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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
HELP with CGS 66 PSU!
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Tronato



Joined: Sep 21, 2007
Posts: 274
Location: Florida
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PostPosted: Sun Dec 14, 2008 10:20 am    Post subject: HELP with CGS 66 PSU! Reply with quote  Mark this post and the followings unread

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
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PostPosted: Sun Dec 14, 2008 2:08 pm    Post subject: Re: HELP with CGS 66 PSU! Reply with quote  Mark this post and the followings unread

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

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Tronato



Joined: Sep 21, 2007
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PostPosted: Sun Dec 14, 2008 2:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

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
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PostPosted: Sun Dec 14, 2008 2:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

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

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"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
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PostPosted: Mon Dec 15, 2008 3:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

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
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PostPosted: Mon Dec 15, 2008 4:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

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

PostPosted: Tue Dec 16, 2008 11:02 am    Post subject: Problem Solved! Reply with quote  Mark this post and the followings unread

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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