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F-5 Turbo boards
F-5 Turbo boards
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Old 19th November 2015, 11:11 PM   #61
Ezcl is offline Ezcl  United States
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Scratch my previous post (why can't I edit my post?), I have better questions.

I got bored and so I've started a SMD layout. The biggest question I have is: Should the MOSFETs be as far apart as possible, or is it okay if they're somewhat close together? I currently have the N-channel devices and P-channel devices on opposite sides of the board, 2cm from each other and about 8cm from the other type of device. Since the 4U chassis heatsinks are so massive, I think it would be okay with them bunched closer together, but I want to make sure.

Or, instead of having them arranged as they are (think SOT-6 package), maybe I should angle the ones in the corners of the boards so they are arranged in more of a circle. That might look cooler too.

Any input would be much appreciated.
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Old 20th November 2015, 05:47 AM   #62
sangram is online now sangram  India
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Distance is always better, but you can run them very close together if your dissipation targets per device are more modest. Look at pictures of the Pass XA 30.5 for example, lots of device pairs packed tight together but each runs around 8-10 watts (I guess).

I have tried MOSFETs just next to each other (you can see some pictures I posted and got flamed for) in a very dense layout and it is still capable of decent level of bias. I saw 1.6A per amp PCB without the sinks hitting 50 degrees, but it is a massive sink with a 4x10 copper heatspreader to suck the heat from the devices. The device packages measure 50 degrees and the sinks 45. The usual wisdom is that if your sinks are large, you should spread devices as far as possible and if they are small (for example assisted by water or forced cooling) then a denser packaging helps more devices avail the benefits of the cooler surface.

I implemented SMD on a recent layout with 3 pairs per channel. Not built yet, but frees up a ton of space for the more important stuff and really simplifies routing by being able to use both sides of the board. You have to watch the dissipation on a few parts. We are using MELF resistors by Beyschlag for the build, better tempco and cheaper than the Dale RN55D we get here.
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Old 21st November 2015, 05:56 PM   #63
Ezcl is offline Ezcl  United States
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Thanks for the information sangram.

My first version for this layout is done, I'd love some input:
Imgur: The most awesome images on the Internet
(Credit to Nelson Pass is on bottom silk, hidden for this picture)

I am using Stackpole's RNCP line of 1/4W resistors, which are rated for 200V, 400V overvoltage, in the 0805 package. Also rated to 155C.

The 3W resistors are rated for 500V and a ridiculous 200C temperature.

Let me know if things look too close or otherwise wrong. Thanks!
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Old 6th August 2016, 02:32 AM   #64
anystereo is offline anystereo  United States
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I just come across some real nice heavy duty mil spec 32 v regulated power supplies good for 10 amps at 41 deg c. and I am thinking about finally building the turbos v2. From what i can tell the ps's should handle at least 50watts a channel with plenty of headroom. Has anyone experimented with a regulated supply for the turbo's or have advice for such?
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Old 29th May 2019, 05:44 AM   #65
5k7 is offline 5k7
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Default JFETs grade for F-5T

I see in store there is only grade B JFETs. Shouldn't be matched pair in grade A ? I'm not an expert, but i think that if amp is working in class A then should be using transistors in this same class.

Can I use grade A matched pairs ? Does this replacement changes anything in circuit ? Do i need to use other/diffrent components then ?

Thanks
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Old 21st July 2019, 07:12 AM   #66
cobar53 is offline cobar53  Australia
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Default Old or New BOM

Hi all
I started making the F5 turbo but soon found that the Mosfets are now obsolete.


The resistor values on the BOM are largely different to the old F5


Do you suggest I just make an 'old =' F5 with IRFP9240 and IRFP240 or is there something I do not know of?


Cheers Wayne


PS on the V3.0 board I am sure there is an error on R 9 and R10 which seem to be 3W resistors but are listed as 1/4W on the old BOM
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Old 21st July 2019, 12:49 PM   #67
6L6 is online now 6L6  United States
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F-5 Turbo boards
Lots of information here - http://www.firstwatt.com/pdf/art_f5_turbo.pdf

IRFP240/9240 are functionally and sonically identical to the Fairchild Mosfets in the article.

Some resistor values are a bit different in a Turbo vs. a standard F5 to accommodate the larger amplifier.
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Old 25th July 2019, 04:59 AM   #68
Variac is offline Variac  Costa Rica
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F-5 Turbo boards
The grading of JFETs as ABC&D has absolutely nothing to do with “Class A” or Class AB or Class D or whatever class an amp is.

Also “Grade A” isn’t “better” than “Grade C”

So you should use the CORRECT JFET grade for the amp you are building. In the case of most Pass amps that is usually “Grade B” which is why we mostly stock matched “B”s in the store.

Quote:
Originally Posted by 5k7 View Post
I see in store there is only grade B JFETs. Shouldn't be matched pair in grade A ? I'm not an expert, but i think that if amp is working in class A then should be using transistors in this same class.

Can I use grade A matched pairs ? Does this replacement changes anything in circuit ? Do i need to use other/diffrent components then ?

Thanks
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Old 10th October 2019, 07:06 PM   #69
thompsontechs is offline thompsontechs
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Default F5T V2 Just bout ready..

Well people, it's coming down to it. There are only six wires to hook-up power FEs and then bias. I think I will do that tomorrow, today has been pretty good and I don't want to go into the evening bummed if something smokes lmao.


I was going to post a few pics, but think I will wait until it's working.


Until then, check out badkitty....
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Last edited by thompsontechs; 10th October 2019 at 07:29 PM. Reason: change title
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Old 11th October 2019, 03:08 AM   #70
thompsontechs is offline thompsontechs
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Well, pictures tomorrow... got some liquid courage and came home and couldn't go to sleep without knowing! Have a couple speakers hooked up gorilla style an the power supply to FE are temp, need tidy, but biased her up to about 300mV and zeroed the offset... listening to Whinehouse and grinning. Damn she should have, "went to rehab." I'll get you all some amp porn tomorrow after I make it look pretty. I still have to tweak and check heat levels, but wow, I can already tell this baby will be able to heat the room.


Thanks to all who took the time to answer my puerile questions and especially to Papa Pass, for giving so much back to us all... Thanks Papa!


JT
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