sandall

Seems like high voltage coming out of the transformer at about 200volts.

 

I've just got around to checking mine (both Calrec originals with the DIN connectors rewired to DIN standard). One was 198v, the other 199v, on a 240.5v supply, so yours sounds spot-on. The mic spec sheet quotes 45 - 50v at 2.6mA - my re-cap'd one gives 52v no-load, the other (newer) one gives 54v, so I suspect I'm measuring some ripple & it needs new caps.as well.

Choke goes in series - it's a near short-circuit to DC, but high-impedance to your HF "noise". It really doesn't matter how you generate your 48-50v, provided there is enough filtering, & you keep audio & mains earths separated, but most off-the-shelf units will need a minimum load current to work correctly (as you say, the mic itself only draws a few mA), so may need a load resistor across the output.

 

Thanks for the tip about µ - in return, may I offer Alt 937 for Ohm (works in MS Word, but doesn't seem to here) - in theory Alt 234 should also work, but doesn't on my keyboard

The output from the transformer seems very high at about 200volts

Not sure about 200V, but I remember it was quite high. There is a big voltage drop across the first (2W) resistor. I'll check mine when I'm back in civilisation.

Ignoring the rest of the saga.....

 

If you are worried about an unearthed metal case (as you have now), why not connect the case to mains earth & connect signal earth to the case via a low-value resistor (say 10R - 47R, 1/2W)?

Or the 51V zener has been replaced with a 5.1V zener by mistake!

 

That's an interesting thought......

 

 

That didnt work very well!. How on earth are pictures etc uploaded?

Anyway the diagram is

xfmr.....diode..>|...47R ......32uF 300v to -ve rail.....39k R.....32uF 300v to -ve rail....|< diode to -ve...48v

Hope that makes sense! But anyway - I will change the single capacitor for 2 x 32uF

 

(I had to learn Postiimage)

 

Yes that sounds like the diagram I posted, except that the 2nd capacitor only needs to be 63v rating. The caps must be getting on for 40 years old, so it's hardly surprising they have died. If you are London-based you must have a Maplin within a mile or so - Radial caps; 47u 450v, JL18U @ £1.69, 47u 63v, N83KF @ 49p. Mine uses axials, which are 99p & 29p. You may need to drill out an extra ground hole or solder the negative legs together.

 

 

It could be 2x 32u used in parallel to make 64u or (perhaps more likely) used for C1 + C2 on the diagram. Is there another capacitor on the PCB, & is yours a single-channel unit, in which case the load current (under 3mA per mic) would be halved? What voltage rating is it? The use of a single-diode rectifier & relatively tiny capacitors look like a recipe for hum, but Calrec were canny Yorkshiremen, not fools, & it obviously worked.

I dragged out my Calrec-made PSU - just as well, as the larger (33/350v) capacitor had acquired what my gardening wife would describe as a bracket-fungus. A quick trip to Maplins produced a 47/450v can the same size for 99p. All is now well. Circuit Diagram (+ simplified sketches) attached (hopefully) circuit

 

The OP's voltage of 5 or 6v suggests the smaller (47/63v) capacitor may have gone short-circuit - I see I had to replace mine sometime in the past.

 

The circuit couldn't be simpler. I made up some1:1 transformers to give balanced outs, but it's easy enough to have the power unit by the mixer, as the mics will quite happily run unbalanced 20m away.

 

Edit to add - Beware, the box is connected to signal earth, NOT mains earth.

 

 

I've still got 4 of them somewhere. I made a homemade PSU, cribbed from the Calrec design, with (IIRC) balanced outs for the first pair; the 2nd pair came with a genuine Calrec PSU. If you are still stuck I can drag out the PSUs & see what's inside.

Are any, unless covered in flame-resistant canvas?

Side panels are useful cosmetically but once the wind gets up they are the first thing you need to remove.

Last time I used it in bad weather (drenching rain & wind strong enough to blow K & M mic stands right off the stage) we had to ratchet-strap the legs to trees, lengths of truss, etc, as all 4 feet were lifting off the ground, but I managed to keep 3 side panels on, & all the gear stayed dry.

I bought this (steel legs & waterproof) 2.5m x 2.5m a few years ago for £79 , have used it for FoH in all weathers & can't fault it. Still £79, but now comes with wind-bars & weight bags as well -. https://www.amazon.c...0?ie=UTF8&psc=1 They claim it goes up in 60" - I would say nearer 5' with 4 people, 10' with 1 or 2.

 

My 3m B&Q special, which cost about the same by the time I'd bought the sides, might well be waterproof (I haven't risked it), but has push-together legs, so might disintegrate in a high wind.

If anyone else wants to install SDR on an XP machine there is a link to the 2015 XP version (same GUI as the Win 7/10 version) on http://www.sdrplay.c...topic.php?t=248 which works fine, once you find where the dongle is hidden in the devices list

In the current version that seems to be the only one

Anyone know where / how to find the pre-2015 version of SDRSharp ? My "toolbag" laptop is still XP, which the current version of SDRSharp doesn't support.

I was looking for a "Front end" tab, but I see in the current version it's been replaced by the Config cog. Offset now sorted, though as expected it drifts quite a bit while warming up.

 

Thanks to all for your help. It's a great little toy.

Thanks Bruce. It's a nice clear guide, but unfortunately the current software (v1.0.0.1444) has a different GUI, which doesn't appear to offer frequency correction (mine varies from 4.5kHz low at VHF to 38kHz low at the top of Ch.70), unless there is a less-visible work-round.

 

I downloaded (& printed-off) that guide yesterday - today I'm locked out - curious.

 

 

Well, no - that really is it.

Not impressed with 3-weeks shipping from US (though it actually arrived in nearer 2), having just had some DMX stuff arrive from Hong Kong (with free shipping) 4 working days from order, & the set-up guide isn't the clearest I've ever met, but most impressed once I'd got it working. Next task is to get it working with XP.

 

2 questions - is there a frequency offset I haven't discovered (all my radio-mics appear to be slightly off-frequency), & is there a way of displaying a wider frequency range (ideally a whole TV channel) ?

Well, no - that really is it.

I hope so - I've just ordered the RTL one - just under £13, inc. carriage (would have saved a £ or so if I'd ordered before Brexit, as it's priced in USD). In theory they are about $10.80 with free carriage, but that seller won't ship to UK.

 

Thanks, Ian

I'm probably being dense here (it's the outdoor season & I'm feeling old), but to give me a RF spectrum analyzer for 170-ish MHz & Ch.38-70, do I just need one of the SDR dongles mentioned above, a bit of free software & a laptop, or is there a lot more to it than that?

It is really important to make sure the centre (0v) connection is good, otherwise your +/- 25v DC rails can suddenly become +45v & -5v (or the other way round), which is not good news!!