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Old 27th August 2012, 04:24 AM   #1
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Default Audionics from Oregon CC3 power amp

Thanks

Last edited by analogrules; 27th August 2012 at 09:03 PM.
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Old 27th August 2012, 07:22 AM   #2
Mooly is offline Mooly  United Kingdom
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Sounds like you got away with that one. If an output transistor had blown it wouldn't work and there would be obvious signs of distress.

(I've deleted your post in the pictures thread as you have started ths one.)

You asked how to post pictures ?

Too add a photo,
First click "go advanced" in the box below the "quick reply" message box. Doesn't matter if you decide half way through a message to do that, it carries it foward.

Then click "Manage attachements"
Click browse in the first box at the top and find your picture. Repeat for any more pictures.
Click upload... a message appears "uploading"
When complete, scroll down to the bottom of page and click "close this window"

The pictures should now be attached and when you post will appear. I don't think they show in message preview... they never used to anyway.

Make sure your pics aren't too big, a couple of 100k is plenty, and many object when they are massive and it alters the margins
It tells you in the attachments window what max sizes are allowed.
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Old 27th August 2012, 08:04 AM   #3
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My 1980s Audionics CC3 power amp.
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File Type: jpg P1010054.JPG (117.9 KB, 191 views)
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Old 27th August 2012, 08:11 AM   #4
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Without a manual you don't know what the recommended bias is. So first thing is to mark the position of the pots so you can put them back where they are.

The DC offset pots will usually be around the input circuitry side of the amp. Adjust for 0.00 DC volts across the speaker terminals.

Bias is usually checked by measuring the voltage across some low value resistor and calculating the current. Maybe those four wirewond resistors I can see. There would be one in each output transistor "emitter" connection. I would guess they are around 0.1 to 0.22 ohms in value.

There are various ways of determining the correct bias but we would need to see the circuit for that. If in doubt aim low and make sure it doesn't drift upward. The value could be as low as 20ma or so.

A bulb tester in series with the mains might be an idea until you identify all the pots. Also have no speakers connected for these adjustments.
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Old 27th August 2012, 02:00 PM   #5
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Hey Mooly , Thanks for your help!
The four wire wounds ? Is that those wight resisters about 3/4'' long? So those pots on the output board are not for bias? Ok the pots on the input board is should be set a 0v . Put my tester leads +to+ and -to - on the speaker post ? Amp on or off? Also can you explain in more detail? Im really trying to do this myself , being we have no techs here where I live , it sucks ! Iv bin into gear my hole life but really have never learned any of the this . I was worried when I bout this , do to age ! The guy said it was fully checked and serviced .
Well anyway do you think that stunt on did would have anything to do with getting the bias off?
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Old 27th August 2012, 05:29 PM   #6
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Without a circuit diagram we are guessing as to the exact function of all the pots. Without having the unit in front of me its impossible to make out. Those on the rear panel ?? might be to set a stabilised voltage (a voltage regulator).

What you can do is measure the DC voltage across the speaker terminals with the amp on. It should be under 50mv. Lets confirm what the offset voltages are first.

Also with the amp on measure and record the voltage across each of those four white wirewound resistors (the big white ones ). The channel that runs hottest will have the largest voltage. The voltage across each pair of resistors in each channel should be equal. The voltage will be small, probably in the millivolt region assuming these resistors are what I believe they are. Be very careful not to short anthing making the measurements. The pots (what look like pots anyway in the pic) on the two side panels are probably bias but don't alter anything yet.
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Old 27th August 2012, 08:08 PM   #7
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Quote:
Originally Posted by Mooly View Post
Without a circuit diagram we are guessing as to the exact function of all the pots. Without having the unit in front of me its impossible to make out. Those on the rear panel ?? might be to set a stabilised voltage (a voltage regulator).

What you can do is measure the DC voltage across the speaker terminals with the amp on. It should be under 50mv. Lets confirm what the offset voltages are first.

Also with the amp on measure and record the voltage across each of those four white wirewound resistors (the big white ones ). The channel that runs hottest will have the largest voltage. The voltage across each pair of resistors in each channel should be equal. The voltage will be small, probably in the millivolt region assuming these resistors are what I believe they are. Be very careful not to short anthing making the measurements. The pots (what look like pots anyway in the pic) on the two side panels are probably bias but don't alter anything yet.
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Old 27th August 2012, 08:15 PM   #8
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Ok I checked the dc offset from the rear pots and the cold side 18 and there warm side was 3 so adjusted them both for around 15mv. Now the bias is done on those transistors , but what should i set my meeter at and How show I put my leads . Thanks for your help, i went to my local tech today and he said he could not help! Mooly if we can talk over the phone that would be great ?? This is my email for my number. If so ! hemihead05@yahoo.com
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Old 27th August 2012, 08:16 PM   #9
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Quote:
Originally Posted by Mooly View Post
Without a circuit diagram we are guessing as to the exact function of all the pots. Without having the unit in front of me its impossible to make out. Those on the rear panel ?? might be to set a stabilised voltage (a voltage regulator).

What you can do is measure the DC voltage across the speaker terminals with the amp on. It should be under 50mv. Lets confirm what the offset voltages are first.

Also with the amp on measure and record the voltage across each of those four white wirewound resistors (the big white ones ). The channel that runs hottest will have the largest voltage. The voltage across each pair of resistors in each channel should be equal. The voltage will be small, probably in the millivolt region assuming these resistors are what I believe they are. Be very careful not to short anthing making the measurements. The pots (what look like pots anyway in the pic) on the two side panels are probably bias but don't alter anything yet.
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Old 27th August 2012, 08:28 PM   #10
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Hi,
You'll be fine doing as outlined here, and putting it all on the forum helps others

OK, so I'm a little confused as to what you have actually measured and adjusted.

1. The DC offset is measured on the speaker terminals on the back of the amp (you mention the "DC offset from rear pots" ?). So you put the meter on DC volts and connect the red meter lead to the red speaker terminal and the black meter lead to the black speaker terminal for one channel. The voltage you measure is called the DC offset and should be as low to zero as possible. Anything less than 50 millivolts is good.

2. Next you connect the meter leads ACROSS any of those four resistors. Those horizontal ones at the front of the amp seem the easiest to get to. The DC voltage you measure here can be converted to a bias current (by using ohms law). Repeat the measurement for the same resistor on the other channel. It doesn't matter which way round the meter leads are for this.

Also what is the value of these resistors ? What are the markings ? Measuring the value may not be accurate if you are not used to measuring really low value resistors in circuit as the meter lead resistance can be nearly as much as the resistor itself. So what are the markings
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