Hi all
I have a cassette stereo from an early 90s Volvo (stereo model TD-603) which I've got working again and now am putting Aux/Bluetooth inputs and removing the cassette player.
So far I've had good results tracing the tracks from the cassette pre-amp to what appears to be an audio processing chip (DIP20 Toshiba TA7764P). I've inserted new audio signal input leads close to the chip, leaving in the caps between signal lead and the chip (2.2uf 50v electrolytics). I cut the tracks near there, removing all the cassette pre-amp circuitry. This seems to work as it should with reasonably clean signal at the right level.
My questions would be...
* Should there be different caps (to the pair of elec. 2.2uf) or any other circuitry before the TA7764P? Both from an audio quality and protection point of view? It's going to have both Aux in, and a Bluetooth unit. I guess the Aux input may need to be a bit resilient because it will take various input devices - eg phones, mp3 players etc with different output levels etc.
* And on the subject of caps - I did have to replace one or two of the large ones - the biggest one had leaked and caused PCB damage. The circuit board is full of electrolytic caps (40 odd). If it was only a handful I might consider re-capping just to re-furb a 30-year-old device, but is there any in particular caps that would be a worthwhile swap? And if so, should I replace any with Tantalum or like-for-like LESR caps - or so-called 'audio' caps? (Without wishing to start a bar-room fight).
* I've read that it's good to short/ground unused audio inputs, to remove unwanted noise - but is it always the case? I am nervous about shorting anything! So should the Aux jack socket be shorted when there's no input (given it's in a car)? The 1/8" socket unit I have has extra pairs of pins that short when there's no jack in, giving that option. And - the Bluetooth unit I ordered (when it arrives) has an Aux input, which gets over-ridden when Bluetooth is active - is it OK to have a shorted Aux input into that, if I use that?
* The power supply for the Bluetooth unit: It hasn't arrive yet, but just to get it ready (the BT unit takes 5v-32v): I have a 7805 and a B0505S DC-DC isolator (incase it needs that). What would be the advisable circuit component sequence here, combining the 7805 and B0505S plus caps?
With caps, in the datasheets the B0505S specs 4.7uf in 10uf out. For 78XX it's 0.33uf in 0.1uf out.
Thanks for looking at this.
Cheers
Jim
I have a cassette stereo from an early 90s Volvo (stereo model TD-603) which I've got working again and now am putting Aux/Bluetooth inputs and removing the cassette player.
So far I've had good results tracing the tracks from the cassette pre-amp to what appears to be an audio processing chip (DIP20 Toshiba TA7764P). I've inserted new audio signal input leads close to the chip, leaving in the caps between signal lead and the chip (2.2uf 50v electrolytics). I cut the tracks near there, removing all the cassette pre-amp circuitry. This seems to work as it should with reasonably clean signal at the right level.
My questions would be...
* Should there be different caps (to the pair of elec. 2.2uf) or any other circuitry before the TA7764P? Both from an audio quality and protection point of view? It's going to have both Aux in, and a Bluetooth unit. I guess the Aux input may need to be a bit resilient because it will take various input devices - eg phones, mp3 players etc with different output levels etc.
* And on the subject of caps - I did have to replace one or two of the large ones - the biggest one had leaked and caused PCB damage. The circuit board is full of electrolytic caps (40 odd). If it was only a handful I might consider re-capping just to re-furb a 30-year-old device, but is there any in particular caps that would be a worthwhile swap? And if so, should I replace any with Tantalum or like-for-like LESR caps - or so-called 'audio' caps? (Without wishing to start a bar-room fight).
* I've read that it's good to short/ground unused audio inputs, to remove unwanted noise - but is it always the case? I am nervous about shorting anything! So should the Aux jack socket be shorted when there's no input (given it's in a car)? The 1/8" socket unit I have has extra pairs of pins that short when there's no jack in, giving that option. And - the Bluetooth unit I ordered (when it arrives) has an Aux input, which gets over-ridden when Bluetooth is active - is it OK to have a shorted Aux input into that, if I use that?
* The power supply for the Bluetooth unit: It hasn't arrive yet, but just to get it ready (the BT unit takes 5v-32v): I have a 7805 and a B0505S DC-DC isolator (incase it needs that). What would be the advisable circuit component sequence here, combining the 7805 and B0505S plus caps?
With caps, in the datasheets the B0505S specs 4.7uf in 10uf out. For 78XX it's 0.33uf in 0.1uf out.
Thanks for looking at this.
Cheers
Jim