Hi there,
So I finished my F5 and then Aleph J as per Jim's build guides. I use the same chassis 5U and power supply (just swapped boards). I would like more power 🙂 and I was thinking: can I do just the first part (simplest) of F5 Turbo V1 in Mr. Pass' article.
If I understood that part correctly, what I would need to do to push the amp to around 50w in 8 ohms is :
Change the transformer to 2 x 24v (I have now 2 x 18v)
Change the caps on the power supply board (maybe 50v or 63v)
Replace R9, R10, R11 and R12 with 5w resistors on the amp boards.
Would it work with these simple adjustments? Will I risk burning out something 🙂? Am I missing anything? You advice is really appreciated. thanks
KJ
So I finished my F5 and then Aleph J as per Jim's build guides. I use the same chassis 5U and power supply (just swapped boards). I would like more power 🙂 and I was thinking: can I do just the first part (simplest) of F5 Turbo V1 in Mr. Pass' article.
If I understood that part correctly, what I would need to do to push the amp to around 50w in 8 ohms is :
Change the transformer to 2 x 24v (I have now 2 x 18v)
Change the caps on the power supply board (maybe 50v or 63v)
Replace R9, R10, R11 and R12 with 5w resistors on the amp boards.
Would it work with these simple adjustments? Will I risk burning out something 🙂? Am I missing anything? You advice is really appreciated. thanks
KJ
oops... sorry, I should know better as I messed up my first board by following the wrong schematics 🙂. I am using the diyaudio store boards (ver 3) F-5 clone boards (2 PCBs, makes 2 channels; Rev 3.0) - First Watt Clones - Power Amplifiers - Circuit Boards and the official schematics from Mr. Pass' article (http://www.diyaudio.com/forums/pass-labs/261187-f5-build-power-smoke-r19-r20-4.html#post4050367). I also use the store universal power supply board ver 3 (Universal PSU V3 - Power Supplies and Accessories - Circuit Boards)
Thanks
Thanks
okei. you can not do this with just 1 pair of output devices. you will need 2 pairs as the dissipated power will be a lot higher.
your bias point for 50W class A @8ohm is 1.8A and +/-32VDC rails. thats 57.6W dissipation pr device with only 1 pair.
your bias point for 50W class A @8ohm is 1.8A and +/-32VDC rails. thats 57.6W dissipation pr device with only 1 pair.
Thanks AudioSan. Am I misreading what Mr. Pass wrote in his article? He says
"Increasing the power supply voltage is the obvious way to get more power out
of an F5. You can simply raise the supply rails to +/-32 Volts and get 50
watts into 8 ohms right away without other modification."
http://www.firstwatt.com/pdf/art_f5_turbo.pdf
"Increasing the power supply voltage is the obvious way to get more power out
of an F5. You can simply raise the supply rails to +/-32 Volts and get 50
watts into 8 ohms right away without other modification."
http://www.firstwatt.com/pdf/art_f5_turbo.pdf
that is correct. but that is 50W class A/B. to stay in class A you also need to crank up the bias.
When I need the volume to go a bit louder, I don't mind A/B. I have a Parasound A/B amp and it sounds very good 🙂
So, are the changes I listed the only ones needed to achieve the 50W in A/B?
Thanks
then you can do it. but you might want to readjust the bias a little bit. down to around 1A.
so around 0.470mV across the source resistors.
so around 0.470mV across the source resistors.
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read the F5 and compare to the F5x and the F5t
They are all basically the same and yet they are all different.
These variations all dissipate similar power in each output device, about 30W
If you run @ +-15Vdc you can bias to ~ 2Adc
+-30Vdc and bias 1Adc
+-60Vdc and bias 500mAdc
Use 1pair as in F5.
Use 2pair as in F5x
Use many pair as in F5t
The maximum output voltage (into the specified load) is very roughly 5V below the supply rail voltage.
Using +-25Vdc, the maximum output voltage is ~ 20Vpk into 8r0.
That is equivalent to 14.142Vac
Maximum Power = Vpk²/Load/2 = Vac²/Load, i.e 20²/8/2 = 25W
They are all basically the same and yet they are all different.
These variations all dissipate similar power in each output device, about 30W
If you run @ +-15Vdc you can bias to ~ 2Adc
+-30Vdc and bias 1Adc
+-60Vdc and bias 500mAdc
Use 1pair as in F5.
Use 2pair as in F5x
Use many pair as in F5t
The maximum output voltage (into the specified load) is very roughly 5V below the supply rail voltage.
Using +-25Vdc, the maximum output voltage is ~ 20Vpk into 8r0.
That is equivalent to 14.142Vac
Maximum Power = Vpk²/Load/2 = Vac²/Load, i.e 20²/8/2 = 25W
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Thank you Andrew, I think I understand what you're saying 🙂
I am planning on using a 2 x 24v transformer, I should get around 32vdc in the rails, so a peak voltage of about 27vdc. Output power into 8ohm speakers would be ((27*27)/8)/2 = 45.5w ... It should be a nice improvement as if I push the amp harder I can hear some kind of distortion which I presume is the amp clipping.
I will adjust the components as per AudioSan suggestions and hope not to fry anything in the process 😀
KJ
I am planning on using a 2 x 24v transformer, I should get around 32vdc in the rails, so a peak voltage of about 27vdc. Output power into 8ohm speakers would be ((27*27)/8)/2 = 45.5w ... It should be a nice improvement as if I push the amp harder I can hear some kind of distortion which I presume is the amp clipping.
I will adjust the components as per AudioSan suggestions and hope not to fry anything in the process 😀
KJ
+-32Vdc will allow about 27Vpk as maximum output.
maximum ClassAB power is 27^2/8/2 = 45W
maximum ClassA power (Ibias*2)^2 * load /2 = (1A*2)^2 *4 = 16W
you could get a bit less depending on the bias you set for the supply voltage.
maximum ClassAB power is 27^2/8/2 = 45W
maximum ClassA power (Ibias*2)^2 * load /2 = (1A*2)^2 *4 = 16W
you could get a bit less depending on the bias you set for the supply voltage.
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Out of curiosity, anyone tried this? Can you hear a difference when the F5 transitions to class B?
Thank you
KJ
Thank you
KJ
F5c was a board in the diyaudio-shop with 2 parallel Mosfets.
I recalled that as you wrote "2 pairs".
F5x also has 2 pairs, right.
Ulf
I recalled that as you wrote "2 pairs".
F5x also has 2 pairs, right.
Ulf
kj123:
Why don't you try increasing bias on your F5 as it is now? If you have the 5U chassis it can take more bias than the stock 1.3A because the big heatsinks can deal with the increase in temp. It depends on your ambient temp but since you are in Canada I don't think it will be a problem. I have the f5 w/the 5U chassis biased at 1.7A and it seems to have more power and drive and just plain sounds better. I can still hold my hand on the heatsinks forever except in the summer when it's hot. Which is almost never. I have no AC here in Seattle (which is almost Canada) so I tend not to use the F5 too much in the summer anyways.
This may not be the solution but it's free to try.
Why don't you try increasing bias on your F5 as it is now? If you have the 5U chassis it can take more bias than the stock 1.3A because the big heatsinks can deal with the increase in temp. It depends on your ambient temp but since you are in Canada I don't think it will be a problem. I have the f5 w/the 5U chassis biased at 1.7A and it seems to have more power and drive and just plain sounds better. I can still hold my hand on the heatsinks forever except in the summer when it's hot. Which is almost never. I have no AC here in Seattle (which is almost Canada) so I tend not to use the F5 too much in the summer anyways.
This may not be the solution but it's free to try.
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