F5 loaded rail-to-rail voltage? - diyAudio
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Old 18th March 2011, 06:20 PM   #1
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Default F5 loaded rail-to-rail voltage?

I just fully biased my F5 for the first time, and have let it "soak".

I'm currently running 0.6 volts across R11 and R12, in both left and right channels (i.e., about 1.3 amps per rail, per channel). Inputs grounded, outputs open, output DC offset about 0.2 mV in each channel. All seems normal--heatsinks only slightly warm to the touch (after 20 minutes), and no smoke or "aroma therapy" rising from the amp.

PSU uses a 400 VA dual 18v secondary Antec transformer. Full wave brige rectifiers.

My rail-to-rail voltage, under these stated loads in 40.2 VDC.

In addition to the "standard" Pass PSU recommended for the F5 (with 8 x 18,000 ufd electrolytics) I'm running a SECOND RC filter (with 0.09 ohm resistors and two additional 18,000 ufd caps for each rail, for each channel).

While I would suspect an additional ~ 0.12v drop (1.3a x .09 ohms = 0.117v) in my added RC stage, it seems to me 40.2 VDC is low.

Please advise--what are you getting for rail-to-rail voltages in your F5s, under similar conditions?

Thanks,

Ken
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Old 18th March 2011, 06:59 PM   #2
Zen Mod is offline Zen Mod  Serbia
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1. you don't need new thread for every question , which is - by the way - beaten to death everywhere

2. everything is normal

3. go to duncanamps.com , download PSUD software and play with it ; you'll gain some knowledge about power supplies

4. before that - you can go to Papa's FW site , download all articles and read first "power supplies for A class " , or something like that
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Old 18th March 2011, 07:41 PM   #3
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Re: "Don't need a new thread....." Thanks--still learning the diyAudio "etiquette" here, as a newbie.

WIll try out that PSUD software. I've hit most of the passdiy and FW articles--except for the power suppies ones. I guess I'll add them to my list..... (reading about audio at night, is a LOT MORE fun than listening to the international news, these days)
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Old 19th March 2011, 12:49 AM   #4
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not quite sure why you added the extra parts CanAm , but my rail voltages are 23 each side or 46 as you're measuring it .

cheers Woody
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Old 19th March 2011, 12:55 AM   #5
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Try measuring the resistance of your secondaries
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Old 19th March 2011, 12:58 AM   #6
AndrewT is offline AndrewT  Scotland
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Is your voltmeter accurate?
Is the rail to rail across the rectifier the same or similar or vastly different from rail to rail across the amplifier?
Have you tried measuring the voltage drops along the supply rails?
Did you neasure rail to rail for the unloaded PSU?
Did you measure the quiescent rail to rail when zero biased?
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Old 19th March 2011, 02:08 AM   #7
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Quote:
Originally Posted by AndrewT View Post
Is your voltmeter accurate?
Is the rail to rail across the rectifier the same or similar or vastly different from rail to rail across the amplifier?
Have you tried measuring the voltage drops along the supply rails?
Did you neasure rail to rail for the unloaded PSU?
Did you measure the quiescent rail to rail when zero biased?
Guys, additional readings, with the same amp parameters (grounded input, open output, output DC offsets about 2 mV, and R11 and R12 voltages at 0.600 v (1.3 amps/rail, per channel).

Transformer secondary voltages: both at 18.0 VAC

Bridge rectifiers output voltages: both at 21.6 VDC

Output of the "standard" Pass PSU CRC outputs: both + and - rails are at 21.3 VDC

Output of the added PSU RC filter: both + and - rails, for both left and right channels are at 21.15 VDC

I haven't measured the Rint of the transformer secondaries, but again, their output voltages are to spec (18 VAC).

I've measured with three DMMs and all agree to within 0.1 V on all DC readings.

Seems to me, based upon the secondary voltage x 1.414, I should have a higher bridge rectifier output, no? Both bridge rectifiers are running cool (room temp).

Also seems like the voltage drops of the resistors in the RC filters are "about right", based upon current flow and Mr. Ohm......

First PSU resistor bank: 4 x 0.47 ohm in parallel = ~0.12 ohms x (2.6 amps in each rail) = 0.31 V drop (correlates well with actual measurements)

Second PSU resistor bank: 1 x 0.09 ohm = 0.09 ohms x (1.3 amps in each rail, for each channel) = 0.12 V drop (correlates well with actual measurements)

Help? Thanks,

Ken
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Old 19th March 2011, 02:11 AM   #8
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Quote:
Originally Posted by Woody1911a1 View Post
not quite sure why you added the extra parts CanAm , but my rail voltages are 23 each side or 46 as you're measuring it .

cheers Woody
Are you running the Antek 18 volt, 400 VA power transformer?

At your referenced 23v each rail, what current are you running thru your MOSFETs? (I'm running 1.3 Amp, per rail per amp channel; i.e., 2.3 Amps per rail total, quiescent)
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Old 19th March 2011, 02:17 AM   #9
tinitus is offline tinitus  Europe
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it wouldnt happen to be 15V trafo with 4% regulation ?
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Old 19th March 2011, 02:18 AM   #10
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All, please note that in my earlier post (Post 7 in this thread), my PSU output voltage is given as 21.15 v per rail, or 42.3 v rail-to-rail.

A day prior I had read this as 20.1 v. per rail, and 40.2 v rail-to-rail. (Same loading conditions)

Unknown why the rail voltages have seemed to "improve" over the last two days, when all else has remained constant.
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