GB F5 Guide (pcb version 2) - diyAudio
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GB F5 Guide (pcb version 2)

Posted 3rd February 2010 at 02:17 AM by cviller
Updated 14th February 2013 at 08:14 PM by cviller

As promised, I would make a guide to the boards and in particular to the additions I have made to the F5. I decided to do this in the blog, because then you can give me comments which I can use for improving the doc. However I'm not done at all, but I thought it would be nice to give you access to the BOM I have made.

IMPORTANT: Before you start stuffing your boards, you must read the manual/article written by Nelson Pass available for download on the First Watt website (First Watt: Products: F5).

Detailed guide by Steve and Matt: http://www.diyaudio.com/forums/pass-...mentation.html

PCB
Here is a picture of the pcb.
Click image for larger version

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There are no more boards available, but you can order F5 boards on the diyAudio store.


Schematics
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Optionality
With the addition of optional extra output mosfets and cascoding, there are many possible ways to build the amp. Here I'll try to explain some of them.

Stock F5 example
Greens are populated and reds are left open.
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Here I have used the outputs farthest apart and notice I have also used the corresponding thermistor and sensing resistors.

Double Ouput Mosfets
Greens are populated and reds are left open.
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When the other output device is populated, you should not add extra thermistors, but you can chose if you want to use the inner our outer mosfet as reference - I have chosen the outer.

The output fets must be matched in pairs - the two N's should have same vgs and the P's must have same vgs.

The extra output devices will allow you to run the amp at higher currents, which is good for driving low impedance speakers. But be sure to have a large enough heatsink if you chose to crank up the bias.

Cascode and Double Output
Greens are populated and reds are left open.
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The cascoded option with double outputs requires two extra transistors and the voltage dividers. Notice that one of the legs of both jfets has to be bend slightly to connect to the hole designated "casc.".

The cascoded option is mainly there to allow for slightly higher supply voltages. Doing the cascode does require some electronics skills, because you may need to adjust some values to get the required headroom for operations. You can read more about cascodes in Nelson Pass' excellent article on the topic: http://www.passdiy.com/pdf/articles/cascode.pdf

BOM
bom.pdf

Output devices
You can use many different output devices for this amp, but the standard is Fairchilds FQA19N20C and FQA12P20C. They can be difficult to get your hands on, so you can use the IRFP parts instead.

Sourcing components
You can order component kits from various diyAudio members.

North America
jackinnj: Tech DIY Company Store (many full clone kits)

Europe
h_a: F5 amp transistor kits


FAQ
Quote:
What happen in F5 if I use 60 or 75 ohm in place of 50 one ?
Increasing the feedback resistor will lower the amount of feedback, so you'll get more gain and distortion.

Quote:
What cables do you use?
I use 14-16 gauge wire for the PSU and outputs and shielded wires for the input. I don't think this is the place where you will see the most improvement from exotic parts, but don't use crummy wire either.

Quote:
Could you give more information about possible changes in bias and other settings for double mosfet option comparing to stock. What are your recommendations for the power supply/transformer and heat sinks?
You can use double outputs to lower the load on each mosfet or increase the total bias. If you increase the bias to twice the stock value, then your heatsink needs to dissipate twice as much heat.
With the stock F5, you are dissipating around 60 watt per channel, so you need a 0.3C/W sink to stay below 20C over ambient temperature.
With the double amount of dissipation, your sinks need to be 0.15C/W per channel.

Quote:
Thanks to AudioSan for this guidance to cascode calculation:
Rail voltage divided by (R103+R102) multiplied by R102 = coscoded voltage.
so f.ex: 35V rails / (4.75K+4.75K) x 4.75K= 17.5V to the J-fets. to get higher voltage for the J-fets, just increase R102 and/or decrease R103. and the other way around to lower the voltage.
the caps can be around 10uF. not very important
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Comments

  1. Old Comment
    Christian, I purchased two pcb v1.1 earlier and am considering replacing them with v.2 since I haven't begun to build the F5 yet. What are the v.2 pcb dimensions?
    permalink
    Posted 24th March 2011 at 09:26 PM by drcg drcg is offline
  2. Old Comment
    cviller's Avatar
    I don't have any left of my V2, but diyAudio is selling a standard F5 board called F5 V2.0 (170x50 mm) and will soon be selling the cascoded F5 which will probably be called F5c V2.0. You can find the board outlines here: Index of /audio/pcbinfo
    permalink
    Posted 25th March 2011 at 07:47 AM by cviller cviller is offline
    Updated 25th March 2011 at 09:40 AM by cviller
  3. Old Comment
    Thanks Christian. Just now ordered a pair of F5 V2.0.
    The info. you provided was helpful.
    permalink
    Posted 25th March 2011 at 07:08 PM by drcg drcg is offline
  4. Old Comment
    Hi ,
    I am in a bit of a mess with the F5 project. I purchased my boards back in September 2009. I have only just got around to (starting) to build them... too many other projects.
    Firstly I have found that the resistors provided do not match what is on the F5 BOM (from TechDIY). I was about to ask for replacements when I found that I do not have a current schematic showing what resistor values are actually wanted (this is a V1.0a 2009-03-14 board.)
    Can anyone point me to a schematic for the V1.0a which defines which resistors should have been provided?
    Thanks for the help
    permalink
    Posted 25th July 2011 at 08:27 AM by georgebrooke georgebrooke is offline
  5. Old Comment
    cviller's Avatar
    Talking about R21 and R22? Those should be 22k based on Papas comments - you can read the whole F5 thread if you want and you'll find it a mentioned quite a few places.
    The schematics on this page is the same as V1.0a - just ignore those with numbers that are above 99, e.g. R114.

    Br,
    Christian
    permalink
    Posted 25th July 2011 at 08:34 AM by cviller cviller is offline
  6. Old Comment
    Hi

    thode casco. pin near Q101 and Q102 where they need to be conected? http://viller.eu/audio/pcbinfo/diyAu...e-letter.pdf:(


    is Ok like this?

    http://www.diyaudio.com/forums/blogs...rs_cascode.jpg
    permalink
    Posted 15th December 2011 at 10:14 AM by potepuh potepuh is offline
    Updated 15th December 2011 at 10:21 AM by potepuh
  7. Old Comment
    cviller's Avatar
    You only need to use those if you are running cascoded.
    permalink
    Posted 15th December 2011 at 10:21 AM by cviller cviller is offline
  8. Old Comment
    Yes i will drive it cascoded
    permalink
    Posted 15th December 2011 at 01:19 PM by potepuh potepuh is offline
  9. Old Comment
    I just have a question about the R35 value, said to be 33k in the bill of material. It seems to me that this R35 is in serie with the LED, between GND and V+. I assume that the voltage between GND and V+ is around 18V, and with a red LED (Vf=1.2V), I would expect R35 to be: (18-1.2)/0.02=810ohm.
    So can you explain why R35 is rated at 33K ?
    Thanks
    permalink
    Posted 18th December 2011 at 12:36 PM by Nounours18200 Nounours18200 is offline
  10. Old Comment
    cviller's Avatar
    potepuh, you then need to put the drain pins in the casc holes - see the illustration under cascoded and double output above.

    Nounours, you can put any value you like depending on how bright you want the led. The VDC is 23V, and 20mA in my opinion is too much for most leds. But please remember to also calculate the power requirements of the resistor!
    permalink
    Posted 18th December 2011 at 02:49 PM by cviller cviller is offline
  11. Old Comment
    dvb projekt's Avatar
    Hi Christian,

    did you have one of your F5 PSU PCBs that i could order?


    Best regards,
    Oliver
    permalink
    Posted 30th December 2011 at 04:31 PM by dvb projekt dvb projekt is offline
  12. Old Comment
    cviller's Avatar
    Hi Oliver,

    I'm all out - however, I have heard that diyAudio store might be looking into making a general purpose psu board available at some point.

    Br,
    Christian
    permalink
    Posted 30th December 2011 at 04:57 PM by cviller cviller is offline
  13. Old Comment
    dvb projekt's Avatar
    Quote:
    Originally Posted by cviller View Comment
    Hi Oliver,

    I'm all out - however, I have heard that diyAudio store might be looking into making a general purpose psu board available at some point.

    Br,
    Christian
    Hi Christian,

    1st i will wish you a happy new year!

    In the meantime, i have found the PSU pcb at ebay...

    I saw in the BOM that you recommend 1W for R1 & R2.
    If i remember Papas original schematic right, he use 1/4 W here.
    Could you give me a short explanation?

    Best regards,
    Oliver
    permalink
    Posted 3rd January 2012 at 07:46 AM by dvb projekt dvb projekt is offline
  14. Old Comment
    cviller's Avatar
    Hi Oliver,

    The short explanation is that jackinnj (the guy behind techdiy store) has done some testing and feels 1W is safer. If you work through the math worst case, you'll see that this is true. However for music signals, the lower rating is probably ok.

    Br,
    Christian
    permalink
    Posted 3rd January 2012 at 08:29 AM by cviller cviller is offline
  15. Old Comment

    R117/118

    I will run it cascoded, do I need to mount the res. R117 and R118?


    Thanks
    permalink
    Posted 14th February 2012 at 10:12 PM by potepuh potepuh is offline
  16. Old Comment
    cviller's Avatar
    potepuh, You need to use "R17 & R18" or "R117 & R118", but not both sets. The resistors are there to measure the current for the current protection, so you populate the "R117 & R118" if you are using the outer most mostfet locations.
    permalink
    Posted 15th February 2012 at 07:57 AM by cviller cviller is offline
  17. Old Comment
    cviller's Avatar
    tehrkn, sorry I didn't see your question earlier. The heatsinks looks good for one channel each.
    I can't use google translate at work, but if the thermistor is sufficiently rated, it should not be a problem to use it.
    I don't excatly understand what you want to do with both the F4 and F5 - there is a quite big difference in gain on the two amps, so that is your main challenge when bi-amping them. Basically, you need a preamp with around 16 db gain on the F4 to run them together. If you use the outputs of F5 to drive the F4 you are losing signal quality compared to a good preamp.
    permalink
    Posted 15th February 2012 at 08:04 AM by cviller cviller is offline
  18. Old Comment

    boards different than the ones in blog

    I see two thermistor outputs in the pictures. But the new boards which I got today have the thermistor, on the inner outputs.

    Can you put the picture of what needs to populated if I want to do standard F5 using cvillier boards.

    Also it will be better if you update the pictures with the newer version of boards. They are dated 2011-02-09

    Thanks
    Pandu
    permalink
    Posted 28th February 2012 at 05:17 AM by pdhanwada pdhanwada is offline
  19. Old Comment
    cviller's Avatar
    Hi romanescu and Pandu,

    I do not have any more boards for sale, and this blog is about my original "version 2" board. I believe diyAudio has made an effort on documenting how to build the boards they currently stock, but let me know if that description is not enough - I can probably help them add some more explanation.

    Br,
    Christian
    permalink
    Posted 28th February 2012 at 08:14 AM by cviller cviller is offline
  20. Old Comment
    Hi,
    The BOM.pdf lists parts needed for "one channel only". Is that correct? Since for example it lists 4 resistors for R13 and R14 (wouldn't that be 2 channels?)

    Thanks
    permalink
    Posted 21st March 2012 at 11:48 AM by studiostevus studiostevus is offline
 
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