Loud “snap” when turning on Sony TA-1150 integrated

Two days ago, I could not resist temptation and bought a Sony TA-1150 integrated amplifier. Advertised as being in working condition, and it is but exhibits a loud “snap” or “pop” when turning on the power switch.

It was not possible to audition the amp at point of sale, I was unprepared and the owner had no signal source with compatible plugs. All I brought along was a DMM to check DC offset which was low enough - 16mv & 30mv.

The owner was a personable fellow and I accepted his saying he successfully used the amp a number of years before retiring it some 5 years ago. The price settled on was about what the amp sold for brand new in 1973. I paid such a price because the model is not common and was the first brand new stereo amp that I ever bought.

Once at home and hooked up I confirmed it was as described meaning it worked. A pleasant surprise was none of the controls were noisy at all and that includes two sliders.

However, as the thread title states, there is a loud noise when turning on. Having previously lived with a TA-1150 I can attest that is not typical.

Gleaning information from forums, a capacitor at the power switch
is generally employed to counteract this occurrence. My observations of amplifier “innards” is somewhat minimal but capacitors I’ve seen connected to power switches have been the ceramic disc type. Those, I thought, lasted indefinitely.

Purchasing this amplifier may have been bad timing as I am midway through an out of town move. Consequently, nearly all I own is packed and in storage so no tools handy.

If there is one, is replacing that capacitor the most likely fix? If so, I can accomplish that in short order at a friend’s place before I move. And, while there is still a components parts store near by.
 
If the two rails have very different capacitances now due to one of them deteriorating that would make any turn-on thump much worse as one rail rises much faster, so I'd definitely want to check the main filter caps. The arcing of the power switch happens long before the amplifier is able to respond to its EMI, so the switch can only be a source of noise at switch-off, not switch-on.


Its old enough for many capacitors to have deteriorated, so I suspect those first, after checking the bias settings (underbiased can produce instability)
 
Most likely, the power switch's contacts have oxidized, loaded with carbon now from "sparking".
If possible, dissassembling, burnishing the contacts, cleaning, and adding a fresh .047uf/630v mylar cap across the switch should eliminate the problem.
Been there, done that many times for vintage equipment.
 
The service manual is HERE

Leave it to Sony to do something different... there does not appear to be a delay turn on relay on the speaker outputs of this amplifier. There is a muting circuit that is described as preventing turn on thumps (See Thumbnail).

Most likely the timing capacitor C534 has gone defective. The delay circuit is described on page 4 of the PDF file.
 

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Most likely, the power switch's contacts have oxidized, loaded with carbon now from "sparking".
If possible, dissassembling, burnishing the contacts, cleaning, and adding a fresh .047uf/630v mylar cap across the switch should eliminate the problem.
Been there, done that many times for vintage equipment.


That would lead to continuous/intermittent arcing interference during operation, not just a single crack at switch on.


The amp is unpowered at switch on, by the time the rails are rising and the amp can do anything to the speakers the mains switch will have long since (many ms) settled down (unless its really bad and causing continuous problems and melting down!)


Cracks are due to the amp's feedback loop snapping into lock as the rails rise and is usually much worse if the rails don't rise together or rise too slowly, or if the power amp stabilizes before the preamp.


Single-rail amps always have a big thump due to charging the output capacitor, dual-rail amps can be pretty well-behaved by comparison especially if constant current sources are used (the amp can then work from low rail voltages, ie it locks early in the rail-power-up sequence).
 
Thank you to those who posted the good replies. It’s unlikely I’ll be able to pay any attention to this amplifier until this spring, after I’ve moved. My spare time must now be devoted to getting the suite I’ve lived in for 20 years onto the market.

Logic800, that is an interesting test. I will try it but by the time I get home tonight, the amp will have been idling for 24 hours. Might or might that not have a bearing on the result?
 
The test suggested be Logic800 was informative, I think. Since the amp was idling for 24 hours, I unplugged it, waited an hour then plugged it back in.

Powering up that way does produces a noise, maybe more of a “pop” than a “snap” but good & healthy (as in fairly loud) nonetheless.
 
The test suggested be Logic800 was informative, I think. Since the amp was idling for 24 hours, I unplugged it, waited an hour then plugged it back in.

Powering up that way does produces a noise, maybe more of a “pop” than a “snap” but good & healthy (as in fairly loud) nonetheless.

That is a turn on thump. It results from momentary instabilities in the amplifier and power supply while capacitors charge up and settle in.

As I noted in Post #4 that amp does not have the usual relay on it's outputs but rather uses a muting circuit in the pre-amp section. If the muting circuit is working as designed, that thump you're getting may become unavoidable as your amplifier ages.

Please be aware that turn-on thumps like that have been known to damage speakers.
 
Yes, I was aware a relay was not present. At this point I cannot say if that muting circuit is functioning properly or not. I have still not removed the cover yet but may have the opportunity to do so within the next 48 hours. But I’d like to have in hand a suitable replacement capacitor. Unfortunately the shop I’d visit to get one is in the opposite direction of where I must travel tomorrow. So I’ll check for an alternate source where I’m heading but am not optimistic.

The place where I’m sure to find one is a 3 hour round trip and preparing for my impending move plus my employment leaves very little time for side trips.
 
Built on a 2" by 2" perfboard and mounted in several amps/receivers already.
Works excellently, simple to build.

Eliminates any turn-on thumps, plus if volume is cranked upon turning the unit on, it will mute sound until volume is lowered.
 

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Built on a 2" by 2" perfboard and mounted in several amps/receivers already.
Works excellently, simple to build.

Eliminates any turn-on thumps, plus if volume is cranked upon turning the unit on, it will mute sound until volume is lowered.

Thanks for the diagram and if circumstances were different I'd enjoy cobbling one of those together then be pleased as punch with myself if it worked. But at the moment, I'd rather restore the mute circuit, as it sounds like that's what's creating the noise.
 
Now have 2 issues - new cap @ C534 ineffective & now need new pilot lamp.

This morning, from a chance meeting, I got a 10V 33uf capacitor from a tech I encountered who repairs industrial controls.

I checked the old one with my DMM and obtained a reading of 10uf or there abouts. The new one was 33.1uf so in it went. Unfortunately, the "snap" or "pop" is still present at turn on. My skill for interpreting schematics is weak but might there be a problem with the 2SC634A at Q501?

*I ask because some time ago, a Hafler DH-110 had a problematic transistor within one channel's mute circuit. The required transistor was still available and replacement fixed it*.


But my luck being as bad as it is, I've created for myself a 2nd problem involving the neon pilot lamp. Unknowingly one of it's leads broke off right at the glass. There's no number that I can see except Sony # 1-519-072-00 from the parts list (or PL1 on the schematic).

I sampled the voltage and got (give or take) 100V AC both before and after an inline 56K resistor.

My assumption is a direct replacent lamp is long gone so I ask if anyone can suggest a replacement? It glowed green.
 

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Depending on how 'original' you need the amp to be, you could replace it with a green LED, pulling the power from a low voltage line instead of mains.


That would be my way of doing it also.
LED's don't consume any power that would disturb things.


As for that old neon lamp, it can be replaced with any standard NE2 lamp (lights up redish-orange) and be just fine.
 
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'Not sure of your local supply situation but Vancouver is big enough to have many suppliers of the still common miniature neon bulbs as well as the usual Mouser, Digi key and Newark distributors. e.g.https://www.digikey.com.au/products/en?keywords=Neon bulbs
They're still fitted in simple mains operated switchgear and appliances so they'be with us for a while yet.

A green colour would be the result of a coloured plastic sleeve, tinted varnish coating or a coloured lens etc - seldom by a particular coloured glass bulb. I guess if you must have a green glow, you must but they don't get hot and there are many ways, including just rolling some dark green tinted plastic film around it. This should be obtainable from gift wrapping or craft stores.
 
Depending on how 'original' you need the amp to be, you could replace it with a green LED, pulling the power from a low voltage line instead of mains.

A few years ago I gave LED's a try in an Akai component. At the time, I was provided a circuit diagram for a power supply involving a rectifier and capacitor. It worked but I no longer have that diagram. But I'm going to try the quick fix of an NE-2.

That would be my way of doing it also.
LED's don't consume any power that would disturb things.

As for that old neon lamp, it can be replaced with any standard NE2 lamp (lights up redish-orange) and be just fine.

Ditto.

'Not sure of your local supply situation but Vancouver is big enough to have many suppliers of the still common miniature neon bulbs as well as the usual Mouser, Digi key and Newark distributors. e.g.https://www.digikey.com.au/products/en?keywords=Neon bulbs
They're still fitted in simple mains operated switchgear and appliances so they'be with us for a while yet.

A green colour would be the result of a coloured plastic sleeve, tinted varnish coating or a coloured lens etc - seldom by a particular coloured glass bulb. I guess if you must have a green glow, you must but they don't get hot and there are many ways, including just rolling some dark green tinted plastic film around it. This should be obtainable from gift wrapping or craft stores.

There is a parts store in Vancouver, albeit a 3 hour round trip. Their website says they have on hand NE-2 bulbs. Two different ones it seems and one is described as blue/green. The other presumably is regular orange. No voltage is quoted for the blue/green bulb but I'm going to assume it's 110V which is the voltage cited for the regular bulb.

I'll make that trip this morning, get a few of both and see what works. I'm a bit skeptical if my voltage will be sufficient. Because as mentioned, when I checked it, the reading was 100V.


Any educated guesses whether that 2SC634A transistor at Q501 could be causing the turn on "snap/pop"?
 
A few years ago I gave LED's a try in an Akai component. At the time, I was provided a circuit diagram for a power supply involving a rectifier and capacitor. It worked but I no longer have that diagram. But I'm going to try the quick fix of an NE-2.

Ditto.

There is a parts store in Vancouver, albeit a 3 hour round trip. Their website says they have on hand NE-2 bulbs. Two different ones it seems and one is described as blue/green. The other presumably is regular orange. No voltage is quoted for the blue/green bulb but I'm going to assume it's 110V which is the voltage cited for the regular bulb.

I'll make that trip this morning, get a few of both and see what works. I'm a bit skeptical if my voltage will be sufficient. Because as mentioned, when I checked it, the reading was 100V.

Any educated guesses whether that 2SC634A transistor at Q501 could be causing the turn on "snap/pop"?


NE2 lamps in general "fire up" at around 55 to 60 volts AC.
So there should be no problem at 100 volts.
 
NE2 lamps in general "fire up" at around 55 to 60 volts AC.
So there should be no problem at 100 volts.

So far, so good with the new neon bulb. What they called blue/green is just green and closely duplicates the original colour. And I'm going to say, of equal intensity.

I'll have to pursue the turn on noise later on in the year. Moving out chores plus my employment are occupying nearly all my time.

Thanks to all for giving of your time, responding to this thread.