I would think that you would want to try biasing slightly below the initial 200mv when warm to start with and see how hot it gets. I take it you are using 2 enclosures?
I share interest in the transformer voltage question. next winter I would like to build a balanced F4 monoblock, and then convert my Aleph30 to another one. my A30 has a 20-0-20V trafo and runs on 25.5V rails. I wonder if I should make the other mono "the proper" way with 18-0-18V and 23V rails or stick with the same "mistake" of having the slightly higher rails on both? any values to adjust for the higher rails?
right now I am leaning towards another 20-0-20 Xformer but maybe I use CLC instead of CRC (if it can package) hoping to lose an extra volt there?
right now I am leaning towards another 20-0-20 Xformer but maybe I use CLC instead of CRC (if it can package) hoping to lose an extra volt there?
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Yes, two enclosures. The main reason I have for choosing the two 18V transformers is it may be easier to bias - reading what numbers others were using and trying to match those vs having to guess at proper bias numbers and posting more questions with about my confusion. I've never tried to bias anything so will be learning on these - unless there is a cheap option to learn on.
biasing (setting Iq ) is easy
whatever you meet first
- 55C at heatsink (summer , Papa's palm rule) or
- chosen dissipation per single output device
say that 35W/piece will last ........ long
whatever you meet first
- 55C at heatsink (summer , Papa's palm rule) or
- chosen dissipation per single output device
say that 35W/piece will last ........ long
If you have a decent bench supply that can handle it it's worth hooking the boards up to that so you can start low and make sure which way the trim pots work.
Don't worry about trying to trim off the extra volt. The 20V-0-20V is completely fine.
A question for those folks with more knowledge than myself. I have built one F4 using some Peter Daniel boards that were already populated by the person I bought them from.
I am building a second F4 so I can use both of them in a mono balanced configuration. Love more of those Class A watts!
So I know I need to match the N and P channel MOSFETS. My question is, do I match the N channels as a group and the P channels as a group or do the N and P channel groups need to match each other?
Example I have 3 P channel devices with a Vgs average around 3.650 and another 3 P channel devices with a Vgs average around 3.110. I am guessing I can use one group for one audio channel and the other group for the other audio channel.
My 3 N channel devices group have a Vgs average around 3.387 and the other 3 N channel devices group with a Vgs average around 3.285.
Thoughts appreciated.
Thanks
David
I am building a second F4 so I can use both of them in a mono balanced configuration. Love more of those Class A watts!
So I know I need to match the N and P channel MOSFETS. My question is, do I match the N channels as a group and the P channels as a group or do the N and P channel groups need to match each other?
Example I have 3 P channel devices with a Vgs average around 3.650 and another 3 P channel devices with a Vgs average around 3.110. I am guessing I can use one group for one audio channel and the other group for the other audio channel.
My 3 N channel devices group have a Vgs average around 3.387 and the other 3 N channel devices group with a Vgs average around 3.285.
Thoughts appreciated.
Thanks
David
match the like devices as amplifier groups.
It is usually nearly impossible to get N to P matching.
It is usually nearly impossible to get N to P matching.
6L6 F4 output mosfets question
Hi 6L6,
I see in the build that you've used Fairchild 12P20s & 16N25s.
1}Are these the better choice over say the IRF 240 / 9240 mosfets?
2}I have the 12P20s but 16N25C's. Does the C version matter ??
ICHI
Hi 6L6,
I see in the build that you've used Fairchild 12P20s & 16N25s.
1}Are these the better choice over say the IRF 240 / 9240 mosfets?
2}I have the 12P20s but 16N25C's. Does the C version matter ??
ICHI
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Check the pin assignment on the c version. I have a feeling it's different. Sometimes the data sheets can be ambiguous on this matter so need a careful second look.
Ichiban - no difference between the Fairchild and IRF in use or sound. Use what you can easily get.
Thanks for such a beautiful and thorough build guide!
I've got a question - If I were to create my own board using this schematic in order to use SMD parts, would it work? Would it work well? I would of course credit Nelson on the silkscreen as the designer of the circuit, and any other credits that would be required. I'm just wondering if this is even a feasible idea.
Thanks!
I've got a question - If I were to create my own board using this schematic in order to use SMD parts, would it work? Would it work well? I would of course credit Nelson on the silkscreen as the designer of the circuit, and any other credits that would be required. I'm just wondering if this is even a feasible idea.
Thanks!
The only thing I can think of is why you would want to do this. The size of the current DIY Audio board is to ensure that the MOSFETs are spaced out wide from each other for heat management, and to fit the DIY Audio offered heat sinks. You would have a very sparsely populated SMD board.
I have a few reasons:
1) Because I enjoy laying out a board as effectively as I'm able to. It's like a tiny puzzle!
2) If I go through my usual board fab company, I'll get three copies for a price similar (I think $10 more) to what I would be paying to get two of the diyAudio boards - letting me more easily add a center channel once I finish construction of that speaker.
3) It's one more facet of the construction that I get to do myself. I don't mind building kits, but if I ever feel like showing off my amps to classmates or colleagues, I'd like to be able to say "I designed that board layout."
1) Because I enjoy laying out a board as effectively as I'm able to. It's like a tiny puzzle!
2) If I go through my usual board fab company, I'll get three copies for a price similar (I think $10 more) to what I would be paying to get two of the diyAudio boards - letting me more easily add a center channel once I finish construction of that speaker.
3) It's one more facet of the construction that I get to do myself. I don't mind building kits, but if I ever feel like showing off my amps to classmates or colleagues, I'd like to be able to say "I designed that board layout."
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