The diyAudio Firstwatt F6

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#921
Generg does some tests of Papalikeamp , using Lundahls , ancient Iskra and xformers originally used by Pa

fact is - Lundahl wasn't sounding better , even if being much more expensive

in some other configuration maybe performance will follow price , but not necessarily here

try it , but trust only your own ears


however , without checking exact type you mentioned , do not forget that you need two secondaries , one primary

so , if exact type can be arranged as 1:1+1 , then good
 
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#923
ammel68 said:
I didn't order those as they are odd-shaped LED's instead of the standard round.

The longer lead on the LED is the positive lead and should go in the pad that is connected to R13.
Looking at my F6 boards it isn't consistent with the writing on the board, so don't go by the silkscreen on the board.

If whoever designed the boards had just placed a "+" next to the pad going to R13, it would eliminate some confusion.
But it's difficult to think of everything when laying out a PCB.
I do that on any boards I design to eliminate any confusion as to which way the LED goes.
Click to expand...

For anyone wondering, I am getting continuity from the top of R13 and the hole OPPOSITE from the "led" silk screening for both led positions. So longer lead (positive) should go in hole opposite "led" writing I suppose.

Russellc
 
#927
palstanturhin said:
I sent an email to Per Lundahl about LL1582 and LL2811 regarding a possible group buy.
It would be possible to get the transformers directly from the factory if big enough order.
The cost would then become around 50e/pc.

Anyways, I would need to make a prototype to test it first.
The problem is, there is no such a thing as a free sample from Per and the cost of just one tranx is 100e...

We also must forget a JFET buffer if the xformers in question was used.
I was therefore thinking something like LME49610 or something...
Click to expand...

Nice transformer. generally the Lundahls excel in shielding and winding.
with a frequency response (source 10 Ω, load 600 Ω, 0 dBU): 10 Hz -- 100 KHz +/- 0.3 dB, that is very good; balance is good too. Does this imply a 600 Ω resistor across the secondaries (going to the gates)?
10 ohms: the 2SK170/2SJ74 buffer does not get that low, probably 15 ohms if you have luck.
How does a diamond fare? Thought that would do well.

Puzzling: "Ideally used 2 : 1", what does that imply for our use?
The transformer might be designed for a mixed feedback, 2:1. That could imply a negative impedance; I saw a negative impedance in another transformer of -10 ohms, specifically for solid state (i.e. opamp) drivers. That is not to my liking (the opamp haters).
 
#930
ammel68 said:
Yes, I saw something about "continuity" to R13, but then you keep referring to something about silkscreening on the board.

I thought your were legitimately confused about which way the LED went on the board.
Click to expand...

I've never used any but the basic ones with a flat on them, but I've got these and I think the worst that happens is they croak if fired up backwards.

Russellc
 
#932
For my build I'm going with the 5U case as my voltages are slightly higher than the 23Vdc.

Currently I'm testing a one channel F6 on a shared heatsink the size of one 5U type and its is just able to keep stable. I think 4U would be adequate other people may chip in here.
 
#933
JPeitzman said:
Question for the experts; is a 3U case (heat-sinks approximately 0.40C/W) sufficient for the F6 or is it a safer bet to stick with a 4U case?

:cheers:
Click to expand...

I've built it in a 3U case and it is to small. If you center the PCB's over the heatsinks, the outputs on the back of the case are getting to hot. Around 70 C at the MOSFET body.
You can gain something by mounting the PCB more to the right, but better go for 4U or a 40 cm deep case with 2 heatsinks each side.
 
#937
Hello,

has anybody thought about doing a group buy for parts for the F6? I know there aren`t many part`s on the amp, but if you include PSU i think one can save some money..
I don`t know how manny pcb`s the store has sold, but i would imagine there are a lot of people that need parts theese day`s...
 
#939
I have recently finished a F4 amp along with a BA3 preamp. Very nice combination. My question is for anyone that has finished a F6 and owns an F4, how would you compare the too. I fear I may need to build another amp!!

Thanks
David
 
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