RMI-FC100, a single stage audio power amplifier

[Sheldon]

Lots of projects already, but if someone makes some boards I'll do it.

Sheldon

 

[kv2]

Boards for FC100?

This amp looks VERY interesting to try - particularly given all the good press!
Has anyone fab'd any PCBs for this amp yet?
If so, PM me with the price please.
Thanks
KVV

 

[pzogal]

jfets

Hi Mihai,

another question, I have here a pack of 25 2sk170bl here, they match very well, however only one is above 9mA, could one employ ones with lower Idss ? or do you need any adjustments ?

Greetings,
Pawel

 

[rec]

Salut Mihai,

te rog, poti sami trimiti adresa ta de internet, unde ati pot scrie?
scuzama ca scriu pe romaneste dar an engleza sant afon

Cu sanatate Cornel

 

[Cal Weldon]

Hi rec,

This is an English speaking forum. If you wish to post in another language, post also in English.

Thank you.

 

[rec]

Hello,

I am sorry, I can read a little, but write is difficult for me.

best regards

 

[pzogal]

Hi,

I am trying to understand some design issues of the amp 🙂 could someone explain me the reason for choosing 13.5mA current value in the diff amp at the input ?

Greetings,
Pawel

 

[roender]

Hi,

I am trying to understand some design issues of the amp 🙂 could someone explain me the reason for choosing 13.5mA current value in the diff amp at the input ?

Greetings,
Pawel

Hello Pawel,

Sorry for this late response ... I was in vacation.
One of the reasons for high LTP current is related with topology chosen, folded cascode, where the gain is highly dependent by the transconductance of the first stage.

Mihai

 

[destroyer X]

I feel good to have you back home.

Carlos

 

[pzogal]

Hi Mihai,

and what about lowering the CCS current to , say, 10mA ? One would have ca. 4.5mA per JFET (against 6.25 now). Having Idss around 7mA one would be in the safe area. Are there any trade offs ??

Greetings,
Pawel

 

[roender]

Hi Mihai,

and what about lowering the CCS current to , say, 10mA ? One would have ca. 4.5mA per JFET (against 6.25 now). Having Idss around 7mA one would be in the safe area. Are there any trade offs ??

Greetings,
Pawel

Hi Pawel,

Take a look at the attached picture and do yourself the math if you want I1=10mA.
I will suggest you to keep FC VAS current at the designed value, I7=I8=2mA.

Cheers,
Mihai

 

[pzogal]

Hi Mihai,

did my math 🙂 120 for LTP and 180 Ohm for FC VAS do the job 🙂

thanks again for support!

 

[roender]

In this case you'll need jfets with Idss >= 6.5mA, 4.5mA half ltp current +/- 2mA max VAS swing.

 

[ernesternest]

pcb

Hi Roender,

after all I read I am going to build this amp. Since up to now no pcb is available I tend to do order a small sample on my own. If my memory doesn't fool me, you already have given your ok for doing so. Still ok?

Cheers Ernst

 

[roender]

Re: pcb

Hi Roender,

after all I read I am going to build this amp. Since up to now no pcb is available I tend to do order a small sample on my own. If my memory doesn't fool me, you already have given your ok for doing so. Still ok?

Cheers Ernst

http://www.diyaudio.com/forums/showthread.php?postid=1504684#post1504684

http://www.diyaudio.com/forums/showthread.php?postid=1503619#post1503619

The latest mod will fit with the existing PCB

 

[ernesternest]

pcb

Mihai,

my intention was to ask for your permission. Might be, that this did not come out in my recent post. Since you sent both links, I think your permission is given.

Thank you very much 🙂
Ernst

 

[roender]

Hi Ernst

This project is free IP for DIY (non commercial) community.

Cheers,
Mihai

 

[pzogal]

Hi Ernst,

what would be the price for the PCBs ?

Greetings,
Pawel

 

[ernesternest]

Hi Pawel,

it depends on the number, one orders. I will order it from Multipcb and I will order at least 20 pcs. If the measures I figured out (20,5x6,3cm) were ok, one ampboard would be about 16 € incl. VAT. If I ordered 50 pcs it would be 11 € incl. VAT.

psu probably 2/3 of this. Have not checked this so far, because I can't read gerber or eaglefiles.

Cheers Ernst

 

[AndrewT]

11euros is very attractive.

Let's see what we would be getting (PCB layout) if you order PCBs on our behalf.