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Rudi_Ratlos 18th March 2012 10:35 AM

Roender's FC-100 Rev.1 Group-Buy
1 Attachment(s)

last December METAL and I made up our mind and did our own layout for Mihai's (Roender's) FC-100 AMP.

This is Mihai's original thread:

The reasons for our decision have been:

- the frontend of Mihai's FC-100 belongs to the best (!) designs I have ever seen in the AMP's world
- we had a couple of NJL - ThermalTrak - transistors at hand and wanted to use them on the backend

We offered our layout in a Group-Buy thread, but after some discussion have been asked to prototype
our PCB first before offering it to the community.

I ordered a couple of professionally etched prototype PCBs and ZSAUDIO and I built the prototypes.

The result:

An absolutely "rock-stable" amplifier playing at its best.

Two comments about its sound-quality:

by ZDR (who did his own layout):
"Well, I am done now. I just have one little problem - how do I stop those little hairs on the back of my neck from standing
up while this baby is playing?"

"All of you guys who plan to build this amp just do it. The PCB what Rudi and Metal offer is an art."

I had a problem related to my own build though.
The typcial forward voltage drop of the integrated TT - diodes of my charge of NJL-transistors was higher than of Mihai's transistors,
and I was not able to activate 5 diodes in the TEMPCO - string.

Thanks to a sudden inspiration of FranzM. I bypassed one TT - diode by an external SCHOTTKY diode and fixed my own problem.
Since then I have been able to listen to the beautiful sound of the FC-100.

My "Prototype - Experiences" are documented in this thread:

I have incorporated ZSAUDIO's and my own experiences and your requests into the Revision 1 of the FC-100 PCB
and will offer you in this group-buy:

- the FC-100 Rev.1 PCB:

The PCB includes the Frontend, the Backend and a complete, high-quality Backend - PSU.
Its size is 245 x 74 mm.
For those of you who plan to use your own PSU, reservoirs CAPs, etc..., I have inserted a pre-determined breaking line on the PCB.

The quality of this PCB is the best that you can imagine:
- 2 mm thick FR4 PCB, double-sided, 70m copper traces covered with Gold immersion, soldermask, silkscreen, ...
Its price will be 15€.

- Mihai's FrontEnd Shunt-PSU:

Its size is 76 x 74 mm; its price will be 8€.

- whatever you like to have to "make this group-buy complete", for example:
Futaba 0R1 / 5W emitter resistors, MKP 1839 / 1F capacitor, input capacitor, Speaker Protect PCB, Soft-Power-On PCB, ...

One of the pre-requisites to make this AMP a real success is to match certain transistors: the input differential pair,
the output- and pre-output drivers, LEDs, ...
I am currently thinking about designing a "Transistor-Matching-PCB" (if you would like to have).

I will leave this group-buy open, until all of your questions have been answered (but will terminate it on April, 15th at least).

I feel a little bit sad, right now.
Mihai's FC-100 is beating my current favourite DIY - AMP, the TO3-SYMASYM.
This is the best-sounding DIY amplifier I have come across so far.

Will there be any AMP - PCB that I will be going to offer you in the future?

Find the current order list below.
Feel free (you would be a fool if not) and join this group-buy.

Best regards - Rudi_Ratlos

meanman1964 18th March 2012 02:59 PM

Is there a difference between amp boards of the previous batch and this one?Did you make the solder-pads bigger?
For me 2 FrontEnd Shunt PSU boards and a set of resistors.
Those matching boards are a good idea

Rudi_Ratlos 18th March 2012 04:50 PM


the main differences are:

- 4 reservoir CAPs (instead of 2)
- filter and space for bigger heatsinks in the backend PSU - section
- bigger solder PADs for the emitter-resistors
- each TT - diode can be jumpered individually

I did not change anything regarding the frontend- or backend - section of the AMP.

Best regards - Rudi

meanman1964 18th March 2012 04:57 PM

There is no need for me to take the other amp boards from upcoming groupsbuy?

franzm 18th March 2012 05:59 PM

I'm in with 2 complete sets.

zsaudio 18th March 2012 06:19 PM

Hello Rudi and Metal,

i'm with you guys and will order my next boards.

rellum 18th March 2012 06:34 PM

Hi Rudi and Metal,

Nice work, I like the pcb.
Count me in for :
- 4 amp boards
- 2 shunt psu boards
- 2 set of 0.1R resistors

Any chance for the TT transistors to be included in your offer ?


Rudi_Ratlos 18th March 2012 06:37 PM

1 Attachment(s)
Patrick, the Rev.0 - PCBs that you have, work very well!
You do not necessarily need the Rev. 1 - PCBs.

A small update of the order-list.

Best regards - Rudi_Ratlos

meanman1964 18th March 2012 06:46 PM

For me 2 FrontEnd Shunt PSU boards and a set of resistors
Do you've also four 0,22 emiter resistors left?

Rudi_Ratlos 18th March 2012 07:04 PM

1 Attachment(s)

if you want to: I will order NJL0302DG / NJL0281DG from MOUSER or FARNELL or ...

In the original thread Mihai recommends to closely match the output-transistors (hFE and VBe).
I had a dozen of each of the transistors and the Hfe varied from 91 to 117 (for the NJL0281DG, f.e.).
But I found 2 closely matched triples of each.

I will contact ZSAUDIO and ask him for his experience.
Then I know what I can offer you.

Patrick: I have 4 0R22 resistors left.

Best regards - Rudi_Ratlos

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