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Old 11th May 2012, 10:27 AM   #1
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Default My F5T V3 build

I have been cluttering the other thread with my post, so I fugred I would start a new one. I'll try to keep things to a minimum, but you know how thaht goes, especially with a chatty kathy like me. I will post pics of the beta build later on for those who have not seen it. Hopefully later this week I will have iteration in main case. I am using Tea Bag's boards.

I plan on a two pair output. Going bigger from there will depend on whether or not i hear an improvement in the sound when adding the second pair. If I do, I may not just bump up to more pairs, but instead try increasing the bias of existing pairs first. Current bias setting got up to around 400-410 across source resistors. Fets were mounted on Heatsink USA 10.08 profiloe that was 4" long. With 27V rails, temperatures never got above 42C, but this was open air. Each channels diodes were mounted differently. One on the main heatsink and the other on two unimpressive standoff heatsinks. This will be obvious when pics are posted.The standoff version was cooler, naturally, as it was not attached to the heat generated by the mosfets. THis is how I will mount my diodes. THey will be on a seperate heatink that will be tied to the main heatsink. The diodes will generate very little heat on their own, in my estimation. YMMV. The final main heastinks will be a similar product to the Heatsink USA version above, but will be 6" long and 16" deep. Should have no problem with 2 pairs, even at higher bias.

Here is a pics of the PSU board I will use. It may need revising as I am a PCB novice. Other members feel free to offer suggestions. THE board is free to use by anyone who wants to. I will add a copy without the detail to use as layout for etching. It is single sided with no jumpers. YEY! Will mount perfectly above a toroid on 3.5" standoffs and still be beloow my 6" ceiling by a 1/2". two can be added to my case for dual mono if needed, one over each of the dual trafos. My current ones are 400VA Antek shielded. I may move up to 600VA if necessary.

Any way, more info to come.
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Old 11th May 2012, 11:22 AM   #2
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For Andrew, FLG, and others who might be interested. I have found a thread and an article that might explain further what we are delaing with. Aven't even looked at them thouroughly yet, but in the thread, there is the suggestion to actually have the diodes conducting slightly. How about them apples. Twaeking this thing to where the diodes is on seems dangerous, but exciting.

Square Law Class A Amps

Article realted to subject

http://francis.audio2.pagesperso-ora...AmpHegglun.doc
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Old 11th May 2012, 11:54 AM   #3
Itsmee is offline Itsmee  England
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The mounting of the heatsink to the far right is shorting two tracks together.
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Old 11th May 2012, 12:06 PM   #4
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Thanks Itsmee. Everything else look OK?
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Old 11th May 2012, 12:54 PM   #5
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Here is updated layout. I went ahead and seperated the copper layer from the silkscreen. Stuff will not be here till monday, so I will be using the old PSU until then. Board outline is exactly 7" square.
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File Type: jpg PSU-V3 Etching layout.jpg (192.4 KB, 1386 views)
File Type: jpg PSU-V3 silkscreen.jpg (194.2 KB, 1287 views)
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Old 11th May 2012, 04:29 PM   #6
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Hey buzz, what is the max diameter cap that your PS board accepts? Just curious.
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Old 11th May 2012, 04:41 PM   #7
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40mm. Some 40mm caps have a third pin. I did not add that to the drawing, but it should be no problem drilling it if needed and it doesnt affect anything. I may repost with it added in a little later. You acn always clip the thrid lead. I have done this before as well.
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Old 12th May 2012, 12:01 PM   #8
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Last night I spent some time both listening to the V3 and working, or trying to rework, the PSU. There is not an easy way to reduce the size of the PS board. Even double sided, you r real state is created by the size of the caps and components more than the layout. I realized that the 7" square version will not fit my current setup unless I mount the diodes to the main heat sink. This was not my plan, so a redesign is in order. I will make the boards longer, reducing the width. Hopefully I wil have an alternative layout for those who want it.

The listening. I listened to a two pair version last night. Keeping in mind that the mind is deceitful, I have to say it sounded better. Objectively, the only reason I can think of for this is extra dampening factor and shared load on fets. I don't think the DF is a big deal, so my theory is as follows. Savy veterans please correct me if I am wrong in my thinking. With two pairs, you have each fet pair contributing half what it would if standing alone. So what, no big deal, right. Perhaps, but the way I am looking at it is this. The less power you use from an amp, the more likely you will be operating in its wheelhouse. This is the whole notion behind Firstwatt. If you have two pairs vs one, you could view them as two separate amps operating into the load. Individually, they may push into power levels above their optimal operation and as result, you get increased distortion as compared to the firstwatt. Operating together, they share the load, and as a result, spend more time in the low power, low distortion region. In other words, now yo have two firstwatt region, vs one. I know, I know, very unscientific. Sy would eat me alive. Perhaps Jacco, ZM and Andrew will have a shot Any way, this is how I am viewong the idea that a higher power amp can sound better, even if the power is unecessary and beyond the needs of the speakers being used.
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Old 12th May 2012, 12:04 PM   #9
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what was Iq of one pair , and what of 2 pair version ?
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Old 12th May 2012, 12:49 PM   #10
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Rhetorical question, I presume. 400mV across bothe Rs. Roughly 3.2 A available bias with dual vs 1.6A with single pair. While i understand that more current is available, lets assume i never need more than 1A of current to drive my speakers to deafining levels. Why would two pairs ound better than one?
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