Gary's good tunes 700 build

62vauxhall said:
Seems the 700B is OK. I did what I do best and assumed....that since rotating the preamp's volume control did not increase or decrease the spurious noise, that the cause must be within the power amp.

I disconnected the PL and placed it where I could keep a convenient eye on it at idle while hooked up to a small pair of speakers. Several hours passed and no noise. I then installed a different power amp in the system and there was the noise. This is somewhat distressing because the preamp I've been using for the past 2 or 3 weeks was the one in which I replaced 41 capacitors and it was fine until recently. My hope is the fact the noise is not affected by the volume control, that it will narrow down where I should be looking for a fault.

That preamp is in front of me as I type this, powered up with a a pair of headphones plugged in and I now know that operating any control or switch does not affect the noise at all. It is sporadic, just on the right channel and nothing increases or decreases it's loudness.
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That would appear as either a semiconductor going bad (bad bond wire) or a poor solder joint somewhere in the preamp.
 
Gepetto said:
That would appear as either a semiconductor going bad (bad bond wire) or a poor solder joint somewhere in the preamp.
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And you have it narrowed down to something after the volume control circuit section of the preamp. That will help you pinpoint it.
 
The noise is from the right channel.

It's been conveniently beside me all day so I could monitor it and this morning, was hearing it sputter, crackle and pop through headphones but it seemed to go away after a time. Just the opposite of what it was doing yesterday. Even though it settled down and didn't make noise for an hour or two, I took off the covers, unplugged it, and examined the solder connections with an illuminated magnifier. I planned to do some poking around with an eraser tipped pencil after I turned it on thinking that's when the noise would probably start up but it didn't.

I think someone is having a bit of fun with me because I've had the cover off all afternoon, it's been on and idling right beside me but has not made any noise. Even though it was behaving itself, I re-soldered a couple of connections I noticed earlier that were physically solid but looked iffy.

I'll let it sit overnight and see what it does tomorrow.
 
Gary....the only way to know for sure whether it's the pre or the amp is to install shorting plugs in the RCA Jacks in the amp. As you've seen, you can have a problem in the pre post volume control. In your case where you don't have volume controls on the amp, direct from a CD player with adjustable output also works.
Did you replace any semiconductors in the pre along with the caps??
 
62vauxhall said:
The noise is from the right channel.

It's been conveniently beside me all day so I could monitor it and this morning, was hearing it sputter, crackle and pop through headphones but it seemed to go away after a time. Just the opposite of what it was doing yesterday. Even though it settled down and didn't make noise for an hour or two, I took off the covers, unplugged it, and examined the solder connections with an illuminated magnifier. I planned to do some poking around with an eraser tipped pencil after I turned it on thinking that's when the noise would probably start up but it didn't.

I think someone is having a bit of fun with me because I've had the cover off all afternoon, it's been on and idling right beside me but has not made any noise. Even though it was behaving itself, I re-soldered a couple of connections I noticed earlier that were physically solid but looked iffy.

I'll let it sit overnight and see what it does tomorrow.
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having the cover off changes the thermal environment. Smells like a semiconductor bond wire to me. You will never see that as it is inside the encapsulation
 
laatsch55 said:
Gary....the only way to know for sure whether it's the pre or the amp is to install shorting plugs in the RCA Jacks in the amp. As you've seen, you can have a problem in the pre post volume control. In your case where you don't have volume controls on the amp, direct from a CD player with adjustable output also works.
Did you replace any semiconductors in the pre along with the caps??
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No semi conductors were replaced, just capacitors and only electrolytics.

I've not had this particular preamp connected to the PL since yesterday morning. It's been in a different room, by itself with only headphones plugged in and was producing that noise. When I pulled it, I stuck my Hafler DH101 back in the system and it is without that issue.
 
Gepetto said:
having the cover off changes the thermal environment. Smells like a semiconductor bond wire to me. You will never see that as it is inside the encapsulation
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I need to learn what a semi conductor bond wire within encapsulation is.

But the thermal change without the covers on is interesting. When I get home tonight I'll put them back on to see if the noise returns.

I noticed this morning that with covers off and although there was not the spurious noise it was making before there was some but different in nature and less intense. It was on both channels, not just the right and also sporadic - more like a "pop".

I thought perhaps that my reflowing a couple of solder joints might have contributed to " noise reduction" but re-installing the covers might dispel that idea.
 
A bond wire is the internal connection inside the device...IE..transistor or diode etc...
 
Another trick is to use a hair dryer to apply some heat....don't cook the device to destruction though. A hair dryer is plenty hot enough to do that....just warm it up.....rare, not well done.
 
laatsch55 said:
Another trick is to use a hair dryer to apply some heat....don't cook the device to destruction though. A hair dryer is plenty hot enough to do that....just warm it up.....rare, not well done.[/QUOTE

Interesting, I'll hit a thrift store today for a hair dryer. I personally haven't used one since the mid. 70's and all's I got's now is a hot air gun.
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Any such thing as solid state microphonics?

laatsch55 said:
A hot air gun will do....just use it in low setting..
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Darn, I read your post after buying a used hair drier. Oh well, only the price of a Happy Meal.

A dangerous pastime I know but I was thinking. Before I took off the covers yesterday and with headphones plugged in, I tapped around on the top case. I did this in between "noise events" in order to see if I could induce one. That did not occur but what did happen was a sound like tapping on a microphone. I know tubes can be microphonic, I've witnessed it first hand, but can a transistor also do this?
 
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laatsch55 said:
Gary, I don't know for sure...that's a Joe question.
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If you have a broken bond wire connection inside a semiconductor then yes you can get popping and microphone like sounds when tapping or causing mechanical shock. When the bond wire breaks, the weld connection between the die and connection wire is only there under the pressure of mechanical contact. So any shock motion will aggravate such a connection. It is not microphonics in the sense of tube vibration but it is a mechanical phenomena.
 
Gepetto said:
If you have a broken bond wire connection inside a semiconductor then yes you can get popping and microphone like sounds when tapping or causing mechanical shock. When the bond wire breaks, the weld connection between the die and connection wire is only there under the pressure of mechanical contact. So any shock motion will aggravate such a connection. It is not microphonics in the sense of tube vibration but it is a mechanical phenomena.
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Thanks. That could help track down the offender. If it is a transistor, I'm hoping that a direct tap will identify it. I'll try that when I get home in a couple of hours. Would doing that be of any use or should I be digging out the DMM?
 
62vauxhall said:
Thanks. That could help track down the offender. If it is a transistor, I'm hoping that a direct tap will identify it. I'll try that when I get home in a couple of hours. Would doing that be of any use or should I be digging out the DMM?
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Very possible, depending on how bad it is. It seems like it is more prevalent when warm which is the usual case for failures like this.

The alternative to heat that we use is a can of cold spray. Those come with the pinpoint nozzle which can really target the right area.
 
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