OEM Door Speaker Amp Disassembled

[FR-S2GT86]

For those that do not know, this OEM amplifier is located in the trunk next to the spare tire underneath the floor panel, on the driver's side of a left-hand drive model BRZ, FR-S or 86 from 2013 model on up to the final year of the first generation.

It gets its signal input by tapping off of the dash speakers and sends that amplified signal to each door speaker. It has a non-adjustable low pass crossover and a subsonic filter built in.

Here it is removed from the vehicle in it's factory bracket:



Here are a few pictures from different views with the bracket removed:







Here it is with the top panel removed:



And a closer view of that:



And with the circuit board removed from the housing and flipped over:



There are no switches and no adjustment potentiometers on the circuit board at all. It is matched to the factory head units that utilize it. If you find that your amplifier is not plugged in and has a bypass plug installed in the signal input/speaker output connector instead, then your OEM head unit does not provide a 12-volt signal to turn this amplifier on and it is powering your door speakers directly along with the dash mids and tweeters.


*Edit*
I have done some preliminary signal voltage input and output tests on this amp so far using a test CD at 40Hz, 100Hz, 400 Hz, 1kHz, 4kHz, and 8kHz and that's how I came to the general conclusion about the low-pass and subsonic filtering. Out of curiosity, and I'm sure some people here will appreciate it, I will go into a more thorough test using a tone generator now that I have this amp on the test bench.

Here are the preliminary results measured attempting to maintain an input signal voltage of .250 VAC, measured across the left positive and right negative inputs. The output voltage was measured at the left positive and right negative speaker outputs. Note that at no time is there any amount of audible clipping in either the signal input or speaker output and the output was measured with 4-ohm speakers connected.

At 40Hz, the output is 2.130 VAC

At 100Hz, the output is 2.436 VAC

At 400Hz, the output is 2.234 VAC

At 1kHz, the output is 1.565 VAC

At 4kHz, the output is 0.484 VAC

At 8kHz, the output is 0.201 VAC

More measurements to come.

[LimitedSlip]

For further reference, here is the schematic for the factory speakers and trunk amp.

[soundman98]

top left corner is labeled "HPF" and "LPF". can you read the model numbers of IC 101, and 201 chips in those area's?

it would seem to indicate the top one is a HPF/subsonic filter, and the lower one is a LPF.

that is where any alteration of crossovers is going to happen, or at least knowing what they setup the oem crossovers at...

i love how they nicely labeled everything!

[Compelica]

Seems pretty empty for such a big box...

[FR-S2GT86]

Originally Posted by soundman98

top left corner is labeled "HPF" and "LPF". can you read the model numbers of IC 101, and 201 chips in those area's?

it would seem to indicate the top one is a HPF/subsonic filter, and the lower one is a LPF.

that is where any alteration of crossovers is going to happen, or at least knowing what they setup the oem crossovers at...

i love how they nicely labeled everything!

Here's a better close-up of the two chips.



Looks like they both read

4580
EC7
JRC

[LimitedSlip]

RC4580 Dual Audio Op-Amp

Here is the full data sheet for the Texas Instruments version of the chip:

https://www.ti.com/lit/ds/symlink/rc4580.pdf

The RC4580 device is a dual operational amplifier that has been designed optimally for audio applications, such as improving tone control. It offers low noise, high gain bandwidth,low harmonic distortion, and high output current, all of which make the device ideally suited for audio electronics, such as preamplifiers, active filters, and industrial measurement equipment. When high output current is required, the RC4580 device can be used as a headphone amplifier. Due to its wide operating supply voltage, the RC4580 device can also be used in low-voltage applications.

• ±2-V to ±18-V Operating Voltage

• 0.8-μVrms Low Noise Voltage

• 12-MHz Gain Bandwidth Product

• 0.0005% Total Harmonic Distortion

• 5-V/μs Slew Rate

• Drop-In Replacement for NJM4580

• Pin and Function Compatible with LM833, NE5532, NJM4558/9, and NJM4560/2/5 devices

As @soundman98 observed, the secret to modifying the input filters will likely be the components associated with these chips.

@FR-S2GT86 - Any possibility of getting a number for the main power amp chip, IC301, the one attached to the heat sink?

FYI - Regarding the power output chip:

https://datasheetgo.com/pal007e-pdf/

http://www.datasheetcafe.com/pal007-...osfet-poineer/

The PAL007E is a breakthrough MOSFET technology class AB audio power amplifier in Flexiwatt 25 package designed for high power car radio.

Features
1. MOSFET output power stage
2. Excellent 2 Ohm driving capability
3. Hi-Fi class distortion
4. Low output noise
5. ST-BY function
6. Mute function
7. Automute at min. supply voltage detection

PAL007C ( equivalent TDA7386)

4 x 40W QUAD BRIDGE CAR RADIO AMPLIFIER

[LimitedSlip]

The input attenuating resistors are reducing the speaker level input signals down to a level that the op-amps can deal with.
The input filter capacitors appear to be a subsonic filter that is certainly protecting the op-amps from any DC voltage that may be present offsetting the input signal. They may also be rolling off some of the very low frequency audio depending upon their value.

Figuring out how the circuit is configured is one matter but coming up with any modifications that can be implemented by mere mortals might be a whole 'nuther matter.

[FR-S2GT86]

@LimitedSlip

Had to de-solder and remove the heatsink brace from the board to get a look at the numbers on the IC301 chip, but here it is, as requested.

[FR-S2GT86]

@LimitedSlip

And the different angled close-up views of the filter area on the board as requested.

[FR-S2GT86]

Here is a good close-up of the input attenuating resistors as well, just in case someone ever wants to replace them with a potentiometer to act as a gain control for a future system integration project.

*Edit* These attenuating resistors are 8.2kOhm, as the code on them indicate and as I personally verified with an ohmmeter.

[FR-S2GT86]

Originally Posted by Compelica

Seems pretty empty for such a big box...

It's really not that big of a box. The whole thing could easily fit inside the shell of a standard DIN sized radio.

[soundman98]

i've been staring at those pictures for the past hour. i'm still no closer to understanding how the circuit works. part of me thinks that ti datasheet isn't correct, but at the same time, the pins make perfect sense.

it really looks like a single bypass capacitor is all that's controlling each channel on the op-amps(LPF, C111 neg L, C117 pos L, C112 neg R, C118 pos R). what's weirding me out is how the 'out' and negative pins are tied together on the HPF section. almost like it's converting a positive input signal to a negative signal for the pioneer amp chip...

[LimitedSlip]

Originally Posted by soundman98

what's weirding me out is how the 'out' and negative pins are tied together on the HPF section. almost like it's converting a positive input signal to a negative signal for the pioneer amp chip...

Are you referring to what would be RF in the diagram below? If so, if I recall correctly, RF (the Feedback Resistor) in an op-amp circuit is used in conjunction with RG (Gain Resistor) to determine the overall gain of that stage. If RF is zero (a short circuit, just a piece of wire) it sets the gain to unity or "1". This would be appropriate for a buffer stage or one that is doing signal shaping (filtering, tone control) rather than an actual "pre-amp" function. By connecting Vout back to the inverting input they are creating "negative feedback" which makes for a very stable circuit configuration.

[LimitedSlip]

We can probably figure out the circuit topology and the resistors are clearly marked on their top sides. Unfortunately, the capacitors are either unmarked or their markings have all been very consistently placed face down prior to soldering. You can sort of guess at a range of values based on physical size but if they are truly unmarked they would have to be unsoldered and measured to determine the actual capacitance. Almost like it was intentional . . .