Bluetooth injection point on a Roberts RM20 - UK Vintage Radio Repair and Restoration Discussion Forum

stebur1965 · 21st Apr 2021, 2:48 pm

I have a Roberts RM20 which is lovely. The amplifier section works great but the receiver isn't very good. And let's face it, who wants to listen to MW these days?
I want to make a bluetooth conversion but keep it as original as possible, and certainly not chop anything out of it.
Looking at the circuit diagram I think that if I disconnect the C12 end of R14 and inject the output of a bluetooth receiver card between R14 and GND then that will work - injecting it into the amplifier section.
Any thoughts?

Gabe001 · 21st Apr 2021, 4:04 pm

If I were you I'd contact Andy 1964, he did about 3 Roberts BT conversions over the last few months

If memory serves, he simply installed a switched stereo female socket right before volume control, merged L+R via 2 resistors and used an external BT adapter. Plugging a jack into the socket mutes the radio and allows you to listen to your BT stream.

Alternatively, I've seen some good threads here on how to power BT from the radio, but require a bit more work.

unitelex · 21st Apr 2021, 10:24 pm

The suggested injection point looks ok. Might need additional attenuation to balance with legacy audio level if you are switching from legacy to BT from time to time.
On my BT conversions I have always incorporated the BT internally, it’s more effort but a neater and more convenient end result.
Best Regards
Chris

21st Apr 2021, 2:48 pm	#1
stebur1965 Diode Join Date: Apr 2021 Location: Didcot, Oxfordshire, UK. Posts: 1	Bluetooth injection point on a Roberts RM20 I have a Roberts RM20 which is lovely. The amplifier section works great but the receiver isn't very good. And let's face it, who wants to listen to MW these days? I want to make a bluetooth conversion but keep it as original as possible, and certainly not chop anything out of it. Looking at the circuit diagram I think that if I disconnect the C12 end of R14 and inject the output of a bluetooth receiver card between R14 and GND then that will work - injecting it into the amplifier section. Any thoughts? Attached Thumbnails Last edited by Cobaltblue; 21st Apr 2021 at 3:22 pm. Reason: Forum Rule B8

21st Apr 2021, 4:04 pm	#2
Gabe001 Octode Join Date: Oct 2019 Location: Stockport, Greater Manchester, UK. Posts: 1,641	Re: Bluetooth injection point on a Roberts RM20 If I were you I'd contact Andy 1964, he did about 3 Roberts BT conversions over the last few months If memory serves, he simply installed a switched stereo female socket right before volume control, merged L+R via 2 resistors and used an external BT adapter. Plugging a jack into the socket mutes the radio and allows you to listen to your BT stream. Alternatively, I've seen some good threads here on how to power BT from the radio, but require a bit more work.

21st Apr 2021, 10:24 pm	#3
unitelex Hexode Join Date: May 2005 Location: Greater Manchester, UK. Posts: 496	Re: Bluetooth injection point on a Roberts RM20 The suggested injection point looks ok. Might need additional attenuation to balance with legacy audio level if you are switching from legacy to BT from time to time. On my BT conversions I have always incorporated the BT internally, it’s more effort but a neater and more convenient end result. Best Regards Chris