Hi guys,
I am working on Sony v-fet gear for about 15 years as hobby. Mainly cleaning overhauling and readjusting them. I have worked on at least 50 Sony TA-4650 in that period and saved many of them from becoming just a big and lumpy paper weight.
And one issue is still hard to solve; popping speakers when turning off the amp. Renewing the relay and capacitors is standard procedure, since the old ones are unreliable. Checking all the transistors and when needed, changing the transistors and resistors aswell. Still sometimes it is impossible to not have this annoying pop in the speakers. Yes I do check all the parts in the speaker protection circuit.
And yes I am also aware of the later changes in the circuit advised by Sony.
Anyone an idea how to solve this annoying issue ?
I am working on Sony v-fet gear for about 15 years as hobby. Mainly cleaning overhauling and readjusting them. I have worked on at least 50 Sony TA-4650 in that period and saved many of them from becoming just a big and lumpy paper weight.
And one issue is still hard to solve; popping speakers when turning off the amp. Renewing the relay and capacitors is standard procedure, since the old ones are unreliable. Checking all the transistors and when needed, changing the transistors and resistors aswell. Still sometimes it is impossible to not have this annoying pop in the speakers. Yes I do check all the parts in the speaker protection circuit.
And yes I am also aware of the later changes in the circuit advised by Sony.
Anyone an idea how to solve this annoying issue ?
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Its all down to timing and speed of the relay being de-energized .
Have you cleaned the wafer switches the relay contacts route to as they are in the last position before reaching the speakers ?
Otherwise check out the components connected to the relay coil in case a change of value due to old age.
Have you cleaned the wafer switches the relay contacts route to as they are in the last position before reaching the speakers ?
Otherwise check out the components connected to the relay coil in case a change of value due to old age.
I am always suspicious of the speed the relay can de-energise after power down in such circuits. The only way to make this fast is to monitor the AC waveform. So, perhaps the relay is switching off at its designed speed but some amps are producing a significant transient during this time.
It is worth trying to establish how fast the relay turns off in a good and a bad amp and if different proceed with repairs/improvements of the relay circuit. At the same time it is also worth examining the turn off transient at the output of a good and a bad amp.
It is worth trying to establish how fast the relay turns off in a good and a bad amp and if different proceed with repairs/improvements of the relay circuit. At the same time it is also worth examining the turn off transient at the output of a good and a bad amp.
Hi Duncan,
Yeah it is some consolation haha. I don't feel like a total fool.
The weird thing is that the plopping in the speakers does not happen when using the poweramplifier seperately or coupled with an external preamplifier. As you might know, the power amp and preamp can ben used seperately.
Yeah it is some consolation haha. I don't feel like a total fool.
The weird thing is that the plopping in the speakers does not happen when using the poweramplifier seperately or coupled with an external preamplifier. As you might know, the power amp and preamp can ben used seperately.
Thats a clue Roerdomp , just as a test connect a 0.1uf capacitor in series with the preamp output and the power amp input externally and tell me if it makes any difference.
Yes I know there is a series capacitor in the preamp output but just try that , it might make no difference but you have to locate faults in stages.
Yes I know there is a series capacitor in the preamp output but just try that , it might make no difference but you have to locate faults in stages.
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As you have said it only happens with the built in preamp then a fast pulse must be coming from it ,faster than the safety relay timing cut-off .
Try cutting out all other sections of the preamp like switching off the tone control section -loudness switch-mode switch and filters so that we can narrow it down further .
Try cutting out all other sections of the preamp like switching off the tone control section -loudness switch-mode switch and filters so that we can narrow it down further .
You have a number of 3.3uF local decoupling capacitors in the preamp. The relay should trip before the dc level in these capacitors reduces significantly - if any of these is leaky that is a possible cause of a pulse at switch off. You could check this with a meter at these points and with other capacitors in the signal path.
Hi Mjona,All of the electrolytic capacitors (including the 3,3uF caps you mention) have been replaced with high quality Panasonic caps from a reliable source. I also just changed the 1/2 Watt 470 Ohm resistors on the relay board. They were more off than I suspected. (the attached pic shows the original resistors on the relay board). No difference either. I was thinking of taking a good working non popping 4650 (I have quite a few) and change the boards one by one to narrow down the search. I am quite motivated to find the bug ;-). And great to have some help with this.
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i will check the coil. But to be honest. I have used these replacements for many 4650 amps and other v-fet amps. If the amp pops with the original relay, it will pop with the replacement relay. If it does not pop with the original relay, it will not pop with the replacement. I only replace them because the contruction of most of the originals is unreliable.