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Author Topic: Trick circuit or not??  (Read 10305 times)

Bob Leonard

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Trick circuit or not??
« on: January 08, 2015, 12:14:20 PM »
I thought it might be fun to post the circuit below, the power supply section for a very popular late 60's early 70's product manufactured by a company known to us all. Well at least the old timers.
 
Points for spotting what some may call an issue with this power supply, and 1 million wizard points if you can tell me who's circuit this is, and for what product.
 
 
 
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Kurt J Nemer

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Re: Trick circuit or not??
« Reply #1 on: January 08, 2015, 01:42:04 PM »
Shure Vocalmaster?
My guess with the power supply issue is the thermal OL circuit which forms a voltage divider with the transformer primary, not really de-energizing it at OL.
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Mac Kerr

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« Reply #2 on: January 08, 2015, 01:44:34 PM »
Quote from: knemer on January 08, 2015, 01:42:04 PM
Shure Vocalmaster?

Please go to your profile and change the "Name" field to your real first and last name as required by the posting rules displayed in the header at the top of the section, and in the Site Rules and Suggestions in the Forum Announcements section, and on the registration page when you registered.

Mac
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John Roberts {JR}

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Re: Trick circuit or not??
« Reply #3 on: January 08, 2015, 02:10:27 PM »
I have no idea who/what that is, but i would put fuse F2 to the left of C1 so it will protect a shorted cap, a fairly common fault.

JR
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Lyle Williams

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Re: Trick circuit or not??
« Reply #4 on: January 08, 2015, 02:35:00 PM »
I'm not sure I understand why there is an AC polarity switch (on/off/on) just before a bridge rectifier.
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Kurt J Nemer

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Re: Trick circuit or not??
« Reply #5 on: January 08, 2015, 02:49:47 PM »
also, the AC power switch should be ahead of the fuse holder so it can be de-energized when changing fuses. I don't get the polarity swap on the transformer either-especially with out a death cap.
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Mike Christy

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Re: Trick circuit or not??
« Reply #6 on: January 08, 2015, 02:57:04 PM »
What's with the different GND symbols?  The blue and purple power leads are not referenced to GND via those 2 400uf caps, they are floating...
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Jerome Malsack

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Re: Trick circuit or not??
« Reply #7 on: January 08, 2015, 03:02:13 PM »
Why does it have the speaker output in bottom left with the power plug ? 
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John Roberts {JR}

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Re: Trick circuit or not??
« Reply #8 on: January 08, 2015, 04:14:47 PM »
Quote from: Mike Christy on January 08, 2015, 02:57:04 PM
What's with the different GND symbols?  The blue and purple power leads are not referenced to GND via those 2 400uf caps, they are floating...

I joke that ground is a concept not a voltage node. Just like in plumbing the kitchen sink drain ultimately connects to the toilet drain, the order and how they connect together matters. Inside a product the circuit grounds often get different symbols to denote different sub nodes that they connect to, even if they ultimately end up connected together how exactly matters. The caps that appear to be floating probably connect to ground on another PCB or terminal strip.

JR
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Simon Hutson

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Re: Trick circuit or not??
« Reply #9 on: January 08, 2015, 04:37:14 PM »
Quote from: Jerome Malsack on January 08, 2015, 03:02:13 PM
Why does it have the speaker output in bottom left with the power plug ?

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ProSoundWeb Community

Re: Trick circuit or not??
« Reply #9 on: January 08, 2015, 04:37:14 PM »

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