No Load Voltage on Zen V4 Power Supply - diyAudio
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Old 3rd May 2003, 10:26 PM   #1
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Question No Load Voltage on Zen V4 Power Supply

My unregulated voltage coming out of the Zen Power Supply (measured across the capacitor) is turning out to be close to 57 V!!! I am using the same Piltron transformer recomended in the Pass Zen V4 article on the pass website. I am measureing this WITHOUT connecting the amp PCB. This is a no load measurement. The question is, is this value too high. I recently blew R0 and R1 on one channel, Is this high voltage causing this?

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Old 3rd May 2003, 10:41 PM   #2
Join Date: Apr 2002
Location: Germany, Clausthal
For Q5 you use IRFP240 right? If Q5 is IRFP044 i can imageine with a little more than 57V it would die.

OK, in case the regulator is wotking it should be no difference for R0 and R1 if power supply delivers 50V or 57V unreg. into Q5 because past regulator there would be ca. 42V in both cases. But with 57V Q5 would be a little more warm... no problem with enough heatsink.

Also this 57V may go down when the transformer is under load, test it.

In case you unsoldiered Q2 and/or Q1 and/or R0/R1 please test the regulator. is there ca. 46V between zehners and R17?
is there ca.42V past Q5? Did you soldier D1 right way, all zehners ok? else there may be more than 42V.

Please measure and post else it will be difficult to locate errors.
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Old 4th May 2003, 01:14 AM   #3
moe29 is offline moe29  United States
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yeah, experience says "triple check your zener diodes!"
make sure your fets have been pinned out correctly.

take a walk around the block - come back with a clear head
and check it again. then do as Till says!

good luck
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Old 4th May 2003, 05:30 PM   #4
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Default B+ on v4

58 volts sounds a little high, but with Q1 in shut off the voltage will come down once the boards are connected.. I think that with the amp idling at 2 amps you will see about 50 volts on the raw power supply.
I am running a 38v winding instead of series connected 18 volt and get 57 volts with Q1 shut off, and 53v with it running at 1.25 amps.
Check all the connections to the big transistors. the smoking of the resistors across the current source sounds like a lot of current is being pulled across the source.

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Old 4th May 2003, 10:29 PM   #5
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Angry Zen V4

Thanks all for your prompt replies. I will post the values soon. I had one question regarding the measurement of values when using a 150W bulb in series with the primary of the transformer. There is a schematic given with the expected values. It gives the unregulated voltage as 23V. Does anyone know whether this is with the R4 adjusted or turned all the way anit-clockwise?

Heres what I have so far -

1. Turned up the circuit with a 150W bulb in series with the primary. The measured voltage across R0 it is constant at about 0.38V. The unregulated voltage measured at the power supply CAP was about 37V.
2. I started adjusting R4 by turning it clockwise. The Voltage across R0 did not change. The voltage across the CAP started coming down all the way to 28V. At this point the voltage across the Q1 drain was about 16 V.
Everything seems ok at this point, no smoke, no smell.
3. I tried turning the R4 further clockwise and started to see the voltage across Q1 rise but also a lot of heat and the solder on the drain of Q1 actually started melting!!!
4. I adjusted the R4 back to what it was to get a Q1 voltage of about 16V. It seems fine here. there is a fair amount of heat from Q1. A quick measurement on the drain of Q1 tells me that the heat is close to 90+C. The heatsink itself is pretty cool. I know that the heatsinks I have were used in an Aleph 2 so 100W should be easy for it.
I used a discman for an input at this point and ran the output to a speaker. The sound seemed nice but I didnt run it long enough in this configuration.

I checked all the zeners, they all worked out.
Questions -

5. Is the 23 V unregulated shown in other web postings measured after adjustment of R4?
6. Is 90+ C very high on the transistor drain?

Next, if these are correct should I go ahead turn up the amp without the bulb? the only scary part so far is the Q1 temperature?

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Old 4th May 2003, 11:44 PM   #6
Join Date: Apr 2002
Location: Germany, Clausthal
melting solder and 90°C sound not so good. Did you use thermal grease (or at least any grease) between FET and heatsink, does the FET sit tight on heasink? try to move it for test.

0.38V (should be 0,5 - 0,66V, maybe use another Q3 )across R0 = 4.47R means about 0,8A

0,8A * 16V or more means about 13W. This should not be much, not enough for 90°c if there is a heatsink mountet correctly.

Also 0,8A should not melt a solder point, if soldered correctly. please check.

Do you have a DMM with option for frequency measurement or a oscilloscope?

could you check for oscillation?

Please make sure every connection is made big enough, low resistance, good soldered etc.

At least, could you post a high resolution picture of both sides of PCB?

For adjustment: As far as i understand it there is an area were you close the Fet, not enough voltage at gate. No currrent, no load for PS. Then you reach 4V or so at gate, Q1 opens and nominal current (1,3A or 2 A or whatever results from R0 and VBE) goes trough Q1, Q2, R0. In this area were Q1 is open current is not affected by adjustemt. But the voltage at drain of Q1. You adjust for 1/2 voltage to reach maximum voltage swing, but amp will work (with less watt until clip) with more or less than1/2V (0.5*42V).

So at the moment i think absolut adjustment of R4 is not important, important is to get the amp working with less temperature at the Fet and no solder melting. For this check heatsink connection (mechanical, termal) and oscillation.
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Old 5th May 2003, 12:31 AM   #7
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Hi Till
I dont think the FET mounting is the problem since I did check to see if I could wiggle it or move it and it is tight. I am using sil pads, so I did not use any thermal grease.
The soldering looks good (has the shine and is a tight connection). I posted a few days back that I blew one channel - that did have bad soldering on there, but for this channel I got another soldering iron and made sure that all connections were tight.
Unfortunately I dont have any way to check for oscillations. If I were to check for oscillation, where would I be checking it?

I dont have a digital camera but will post pitcures as soon as I can get hold of one.
Meanwhile I will try a different heatsink mounting and see if that makes a difference. I am measuring the voltage on Q1 between drain and ground.

thanks again
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Old 5th May 2003, 12:46 AM   #8
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Location: Germany, Clausthal
ok, just check for oscillation between drain and ground or at speaker output.

Try to borrow somewere at DMM wich can measure frequency.

I donŽt think we will find something related to the heatsink in case mounting is ok and heatsink big enough, what you confirmed both.

Is it possible the turn on the amp for longer time with the series lightbulb and adjustment of R4 for a voltage at drain between 5V and 16V, or does it get too hot?

Is your Multimeter able to measure AC and DC voltage? what voltage is there at speaker output (behind the output capacitor) in the both modes?
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Old 5th May 2003, 12:56 AM   #9
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I ran the amp for about 10 minutes at about 16V on Q1 drain. The temperature of drain pin is high but there is no melting of solder or any visual problem. I played about 3 songs and it seems to have ran clean although definitely at lower volume.
When you ask if it is possible to turn the amp on for a longer time at around 16V, how long - 30 mintes? 1 hour? I can try that.

The DMM I have can do both AC and DC voltages. I will take both measurements and port what it works out to.

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Old 5th May 2003, 01:08 AM   #10
Join Date: Apr 2002
Location: Germany, Clausthal
ten minutes is good information, this means temperature doesnt run away instantly. lower volume meaŽns it was not too loud, or it got less loud over ten minutes? was there a change in this ten minutes or not?

The question with the DMM is, can it really measure AC, or would it interpret DC in AC mode as voltage too. My DMM for example shows at 10 V DC in AC mode 0V. This means in case there is oscillation at output we would have a hint when it shows voltage in AC mode at speaker connector without signal at input.

What says the temperature of R0 in these ten minutes?

Did you use better wires and connections between power supply and PCB at this ten minutes test that that time it smoked?

In my case everything worked ok, with good connections, with thin crococabels in test setup it oscillated and blew resistors.

Do you use a thermistor in series to transformer primary? I need to use one, else sometimes fuse of power mains trips.
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