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KGST headphone amp transient misbehaviour


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I've got a pair of Stax SR-009 driven by a custom built (Headinclouds) KGST amplifier that I bought second hand. It sounds great but every so often misbehaves. The pattern of misbehaviour is consistent - about 5 minutes after turning the amp on, one channel plays lower and sounds very distorted. This continues for about 10 minutes, and then the amp is fine from then on no matter how long I listen to it for. I've checked the valves with an IR thermometer and they're all running the same temperature at the time, but don't really have the facility to check them any other way. I've tried switching the valves around, and replaced them with different sets but it doesn't seem to impact the problem and channel affected, suggesting to me the problem is elsewhere. I can work around it by turning it on half hour before but this isn't always practical. I don't know the first thing about the internals of an amp or who to seek that might be able to help test/fix it. Anyone got any suggestions? Thanks.

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Thats an unusual issue.  I have no idea but it seems like when warming up there's an issue. Maybe a poor connection with thermal expansion? Is it worth checking the solder joints or cleaning the tube socket contacts just to ensure its not something simple?

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Have the same amp(built by Soren Brix) and I actually never listen to it for the first 30 minutes...would solve your problem but there might be something more serious further down the line.

Have you tried to contact 'Headinclouds' on HeadFi for advice?

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Thanks guys. I'm not sure where to begin when looking for dry solder joints. I've cleaned the valve contacts and sockets without any improvement. I might give headinclouds a ping.

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4 hours ago, Ittaku said:

I've got a pair of Stax SR-009 driven by a custom built (Headinclouds) KGST amplifier that I bought second hand. It sounds great but every so often misbehaves. The pattern of misbehaviour is consistent - about 5 minutes after turning the amp on, one channel plays lower and sounds very distorted. This continues for about 10 minutes, and then the amp is fine from then on no matter how long I listen to it for. I've checked the valves with an IR thermometer and they're all running the same temperature at the time, but don't really have the facility to check them any other way. I've tried switching the valves around, and replaced them with different sets but it doesn't seem to impact the problem and channel affected, suggesting to me the problem is elsewhere. I can work around it by turning it on half hour before but this isn't always practical. I don't know the first thing about the internals of an amp or who to seek that might be able to help test/fix it. Anyone got any suggestions? Thanks.

 

Well, you bring these things down on your head, Con, by your persistence with rarely-travelled hifi byways.

 

If you stuck to the 'straight & narrow' - Bose, for instance - you wouldn't have such problems  :winky:

 

Andy

 

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46 minutes ago, andyr said:

 

Well, you bring these things down on your head, Con, by your persistence with rarely-travelled hifi byways.

 

If you stuck to the 'straight & narrow' - Bose, for instance - you wouldn't have such problems  :winky:

You know that kind of hurts now that I think about it...

Preamp - choke was loose when I got it, started tripping breakers, got rebuilt, then had a hum problem and needed someone else to fix it.

Power amps - had the logic board for power on fail and needed replacing.

DSP - Output issues and hanging firmware

DAC - Sometimes synced at 95k with the output from the DSP instead of 96 and needed a workaround to sync properly.

Headphone amp - channel cutting out till very warm.

Subwoofer - Plate amp failed needing replacing

The most reliable part of my hifi has been the speakers... AND I BUILT THE DAMN THINGS MYSELF!

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  • 10 months later...

Just as a long term follow up to this thread, I contacted headinclouds directly (who built the amplifier) and although he no longer builds amps, he was very helpful at how to test the amp , valves, and fine tune bias and tighten a few potential points of poor contact and one of the above seems to have fixed the issue.

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