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Tronato
Joined: Sep 21, 2007 Posts: 274 Location: Florida
Audio files: 2
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Posted: Sun Dec 14, 2008 10:20 am Post subject:
HELP with CGS 66 PSU! |
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Hello!
I am feeding 20VAC into the CGS 66 from a supposedly 120/36VAC CT transformer, no load, leds light as expected but after adjusting the trimmers the maximum that is being output is (+/-) 12.75VDC.
Isn't it supposed to be (+/-) 15 VDC at least?
Thanks!
TRON |
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RF
Joined: Mar 23, 2007 Posts: 1502 Location: Northern Minnesota, USA
Audio files: 28
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Posted: Sun Dec 14, 2008 2:08 pm Post subject:
Re: HELP with CGS 66 PSU! |
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Tronato wrote: | from a supposedly 120/36VAC CT transformer |
You sound as if you are unsure of the AC voltage from the transformer.
Have you measured it?
Just checking
bruce _________________ www.sdiy.org/rfeng
"I want to make these sounds that go wooo-wooo-ah-woo-woo.”
(Herb Deutsch to Bob Moog ~1963) |
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Tronato
Joined: Sep 21, 2007 Posts: 274 Location: Florida
Audio files: 2
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Posted: Sun Dec 14, 2008 2:21 pm Post subject:
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Hello!
RF: What do you mean that I sound unsure?
I have measured 20VAC coming into the CGS 66...
The maximum output is (+/-) 12.75 VDC...
Why?
Thanks!
TRON |
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RF
Joined: Mar 23, 2007 Posts: 1502 Location: Northern Minnesota, USA
Audio files: 28
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Posted: Sun Dec 14, 2008 2:38 pm Post subject:
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Hi Tronato,
It's just that you used the word "supposedly" - that didn't sound like you were certain of it.
So you are measuring 20 VAC from each side of the transformer to the center tap - right?
What version board are you using?
What voltage do you have at pin 3 of the LM317, and pin 2 of the LM337?
bruce _________________ www.sdiy.org/rfeng
"I want to make these sounds that go wooo-wooo-ah-woo-woo.”
(Herb Deutsch to Bob Moog ~1963) |
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Tronato
Joined: Sep 21, 2007 Posts: 274 Location: Florida
Audio files: 2
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Posted: Mon Dec 15, 2008 3:31 pm Post subject:
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Hello!
The transformer has 36V CT 2A SEC written on one side and 117AC 50-60 Hz PRI on the other side (actually it is a STANCOR P-8672), which leads me to believe it should output 18VAC, not 20VAC.
The fact that I can adjust both positive and negative voltages independently make me believe that the circuit is correctly assembled.
This is a Version 1 PCB.
I am using NTE 956 = LM 317 and NTE 957 = LM 337.
Both regulators deliver 12 VDC (one positive and the other one negative) on their output pin which is #2 (center).
The picture in thread http://electro-music.com/forum/topic-27323.html
is an exact copy of how it has been assembled (with the exceptions or errors having been carefully accounted for, I hope).
What is wrong here?
Thanks!
TRON |
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andrewF
Joined: Dec 29, 2006 Posts: 1176 Location: australia
Audio files: 4
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Posted: Mon Dec 15, 2008 4:17 pm Post subject:
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what is the range of voltages you get on the outputs when you adjust the trimmers?
ie: 12V to xxV
I think Ken's cct should give a range of about 9V to 21V, for the resistor values chosen.
double check you have a 2k trimmer, 1k5 and 220R resistors. These set your output voltage. |
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Tronato
Joined: Sep 21, 2007 Posts: 274 Location: Florida
Audio files: 2
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Posted: Tue Dec 16, 2008 11:02 am Post subject:
Problem Solved! |
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Hello!
The value of the 1K5 resistors was completely wrong...
I'm even looking at them now and can't understand what they are... they look like brown - green and gold!
Thanks andrewF for the tip on checking them!
You made my day!
I now do get the (+/-) 15VDC (adjustable up to 20VDC if desired)
Now let's see which gremlins await me in the SN-VOICE...
Have pity on my soul!
TRON |
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