F5 power amplifier

[Melon Head]

I am using the same voltage but have increased the bias current for higher class A output into 4 Ohms.
I did test it though up to +/- 30 Volt rails with no issues what so ever. In fact it seemed to perform slightly better (not significantly) at higher voltage.

[danieljw]

excellent - nice work man !

[Melon Head]

It will be nice to see how you think it compares to the Jean Hiraga amps.
I would also consider trying this amp with Hitachi (or equivalent) lateral mosfets.
I haven't done that yet, but I will definitely give it a go some time in the future.
It will be a relief once I finish building the cases for all these amps. Then I can really make a lot of progress for future amps.

[samoloko]

Originally Posted by Lucas_G

Hi Samoloko,

Yes, forgot to post their quote.

They deliver a 600 VA 2 x 18 Volt transformer as a basic model for 36 Euro. Delivery is about 25 Euro. So their prices are very nice.

I ordered 4 pieces of these, but in an "audiograde" version that cost 63 Euro each. For this price you get "transformer wound on high inductive, selected and measured core. Core and all the windings will be impregnated. Transformer will also has electric and electromagnetic shields, epoxy filled interior and mounting pads in price."
"Production and delivery time for audio grade transformers ~30 days, for standard transformers ~10 days"

Hope this information will be of help to you...

Regards,

Lucas
E

thx for info
isnt 600VA too much for F5 or you will use It with other project

[Gyuri]

Like that, that too big transformer, does not exist.

Gyuri

[gk7]

I have three questions regarding the power supply:

- Almost everyone seems to like high speed diodes for
the rectifiers except for Nelson Pass himself. (on
all photographs of First Watt equipment I´ve seen so
far I found normal rectifiers, and the service manuals
don´t mention any high speed diodes.)
Is their use really an improvement ?

- I have two powersupply boards from BrianGT (originally
intended for an Aleph 30) left which I might use for my F5.
They have small film type bypass caps on their output.
I´ve read somewhere (can´t find the post now) that this
might lead to HF instability with the F5 (although I think
it was about bypassing direct on the amplifier board.)
Any opinions on this ?

- The powersupply boards mentioned allow for one cap
before the resistors and two caps after them on each rail.
In theory more caps (higher value) after the resitors
will give better filtering, but all recent First Watt
(as well as the BA) have the same amount before and after
the resistors. Is there a special reason to have this symmetrical ?

[TerribleT]

Hello,
Great questions. I'd like to add one more question if you don't mind. What is the range of values for the R between the two cap banks in the PS. All schematics so far show 4 .47ohm resistors in parallel. So that would be equal to .1ohm or so. Can I use .5 or 1 ohm for example? If so how would it change the performance of the PS. Thanks,
David

[bobodioulasso]

Originally Posted by gk7

I have three questions regarding the power supply:

see post 5001

[gk7]

Increasing the R value would lower the the frequency where it begins to filter ( f=1/(PI*R*C) ) but it would increase the voltage drop across them too. With let´s say 3A through them this would be 3V for 1 Ohm and then they would have to dissipate 9W (and loose 3V on each rail).
So the better (although pricier) way to improve filtering would be to increase the capacitor value.

[gk7]

Originally Posted by bobodioulasso

see post 5001

"Actually we are using fast/soft recovery types"

Ok, sorry I did not see that. (And on the photographs they looked like normal bridge
rectifiers.)
Thank you, so question #1 is answered...