F5 power amplifier

[tinitus]

Originally Posted by Nevohteeb

Hmm, actually, I was first thinking about taking a 4U 400mm.

each heatsink on the 400mm design is made from two pieces, and best avoided

from what I can see the price difference between 4U and 5U in 300mm is only 30EUR
I would definately choose 5U, no doubt about it
5U is the one you want, and need

actually, prices on 4U/400mm and 5U/300mm are exactly the same, so I dont understand your argument
no question about it, heatsinks are not where you want to save money

if only the 400mm had properly designed heatsinks

[ramallo]

Originally Posted by Nevohteeb

Hi everyone,

I plan to finalyse my BoM and then purchase the last little things I need.
Nevertheless, I have 2 questions about 1) the transformer 2) the case.

1. according to several threads on several forums I read, it seems that a 400VA instead of a 300VA would be better. Is that true?
2. I plan to buy either a HiFi2000 4U 300mm or a 4U 400mm. According to the attached file, a 4U 300mm should be ok, but isn't it a little bit too tight?

Thank you very much in advance.

I'm using the 4U 300mm chassis and is perfect for the amp, enough dissipation for the Madrid summer.

3U is too small

[lhquam]

Does anybody know if the F5 bias thermal stability can be improved by adjusting the values of R15 and R16 which are in series with the thermistors.

[ichiban]

Originally Posted by nigelwright7557

Just make sure the trafo bolt does touch the top of the chassis as well or you will have a shorted turn.

[mancubus]

What should be changed in F5 schematics , that I could replace irfp240, irfp9240 to 2sk1530,2sj201

[Nevohteeb]

Originally Posted by tinitus

from what I can see the price difference between 4U and 5U in 300mm is only 30EUR
I would definately choose 5U, no doubt about it 5U is the one you want, and need

actually, prices on 4U/400mm and 5U/300mm are exactly the same, so I dont understand your argument
no question about it, heatsinks are not where you want to save money

if only the 400mm had properly designed heatsinks

Hello,

first of all, my mistake, I did not use the proper word. By "tight", I wasn't talking about the dimensions of the case, but I was talking about its power dissipation capacity.

Here is the website I will order the case. I can see :

• 4U 300mm = 119,50€ (0.31 °/W and 165W Max total power dissipation for 2xTO3-P transistors on each sink)
• 4U 400mm = 154,00€ (0.23 °/W and 175W Max total power dissipation for 2xTO3-P transistors on each sink)
• I don't see any 5U 300mm on that shop, and the cheapest 5U is 200€.

So, according to this shop, the difference between those cases is not unimportant, specially about a 5U.
Moreover, it seems that the 4U 300mm fills all the required conditions. All I wanted is the be sure I can chose it

Anyway, again, my mistake.

Originally Posted by ramallo

I'm using the 4U 300mm chassis and is perfect for the amp, enough dissipation for the Madrid summer.

Good to hear.
Thx a lot.

[AndrewT]

Normally a ClassA amplifier has a transformer rated ~ 6 to 10 times the maximum ClassA output power.
300VA would provide adequate power for 30W to 50W of total ClassA power.
400VA would provide adequate power for 40W to 65W of total ClassA power.

There is an alternative method of assessing the required transformer rating.
300VA 18+18Vac gives a current rating of 8.33Aac. This reduces to ~4.17Adc after the capacitor input filter. The 400VA would be rated at 5.55Adc.
The 1.3Adc of a single channel of F5 would use ~31% of the 300VA transformer capability. and use ~23% of the 400VA transformer capability.

A 400VA should be able to power two channels of F5, whereas the 300VA is more than enough for a single channel of F5.

Both assessments show that there is no technical reason for using bigger transformers.

There is the possibility/probability that sound quality might change, but is 33% bigger going to show that effect when both sizes are already bigger than needed for a single F5.

If you were to compare 200VA to 400VA powering a single channel F5, I would expect a difference, even though technically both are big enough.

[Zen Mod]

http://www.firstwatt.com/pdf/art_power_supplies.pdf

[anilva]

Originally Posted by mancubus

What should be changed in F5 schematics , that I could replace irfp240, irfp9240 to 2sk1530,2sj201

F5 power amplifier

[flg]

Originally Posted by anilva

F5 power amplifier

This link I don't believe answers the question It only talks about getting better complementary behaviour from the input stage.
The major difference in setting up the output for Toshiba's is in the Vgs. The IR FETs and most of the other mfg's we typically use have to have 4Vgs or so to get turned on to 1.3A + or -. The Toshiba MOSFETs are going to want to have maybe 2V or so. This means that the drain Rs of the JFETs needs to be smaller. Or, the pot will be adjusted to a very low value swamping out the paralell fixed resister. I don't like pots. I would take it out once I found the necessary value of the Input drain R's. But, it might be best to just reduce the value of the fixed Rs to 1k or so, so more current goes through them than the pot. If you read through this thread and/or the balanced F5 Question thread, you will find JFET drain R values that have actually been used with Toshiba outputs. You would probably have found an expanation similar to this and you wouln't be asking. If you are interested in changing the output Source resistors to a lower value you will need an even smaller JFET drain R value.