Tuesday, March 7, 2023

Vintage Philips speakers restoration with TPA3118 bluetooth amplifier

A few month ago I've restored a vintage Philips RH591 amplifier from 70's. I've sold this amplifier but I've kept the speakers cause I liked it.


They have two 5 inch octagonal AD-5060/M8 midrange speaker each, and one 1 inch AD-0161/T8 tweeter.

First thing I've done was measuring the impedance. One of the speaker had a short circuit. So I decided to open both.

 Opening the two was not so simple. At Philips they have used some kind of glue for the backpanel, even if the backpanel has securing screws. That glue was also used to join the speaker to the case, although also there are screws.

Once opened I've noticed there was also a 2nd order low pass and high pass filter.

One of the tweeter was broken, so I had to change both. I've used two 90's Pioneer tweeter. They do not sound as clear as the AD-0161, but they perform quit good at all.

I had to draw and print a frame to connect the new tweeter to the case, it was a pretty simple piece.

Another thing I've drawn and printed is the bass reflex tube. They speaker were closed but they sound better with a bass reflex. I've drilled an hole on the back panel for the bass reflex.

I've used a simple one capacitor 1st order filter. I prefer to let the midrange speaker works also on high range, and then boost that range using the tweeter. I've found they sounds better with this configuration.

Just a few rework on the wood side and a clean of the front grill and the speaker were ready to be reassembled.

 I also would like to make the speaker active, possibly with a bluetooth amplifier board.

One of the speaker contains the power supply and the amplifier, the other it's a passive one.

I have an adjustable 4A 230V linear power supply, which I put in one of the speaker. I also put a power plug and a power switch. It's regulated to 20V.

I've buy a couple of boards based on the TPA3118 monolithic IC. One of the two (the blue one) has a little hissing noise on the bluetooth, but the other (the black one) sounds really good. The blue one also has a fake TPA3118, even the pins are not 32 but 28, so it may be TPA3110 or a fake one.


In order to move the audio jack mounted on the board, on the backpanel, I've desoldered the jack and find out that the jack tip to GND select the bluetooth input, otherwise the jack input is used by the preamplifier mounted on the amplifier board. So I've added a little DPDT switch to select the audio source for left and right channel, which can be bluetooth or line input from the jack.

For the second passive speaker connection I've used a GX12 screwing connector.

 Because the speker were mounted on the top of a bookshielf, I've added a power switch to the power cord, and I've left the switch activated on the speaker. that way I can power both on from the desk.

So, how they sounds? They are really loud and sounds more crystalline than I tought, the just a little bit low on the bass, not that they don't have but without any equalization I would have preferred a little more of basses.


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