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Old 15th September 2013, 01:54 AM   #1
crcook is offline crcook  United States
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Default Universal PS for F5

I just received the board sets for the F5 and the Power Supply. I noted there are two power supply boards and two diode mounting boards.

Newbie question.
What is the DC current requirements for each channel? Do I need to use both power supply boards? Is the spec'ed diodes capable of running two channels?

I noted several pics of finished units. Some have two PSU boards, some one. The excellent build guide shows two.

Parts on the way, fets from Spencer, rest from Mouser. Any advices appreciated.

Randy
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Old 15th September 2013, 03:52 AM   #2
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The Store's PSU board set is one complete power supply, one filter board is for each rail, positive and negative.

You can use one or two rectifier boards, there are good arguments for either way. You can also ignore them and use a $10 25-35A bridge rectifier or two. There are conflicting reports about the sonic benefits of fast rectifiers in high current class A amps. I haven't tried fast rectifiers, so my next build has them.

To figure the current requirement, P=I^2 * R So, 30 Watts into a 4 ohm load is ~2.75A RMS, or 5.5A if you are running two channels from a single supply. You don't want to run your components at their ratings, so pick a diode rated for at least double the actual current. The price difference is minimal as current rating increases, so for added peace of mind, I use 20A diodes or greater. The large package diodes will be fine. They are rated at 30A with the two diodes in parallel as on this board. You can also use the TO220s if you want. Almost any choice you make will supply sufficient current to the amp.
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Old 15th September 2013, 04:20 AM   #3
crcook is offline crcook  United States
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Default PSU

Thanks Bob. I have a couple of 50 bridges and have a source for surplus high-speed diodes. I think I will try the high speed units, as the additional cost is minimal.

I like the cases in the DYI store. I am planning on mocking up the electronics with some surplus heat sinks and listening for a while before committing US$300 for a case. Meanwhile, I am looking for alternatives. eBay vendors do not have a suitable sized unit.
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Old 15th September 2013, 05:08 AM   #4
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The store cases are great, well worth the money. I'm putting a Leach amp in a 4U case now. I have a 5U on the way for an F5T. Considering how quickly this batch sold out consider a preorder to ensure you get one or two.
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Old 15th September 2013, 05:59 AM   #5
Hikari1 is offline Hikari1  United States
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The DIY store cases are great. The only cheaper cases are from China which cost a lot to ship. I have the 5U case w/an F5 inside. It looks/works great and was a good value when you add in shipping.

Unless you can fab your own it is the way to go.

The 5U case is BIG. But then you can bias higher and/or it will run cooler.
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Old 16th September 2013, 07:03 AM   #6
crcook is offline crcook  United States
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Default PSU

I just ordered the 4U DYI case, hope they fill the backlog soon...

On the PSU, I was a bit confused at first, but after reviewing the boards I understand the design. For some reason, I was expecting two identical +/- boards, one for each channel. But, no matter.

Not clear on the output snubber, however. The BOM show you need a 1 ohm, 3 watt resistor in series with a .1uf cap. The layout on the PCB seems to be for a 1, maybe 2 watt resistor. A 3 Watt will not fit flush. Makes me think there was a typo or change between BoM and the board design.

Also, do you need the snubber resistor at all? Most amp PSUs I have seen simply use one or two .1uf at the output to get rid of any higher frequency trash.

Thanks in advance for any wisdom here.

Randy
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Old 16th September 2013, 08:34 AM   #7
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Snubbers are optional. In the board thread in the store forum is a link to a calculator to get the proper values if so inclined.

I wouldn't bother with a film cap at the output. A better location for extra decoupling is right at the output devices.

Waiting for cases is tough. But it will give you time to mull over parts choices and still have the amp ready when the case arrives.
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Old 16th September 2013, 03:26 PM   #8
crcook is offline crcook  United States
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Default PSU

Thanks Bob and others for the advice.

One additional question. Sorting thru all the post pages and related noise, still not clear on if matching outputs are needed. If the outputs are way off a match set, I assume that would show up in the bias settings, correct?

I purchased the jfets from Spencer, bipolars are in my Mouser order, along with outputs. If I need to have outputs matched, OK. If there is an easy way for me to make some basic measurements for matching, I can do that. Have a scope, sig gen, lab power supply available.

Randy
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Old 16th September 2013, 05:03 PM   #9
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Yes, the output mosfets need to be matched. The N channels must match each other and the P channels must match each other. You likely won't get N channel to match P channel.

Papa Pass answers all matching questions here https://www.passdiy.com/project/arti...tching-devices
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Old 16th September 2013, 05:11 PM   #10
crcook is offline crcook  United States
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Default was PSU

Thanks again Bob. I missed that section of the Pass website. Lots of good stuff there..... still learning.

Randy
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