What did you last repair?

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Funny you meantion the "wattage wars"...
I was just talking about how great the sound proofing is in a 1970's building. That's when people liked to blast their tunes and you couldn't have that with neighbours getting mad all the time :)
I've lived in a building build in 1949 and there was no soundproofing to speak of, and terrible acoustics.
I've lived in a few 1960's buildings and they were better but you could still hear people watching TV or walking above you.
But here, there's only a slight hint of bass when someone blasts their tunes - all because of those wattage wars :)
A new condo would have less sound proofing because nobody even has a stereo these days. Not gonna knock pictures off of the wall with a soundbar LOL

It's yet another reason I don't want to move from this place - The best acoustics of any place I've lived.
The fact electric is included in the rent is also unobtainable now.
You got lucky. There's lots of poorly built buildings since the 70's, some with law suits pending due to unscrupulous builders. I know because I'm involved with that industry. I frequently get calls by people to come sound proof their units because of this. These are condos built long after your "wattage wars". In fact mostly within the last 20 years. And the complaints are rarely because of loud music since everybody's using buds these days. Screaming kids, walking on the floor, literally just talking. It's nuts what these goofballs are getting away with. Nobody cares.
 
Ya I mentioned that new buildings are made cheaply... The early 1970's seems to be the sweet spot in Toronto.

"Literally just talking" that's a 1940's kind of thing in this area.

I can have 85db in here and it's less than a whisper in the hall by the chute (20 feet).
 
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Normal use doesn’t knock pictures off the wall. It takes at least a small DJ rig to do that. Back in the day, we used receivers like this for that purpose. With the most efficient speakers we could get our hands on. With todays 75 dB per watt speakers no way you could get it that loud with that level of amplification. Loud enough for the neighbors to bitch, but not earth moving.

You can get the cops called with a two watt amplifier and toy speakers. I’ve done it. There will be distortion. I lived in a trailer at the time and you know how well built they were back then, right? Might just as well have been made out of cardboard.
 
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Normal use doesn’t knock pictures off the wall. It takes at least a small DJ rig to do that. Back in the day, we used receivers like this for that purpose. With the most efficient speakers we could get our hands on. With todays 75 dB per watt speakers no way you could get it that loud with that level of amplification. Loud enough for the neighbors to bitch, but not earth moving.
And back in the disco-era, as a sideline, I DJ'd in several clubs/bars, as well as doing some events at churches and hotels, even private mansions for corporate events.
I even got on TV news for an event that Easter Seals and a local radio station promoted.
The event was called the "Easter Seals Disco Dance-a-thon", held in 1976, and I still remember mom telling me "Hey Matty, I saw you on the tv news that night!"

My system back then was a Dual 1229 and 1219, feeding a Newmark mixer which fed a Dynaco 120 (60/60W), which then fed a pair of Smaller Advents. (known for their inefficiency)
The result, regardless of room size, was quite satisfactory and plenty loud for the enjoyment of the clientel.

Of course since then, being reasonable and satisfactory has been tossed aside for eardrum-shattering nonsense.
Just like the "bigger is better" propoganda and the superficial "wattage wars" of the late 70's.
Indeed, I'm more of a "conservative" type in many ways, while watching the world going to sheepsville.
 
These days, a stereo 60W amp isn't enough to throw a party in a closet! LMAO
People want SPL! People want to feel it and wear "hi-fi" ear plugs to stop from damaging their hearing :)
People want the Valve Sound System and the three trucks it takes to transport it. It's 96kW.
I'm not one of these people. I generally find any live music or party to be too loud these days.
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One of those cheap <$10 pulse oximeters. These are cheaply made, you need to basically pull hard on the battery spring contacts to lengthen them enough to hold the AAA's in place for reliable contact to even get them to work out of the box. Had done this a long long time ago, stopped working in the meantime, finally noticed that one of the wire leads had fallen off in the meantime, resoldered and all is well. Unfortunately, this immediately confirmed my daughter was quite sick so rushed off to emerg...
 
Now you see why I like to add current limiting to a VAS Even if it’s not “needed”. All it would have done is sent DC to the speaker. The high VAS current likely took out the VAS, the vbe multiplier, and all outputs/drivers after that. If it would have been limited to say 20mA (limit the voltage on the emitter resistor) it just sticks to the rail if the collector “load” fails. Or goes out of range.


That must be what happened. The bias spreader was cooked. It's just a STV-4H -- four series diodes in a package, in series with a pot, both open. The drivers were cooked. The 150 ohm resistors from driver emitters to the output rail were cooked. Surprisingly, on each channel, only one PNP output measured bad. A too-thin trace carrying the full PNP half of the output current was burnt on both channels. All original outputs will be trash, even if they hold 600mV on each junction I don't trust em.

The redesigned circuit includes VAS current limiting. I'll have to post the redesigned schematic. It'll have a buffered VAS and a current mirror load for the IPS on a little daughterboard. That's good for >100dB distortion performance in spice.
 
It is well-known in Portsmouth, UK, that a significantly gifted Engineer and Scientist and Mathematician lives at 21C Yarborough Road.

Generally happy to help!

However my Limits were tested today by my good neighbour from No.6, Louisa, who was banging on my window today:

"Steve, I know you are busy, but could I borrow your Drill please?"

S7 Power Drill and Bits.jpg


I politely refused her request. She has NO IDEA what potential financial and legal liability I might incur in acceding to her request.

She might drill into an electrical wire. She might not understand "Health and Safety" aspects of her aimless drilling.

NO. Contact the Landlord. He is insured. I am not.
 
Hantek DSO5102b digital storage o'scope stopped working while making measurements - screen suddenly turned all white, then black. Automatic setup seemed to be still working, but when connecting it via USB port to a W10 PC to operate it with software it didn't show up in OS device manager. Dismantled it, checked PSU to find all voltages being good. Dismatled ist further for visual check, unplugged any flat cable connection - nothing obvious. Assembled it again to store it away and forget it, but turned it on for a last and final attempt - up and running. Thats's not exactly what I would call a repair, but it worked.
 
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Had a fault on a USB transistor tester I designed.
It would register USB with PC but as soon as I tried to test a transistor I got a comms error.
USB circuit all checked out.
Did find a CE short on a transistor but that didnt fix it.
So wrote a test program to test a transistor on the PIC itself and it locked up.
Lock up in software that has previously been fully tested usually means a latch up of the PIC.
So looked at A2D inputs and spotted they were at 4 volts.
This is totally wrong as I have 1k then 2 BAT85's to power rails to clip it.
Getting about 0v7 across BAT85's which again is totally wrong.
Got the BAT85 bag out and used magnifier to read value.
1N5235B which is zener !
My Ebay sent me the wrong diodes.
So 16 diodes to unsolder which was a pain and one blown up PIC micro.
 
People want the Valve Sound System and the three trucks it takes to transport it. It's 96kW.
I'm not one of these people. I generally find any live music or party to be too loud these days.
These days there are rules about SPL at concerts.
I went to see Status Quo in 1976 at the Apollo Glasgow.
It was absolutely deafening and I was stood behind a concrete column !
I couldnt hear for 3 days afterwards.
Saw them again in 2004 and the sound levels were much more sane.

I ran a mobile disco for many years and got away with a Maplin 225WRMS disco amplifier and four Fane 12-50WRMS speakers.
Got asked to turn it down a couple of times.