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Old 4th November 2003, 01:47 PM   #1
Stever is offline Stever  Canada
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Default Novice question - measurement points

Hello,

I'm still having some uncertainties with my bridge connection on my IGC. I'm running one Hammond 160va (22 volt dual secondaries) transformer and two bridges per channel.

I'm getting 22.3 volts across each pair of secondaries - thats good I think. My question is (when measuring with my DVM) where do you actually see the 30 odd volts I will be getting on the rails? What are my actual measurement points?

Can you measure right at the + (top bridge) and - (bottom bridge)points of the rectifier when the supply is not yet connected to the amp circuit, or do you see the voltage (30) later in the amp? Unconnected, I seem to be getting about 20.5 volts from V+ to VG and similiar on the V- side at the rectifier.

I hope I have phrased the question correctly. I have the amp circuit built and would like to make sure I'm getting the right stuff from the bridge.

New and confused.

Stever
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Old 4th November 2003, 03:14 PM   #2
GregGC is offline GregGC  Canada
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First set the DMM to VDC and measure as you pointed between + and Ė of the bridge. Itíll help if you put small (10uF/50V) caps across (watch the polarity of the caps). You should get Vac*1.4 (22*1.4=31V in your case) or something close to it.

Greg
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Old 4th November 2003, 03:19 PM   #3
Nuuk is offline Nuuk  United Kingdom
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If using a single rectifier bridge, you should have a zero volt rail running from the junction of the two zero volt wires coming from the transformer.

Use that point for the black probe on your meter and connect the red probe to the positive rail where it comes off the bridge. That should read about +31 volts DC (as Greg says, make sure you switch your meter to read DC).

Now move the red probe to the negative side of the bridge and you should get about -31 volts DC.
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Old 4th November 2003, 03:42 PM   #4
GregGC is offline GregGC  Canada
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Quote:
Originally posted by Nuuk
If using a single rectifier bridge, you should have a zero volt rail running from the junction of the two zero volt wires coming from the transformer.
Stever:
"I'm running one Hammond 160va (22 volt dual secondaries) transformer and two bridges per channel."
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Old 4th November 2003, 05:13 PM   #5
Stever is offline Stever  Canada
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Thanks Greg and Nuuk,

Sorry for the basic questions - I will investigate tonight.

Greg, even without the caps across + and - , should I see 31 volts at those points on the rectifier?

Thanks for your help,

Steve
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Old 4th November 2003, 07:27 PM   #6
Nuuk is offline Nuuk  United Kingdom
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Quote:
even without the caps across + and - , should I see 31 volts at those points on the rectifier?
Stever, yes with dual bridges you should have the rail voltage across the outputs of the bridges.
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Old 4th November 2003, 07:47 PM   #7
GregGC is offline GregGC  Canada
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I think it would depend on the DMM. You may get the average/RMS of the half sin. So you may read around 22 VDC because you don't have caps to charge-up to the max of the wave form. I'd do it with the caps to be sure (you'll read + or -31VDC or so).

If you set the DMM to AC you'll get also a reading with NO CAPs(not sure what it'll be, suspect around 10VAC). On VAC mode WITH CAPs you should measure 0VAC.

Best thing, use the caps. and check the polarity by reversing the probes (you'll read -31VDC in one and +31VDC in the other direction).

So to recap: Measuring across the +/- of the bridge:

With caps:
31VDC, 0VAC

NO Caps: (not sure about the exact nubers, but will speculate)
~ 20VDC, ~10VAC


Greg
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Old 5th November 2003, 12:24 PM   #8
Stever is offline Stever  Canada
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Thanks Greg and Nuuk,

Your last posts were very helpful. Everything was fine with my connections and after some head scratching over grounding, I fired one channel up and ITS ALIVE!

About 15mV on the speaker terminals - that should be OK? Minimal amount of hum (that shocks me) and fairly quiet. I will strive to learn more about grounding and clean layout in the final design.

More on the sound later (which was very nice), but for now I'm just shocked I hear music. I will get on the second channel tonight.

This forum is great - thanks all.

Steve
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Old 5th November 2003, 03:46 PM   #9
GregGC is offline GregGC  Canada
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You are welcome,

15mV is fine.
You have to be very careful with the GND connections if you don't want oscillations and hummmmm.

For further education read this if you want:

Read from that post and down the tread (some parts may be useful for you to know)http://www.diyaudio.com/forums/showt...413#post254413

Save this AN for future references:
http://www.analog.com/UploadedFiles/...8865AN-202.pdf

Some more stuff about PS and GND.
http://sound.westhost.com/psu-wiring.htm
http://sound.westhost.com/earthing.htm

And of course the many personal pages on the GainClone subject from people that build it.
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