Dansette Apollo to Bluetooth. - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

Gabe001 · 24th Nov 2021, 8:53 pm

3 watts (using "music power") across a 12ohm load is 6v RMS at maximum signal
Power dissipation =v squared/r= 36/100,000 = 0.00036w

Meaning it won't get hot or melt.

As starting point you'd want to aim to drop the voltage in order to supply the BT module with around 400mv rms, so you will need somewhere between 7-10kohms between wiper and ground on the potentiometer depending on whether you believe the "output power" or "music power" figures

Gabriel

bikerhifinut · 24th Nov 2021, 9:18 pm

To The OP.
Just do it.
Frankly the 10x12ohm resistor is probably 3x the rating you'd need and wired across the speaker output you'll get about 4.5 Volts at full chat (rough calculation but suffices).
I wouldn't even bother with the pot on the output before your coupling capacitor, at full volume its going to sound fairly rough anyway so just adjust on the players own volume control until its a comfortable level into your BT device. Your ears are good enough for this.
Thats all you need to do in reality.
If you want a constant output setting independent of the record players controls, then you need to find the point where the signal is inputted to the internal amp.
Me? If i felt the need to do this and frankly I think you'll be disappointed whatever you do as even cheap Bluetooth Speakers/audiosystems will probably outperform the Dansette by a fair way, I'd take a tapping off the top of the dansettes volume control via a DC blocking/ coupling capacitor of around 1uF straight to your transmitter module.
Easy enough if you know your way around a circuit.
And I'd also gently advise you to get a bit of working knowledge around the basics of electronic theory. Plenty of resources online these days and also get at the very least an understanding of Ohms law and its associated Power law as those simple formulae will getyou out of a lot of pickles..

Regards.

Andy.

Test Desk · 26th Nov 2021, 9:22 am

Thanks Andy (and others) . What you suggest about the tap off the volume control is the original way I was going to go but thought my signal would be bass light ( I'm not a bass junkie by the way) due to no RIAA circuit. I'm told here that I don't need equalization with a xtal cartridge , which I don't really understand as RIAA was designed to compensate for reducing large bass excursions on the vinyl ?
Anyway, I'm ultra cautious having destroyed a few working items in the past, both valve and transistor usually by trying to make direct connections to my reel to reel tape recorder where non existed.

Yes I'm conversant with ohms law, just not very good at applying it to real circuitry it seems.
Even did Norton and Thevenin's theorems at college eons ago but all that had to make way for new knowledge relevant to my former employment as a data transmission planner.
I'm still bereft of capacitors so I'll crack on when they arrive.
Cheers.

wd40addict · 26th Nov 2021, 7:41 pm

What is not often appreciated is that the frequency response of the recording on the disc actually looks like this:

Click image for larger version

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The combination of the magnetic pickup's natural 6dB/octave freq rise + the RIAA curve makes this flat. A ceramic or crystal pickup has to use mechanical means to try and equalise the 12.5dB difference between the bass and treble regions, hence by the time it hits the volume control it will be pretty flat.

24th Nov 2021, 8:53 pm	#41
Gabe001 Octode Join Date: Oct 2019 Location: Stockport, Greater Manchester, UK. Posts: 1,646	Re: Dansette Apollo to Bluetooth. 3 watts (using "music power") across a 12ohm load is 6v RMS at maximum signal Power dissipation =v squared/r= 36/100,000 = 0.00036w Meaning it won't get hot or melt. As starting point you'd want to aim to drop the voltage in order to supply the BT module with around 400mv rms, so you will need somewhere between 7-10kohms between wiper and ground on the potentiometer depending on whether you believe the "output power" or "music power" figures Gabriel

24th Nov 2021, 9:18 pm	#42
bikerhifinut Octode Join Date: Nov 2013 Location: Penrith, Cumbria, UK Posts: 1,993	Re: Dansette Apollo to Bluetooth. To The OP. Just do it. Frankly the 10x12ohm resistor is probably 3x the rating you'd need and wired across the speaker output you'll get about 4.5 Volts at full chat (rough calculation but suffices). I wouldn't even bother with the pot on the output before your coupling capacitor, at full volume its going to sound fairly rough anyway so just adjust on the players own volume control until its a comfortable level into your BT device. Your ears are good enough for this. Thats all you need to do in reality. If you want a constant output setting independent of the record players controls, then you need to find the point where the signal is inputted to the internal amp. Me? If i felt the need to do this and frankly I think you'll be disappointed whatever you do as even cheap Bluetooth Speakers/audiosystems will probably outperform the Dansette by a fair way, I'd take a tapping off the top of the dansettes volume control via a DC blocking/ coupling capacitor of around 1uF straight to your transmitter module. Easy enough if you know your way around a circuit. And I'd also gently advise you to get a bit of working knowledge around the basics of electronic theory. Plenty of resources online these days and also get at the very least an understanding of Ohms law and its associated Power law as those simple formulae will getyou out of a lot of pickles.. Regards. Andy.

26th Nov 2021, 9:22 am	#43
Test Desk Tetrode Join Date: Nov 2017 Location: Bromsgrove, Worcestershire, UK. Posts: 63	Re: Dansette Apollo to Bluetooth. Thanks Andy (and others) . What you suggest about the tap off the volume control is the original way I was going to go but thought my signal would be bass light ( I'm not a bass junkie by the way) due to no RIAA circuit. I'm told here that I don't need equalization with a xtal cartridge , which I don't really understand as RIAA was designed to compensate for reducing large bass excursions on the vinyl ? Anyway, I'm ultra cautious having destroyed a few working items in the past, both valve and transistor usually by trying to make direct connections to my reel to reel tape recorder where non existed. Yes I'm conversant with ohms law, just not very good at applying it to real circuitry it seems. Even did Norton and Thevenin's theorems at college eons ago but all that had to make way for new knowledge relevant to my former employment as a data transmission planner. I'm still bereft of capacitors so I'll crack on when they arrive. Cheers.

26th Nov 2021, 7:41 pm	#44
wd40addict Octode Join Date: May 2009 Location: Stevenage, Herts. UK. Posts: 1,518	Re: Dansette Apollo to Bluetooth. What is not often appreciated is that the frequency response of the recording on the disc actually looks like this: The combination of the magnetic pickup's natural 6dB/octave freq rise + the RIAA curve makes this flat. A ceramic or crystal pickup has to use mechanical means to try and equalise the 12.5dB difference between the bass and treble regions, hence by the time it hits the volume control it will be pretty flat.