Is this downstream of a battery alone, or is there some sort of active regulation between this and the battery?
If the former, then no point looking for anything terribly accurate since a battery in use changes every value as it discharges; if there’s regulation, then go for 1% or better.
Current draw will be tiny, so 1W should be plenty. Soon as you go over this, choices decline dramatically.
For peace of mind, I’d use metal film types as self-noise is lower than sanely-priced alteratives.
What R value do you need? I have bucketloads of some values, so if you just need one or two you can have them FOC (or a small donation to forum funds).
So, my initial set up will be the former, so I was looking to use 5% with either 5w or 10w rated resistors, based on a minimum safety factor of 2x the calculated values.
I used an on-line calculator and it stated a minimum resistor wattage of 2.4, with a input of 6v (12Ah Battery) and a required current draw of 0.5amps.
Of course there is the temptation to use the best (most costly) available, but not sure of the benefit - although as we’re talking of such a ‘delicate’ set up then why not to ensure the absolute best performance - its still a fraction of the cost of the Cartridge and let alone a new PSU for AN (UK)…
I have the initial values as per info from @murrayjohnson but as I’m somewhat of a ‘novice’ to electronics I wasn’t sure on the general approach to what to use.
I’ll be using two batteries one in the PSU and one spare for charging whilst the other is in use. I’m not sure how different the output will be from two different batteries so don’t yet know if any further ‘regulation’ would be required, I suppose the simplest approach would be a resistor array per battery I assume and either a manual intervention or a switch?
4.8V drop at 0.5A, so the resistor works out at 9.6 ohms, 2.4 Watts dissipation, so 5W or above is sensible
As mentioned previously you will have loses between the batteries and the coils, as well as change in battery voltage with levels of charge, so a means of adjustment is sensible
I would be tempted to get one resistor which is somewhere between 8R0 and 9R0, and a bunch of values between 1R0 and 2R0 you can switch between in addition to the larger value
Ohmite Audio Gold are affordable and offer a range of values, including 8R2, 0R82, 1R0, 1R2, 1R5 and 1R8, so you can get 9R0, 9R2, 9R4, 9R7, 10R0 in total
Or rather than series connected, maybe go with 10R and parallel with a readily available range of 0.1 / 0.33 / 0.47 etc - experiment with cheap wirewound ceramic coffins to find what works best, then invest in high quality stuff once you know what values work best?
None that I can think of in an application like this - beyond one making it possible to choose easier-to-find resistor values. I don’t really think there’s any point using ‘foo’ resistors here TBH - R self-noise is a thing, and were this the signal side of things I’d say it matters, but to power an electromagnet via a battery… Nup.
Vishay PRO3 range of 3W metal film resistors are cheap and good-enough to scratch the OCD itch - I’ve used them in a number of mods to valve amps to good effect. 10R example here.
With field coil speaker units, the opportunity exists to play around with the magnetic circuit’s damping characteristics (by changing the voltage energising them) which then affects how the driver works in its enclosure although generally the advice is to just drive the electromagnet until it saturates whereupon the field can’t get any stronger. That point is ‘enough’. If I recall, the thinking with the Io Ltd is also to power it until core is saturated (which creates quite a substantial field) as the parts are made of Permendur, a particular nickel iron alloy, which I think is the material that allows the deepest saturation.
I think the answer here is to apply 1.2V across the coil & see what current is being drawn by it. I think you’d find that increasing the voltage from there would mean there’d very quickly become a point where the cartridge would show no increase in output when playing which is the point where the electromagnet is saturated. Overdriving it results in the electromagnet becoming warm which in turn would affect the longevity & behaviour of the neoprene damper.
I think, when you raise the voltage across the field coil, more current is drawn (it’s behaving as a resistor) but there’s a point where you don’t get any more signal out of the cartridge & it’s at that point that the electromagnet is saturated, it can’t get any stronger or induce more signal to be produced by the cartridge’s (moving) coils. I think that occurs when the voltage is about 1.2V
Lovely things, I think that is no 6 or 7 on here from memory.
First one I have seen that looks like a Gold. Most have a black body.
But there is nothing surprising in the AN world!
