Bush DAC90A - Adding Bluetooth

[Gabe001]

Donald, just a thought. Are you using resistors to sum the L+R from the BT output? If so, you may be causing some attenuation of the BT output volume. Paul has assured me in the past that these resistors are not necessary.

Gabriel

[DonaldStott]

Thanks guys for your continuing interest and support.

@wd40addict - even with the volume on the iPhone at 100% I'm still getting breakthrough from the RF/IF signal? I'm wondering to what extent this is a DAC90A issue as we have the classic problem of the volume not bring muted when the control is at zero? Rather than trying to fix these problems with the overdriving option I'll move on and try the switching option later today.

@Gabe001 - there are no series resistors on the L&R outputs from the BT board. Connections are as detailed in my Post #59 above. The only additional component between the board and the radio is the 2.2uF electrolytic in series with the combined L&R outputs.

[wd40addict]

Try the 100k series resistor first!

[DonaldStott]

Originally Posted by wd40addict

Try the 100k series resistor first!

Tried a 100k resistor in series with the connection from IFT2 to the top of the volume control - made no difference to the breakthrough from the RF/IF signal?

[wd40addict]

That's intriguing, there has to be another path. Do you still get breakthrough if you disconnect the 100k resistor, but don't reconnect the wire to the volume control?

Of course I can 'fix' this problem by tuning the radio away from any stations but that really isn't a solution?

It was the solution for some radios without a gram position on the waveband switch "back in the day".

If you are going to use it solely for Bluetooth slip a bit of ali foil twixt the tuning capacitor vanes, that will stop any radio getting through.

Of course I can 'fix' this problem by tuning the radio away from any stations but that really isn't a solution?

It was the solution for some radios without a gram position on the waveband switch "back in the day".

If you are going to use it solely for Bluetooth slip a bit of ali foil twixt the tuning capacitor vanes, that will stop any radio getting through.

How did that happen

[DonaldStott]

As I had the IFT2 to volume control link disconnected to try the 100k resistor in series and partly due to my own frustration I decided just to crack on and try the switching option exactly as shown in Post #44 above from Paul (wd40addict). Checked and re-checked all my work to ensure everything was connected properly.

Same result - I still have breakthrough from the RF/IF signal?

If this is not the same experience as everyone else than I can only assume that either there is something I'm doing wrong or this is a feature of this DAC90A and we have been trying to fix the wrong problem? Of course the other assumption of mine at the start of this Thread was that given the prevalence of the DAC90A surely someone else must have added Bluetooth successfully?

[Gabe001]

I've never done it on a dac90a but I have all the bits so I may experiment next week if I have time

[Radio tirana]

Hi Donald, sorry to hear you are still having problems with this.
In my case there really isn't any significant breakthrough, it has occurred to me that I have also carried out the Kaylee20 modifications to this set and wondered if this had any bearing on the result?

Kind regards RT

[David G4EBT]

I've been lurking around in the background and have nothing to contribute as to what might be the cause and cure of RF breakthrough but I've been doodling away to create PCB for a little full-wave rectified PSU regulated 5V power supply and to add the little Bluetooth module, perhaps fixed to the PCB with sticky pads, with the 5V input on the module ('J1') and the audio output ('J3') and audio input ('J4') connected to the PCB with little wire links shown in red.

(There's been no mention of the audio ground connections and none are included).

Not many places to locate the PCB inside the set. Three locations came to mind:

1) Mounted lengthways on and vertically on a metal strip between the to support pillars for the tuning scale-plate more of less above the valves and IFTs.

That's not a practical proposition due to long wiring runs, and not the best location with heat from the valves.

2) Above the chassis behind the valves and IFTs at the rear of the speaker cut out and dial cord. (mounted vertically, lengthways).

Again, problematic for wiring routing and heat from valves, so not really a runner.

3) On the rear chassis apron adjacent to IFT2 and V2 & V3 valve bases.

That has the merit of being close to IFT2 for wiring, and given that whenever the radio is switched on the module will be powered up with mains voltage from the switch on the pot on the input of the PCB, for safety reasons it would need to be mounted on 10mm standoffs on the chassis apron, perhaps with a strip of 2mm Paxolin behind it for added safety.

The transformer I've specified is 28 mm x 33mm and mounted in its narrow plane, the PCB would be 30 mm wide - the same as the Bluetooth module (30mm x 30mm). It would just fit on the chassis apron. I've laid the board out and the way that I'd envisage it being connected in line with Paul - 'WD40 Addict's' suggestion.

I'm unlikely to want to do the modification myself, but I thought it might help others to 'throw my hat in the ring', so I've attached my doodled circuit, an X-Ray of the PCB and the manner of making the connections in line with the WD4- suggested circuit.

The little PSU circuit (not the layout) is one I've used many times over the years for small homebrew PSUs various voltages. It featured in Elektor Magazine was back in July 1978. A scan is attached.

Hope that might be of interest.

[DonaldStott]

Originally Posted by Gabe001

I've never done it on a dac90a but I have all the bits so I may experiment next week if I have time

I'd certainly be interested in any outcome - thanks.

Originally Posted by Radio tirana

In my case there really isn't any significant breakthrough, it has occurred to me that I have also carried out the Kaylee20 modifications to this set and wondered if this had any bearing on the result?

Are you able to quantify "...there really isn't any significant breakthrough..." - maybe I'm expecting too much?

I've done a couple of the kalee20 mods but can't remember if any of them address the breakthrough I'm experiencing? I now have my homework for the weekend:-

https://www.vintage-radio.net/forum/...ad.php?t=35784

Originally Posted by David G4EBT

I've been lurking around in the background and have nothing to contribute as to what might be the cause and cure of RF breakthrough but I've been doodling away ...

...Hope that might be of interest.

David, what can I say - as you know my DIY 5V DC PSU is based on the Elektor Magazine design you sent me notwithstanding your advice on component types, values and sources! It means that the PSU is fully rectified, smoothed and regulated while in operation it appears to be completely silent.

I have no doubt that you will have carefully considered and assessed the various options for locating any PCB and hopefully I may be able to consider implementing your suggestions in due course? You mention the problem of long cable runs but not sure to what extent any issues could be alleviated by the use of screened cables?

I'd also appreciate some clarification on the audio ground connections? I connected the AGND OUT via the L&R signal cable shield to the screen on the DAC90A volume control, not the chassis, but have nothing connected to the AGND IN?

[Gabe001]

All 3 grounds are tied together. I wouldn't think it makes a difference whether you connect them all but Paul will no doubt add his 2p

I also agree with the comment above by Merlin. There is no shame in having to tune into a quiet area to the band to listen to music via Bluetooth.

If I understand correctly, the mount point David has proposed is highlighted in the attached pic. I don't think you have any other choice Donald - the BT module if I remember correctly is only rated up to a max of 60 degrees Celsius.

[wd40addict]

Try talking one step back, if you disconnect the wire from IFT to volume control do you hear any breakthough?

All ground are connected together on KRC module

[Radio tirana]

Hi
That looks really neat David, I like the idea of a self contained conversion that doesn't require drilling extra holes in the chassis. I fixed mine to a 2mm thick aluminium plate mounted across the back of the tuning scale brackets picking up on the lower set of fixings. The transformer is encapsulated in plastic so is fixed to the bracket directly it is quite heavy as I used a 10vA one in order to also power the scale lamps. The regulator board is mounted on insulated 5mm spacers. The KRC Bluetooth module could be mounted to your PCB by a right angle pin header I have seen this done with small amplifier pcbs by many Hong Kong sellers on ebay. My Bluetooth module is encased in heatshrink and tywraped to the tuning scale brace under the diffuser. I decided to switch to a capacitive dropper to reduce the heat inside the set.
Donald, I could only just hear breakthrough when the set was tuned to a strong signal with the volume set to maximum. I did use screened cable but I hooked it up during initial testing with single core wire and the performance was the same.

Kind regards RT

[David G4EBT]

The screen on the volume control, the lower end of the volume control and the cathodes of V2 & V3 are all connected to each other anyway, as highlighted in blue on the attached part circuit, so there are several points at which to make that connection.

As to the ground connections on the Bluetooth board, the 'J1' 5V input 0Ve connection for both audio in and out are all commoned.

As to the long cable runs, I don't see the point in making life difficult by having to route wires from the IFT beneath the chassis through a hole in the chassis, up one of the Tuning Scale Plate supports to the BT module suspended above the valves, when if the board is fixed under the chassis on the rear apron, there would be short connections of maybe just three or four cms. Furthermore, for the 240V AC to the PSU, you'd either have to pick that up from the Voltage selector panel and chassis, or run a twisted pair back to the the switch on the Volume Control.

I'm not saying don't do it - at the end of the day its your radio and your project - I'm just saying that from my perspective, it's a needlessly convoluted way of wiring up the PCB, apart from it not being an ideal location. I think the shorter the run the better, and the rear chassis location allows a short run to pick up the AC from the switch, and to connect the other end of the PCB to the IFT, with no need to fiddle around with any connections around the pot tags - it's done at the IFT end.

Every success with it - it's clear that several people have successfully fitted Bluetooth to this and other radios, with lots of excellent feedback on their experiences and much food for thought. Hopefully, a successful outcome is within your grasp and it won't be too long now before we can run the Saltire up the flagpole and rejoice!

[rjmusto]

Hi GUys,

An intersting thread...

Just a quick one from me on receiver breakthrough:

I have read recently in an old servicing book about adding a positive bias to the detector diode to mute the front end. I tried this out on a portable set I have been working on and sure enough, adding say 5v to the top of the volume control (via some suitable resistance) and the receiver audio disappears. Get the resistor values right and you can basically switch in an external source with no receiver noise.

It does mean the agc line can go a bit positive when this is switched in, which I think is ok - unless anybody knows more about this than me (not hard).

And making a 5v switch line from the new module is not too hard.

Ralph

[DonaldStott]

Originally Posted by wd40addict

Try talking one step back, if you disconnect the wire from IFT to volume control do you hear any breakthough?

All ground are connected together on KRC module

So when I'm configured for the switching option and disconnect the 0.1 capacitor, which is series between the top of the volume control and the Bluetooth L&R inputs, I can still hear breakthrough! Given that there is no direct connection to the top of the volume control when trying this I'm puzzled as to how the RF/IF signal is still getting through?

Of course the screened wire from the IFT is still connected the L&R inputs on the BT board.

Should anything be connected to the AGND IN on the BT board e.g. the screen of the signal wire?

[wd40addict]

Let me dig my DAC90A out and see how it behaves. Have you replaced the V2 V3 cathode bypass capacitor?