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Old 29th June 2016, 11:13 AM   #1
diyAudio Member
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Join Date: Jun 2009
Location: Hamburg / Germany
Default Roender'S FC-100 - Group Buy

Five years after the first round of group buy (Roender's FC-100 prototype and builder's thread) I would like and start another round right now.

Roender's (Mihai's) FC-100 amplifier is one of the gems of this forum. Not only in my ears and the ears of everyone, who has built it.
But also in the ears of a professional German Audio-Magazine's editor, who has selected the FC-100 as a reference-amplifier in a given price range (see image #1)
- and who did listen to Mr. Pass' F5, to the SYMASYM to ... but chose the FC-100 as reference!

I have only done some very slight, "cosmetic" changes to my original FC-100 layout (changing the input connector, the positions and heatsinks of the backend-rectifiers, ...).
"Never change a winning team". (see image #2).

As the FC-100 frontend-PSU I will happily offer you my Dual LT3062-based PSU (see image #3 and the zipped LT3062 - LTspice model).
A German DIY-friend of mine has soldered the LT3062 prototype, being driven from a 2x30VAC EI42-transformer and has adjusted it to give an output of +/-37VDC.
The prototype works flawlessly.

I myself do not like shunt-regulators at all. They are wasting voltage and power.
In the meantime companies like TI and LINEAR have developped very reliable, low-noise LDO-regulators that can/should be used instead!
For those, who do not trust my proposed dual LT3062 - regulator, I will offer Mihai's original shunt regulator (see image#4).

If you want the FC-100 to be driven from a "Soft-Power-On Circuit", I will offer you my "SPO/TempControl" - PCB (see image#5).

There is constraint though concerning my offer.
You will of course receive my "Builder's Guide", "Drill-Template", ...
But I will only offer the PCBs being ordered and will not offer you "any hard-to-get-component", nor will I select and match any component.

I have in the meantime grown too old to do this for you, but I hope that there is somebody among you, who takes the lead and tells me:

"I will order, select and match the NJL-transistors for you"
"I will order, select and match the input 2SK170 - transistors for you"
"I will order the 2SC3423 / 2SA1360 and MKP1839 and MPC74 - 0R1 resistors for you"

I will support him as much as I can.

Best regards - Rudi_Ratlos
Attached Images
File Type: jpg FC-100 003.jpg (148.5 KB, 1635 views)
File Type: png FC-100_AMP_R1_topview.png (200.5 KB, 1563 views)
File Type: png topview.png (154.9 KB, 1503 views)
File Type: png FC-100_shunt.png (179.1 KB, 1451 views)
File Type: png SPO_topview.png (183.1 KB, 1419 views)
Attached Files
File Type: zip (1,011 Bytes, 114 views)
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Old 30th June 2016, 02:03 PM   #2
aradan is offline aradan  Singapore
diyAudio Member
Join Date: Apr 2015
Location: Born in Russia, living in Singapore
Hi Rudi,

I would be in for stereo set of FC 100 with LT psu and soft start

Do you have more info on the soft start board it looks really interesting.

I am thinking whether it could ve easily re used for the other amplifiers as well. I have M2 in the queue now

Sent from my ONE A2003 using Tapatalk
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Old 30th June 2016, 05:36 PM   #3
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Location: Hamburg / Germany
Aradan, you see 2 OMRON G5LE-relays on the PCB.

The lower one is to pass the mains hot. If is open, no current will flow at all.
If is is closed, the current will flow through 2 NTC resistors, wired in serial. The current will therefore be limited by the combined value of the 2 NTCs.
The current limitation is active, as long as the upper G5LE-relay is open.
If the upper relay is closed (after some delay), the 2 NTCs will be bypassed by the upper relay and the current flows unhindered.

Opening and closing the relays is accomplished by the used µProcessor.
For example: #define SOFT_POWER_ON() { PORTA |= (0x01 << PRIME_RELAY_PIN); __delay_ms(250); PORTA |= (0x01 << SEC_RELAY_PIN); }

Besides the Soft-Power-On circuit the PCB contains a mains DC filter and the functionality to monitor the temperature of a heatsink.
The current status can be displayed on a LCD.
Power_On and Power_Off can be remotely controlled by a IR control unit.

The SPO-PCB can be used for the M2 as well - no problem.

But as I have written: this group buy will not be successful, if you buy everything for your own needs.
You need for example 2 triples of NJL0281 and NJL0302.
If you buy 6 pieces of each or even ten: the chance to have well matched triples is very small. But if there are 5 of you and one of you orders 50 pieces of each transistor and measures and matches them:
the chances are much bigger then. Moreover: the price of a transistor is much less when bought in a quantity of 50.

I hope that you understand my considerations.

Best regards - Rudi
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Old 1st July 2016, 01:28 AM   #4
aradan is offline aradan  Singapore
diyAudio Member
Join Date: Apr 2015
Location: Born in Russia, living in Singapore
Hi Rudi,

Indeed this is FC 100 gb. Not the soft start gb.

And fc 100 requires a lot of good components.

As for 2sk 170 fet audio has the stock of matched pairs.

And it seems that alweyt has got hold of a new stock of the transistors, so he might be offering more matched pairs as well

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Old 1st July 2016, 07:45 PM   #5
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Join Date: Sep 2010
Location: Montreal
Hi Rudi,

I always wanted to build this amplifier and had bought a complete kit from you back in the first GB... I ended up never building it being too busy and selling the whole kit and then regretting it... If someone is willing to buy the output devices and match them for the GB, I will for sure sign in again.

PREAMPs : Bal AMB α10 + JC-80 | Bal DCB1 | Bal LDR3x | AMPs: AMB β24 | ExtremA | FO v1.4 | USSA5 | TSSA | Telos 390 Clone | NX Amp | FC-100
DACs : TPA Buffalo II + OPC's NTD1 I/V | JLsounds | Mirand AK4490 + Discrete Output Speakers : Troels Gravesen ATS-4 | Sagwee LT V3
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Old 2nd July 2016, 12:29 AM   #6
Eldam is offline Eldam  France
Join Date: Sep 2012
Location: France
Hi Rudi,

Thanks for the nice offer

Could you please give again some rapid datas please ?

2 x 65 W if I remember ?
How much gain ? 26 dB ?
what is the lowest impedance it can drive ?

The approximativ range price of the BOM with the matched FET, heatsinks ? Some avaliable at DIYAUDIO Store maybe ?

Do we need a scope for the setuping ?

Last edited by Eldam; 2nd July 2016 at 12:35 AM.
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Old 2nd July 2016, 12:43 PM   #7
wineds is offline wineds  Australia
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Join Date: Apr 2006
Location: Melbourne
This is what I collected on specifications from the threads before building :

RMI-FC100 specs:
Class A power: 2W rms into 8ohm with Iq=0.6A (maximum Iq for optimal B class bias)
Class B power: approx 90W rms into 8ohm
OLG: 94dB CLG: 1:40 (32dB)
SR: +/-75V/us
Phase margin > 67grd Frequency response: DC to 210KHz (-1dB)

At +/-34V we have plenty of SOA margin and:
65W rms into 8ohm
87W rms into 6ohm
130W rms into 4ohm
260W rms into 2ohm (at the SOA limit)

No scope is needed for the build

Last edited by wineds; 2nd July 2016 at 12:47 PM.
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Old 2nd July 2016, 01:01 PM   #8
Eldam is offline Eldam  France
Join Date: Sep 2012
Location: France
Thanks for the nice answer

Maybe not the place to ask but had this amp benchmarked with :

the First-one (LazyCat member) with smps powersupply or the SLewMaster "Spooky Leach" (OStriper member based design).

I have a Chord SPM 1000 B with smps powersupply and also 2 W class A then 250 W/8ohms most-fet (matched from avionics sector) and would like understand if any of these DIY could be better as mine is a 25 years design by Chord great Britain company ???? (some always told me than M2 Audio with smps sounds better, though mine is punchy and soft ?!)

thanks for the feedbacks if any
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Old 3rd July 2016, 07:18 AM   #9
joshvi is offline joshvi  India
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Join Date: Oct 2008
Location: God's Own Country
Matched output devices are available from tech-diy store.

Company Store

I have 500 pairs of 2sc3423/2sa1360 with me . I can do the matching if required
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Old 3rd July 2016, 09:30 AM   #10
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Join Date: Jun 2009
Location: Hamburg / Germany
Joshvi, are you also willing to buy and match the needed NJL-transistors for the participants?

If not, I intend to include a small matching PCB that looks very much the same as the one shown in the inluded image.
Everybody will be able to order, measure and match the transistors by his own then.

But as I have written: the chances to have well-matches triples of the NJL-transistors increase, the bigger the number of available transistors to be measured is.

By the way: the FC-100 PCB costs 12€, every other PCB costs 5€.

Best regards - Rudi_Ratlos
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