Hi,
My friend has one Nait 1 - serial nr.10701 , built 1983 !
But the amp is not working anymore
When i am turning the amp on, then there is a low level noise coming out of the ludspeakers - something like "tsrtsrtststr" and the bass loudspeakers are moving very slowly. It is happening already before the preamp relais is turned on. Both channel are identical and there is not music coming out at all. My friend said, that few months ago after the amp was turned on half an hour, than the noise was away and the amp was working.
Does anybody can help me ?
I am thinking that it is something probably in the poweramp stage, because this is appearing immediately after turning the amp on. The big caps dried out ? or something else ? Any ideas ?
Cheers, Tomek
My friend has one Nait 1 - serial nr.10701 , built 1983 !
But the amp is not working anymore
When i am turning the amp on, then there is a low level noise coming out of the ludspeakers - something like "tsrtsrtststr" and the bass loudspeakers are moving very slowly. It is happening already before the preamp relais is turned on. Both channel are identical and there is not music coming out at all. My friend said, that few months ago after the amp was turned on half an hour, than the noise was away and the amp was working.
Does anybody can help me ?
I am thinking that it is something probably in the poweramp stage, because this is appearing immediately after turning the amp on. The big caps dried out ? or something else ? Any ideas ?
Cheers, Tomek
Tomek,
You have a good chance caps are worn out. Go for the ones in the PSU first, then those located near heat sinks.
/Hugo 🙂
You have a good chance caps are worn out. Go for the ones in the PSU first, then those located near heat sinks.
/Hugo 🙂
Hi Tomek,
I am thinking the bypass caps are open. Main filters may be bad too, but you would hear a hum. The feedback cap, if used, should be replaced as well.
-Chris
I am thinking the bypass caps are open. Main filters may be bad too, but you would hear a hum. The feedback cap, if used, should be replaced as well.
-Chris
Hmmm,
I had some ps caps from recapping of my own nait, old but OK, i exchanged them, but there is no change.
I did some measurement - the tension on both main ps caps is pulsing form 15.5 to 17 Volts and the tension on one preamp ps cap (nait has only one big ps cap for preamp section) is also pulsing in the same range. The feedback caps are tantal, and they are only few electrolite caps in the pa section. And when you look at the picture, one can see that three of pa transistors have different colour ?
Maybe the rectifier is not OK and is not delivering stable dc ? Some mix from dc and ac ?
I have not the schematics, i send a picture for the better orientation.
🙂
I had some ps caps from recapping of my own nait, old but OK, i exchanged them, but there is no change.
I did some measurement - the tension on both main ps caps is pulsing form 15.5 to 17 Volts and the tension on one preamp ps cap (nait has only one big ps cap for preamp section) is also pulsing in the same range. The feedback caps are tantal, and they are only few electrolite caps in the pa section. And when you look at the picture, one can see that three of pa transistors have different colour ?
Maybe the rectifier is not OK and is not delivering stable dc ? Some mix from dc and ac ?
I have not the schematics, i send a picture for the better orientation.
🙂
Attachments
Hi Tomek,
I see two electrolytic caps per channel. The tantalums are not immune either. In the area to the right there are piles of capacitors (13). There are more behind the preamp filter cap.
The reason the voltage is pulsing is current draw. This will affect both channels. It sounds like the circuit is motorboating but the hiss may indicate HF oscillation. An oscilloscope would be real handy right now.
-Chris
I see two electrolytic caps per channel. The tantalums are not immune either. In the area to the right there are piles of capacitors (13). There are more behind the preamp filter cap.
The reason the voltage is pulsing is current draw. This will affect both channels. It sounds like the circuit is motorboating but the hiss may indicate HF oscillation. An oscilloscope would be real handy right now.
-Chris
Hi,
I have a "scope". Where should i connect it ?
I will try it tomorrow. On the right side there is mm premp, there is a lot of caps there ...
But i think that it should be something in the pa section left, because the preamp section right is getting power ~3 seconds after turning the amp on, and this "pump" effect is just from the begining. So i will check the small elcos and tants on the left side tomorrow.
🙂 Thanks for so much attention
I have a "scope". Where should i connect it ?
I will try it tomorrow. On the right side there is mm premp, there is a lot of caps there ...
But i think that it should be something in the pa section left, because the preamp section right is getting power ~3 seconds after turning the amp on, and this "pump" effect is just from the begining. So i will check the small elcos and tants on the left side tomorrow.
🙂 Thanks for so much attention
Hi Tomek,
Look at both the positive and negative supplies to see what's there. Also, check the speaker output terminals. You may get a large HF signal. Check the "top" or feed terminals of the volume control to see what is coming from the preamp circuit, if anything.
-Chris
Look at both the positive and negative supplies to see what's there. Also, check the speaker output terminals. You may get a large HF signal. Check the "top" or feed terminals of the volume control to see what is coming from the preamp circuit, if anything.
-Chris
the circuit looks simple , it shouldnt be a problem to fix it
this is a very old amp and probably got bad solder joints ,i think thats the problem
this is a very old amp and probably got bad solder joints ,i think thats the problem
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