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Old 25th August 2011, 12:11 AM   #431
AKSA is offline AKSA  Australia
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I second that, Nico. Alex is the best pcb artist I've seen on DIYaudio, and he's fast, too.

I spend tens of hours on mine, and it's always difficult to get that artistic look, which necessary or not, I'm driven to achieve. I suspect it's like juggling, you can either do it or you can't.

Cheers,

Hugh

PS: Here are six NAKSA 100 modules, to give some idea of how mine look.
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Old 25th August 2011, 12:26 AM   #432
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I just started playing with Pcb software and quickly realized the time and effort it would take to master, much less do quickly. Alex is gifted.
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Old 25th August 2011, 01:10 AM   #433
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Quote:
Originally Posted by Lazy Cat View Post
Yes I agree, SSA could be a very good RF transmitter amp up to 10MHz bandpass.
On mine PCB there will also be a space for these two caps, to have exact -3dB bandwidth limit. Also I will limit the input signal bandwidth with low-pass filter set to -3dB at 1MHz.



So the input CF diff-amp and unique feedback loop determine the sound character in general.
This is very important info Nico, thanks, cause I only experimented with BIGBT's and for my home amp I have intent to do a little more sophisticated version, hopefully the sound will stay the same.



Yes, IGBT and MOSFET output versions are the simplest.

Regards, Andrej
This schematic, which shows BC550/560 in both bjt stages, should work fine with mosfet output, correct?
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Old 25th August 2011, 04:02 PM   #434
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Exclamation SSA BIGBT Basic

Quote:
Originally Posted by alex mm View Post
......and now rev 1.5 for BIGBT variant ...... please check PCB for errors , not tested .
Alex.
Dear Alex here are the remarks about SSA BIGBT Basic PCB, can you please make all these corrections:

- BC550C, BC560C have different pin layout (base connection pin in the middle)
- left feedback 100 ohm resistor is unconnected, connect it to the GND
- change two 470uF/16V elco to 1000uF/16V
- on the left side of the input connector place a 10 ohm GND lift resistor (opposite side to 10k resistor)
- 1k/2W resistor should be connected to the rails at FUSE output
- in series with each 1k/2W resistor please connect green LED to indicate power
- please put MUR160 (smaller) instead of MUR460
- Vbe multiplier transistor should be BD139 instead of BC550C, screw mounting to heatsink
- please align output transistors symmetricaly from the left/right PCB edge
- please give +1mm more space between outputs/drivers (too close to each other)
- trimer 1k should be near to BD139, you have than only two jumpers wires
- please put (sch below) 10 ohm emitter resistor to Vbe multiplier
- rearrange positions of 1k/2W resistor, 1uF, 10nF, to put 10000uF/63V on PCB
- place one more GND connection (SPK-) in between two existing (three in the line)
- place only one OUT pin connector in the middle
- 1k feedback resistors should be connected at exact OUT pin (not 2 cm away)
- 1k from each gate of IRF to emitter of the output BJT are missing
- please put two 15V/0,5W zener diodes in series (chatodes towards each other) from gate to source of each IRF (overvoltage gate protection)
- heatsink from each power diode MUR860, should have holder solder pin, like at BF's
- the name of the PCB: SSA BIGBT Basic
- the schematic is by Lazy Cat
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File Type: jpg SSA BIGBT BASIC 1.1.jpg (427.1 KB, 785 views)

Last edited by Lazy Cat; 25th August 2011 at 04:18 PM.
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Old 25th August 2011, 04:03 PM   #435
Sheldon is offline Sheldon  United States
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Quote:
Originally Posted by Lazy Cat View Post
According to my current needs and personal taste I will start to make something like this.
http://www.diyaudio.com/forums/attac...-ssa-bigbt.jpg
Why two decoupling caps for the input voltage shunt reg? Why not just put the 1m cap in place of the 16u cap to the LED?

Sheldon
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Old 25th August 2011, 04:08 PM   #436
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Hi Sheldon,

10uF/16V elcos are decoupling current source/sink generators (sense BJT) not +/-15V rails
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Old 25th August 2011, 04:14 PM   #437
Sheldon is offline Sheldon  United States
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Quote:
Originally Posted by Lazy Cat View Post
Hi Sheldon,

10uF/16V elcos are decoupling current source/sink generators (sense BJT) not +/-15V rails
As a practical matter, is there much difference? That node (LED) should present a very low impedance to common, and LED's are very quiet. Just curious.

Sheldon

Last edited by Sheldon; 25th August 2011 at 04:16 PM.
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Old 25th August 2011, 04:23 PM   #438
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I know but this amp has several MHz power bandwidth and replacing current supply resistor with current source/sink is critical. All unwanted AC, RF, ripple, ... must be rejected from sense BJT's collector to prevent any kind of oscillations in CSS generators.
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Old 25th August 2011, 04:26 PM   #439
Sheldon is offline Sheldon  United States
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Thanks.
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Old 25th August 2011, 05:16 PM   #440
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Quote:
Originally Posted by buzzforb View Post
This schematic, which shows BC550/560 in both bjt stages, should work fine with mosfet output, correct?
BC550C/BC560C (2SA970/2SC2240) are suitable for both stages if the rail supply voltages are +/-35V and cascode collector current is 2 to 5mA, so to keep them safe from Vce-max and power dissipation point of view.

If supply voltages are higher I recommend BF471/BF472, 2SA1478/2SC3788 or similar TO-126 case high bandwidth transistors.
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