Bush DAC90A - Adding Bluetooth

[DonaldStott]

The picture I've attached in Post #98 above shows my cardboard mock-up PCB anchored at the top right by by the existing bolt for the trimmers stand-off. The other corners simply have self-tappers to temporarily help with locating and securing the PCB.

Initially I was very reluctant to start drilling holes in the DAC90A chassis and had considered using three Self Adhesive PCB Pillars, for example:-

https://www.cricklewoodelectronics.c...ack-of-10.html

Important to stress that other options and sources are available.

Recently wiser counsel (!) has been brought to bear on this idea of only having one bolt securely holding the board. Although the stick-on stand-offs have quite a large footprint and might be OK, they are not an ideal choice with mains AC voltage on the underside of the PCB. These sticky-pads would be fine, for example, to hold in place a PP3 battery, but it is vital that the PCB is firmly and permanently secured.

At the very start of this Thread I set myself one key test for any Bluetooth modifications which was that it "... would need to be implemented in such a way that it is non-invasive and reversible if required." I am now of the opinion that drilling three 6BA holes in the chassis to secure the PCB isn't a step too far and is 'allowable' for heath and safety purposes?

Thanks again to David G4EBT for advice and guidance.

[Gabe001]

How about something that slots in from underneath? It will be supported between the bakelite of the case and the chassis.

In that scenario the screw would only be necessary to stop it from sliding, but won't be supporting the weight of the module. See quick diagram below.

Aw, just drill a hole or two, it will be safe and in the future* an eBay listing may be "Original Bluetooth DAC90A for sale"

*Not that far either, just look at the questions we get about record players.

[Graham G3ZVT]

I think sometimes we attach too much reverence to our vintage tech, and I am as guilty as anyone else in this respect (pun intended).

I think it may be a British thing, compare our attitude to some stateside restorers one may encounter online!

[DonaldStott]

Bluetooth boards comprising a 5V DC supply and all audio IN/OUT connections just arrived in from JLCPCB:-



Quality is excellent considering the price i.e. £11.02 for ten boards and that includes p&p! All I need to do now is to find the time to populate the board, connect the modified KRC-86B board, fit it all on the underside of the DAC90A chassis and then Test!

P.S. There are Points on offer if you can spot the very small mishap on the screen print layer - doesn't affect the circuit though?

[Helder Crespo]

Originally Posted by DonaldStott

Bluetooth boards comprising a 5V DC supply and all audio IN/OUT connections just arrived in from JLCPCB:-

Attachment 229938

Quality is excellent considering the price i.e. £11.02 for ten boards and that includes p&p! All I need to do now is to find the time to populate the board, connect the modified KRC-86B board, fit it all on the underside of the DAC90A chassis and then Test!

P.S. There are Points on offer if you can spot the very small mishap on the screen print layer - doesn't affect the circuit though?

"N" instead of "IN" in the regulator?

[DonaldStott]

Originally Posted by Helder Crespo

"N" instead of "IN" in the regulator?

Well spotted - the Points are yours!

[DonaldStott]

Update on progress ...

Managed to fit my Bluetooth PCB under the DAC90A chassis - snug:-



A few questions as I'm not quite sure what is going on?

I'm using the switched option as recommended by wd40addict with a 100nF cap in the AudioOut which runs to the VC input wire disconnected from IFT 2. There is also a 47k resistor running to Pin 7 of V2. The AudioIn is connected to the vacated tag on IFT2. 100k resistors on the KRC-86B board have been removed. I've used twin core screened signal cable and the screen is connected to the Ov on the board - as previously advised I understood that all grounds are commoned.

Net result - no audio when in Bluetooth mode and very, very faint audio when in radio mode. Added to that there is very, very loud hum when the VC on the radio is turned up??

Went back and reviewed all the Posts in this Thread and found two intriguing pointers:-

1. " ... do not run 0v down the lead carrying the audio" !

2. "Only ground one end of any signal leads, keep the other end insulated/isolated from other ground connections" !

So I disconnected my cable screen to the 0v from the board leaving only this screen connected to VC shield at the radio end. Both audio grounds are not connected.

Net result - now working very well in Bluetooth mode but there is very strong breakthrough from the radio audio when tuned to a station e.g. Radio 4 LW?? Tuning away from a strong radio station fixes this but still no radio audio when Bluetooth is turned off??

Maybe I should just be happy with what I've got i.e. Bluetooth working with a DAC90A, but I'd really like to know what is going on and why I have no audio from the radio?

NOTE: As I've disconnected and reconnected the screened cable in the DAC90A several times it's starting to fray and crumble! Anything special about this or can it just be replaced with a length of standard 75Ohm co-axial cable?

[Gabe001]

It's very strange that you gave a different outcome with the same setup.

You are right in that the 0v and the AGND are commoned in the krc-86b. When I use half wave rectification to power the board, I don't need to connect AGND. When I use a 5v isolator I do, or I end up with a situation similar to yours i.e faint sound and hum

When I experimented, as you are doing, with an ultra twin and the powered the board with a small transformer off the mains, I am pretty sure I connected AGND to signal ground on the volume control and didn't have any issues.

I don't know if this helps you in any way. I'm sure paul will pitch in

Gabriel

[DonaldStott]

Originally Posted by Gabe001

It's very strange that you gave a different outcome with the same setup.

Strange indeed - tomorrow I'll disconnect all the Bluetooth wiring just to ensure that the DAC90A is still working as a radio!

Kind of hoping that I've done something to stop it functioning properly??

[Gabe001]

Originally Posted by DonaldStott

Strange indeed - tomorrow I'll disconnect all the Bluetooth wiring just to ensure that the DAC90A is still working as a radio!

Kind of hoping that I've done something to stop it functioning properly??

Look on the bright side, at least the UL41 is good!

[DonaldStott]

Originally Posted by Gabe001

Look on the bright side, at least the UL41 is good!

Once this business is sorted it will be back to the EKCO U122 where I have a very interesting development to share!

[DonaldStott]

Disconnected all wiring and components associated with my Bluetooth PCB and reinstated my DAC90A back the way it was!

Good news (?) is that the radio is functioning normally on both MW and LW. Usual background hash but that's the modern scourge of cheap SMPSs for you - currently the worst offender is the charger for my electric toothbrush!

So it may be that I need to make a decision i.e. do I fit the Bluetooth PCB knowing that the audio from the radio doesn't work but that the DAC90A can be reinstated to a functioning radio if required? To be honest, all the radio stations I listen to are available online e.g. BBC Sounds etc. so what am I missing out on that's only available on MW or LW?

But just for the sake of completeness I'd still like to know what's going on (or not) with my Bluetooth PCB and why there is no audio from the radio when the Bluetooth is switched off? Notwithstanding of course the enigma of the PCB ground and AGND connections?

[Gabe001]

Donald, leave the radio original and call it a day imo. You can always use the minimod and you will have ample opportunity to try putting bluetooth into other sets in future.

[DonaldStott]

Originally Posted by Gabe001

Donald, leave the radio original and call it a day imo. You can always use the minimod and you will have ample opportunity to try putting bluetooth into other sets in future.

Thanks Gabe for your continued interest but at times like this my stubbornness genes tend to kick in!

Although many on the Forum don't regard the Bush DAC90A as something that should be tackled by new users, partly due to it being an AC/DC set with potentially a live chassis, I have found it one of the easiest sets to work on. I've now restored a good number of these sets along with DAC10s. Have to highlight that help, support and guidance from this Forum has been invaluable in this respect. So my view is that if I cant get Bluetooth working properly with the DAC90A then it doesn't bode well for any similar work on other sets in the future, if that makes sense?

I've no idea what went wrong when I installed my Bluetooth PCB but will carefully retrace my steps over the next few days?

[murphy512]

Donald,
I added bluetooth to a DAC90A for a friend and it works well. The only permanent modification is a hole in the chassis to fit a 3.5mm audio socket.
The bluetooth unit could be easily removed and the radio would be back to its original condition.
The audio from the BT is inserted into the circuit at the volume point via a two way switch at the back of the radio and it also switches on/off the BT. When the BT is off the radio section is reconnected.
The sound is very good and loud with hardly any distortion at full volume.
The switch also connects the anode of V2 to ground via a .02 cap when the BT is on.

I had the radio for a year now as I cannot take it to her because of travel restrictions. She wanted a cream Dac 90 because it matches her Smeg appliances. This is the only AC/DC with BT that I have done, just for her. In fact I was not sure that it would work satisfactorily, but I was pleasantly surprised with the outcome.
Good luck
Aldo

[Gabe001]

Originally Posted by DonaldStott

Thanks Gabe for your continued interest but at times like this my stubbornness genes tend to kick in!

Although many on the Forum don't regard the Bush DAC90A as something that should be tackled by new users, partly due to it being an AC/DC set with potentially a live chassis, I have found it one of the easiest sets to work on. I've now restored a good number of these sets along with DAC10s. Have to highlight that help, support and guidance from this Forum has been invaluable in this respect. So my view is that if I cant get Bluetooth working properly with the DAC90A then it doesn't bode well for any similar work on other sets in the future, if that makes sense?

I've no idea what went wrong when I installed my Bluetooth PCB but will carefully retrace my steps over the next few days?

I that case Donald reinstate your previous non PCB based BT version and see what happens. I wonder if there's something wrong with the PCB, like a crossed ground pathway.

[DonaldStott]

Originally Posted by murphy512

I added bluetooth to a DAC90A for a friend and it works well.

The switch also connects the anode of V2 to ground via a .02 cap when the BT is on.

Thanks Aldo - interesting to read about a different approach to adding Bluetooth functionality to a DAC90A.

In the interests of my ongoing education in all things Bluetooth, what's the purpose of the 0.02 cap to the V2 anode?

In my PCB based on advice from wd40addict there is a 0.1 cap in the AudioOut which runs to the VC input wire disconnected from IFT 2. There is also a 47k resistor running to Pin 7 (cathode) of V2. The AudioIn is connected to the vacated tag on IFT2. The 100k resistors on the KRC-86B board have been removed.

Originally Posted by Gabe001

I that case Donald reinstate your previous non PCB based BT version and see what happens. I wonder if there's something wrong with the PCB, like a crossed ground pathway.

Thanks Gabe - I'm open to any and all possibilities!

I checked the output from my PCB and I have a steady 4.9V DC going into the KRC-86B board. I don't think I have a crossed ground pathway anywhere but I will carefully check the PCB circuit.

If anyone would like a copy of the circuit diagram from Sprint Layout to check then drop me a PM.

[murphy512]

Quote:
In the interests of my ongoing education in all things Bluetooth, what's the purpose of the 0.02 cap to the V2 anode?

I was getting radio breakthrough when BT was in operation.
The .02 cap silences the radio

[wd40addict]

Resistor should be 470k not 47k, but this wouldn't explain what you're seeing. When I temporarily bodged a KRC module into my DAC90A it worked fine in both radio and Bluetooth mode (post #82). I can only suggest you recheck your wiring and make sure there are no splodges where you removed the resistors.