bernbrue
Well-known member
Hi,
I would like to provide you with some files, information and recommendations for the NU FEDERAL 864 built based on our new developed pcb [Zayance & bernbrue].
The NU FEDERAL is our version of the famous Federal Limiter AM 864/u. We replaced the original 6SK7/6SN7/6SQ7 tubes with 7-/9-pin glass tubes (2x 6BA6, 12AU7, 6AV6), changed the power supply and added a few options like input pad, variable output pad, balancing trimpots, relay based true hardwire bypass, variable attack and release time, ratio and threshold pots, stereo link and so on. Here is a short video with the NU Federal on drums.
https://www.youtube.com/watch?v=0eJVCCYApOw
PCB's are available!! Click below.
https://groupdiy.com/index.php?topic=53011.msg676707#msg676707
Finished unit
Stuffed PCB
BOM and Schematic
BOM: https://docs.google.com/spreadsheets/d/1494R_j2GwApoZcIZ743OuftWG7Q_4nS62gMaNTXq2zE/edit?usp=sharing
Schematic & BOM as PDF
https://drive.google.com/drive/folders/0B125JwaqoqLrbU5EVkRPZ0hYQ28?usp=sharing
Frontpanel
https://groupdiy.com/gallery/0/2575-210117073909.jpeg
fpd files will be available soon.
3HE Frontpanel available here:
https://www.don-audio.com/NU-Federal-864-3HE-Frontplatte
2HE frontpanel (+ enclosure, IEC, XLR etc.) available here:
https://www.don-audio.com/navi.php?a=6537
Transformers
Powertransformer (stereo unit)
Primary: 2 x 115V
Secondary: 2 x 170-200 VAC 100mA, 2 x 6,3 VAC 2A, 1 x 9 VAC 1A
available here:
https://www.don-audio.com/Audio-Toroidal-Transformer-Pri-115/230V-Sek-2x-180V-2-x-63VAC-9VAC
Input:
any decent 1:1 or 1:4 transformer with secondary centertap (test what you've got at hand)
Output:
4:1 (10K/600R) transformer with primary centertap, typically suitable for double Triode push pull circuit. The Edcor XSM 10K/600R works, the XPP 10K/600R might be better (not tested)
!!! Forum member AVDO makes fantastic and price worthy transformers for this project. Contact him and support his good work!!,!
Here you go: https://groupdiy.com/index.php?topic=62494.0
My personal review of his transformers: https://groupdiy.com/index.php?topic=65692.0
Heater wiring
Before you solder the tube sockets you have to solder the screw connectors for the heater supply from underneath. Only the heater connector on the top right is soldered from component side.
Fellow member “Fiat_cc” found out, that a 12AU7 as output tube works fine when changing the heater wiring for this tube.
Measuring points
The small pads with letters from A to H are test points for measuring voltages against ground (G). Next to the tube sockets there are dots indicating pin 1 of the tube.
Here are the voltages from my prototype:
B+ = 215 V
A= 8,35 V
B= 208 V
C= 208 V
D= 155 V
E= 0,58 V
F= 0,58 V
G= 210 V
H= 210 V
Use the trimpots for aligning/balancing the anode/cathode voltages. Trimpot R9 (500R) is a bit small and should be increased to 2,5K or 5K.
Reducing potentiometer range
The original Federal Limiter was a unit with fixed settings for attack/release and trimpots on the back for threshold and ratio, set and forget so to say. The calibration procedure is described in the original manual. When turning threshold and ratio to extreme settings (fully clockwise), the unit (and I suppose the original unit as well, maybe someone can confirm) will start to motorboat. These settings are just ridiculous and completely unusable. So the range of useful settings can be found more or less in the first quarter of the pot range. I strongly advise to "tame" the pots for:
Threshold Limiter: 100 K log pot plus a 400K resistor in series
Current control: 1K log pot with a 1K3 resistor strapped across legs 1 and 3. (resulting in ~ 600 R total resistance).
Tubes
2x 6BA6 (EF93)
6AV6 (EBC91)
12AU7 (ECC82)*
* The 12AU7 is supposed to be very similar to the 6SN7 used in the original unit. Personally I recommend the 12AX7 (ECC83) in this circuit. Please check the “heater wiring “ passage when using the 12AU7 !!
Meter
Any 200uA to 1mA DC meter will work. I successfully tested a Sifam R32 standard VU meter as well.
Reading stuff
Original manual: http://www.preservationsound.com/wp-content/uploads/2014/02/Federal-AM-864-U-Manual-copy.pdf
-------------------------------------------------------------------------
Update 5th of March:
Has anyone built it yet? I have my second channel running. Really nice what it does. Wiring needs to be cleaned up and then I'll close the lid.
Some observations:
- buy a bunch of 6BA6 tubes. I had a NOS pair in and the meter barely moved up. With another pair the meter moved up as it should.
- when linking two channels the already slow attack/release time doubles.
- the meter trimmer is a must, since the meter is very sensitive to the threshold/ratio settings. It's recommended to find suitable settings first, switch in bypass and trim the meter to zero.
update 17th December
This compressor is indeed very special. I tested it for a few days now on different musical material (bass, drums, vocals etc.). It takes some time to understand how it reacts and what it does, since threshold and current control interact somehow. The meter needs to be recalibrated when using extreme settings. It's recommended to use a 6x2 or 4x3 Lorlin for the current control in order to have reasonable fixed settings. The threshold pot needs to be "tamed" as well. A 200uA DC meter works fine with R10(240 Ohm). Revision 1.1 will have a 1K pot in series with R10 in order to calibrate the meter. An ordinary VU meter without an internal rectifier can be used as well. The variable time constants (attack & release) we implemented are very useful, especially the shorter release times. I used a 1:1 input transformer (Haufe/Malotki) without input pad. Output transformer is a 10K/600R Edcor. While I'm testing the unit and searching for some improvements, Tony includes these in the pcb layout revision 1.1. Boards will be available after Christmas. Stay tuned!
Cheers
Bernd
I would like to provide you with some files, information and recommendations for the NU FEDERAL 864 built based on our new developed pcb [Zayance & bernbrue].
The NU FEDERAL is our version of the famous Federal Limiter AM 864/u. We replaced the original 6SK7/6SN7/6SQ7 tubes with 7-/9-pin glass tubes (2x 6BA6, 12AU7, 6AV6), changed the power supply and added a few options like input pad, variable output pad, balancing trimpots, relay based true hardwire bypass, variable attack and release time, ratio and threshold pots, stereo link and so on. Here is a short video with the NU Federal on drums.
https://www.youtube.com/watch?v=0eJVCCYApOw
PCB's are available!! Click below.
https://groupdiy.com/index.php?topic=53011.msg676707#msg676707
Finished unit
Stuffed PCB
BOM and Schematic
BOM: https://docs.google.com/spreadsheets/d/1494R_j2GwApoZcIZ743OuftWG7Q_4nS62gMaNTXq2zE/edit?usp=sharing
Schematic & BOM as PDF
https://drive.google.com/drive/folders/0B125JwaqoqLrbU5EVkRPZ0hYQ28?usp=sharing
Frontpanel
https://groupdiy.com/gallery/0/2575-210117073909.jpeg
fpd files will be available soon.
3HE Frontpanel available here:
https://www.don-audio.com/NU-Federal-864-3HE-Frontplatte
2HE frontpanel (+ enclosure, IEC, XLR etc.) available here:
https://www.don-audio.com/navi.php?a=6537
Transformers
Powertransformer (stereo unit)
Primary: 2 x 115V
Secondary: 2 x 170-200 VAC 100mA, 2 x 6,3 VAC 2A, 1 x 9 VAC 1A
available here:
https://www.don-audio.com/Audio-Toroidal-Transformer-Pri-115/230V-Sek-2x-180V-2-x-63VAC-9VAC
Input:
any decent 1:1 or 1:4 transformer with secondary centertap (test what you've got at hand)
Output:
4:1 (10K/600R) transformer with primary centertap, typically suitable for double Triode push pull circuit. The Edcor XSM 10K/600R works, the XPP 10K/600R might be better (not tested)
!!! Forum member AVDO makes fantastic and price worthy transformers for this project. Contact him and support his good work!!,!
Here you go: https://groupdiy.com/index.php?topic=62494.0
My personal review of his transformers: https://groupdiy.com/index.php?topic=65692.0
Heater wiring
Before you solder the tube sockets you have to solder the screw connectors for the heater supply from underneath. Only the heater connector on the top right is soldered from component side.
Fellow member “Fiat_cc” found out, that a 12AU7 as output tube works fine when changing the heater wiring for this tube.
fiat_cc said:
Measuring points
The small pads with letters from A to H are test points for measuring voltages against ground (G). Next to the tube sockets there are dots indicating pin 1 of the tube.
Here are the voltages from my prototype:
B+ = 215 V
A= 8,35 V
B= 208 V
C= 208 V
D= 155 V
E= 0,58 V
F= 0,58 V
G= 210 V
H= 210 V
Use the trimpots for aligning/balancing the anode/cathode voltages. Trimpot R9 (500R) is a bit small and should be increased to 2,5K or 5K.
Reducing potentiometer range
The original Federal Limiter was a unit with fixed settings for attack/release and trimpots on the back for threshold and ratio, set and forget so to say. The calibration procedure is described in the original manual. When turning threshold and ratio to extreme settings (fully clockwise), the unit (and I suppose the original unit as well, maybe someone can confirm) will start to motorboat. These settings are just ridiculous and completely unusable. So the range of useful settings can be found more or less in the first quarter of the pot range. I strongly advise to "tame" the pots for:
Threshold Limiter: 100 K log pot plus a 400K resistor in series
Current control: 1K log pot with a 1K3 resistor strapped across legs 1 and 3. (resulting in ~ 600 R total resistance).
Tubes
2x 6BA6 (EF93)
6AV6 (EBC91)
12AU7 (ECC82)*
* The 12AU7 is supposed to be very similar to the 6SN7 used in the original unit. Personally I recommend the 12AX7 (ECC83) in this circuit. Please check the “heater wiring “ passage when using the 12AU7 !!
Meter
Any 200uA to 1mA DC meter will work. I successfully tested a Sifam R32 standard VU meter as well.
Reading stuff
Original manual: http://www.preservationsound.com/wp-content/uploads/2014/02/Federal-AM-864-U-Manual-copy.pdf
-------------------------------------------------------------------------
Update 5th of March:
Has anyone built it yet? I have my second channel running. Really nice what it does. Wiring needs to be cleaned up and then I'll close the lid.
Some observations:
- buy a bunch of 6BA6 tubes. I had a NOS pair in and the meter barely moved up. With another pair the meter moved up as it should.
- when linking two channels the already slow attack/release time doubles.
- the meter trimmer is a must, since the meter is very sensitive to the threshold/ratio settings. It's recommended to find suitable settings first, switch in bypass and trim the meter to zero.
update 17th December
This compressor is indeed very special. I tested it for a few days now on different musical material (bass, drums, vocals etc.). It takes some time to understand how it reacts and what it does, since threshold and current control interact somehow. The meter needs to be recalibrated when using extreme settings. It's recommended to use a 6x2 or 4x3 Lorlin for the current control in order to have reasonable fixed settings. The threshold pot needs to be "tamed" as well. A 200uA DC meter works fine with R10(240 Ohm). Revision 1.1 will have a 1K pot in series with R10 in order to calibrate the meter. An ordinary VU meter without an internal rectifier can be used as well. The variable time constants (attack & release) we implemented are very useful, especially the shorter release times. I used a 1:1 input transformer (Haufe/Malotki) without input pad. Output transformer is a 10K/600R Edcor. While I'm testing the unit and searching for some improvements, Tony includes these in the pcb layout revision 1.1. Boards will be available after Christmas. Stay tuned!
Cheers
Bernd
