Sansui BA‑F1 LED backlight

[IgorD]

Hello everyone!

I’d like to share how I made LED backlighting for the Sansui BA‑F1.
Please accept my apologies for the translation — I don’t speak English well.
I made new backlighting for the needle and peak indicators, as well as for the amplifier power button.

My goal was to:
make the indicators’ backlighting yellow, like in the original;
increase the brightness of the backlighting;
add a red backlight for the alarm mode.

I ran many experiments with backlighting colours and came to the conclusion that yellow is the most informative colour. With green and blue, the power scale and the red peak indicator are hard to see. Besides, these colours look unnatural — in my opinion, they’re rather ugly.


I have two such amplifiers: my custom backlighting is installed on the top one, while the bottom one has the stock version.
As you can see in the comparison, the top option is more informative — the needles, power scale, and peak overload indication are much easier to see.



I also added red indicator backlighting that activates when the amplifier is powered on and when the amplifier’s protection circuit is triggered.



The new backlighting was implemented using a three‑colour (RGB) LED strip. I obtained the desired yellow colour by simultaneously activating the red and green diodes on the strip.


I designed and 3D‑printed the backlight holders.


I installed the holders right where the original backlighting was — there are mounting points for that, marked with arrow 1.



An aluminium profile fitted with a matte light diffuser (Feron cab 262) is also used. Inside the profile, two LED strip segments are securely attached with adhesive.


The aluminium profile is first inserted into the holder groove indicated by arrow 3. As you can see, this groove follows the contour of the aluminium profile, ensuring a secure fit. Then, the profile is freely inserted into the groove shown by arrow 2 (refer to the photo above).
A strip of tape can be applied to this location, indicated by the large arrows. My profile fits very tightly, but tape will help ensure better fixation.


Here’s how it looks when everything’s put together. When I was filming a video, the camera kept getting overexposed, so I just stuck a bit of electrical tape on the front — I’ll take it off later.

Unfortunately, I can’t add any more photos right now — there’s a limit on how many I can include here. But don’t worry, I’ll be back with the rest of the story and more images in a little while!

I wonder how correct the translation is, is everything clear in the text?

 

[IgorD]

Back with the continuation! Right now I’m going through all the construction bits — honestly, this is the most boring part so far.


I designed and printed cable holders. Variant 1 is mounted on the circuit board, while variant 2 is installed on the metal chassis base near the backlighting. The holders have grooves that prevent them from rotating. They are secured using existing self‑tapping screws. Arrow 3 shows the cable attachment to the indication and protection board.


This is the holder for the white LED, which is inserted into the amplifier’s power button. The LED leads are bent. Everything is done in the same way as the stock version with a lamp.


This is the holder for the white overload indicator LED. As you can see, a 2–3 mm thick isolon sheet is attached with double‑sided tape to both the base of the needle indicator and the holder. This is done to protect the needle indicator from dust.



To reduce LED localization, an additional light diffuser had to be installed. I used two strips cut from the diffusers of a broken monitor. They cover the top and edges of the indicators and are attached with double‑sided tape at the bottom edges of the indicators.



I use cable pieces from an old USB mouse to connect the RGB strip. The cable is shielded; I connect it to the amplifier chassis at the locations indicated by the arrows.

That’s all for today. It’s already nighttime here. The continuation will follow later.

 

[IgorD]

Continuation. The most interesting part.
At first, I tried using a switch based on a bipolar transistor. However, I abandoned this approach. At such a low supply voltage, it is very difficult to make 12‑volt LEDs in strips work properly. Additionally, the voltage drop across the transistor’s collector‑emitter junction leads to poor performance.
In the end, I used a field‑effect transistor (FET) in the switch. It is voltage‑controlled, the voltage drop during switching is minimal, and the control circuit is simpler.

I drew my circuit in a simulator.

The new components are highlighted with red polygons. The rest of the circuit is as close as possible to the schematic from the amplifier’s service manual (with components and their values specified).
As you can see, there are four segments each of red and green LED strips here — two per indicator.
Each segment on the LED strip includes current‑limiting resistors. An IRF530N MOSFET transistor is used as the switching element.

The existing TR602 transistor (2SC1845 type) has been replaced with a 2SC2328. The 2SC1845 has a collector current of only 50 mA, which is insufficient — the red segments may exceed this current draw. Therefore, we replaced it with a more powerful transistor with a 2 A collector current.

The existing capacitors C609 and C610 (470 µF) were replaced with Panasonic FR 1000 µF/25 V units. Doubling the capacitance reduces power supply ripple and raises the supply voltage (in my case, it went above 9 V). The LED flickering has completely disappeared.

A new 560 Ω resistor between the green segments and the MOSFET transistor may need to be selected individually (your LEDs may have different parameters) — adjust it to achieve yellow illumination.

A white LED in series with a 560 Ω resistor (in the lower part of the circuit) serves as the power button backlight. Select the resistor value based on the desired LED brightness.

The existing LED701 has been replaced with a modern one; resistor R612 was increased to 383 Ω (in my case, it’s a precision resistor — this is not required, I just had plenty of them). In the original circuit, LED701 was connected via D606; I switched it to D605.


This is from the service manual. Naturally, we remove all old lamps and their associated wiring harnesses. We retain only the harnesses for the power button, as well as the pointer and peak indicators.


In the circuit, near the protection IC601 chip, there is a switch KL — this simulates the protection operation. When it is open, this corresponds to the state of the transient protection timer during power‑up or to a fault condition of the amplifier (the red LED on the front panel and the red backlighting of the pointer indicators should be illuminated).

As we can see, there is an opening voltage on transistor TR602 — it is on, and current flows through the red LED and all red backlighting segments. There is a low voltage at the gate of the MOSFET transistor, so it is off, and no current flows through the green segments.


When switch KL is open, this represents normal amplifier operation — the yellow backlighting should be active (produced by a combination of red and green LEDs).
As we can see, the base of TR602 is shunted to ground via switch KL, so the transistor is off. An opening voltage appears at the MOSFET, which turns it on; current flows through both the red and green segments of the strip (producing yellow illumination as a result of their combination).

Now we move on to the peak indicators.

This is a simulator of the peak indicator circuit.
I have removed the original resistors R33 and R34 (refer to the original schematic above — these were resistors for the tubes, which we do not need). New white LEDs and 383 Ω resistors have been installed (highlighted with a red polygon); adjust their resistance value according to the desired brightness.


There are two topology variants for this PCB. One example shows the resistors to be removed (R33, R34). Arrows also indicate two jumpers (JW01, JW02) — I removed them and installed 383 Ω current‑limiting resistors instead. These resistors limit the current to the peak indicator LEDs.
The diagram shows the connection of the power button LED and the modified power supply path routed through diode D605.


Replaced capacitors (1000 μF/25 V), resistor R612 and transistor TR602 are visible.


I did not create a new PCB for just five components; instead, I placed them in a free space using point‑to‑point wiring.

As a result, we have a universal and informative backlighting system. The amplifier’s power consumption decreased by 5–6 W, and it remains completely cool in the upper section of the front panel. All components are readily available, and the backlighting is easy to repair.

For those who cannot perform 3D printing, I will provide alternative options in the final part. Stay tuned for the continuation.