CAUTION: If you're a traditionalist and like keeping your kit original (nothing wrong with that) - LOOK AWAY NOW.
So: Why would anyone buy an old Dansette?
The great smell when they warm up
They will eat your record collection **
NOS replacements for the obsolete cartridges (which cost about half the price of the whole player) are all dying of old age
** Only joking. Properly looked after, they'll outperform most of the new ones on the market.
If you feel like bringing your player a bit more up to date, our friends in China mass produce cheap ceramic (not crystal) cartridges that you can use after some fairly hefty mods to the player. Once the mods are done, you can (and probably should) use any of the modern, better quality, lower output types.
EBay has a particular range that are identical apart from the different quality stylus assemblies. Sometimes known as "red and blacks", they're similar to (or the same as) the ones used on cheap USB decks. Although most of them will be copies, sellers will mention CZ800 and P-188D. Watch out for stylus damage and try them out on something you don't value too much. At any rate they'll do as something to get going with.
The bad news is that output levels are down by about two thirds, so they need a pre-amp. The good news is that they're designed to play stereo records and they track at a lower weight than the originals (sometimes). As an added bonus, they don't sound too bad (feel free to argue).
The original TC8H cartridge was tracking (with the factory setting on the adjuster spring) at 9gms. Just replacing it with a new red and black (plus adapter) brought that down to 8.6gms. The new cartridge, tracking at 5gms, was having problems following old, worn out microgroove LPs, probably not helped by the ancient deck. 6gms seemed to keep everything happy and that's about what you'd expect from a USB deck with this cartridge.
The stereo option obviously won’t work on a mono Dansette, but it’s the mechanical design that’s important and you can just parallel the outputs without a noticeable effect on the sound. Before anybody has a go about load impedance, we're talking Dansette not B&O. Plenty of opportunity to experiment though.
Try to get a cartridge with a mounting clip. They're available separately now and again but are quite expensive.
If you don't want to just glue it in, the clip needs an adapter to convert it from half inch centres to a single 6BA screw. This one is 2mm aluminium drilled and tapped 6BA in three places. The clip needs to be drilled out (a rat tail file would be safer) and relieved slightly to clear the heads of the screws coming upwards.
Measure the old cartridge to get the new mounting hole in the same place relative to the stylus tip.
Schematic and Wiring (as found)
Things To Think About
This isn't a "How To" article, just some some ideas that actually work with a bit of effort and, ideally, some mechanical and electrical experience.
CAUTION: DANSETTE RECORD PLAYERS USE VERY HIGH DC VOLTAGES AND HAVE EXPOSED 240VOLT MAINS CONNECTIONS EVERYWHERE. BE CAREFUL.
Get on with it!
The Senator uses a single EL84 so it needs a lot of drive from the cartridge. Some other Dansette models use two valve stages and they could have easier options.
If you just want to get the player working with a modern cartridge, forget trying to design a preamp. It's not worth it when you can buy a perfectly good, ready made one (or a kit, anyway) for less than a tenner. Getting power to it is more expensive though. The temptation is to use one of the dc supplies on the valve and drop the voltage across a resistor. Rectifying the heater supply might work too, but the valve needs getting on five or six volts peak to peak to get it somewhere near clipping (I did measure it but I can't remember exactly) and that's going to be marginal with a 6.3 volt ac supply by the time it's regulated. It's not really neccessary to drive the valve flat out but it's nice to have the headroom.
Had a quick look around the discussions raging on the forums and came across (and stole) the idea of a Velleman mono preamp kit plus some ideas for mods to match the cartridge and cut down the gain.
Power requirements are 10 to 30v dc at 10mA and aiming at 18 to 20v would be easy and give a useful output voltage swing.
The power supply in the picture in the next section was made from the parts bin, but it would be a lot quicker to buy everything from someone like Rapid.
These parts would work (a 2x12v transformer would work just as well).
Mains Transformer: 2x9v @ 6VA. Vigortronix VTX-126-006-609 (Rapid order code 88-3711). £7.50
Voltage Regulator: 130312 PCB Voltage Regulator Kit for LM317-T 1.2-32VDC (Rapid order code 50-0487) £7.08
(this actually turned up fully built by Conrad, complete with comprehensive German instructions).
Preamp: Velleman K1803 Universal Mono Pre-Amplifier Kit (Rapid order code 70-4084). £6.85
Three 1M and one 22K 1/4w resistors for board mods
Worth noting that any hum and noise pickup that was originally present on the cartridge wiring is going to be amplified as well, so, with a lower cartridge output, the signal to noise is going to get worse. That didn't seem to be a problem in practice though.
The Cheap Way To Do It
This is how the first attempt ended up after some experiments. It works, so it's staying as it is. (edit: No it isn't - see below). The transformer is from an old 24v wall charger. It didn't have any mounting lugs, so it's held down with Velux rooflight flashing (always handy). Grounding the transformer metalwork helps a lot with hum reduction.
The cabinet is quite thin, so the mods are mounted onto 5mm ply glued to the bottom.
Dansette mounted the valve assembly onto wood strips for the same reason, but there isn't a lot of headroom over to the left.
One problem with the pcb kits is the size of the mounting holes. They're designed for small bolts (can't remember which size) not wood screws, so it might be worth mounting them on ally or paxoline and then screwing that down.
The Senator already has four wires going along the arm to the cartridge. This one didn't have terminals on the two spares though, and they were cut short. A couple of spare terminals, a few inches of thin wire and some some small heatshrink or rubber sleeves will probably be needed.
The Expensive (and easier) Way To Do It
The LM317-T board is working at a fraction of it's capacity and needs about a four volt drop across the device to regulate properly, (preferably, five volts to be rock solid). With 18volts ac input, the peak voltage at the input would be about 25.5v and a reliable maximum output would be 20v dc. 18v dc would be fine. All the measurements were done with an output current of 10mA. Power dissipation in the LM317-T with this setup is under 100mW so it's quite happy with no heatsink.
The maximum recommended input from the transformer is 25v ac (about the same as a 12v + 12v Tx with low load current).
Mods To The Velleman Preamp
More Messing About
OK. So it's a wet Tuesday afternoon in February and the wife wants me out of the way.
That's not true!
The old bugger just likes sheds
Took out the DIY regulator and fitted the LM317. It works very well.
Is It Worth Doing?
Definitely. It's a lot of work, but that's what sheds are for and it's lovely to listen to music without worrying about the disc or where the next stylus is coming from. There are obviously much better replacement cartridges available if you want to invest the money and matching them to the amp is just the turn of a trim-pot . These cheap ones will be fine for experimenting with and it's not the end of the world if they get damaged messing with the deck. Best of luck with whatever you decide to do.