^^^^^
What he said!!!
I went with 32V rails because a good portion of my speaker's upper mid-range is between 8 and 13 ohm and 60Hz sees 10 ohm. I crunched numbers based on the impedance plot and made a judgement call. The amp will transition out of class A at the right frequencies if I drive it to what I consider crazy loud, but it never runs out of voltage, and some voltage headroom on the MOSFETs keeps them a bit better behaved. If you don't need more that 20 or 21 volts, don't go with higher rails.
Ah...take it this way:
An F5 is like a Deluxe Reverb or AC15 or other 12" combo amp...really it's more volume than anyone needs. If you are sane it's fine. And the rest of the band will love you. F5 turbo is like having a a bigger 2x12" combo or a Bassman or something. Fun to have! But not really needed.
The high wattage A/B amps are like having a Marshall stack at home. There is no sane reason to have that at home. Unless you actually like to crank it up and live on a farm. And even then, probably overkill.
No, no. It is appreciated. Thank you for your explanations, especially regarding your different permutations and experiences. I’ve decided to stop overthinking things and just dive in on a standard F5. I bought the 4U “deluxe” chassis from the diyaudio store and we’ll see how far I can take things. I’m going keep things simple for now and see if I really need any more power after this.
That's a good plan. If you want more later just get another 4U chassis and build turbo monoblocks...If you want more "tube" sound build an M2 or aleph using the same chassis and power supply.
That's the beauty of these amps...with a single chassis and PSU you can try out lots of stuff without having to build a whole new amp. Same chassis and PSU for all of them.
Hey guys, I just bought an F5 kit from the store, and I'm completely new to amp building. I'm glad this thread came up.
If I wanted to over-build the F5 first, so that I can use it as a standard F5 power-level right now, but just change the transformers later if I decide I want more power, what modifications should I have with component choice?
I'm assuming some resistors go up in value, and that's about all I can imagine. Maybe the power supply has a few differences?
Edit: read the above replies and decided to go with the normal F5 power levels. I guess my question is now, will i gain any benefit by possibly upgrading the resistor's to higher rated wattage ones? Or if there is any other mod to ekk out the most performance out of the F5.
If I wanted to over-build the F5 first, so that I can use it as a standard F5 power-level right now, but just change the transformers later if I decide I want more power, what modifications should I have with component choice?
I'm assuming some resistors go up in value, and that's about all I can imagine. Maybe the power supply has a few differences?
Edit: read the above replies and decided to go with the normal F5 power levels. I guess my question is now, will i gain any benefit by possibly upgrading the resistor's to higher rated wattage ones? Or if there is any other mod to ekk out the most performance out of the F5.
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Very good point! Here's a good test you can do: A Test. How much Voltage (power) do your speakers need?
No benefit to upping resistor wattage. Wattage is just heat dissipation factor.
There is a benefit to having more capacitance in the PSU. And a larger transformer. Not transformer voltage but the VA rating of the transformer. You could also replace the CRC resistors in the power supply with chokes. But really, this is overkill.
I think the best "upgrade" is the largest chassis you can afford or live with. That way you can bias the amplifier higher. And bias is the best upgrade you can make, sound-wise.
There are no capacitors in the signal path of this amplifier and it is very simple. Resistors will change the sound slightly. Different mosfets will as well. But bias and PSU quality is the most important factor. The difference between cheap, unbranded capacitors and a good capacitor in the PSU of this amplifier is very noticeable. And, depending on your speakers, the difference between 1.4A bias and 2A bias is EXTREMELY noticeable. Sounds like a different amplifier.
If you do plan on upping the power at some point, the only real upgrades in parts you should make right off the bat are higher voltage filter caps and higher wattage feedback resistors. If you do go for 32V rails at some point, you'll have to recalculate the resistor values in the current limiting circuits or else the BJTs will just pull all the bias off the outputs. Or you can just delete the BJTs and forget about current limiting.
Using higher wattage resistors where they're not needed doesn't bring any benefit. The F5 Turbo article fully describes what you need to do to turn an F5 into an F5 Turbo V.1 and it's the basis upon which the F5 itself is defines. The F5 manual doesn't describe P3 and how it's used.
I personally recommend that anybody building an F5 really get to know the amp and experiment with what P3 can do to the sound. I don't have the fancy analysis equipment to look at and measure the distortion and I've spent a lot of time listening very careful to the amp as I've tried different things with P3. I've got a little notepad in the drawer under my amps the describes exactly how I have P3 adjusted so I can go back to that setting if I mess with it again at some point. I know the sounds of these amps well enough to tell if one if the P3 pots is off by a quarter turn. Don't ask me what they really measure though! Their just dialed into what I think sounds best, and that's been one of the more rewarding things about building these amps.
Thanks guys! I really have almost no knowledge of these things, so I really appreciate and am relying on good feedback. Thanks again!
Hikari- How much capacitance do you recommend, and what VA power supply? I was thinking using a 500VA with an 8 ohm nominal load. Also, what are the best cap brands?
Also, what does bias do? I'm guessing its something I adjust with a trim pot? And does higher bias = higher dissapation wattage?
Kosst- What does P3 do? Sorry, I dont have my kit yet. Also, what feedback resistor rating would you recommend if I wanted to upgrade down the turbo path eventually?
I dont plan on it... but I want to over-build my amp anyway. I was thinking about Mills MRA-5 (5 watt).
Thanks for answering my resistor questions! I was just concerned because the regular resistors in the kit are the "RN55D" type I believe, which are 1/8th watt spec. I was really expecting atleast 1/4 watt spec.
Hikari- How much capacitance do you recommend, and what VA power supply? I was thinking using a 500VA with an 8 ohm nominal load. Also, what are the best cap brands?
Also, what does bias do? I'm guessing its something I adjust with a trim pot? And does higher bias = higher dissapation wattage?
Kosst- What does P3 do? Sorry, I dont have my kit yet. Also, what feedback resistor rating would you recommend if I wanted to upgrade down the turbo path eventually?
I dont plan on it... but I want to over-build my amp anyway. I was thinking about Mills MRA-5 (5 watt).
Thanks for answering my resistor questions! I was just concerned because the regular resistors in the kit are the "RN55D" type I believe, which are 1/8th watt spec. I was really expecting atleast 1/4 watt spec.
True. But you probably missed F4.
It can drive anything, and its the most transparent buffer there is in classA. It can have any sound signature from your preamp. You want low distortion crystal clear, use such preamp. You want sweet second harmonic oozing sound, use such preamp. Tube or solid state. F4 can do it all, drive it all.
Actually the F4 was in second place. I didn’t pick it because it has the same power rating at 4 ohms, higher THD, capacitors in the signal path, and required a preamp with wide voltage swing. I’m sure it’s extraordinary in use but the F5 seemed like a shorter path.
The little Vishay resistors in most of my F5 are smaller than grains of rice and I haven't managed to pop any of them even whole foolishly blowing out output MOSFETs. The feedback resistors are 5 watt non-inductive wire wound Ohmite parts.
P3 is the pot near the input JFETs. It alters the symmetry of the complimentary halves of the amp giving one half or the other more or less source resistance. It manipulates the kind and amount of distortion the amp makes. It can make the amp very smooth and luscious with gobs of negative phase 2nd order distortion, or it can make it fast and punchy with low amounts of 3rd order, or it can make it forward and a but wooly with positive phase 2nd order distortion. It's an interesting thing to play with and listen to carefully. It's not something you'll sort out in an afternoon. I've experimented with it for a couple of years. 6L6 did a video on how to adjust it.
F4 sounds way better than F5 because it has no feedback
hence minor higher distortion
besides, I doubt you can hear 0.05 vs 0.02 % difference
hence minor higher distortion
besides, I doubt you can hear 0.05 vs 0.02 % difference
again........ F4, when making correlation with any other amp, must always be titled as "F4 in conjunction with XXX preamp"
current buffer can be compared directly only with other current buffers
same F4 can sound divine and can sound like drek, on same speakers and with same sources, just changing preamp in front of it
current buffer can be compared directly only with other current buffers
same F4 can sound divine and can sound like drek, on same speakers and with same sources, just changing preamp in front of it
@xaborus: I suggest the 10 ohm resistors R3 and R4 be higher wattage
ones (say 2W) since a fair bit of current can go through them at high
output voltage levels.
ones (say 2W) since a fair bit of current can go through them at high
output voltage levels.
.05% with no negative feedback is pretty remarkable, but it is a follower. Either way I wanted one project, not two, so I made my choice.
Perhaps in a year I’ll make a set of F4s and use my F5 as the preamp 😱
please ignore everything I wrote above, that's The Spirit!
what did you expect, you just repeated my previous post 🙂
"True. But you probably missed F4.
It can drive anything, and its the most transparent buffer there is in classA. It can have any sound signature from your preamp. You want low distortion crystal clear, use such preamp. You want sweet second harmonic oozing sound, use such preamp. Tube or solid state. F4 can do it all, drive it all."