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Old 2nd November 2009, 03:06 PM   #71
Goto is offline Goto  United Kingdom
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Nic

I am running a placid BP, powering my Counterpoint boards (I am using B24).

Quite an upgrade over LCBPS

Mark
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Old 22nd November 2009, 03:09 PM   #72
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Raising another thought. A shunt doesn't like to drive capacitive loads, right ?

What about the 6 * 220uF on the IVY 2.0 ? Is it wise to remove these to make the shunt operate freely ?
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Old 22nd November 2009, 03:14 PM   #73
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The placid will work fine into any practical capacitance as long as there is some ESL.

Still you could quite safely remove those caps.

I personally sometimes do remove large decoupling caps when using shunt regulators. This minimizes the possibility of having little parasitic tank ccts.

Cheers!
Russ
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Old 22nd November 2009, 03:25 PM   #74
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Thanks for a quick answer Russ.
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Old 30th November 2009, 04:23 PM   #75
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[QUOTE=Russ White;1989370]The placid will work fine into any practical capacitance as long as there is some ESL.

Is ESL the same as esr?

Thanks,
Tom
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Old 30th November 2009, 04:56 PM   #76
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ESL = Equivalent Series Inductance

ESR = Equivalent Series Resistance
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Old 5th January 2010, 06:07 PM   #77
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TPA Guys!

Do you feel that the rails track enough for this to be used with a DC coupled amplifier, that doesn't have any sort of on board regulators (perhaps some of your designs meet this criteria?)

I've done a bit of testing, but haven't formed a solid opinion myself.

Here's one test run zoomed in across both rails (it's configured as a +-12VDC supply)

Click the image to open in full size.

Here is some data over 5 hours of warm-up on a single rail:

Click the image to open in full size.

Unfortunately, waiting two hours for the DC offset to stabilize is not practical, so the question is how well do things thermally track during warm-up.

So far it seems okay. Upon turning on the power supply, I see 0.055VDC difference in the rails. So, assuming this offset would be trimmed via the amplifier, we'll call this value 0. After 1 min. this was 0.046. After another min, this was 0.052. After 5 more minutes, 0.060. After 5 more minutes, 0.064. After 10 more minutes, 0.061. After a final 10 minutes, 0.061. So, during this time there was a +-9mV variance from the initial value.

The next plan is to build a simple circuit to do this math for me, so I can monitor it over a longer period of time.

Anyways, I do wish this was tighter, given the use in a DC coupled amplifier, so my question is, is there any suggestions on how this variance could be nullified somewhat? Any further tests that I could help you with?

Last edited by luvdunhill; 5th January 2010 at 06:15 PM.
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Old 5th January 2010, 06:22 PM   #78
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A small change in the rails over a long peroid of time should not effect a well designed amplifier, DC coupled or not.

The drift you are observing is a function of the tempco of the LED.

You could use a voltage reference with less tempco, but you would likely then have more noise. You could easily put just about any series VREF in there. Even a Zener if you please.

None of our amps would be adversely effected by the slight drift at all.

I would just use the LED VREF unless you have good reason not to.

Cheers!
Russ
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Old 5th January 2010, 06:30 PM   #79
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Quote:
Originally Posted by Russ White View Post
A small change in the rails over a long peroid of time should not effect a well designed amplifier, DC coupled or not.
I wouldn't call 300mV over 2 hours small (per the second graph) in the context I've presented. Also, I'm not sure what you mean by a well designed DC coupled amplifier? Let's assume a servo isn't used. If it uses a bipolar PSU and the rails drift apart by 10mV, this will show up as a DC offset. edit: I'm obviously more concerned about the rails drifting at different rates, then any absolute change over time.

Just trying to help!

Last edited by luvdunhill; 5th January 2010 at 06:36 PM.
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Old 5th January 2010, 06:43 PM   #80
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You would have to show me your amplifier circuit for me to understand. I have never used an amplifier (DC coupled or not) that would show any appreciable offset change with a 300mv rail difference.

In any case you have the solution. Use a VREF with very low tempco drift.

Cheers!
Russ
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