do anything more complex. A 1uF 63v or 100v electrolytic would be fine and observe the polarity as + of the cap goes to ground.
The 220uF is the time delay setting component and might be worth swapping but its not the prime suspect here.
In the first post you mentioned 'distortion' but now you say it all works fine when the relay is engaged. I would concentrate just on the relay not engaging and what I would do is measure (during the time the relay is not engaged) the actual triggers to the protection circuit to see if anything is tripping it. There are numerous interwoven trips and triggers within the whole circuit but ultimately the relay is driven from IC601 and so that is where I would look, at all the inputs to the chip.
The four at the left are DC offset inputs and over current inputs. The two lower ones on the 100k resistor should be at close to zero volts. I think the other two will be 'floating' and so appear 'high' and if there is a trip condition they will go 'low' to zero volts but I recommend checking the status of these when it is working OK as that will be the normal status of them.
Also the two caps circled (particularly the small 1uF) could be favourite. C606 (which provides AC power detection)has a hard time and is exactly the type and location of a part that could fail/deteriorate. That is well worth just swapping before you do anything more complex. A 1uF 63v or 100v electrolytic would be fine and observe the polarity as + of the cap goes to ground.
The 220uF is the time delay setting component and might be worth swapping but its not the prime suspect here.
Hello Mooly, thanks for your earlier response. Apologies for the delay in my response. I wanted to get some things sorted out and gather as much info as possible before writing you a reply here. This way, you will have a clearer picture of what I am dealing with and how far we have progressed with this amp. At this moment, the amp is sent in for service. Kindly allow me to clear a few things below.
Referring to the 'distortion' that I mentioned in my original post, I should have been clear. I was trying to say that the amp working as it should after the relay clicked. In other words, when the amp's status lights go from red/amber to green, the amp works normally. It did not go into protection mode whilst in use at any time as well. What I did was plug the speakers into the integrated amp without the NAD power amp to see if this produced the same distortion. It did. So, it is clear that the distortion issue is being caused by damaged speaker cones and not from either of the amps.
During the time after your last response, I noticed a few things. However, the delay in the relay clicking was getting slower(6-8mins on average) each passing day when I powered up the amp. There were a few times the relay clicked within 2-3mins. One other thing I observed was that when the relay has clicked and it was ready for use or in use, switching it off and powering it on again within a few seconds or minutes would get the relays to click immediately. The delay seems to only happen when it is switched on for the first time. Subsequent power offs and ons do not recreate this issue. The techs at NAD got me to perform this. I was thinking if it was to establish something thermal-related but I was wrong.
Also, you were right about the mains. We can rule out the mains being the culprit here. When the unit was with them, it was powered on whilst connected to a DAC and a set of speakers. It displayed the same symptoms I was facing at home. The techs earlier thought that it could be the power drawn from my mains at home that was causing the amp's relay to be delayed.
I have provided the NAD techs with the guidance in your earlier post. They were not entirely sure what could be causing this problem but your explanation was immensely helpful, which gave us some hope. I will be closely following their findings and will come back to this thread with an update as soon as I get one. I am extremely grateful for your time and guidance on this matter. Thank you very much for your help with this. I really hope we find a solution.
Referring to the 'distortion' that I mentioned in my original post, I should have been clear. I was trying to say that the amp working as it should after the relay clicked. In other words, when the amp's status lights go from red/amber to green, the amp works normally. It did not go into protection mode whilst in use at any time as well. What I did was plug the speakers into the integrated amp without the NAD power amp to see if this produced the same distortion. It did. So, it is clear that the distortion issue is being caused by damaged speaker cones and not from either of the amps.
During the time after your last response, I noticed a few things. However, the delay in the relay clicking was getting slower(6-8mins on average) each passing day when I powered up the amp. There were a few times the relay clicked within 2-3mins. One other thing I observed was that when the relay has clicked and it was ready for use or in use, switching it off and powering it on again within a few seconds or minutes would get the relays to click immediately. The delay seems to only happen when it is switched on for the first time. Subsequent power offs and ons do not recreate this issue. The techs at NAD got me to perform this. I was thinking if it was to establish something thermal-related but I was wrong.
Also, you were right about the mains. We can rule out the mains being the culprit here. When the unit was with them, it was powered on whilst connected to a DAC and a set of speakers. It displayed the same symptoms I was facing at home. The techs earlier thought that it could be the power drawn from my mains at home that was causing the amp's relay to be delayed.
I have provided the NAD techs with the guidance in your earlier post. They were not entirely sure what could be causing this problem but your explanation was immensely helpful, which gave us some hope. I will be closely following their findings and will come back to this thread with an update as soon as I get one. I am extremely grateful for your time and guidance on this matter. Thank you very much for your help with this. I really hope we find a solution.
Hey Mooly, glad to hear that the problem is within this particular circuit. I got an update from the tech who followed your guidance. The 1uf cap(C606) was desoldered and measured and seems to be within specs. The relay contacts are good as well. He suspects the IC601(TA7317P) to be causing the problem. More inspection is to follow this week. I have been searching for this part and it seems to be discontinued. Also, there seem to be counterfeits floating around online; some of the reputable part stockists don't seem to have them as well.
Caps fail in many ways and its normal for a failed cap to still read as correct in terms of its value.
A scope check would confirm if there is excess ripple on that cap but normally you would just replace anything like that to eliminate it once and for all tbh.
Measurement is always key to diagnosis. If the chip is suspected then first step is to go around all the pins with a meter and a scope and make sure all inputs are at the expected values and that inputs are clean with no ripple or unexpected noise.
A scope check would confirm if there is excess ripple on that cap but normally you would just replace anything like that to eliminate it once and for all tbh.
Measurement is always key to diagnosis. If the chip is suspected then first step is to go around all the pins with a meter and a scope and make sure all inputs are at the expected values and that inputs are clean with no ripple or unexpected noise.
Hello Mooly. I got an update from the techs earlier today. The cap C604 220uf 10v cap gave a reading over specs—something like 290uf. The tech went on to check the values around the chip IC601, and they came out within specs.
So, is this indicative that this cap C604 has gone bad, or is it still within what most would call 'within tolerance'? I will process with your advice.
Also, what else should I replace? I might as well get them to replace those likely to cause problems in the future.
So, is this indicative that this cap C604 has gone bad, or is it still within what most would call 'within tolerance'? I will process with your advice.
Also, what else should I replace? I might as well get them to replace those likely to cause problems in the future.
Tolerance on electrolytic caps is very wide, historically even +50% and -20% was acceptable. If these techs are knowledgeable then they should know all this 🙂 and also know that measuring capacitance values doesn't tell us much in a lot of cases.
https://www.digikey.co.uk/en/articl...-esr?msockid=1ca4d3658d5268ca0f72c6aa8c756935
If all the values around the chip really are correct then the output pin of the chip (which will be an 'open collector' output should go low and energise the relays. So this is where absolute accuracy in interpreting results comes in. If... IF all the conditions around the chip really are correct then the output pin should be at zero volts and the relays should close.
If that is not happening then you have to suspect the chip but that in reality is the last part to suspect normally... but if measurements have been to prove otherwise then you have to replace it.
https://www.digikey.co.uk/en/articl...-esr?msockid=1ca4d3658d5268ca0f72c6aa8c756935
Think that through 🙂
If all the values around the chip really are correct then the output pin of the chip (which will be an 'open collector' output should go low and energise the relays. So this is where absolute accuracy in interpreting results comes in. If... IF all the conditions around the chip really are correct then the output pin should be at zero volts and the relays should close.
If that is not happening then you have to suspect the chip but that in reality is the last part to suspect normally... but if measurements have been to prove otherwise then you have to replace it.
Hey Mooly, I told them they should have sound knowledge about the cap tolerance levels, but in a nice way. 🤣Strangely, they only use a voltmeter and nothing more like an oscilloscope. No idea why they don't have one when it would be of great benefit to their work. I think they have adopted a policy to do only work on a component level- some basic swapping out of caps when they measure out of spec, and other simple soldering work. Mind you, this is NAD's service centre that we are talking about.
For the IC601 chip, I was told that the values around it are within spec. They measured around the chip and concluded that it is fine. The resistors are also within spec. What they did was replace the C604 cap. According to them, they are not taking chances with this cap, showing that reading. So, after replacing it, the amp has been coming on from AMBER/RED to GREEN within 5-10 seconds. It has been 2-3 days, and each time it is powered up, it comes on within this time frame. I used to see it come on quite immediately(2-3 seconds). Do you think this is acceptable, or is there more to this despite the change in cap? I was told by someone else that a capacitor normally decreases in value, but the equivalent series resistance will increase. The capacitor with a higher value will take longer to charge, so in this case, it makes sense to replace it, which eliminates the capacitor as a possible cause.
The relays were removed and checked. The contacts were cleaned. Works fine. Next week, if this startup of 5-10 seconds remains, they will swap out the C606 capacitor as well and see if it comes on much quicker. Like you said, the chip would be the last thing they would want to replace for now.
For the IC601 chip, I was told that the values around it are within spec. They measured around the chip and concluded that it is fine. The resistors are also within spec. What they did was replace the C604 cap. According to them, they are not taking chances with this cap, showing that reading. So, after replacing it, the amp has been coming on from AMBER/RED to GREEN within 5-10 seconds. It has been 2-3 days, and each time it is powered up, it comes on within this time frame. I used to see it come on quite immediately(2-3 seconds). Do you think this is acceptable, or is there more to this despite the change in cap? I was told by someone else that a capacitor normally decreases in value, but the equivalent series resistance will increase. The capacitor with a higher value will take longer to charge, so in this case, it makes sense to replace it, which eliminates the capacitor as a possible cause.
The relays were removed and checked. The contacts were cleaned. Works fine. Next week, if this startup of 5-10 seconds remains, they will swap out the C606 capacitor as well and see if it comes on much quicker. Like you said, the chip would be the last thing they would want to replace for now.
Hey Mooly, I was disappointed as well. I am equally frustrated that all the help you have been providing me with is not fully utilised to diagnose this problem. My sincere apologies. If it is not resolved next week, I will find a competent person in this field who is properly equipped to service it, or I will just get hold of these devices to fix this myself. The only thing I am afraid of is working with equipment that is plugged in. I have a V-meter, soldering tools etc. A scope it is then. 😢