I was recently given a Great British Spring reverb unit - black tube, XLR connections, and flying 5-pin DIN power lead - but there was no power supply with it. I want to build one.

I'm finding it hard to come across useful, reliable info on this, but if anybody knows for sure what the voltages should be on each pin, and what current is required, I'd be very grateful. If there are schematics, even better.

Many thanks in advance!

Found this on an old gearslutz thread-

"Thomas,

There was a couple of GBS versions from beginning of 1980, but the most common version was the "mk-2" around 1981/82, in a grey plastic tube with two separate mounting bracket, and have two TSR-jacks, level knob and a 3 pin DIN-connector for PSU input on the top panel.

The pin-out for this DIN-conector was:
pin 1= approx. +24 volt/100 mA from a normal un-regulated dc plug-in adaptor.
pin 2= 0 volt/ground
pin 3= +20 volt/100 mA, regulated voltage, as a alternative for the un-regulated.

Other versions with un-balanced XLR:s or transformer balanced XLR:s have a fixed PSU cable with out DIN-connector on the top panel, and this was wired for only +24 volt un-regulated supply.

Around 1984 come the MK-3, in a black plastic tube with integrated wall mounting on the top and bottom.

--Bo
__________________
Hansén Audio
Gothenburg, Sweden
http://www.hansenaudio.se "


Might be worth getting in touch with Bo at his website there for more info ?

best of luck, they're great units.

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http://anotherfineday.bandcamp.com/ http://anotherfineday.co.uk http://apollomusic.co.uk

Hi,

Can anyone give me some advice on getting my GBS reverb running please?

I didn't have a power supply with the reverb unit I was given (I looks like it's the MK2) but after reading the post above, I bought a Electro Harmonix 24V 100ma PSU and made up a connector to the DIN plug. Looking at the circuit board only the central pin and one of the outside ones was connected to anything so I linked the power to them.

Plugged in and all seems to work with a beautiful reverb sound.

Only one problem, lots of 50Hz hum. Really too loud to make the reverb usable.

Again looking at the circuit board, the input socket seems to have only the sleeve and tip connections connected although it's a stereo/balanced type socket.

The output socket has connections to tip, ring and sleeve. I'm wondering if using the output as a balanced output and converting it to unbalanced by connecting the ring to the ground will kill the hum. However, when I try to do this it seems to produce regular pulsing feedback.

If anyone knows how to get rid of the hum or properly use the balanced output, if that'll make a difference, I'd be most grateful.

Thanks

Ris

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Electronica: http://soundcloud.com/army-of-mice

Quote Ris of Serig:

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Hi,

Can anyone give me some advice on getting my GBS reverb running please?

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Get in touch with Andrew Stirling of SCV London.

The "Great British Spring" was a product of Andrew's old company "Turnkey" (this was the original Turnkey in Barnet and not the later version in Charing Cross Road) and Andrew may still have access to details, of know someone who would.

Sorry, that's all I can suggest.

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John - Sound-Link ProAudio
President - Federation Internationale des Chasseurs de Sons

Quote Ris of Serig:

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Only one problem, lots of 50Hz hum. Really too loud to make the reverb usable.

---

To solve the problem, you need to know where the hum is coming from -- there are several possible causes, each requiring different solutions.

The easiest possibility is a ground loop. To test that, try connecting the output via a DI box (so that the transformer in the DI box provides galvanic isolation). Leave the input disconnected initially.

Is the hum still there?

If yes, then it's not a ground loop problem. If not, then you will need to look at ways of dealing with the grounding in the unit, which we can come back to later once you've run the test.

If the hum is still there, is there a way of adjusting the wet/dry balance? If so, try shifting to entirely dry.

Is the hum still there?

If yes, then we still haven't ound the bugger... but if not, then it could be magnetic coupling to the spring or pickups. Try moving any mains cables or equipment with mains transformers well away from the spring unit (or vice versa).

If the hum is still there with the mix contro, set to dry, then it could well be hum being injected from the power supply, implying faulty or insufficient regulation.

Hugh

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Technical Editor, Sound On Sound

Nice thread resurrection!

While trying to fix mine, I traced the circuit on the input side - I believe the output section was buried at the other end of the pipe with the springs, but never managed to get round to digging it out.

From my drawing, the inputs are on XLRs, with pin 1 connected to the outer and also to ground, and pin 2 connected to ground also. Pin 3 is the hot signal. The output connectors on mine were also XLRs, again with pin 3 hot, pin 2 grounded and pin 1 connected to both shell and ground.

I don't know if that helps, but I'd be happy to post a copy of what I did manage to sketch out if you like.

I got rid of it in the end, never had the time to fix it. Shame, I've wanted a spring reverb ever since I sold my last one in 1994...

Hi Hugh,

Thanks for your reply.

Yes, the hum is still there when I use a DI box, There's no difference in the hum level if the input is connected or not.

The input level control makes no difference to the level of the hum.

Moving the reverb as far away I can get from any power supplies in the room possibly reduces the hum a little, but not significantly.

The power supply is a brand new adaptor 24V 100ma. So shouldn't be faulty. It's this one:

Electro-Harmonix 24v 100ma PSU

Can I try grounding the unit somehow, as you suggest?

Thanks for your help.

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Electronica: http://soundcloud.com/army-of-mice

Hi Nathan,

Thanks for your reply.

My version has jacks not XLRs.

The output seems to have connections to the tip, ring and sleeve contacts on the jack socket, though when I try to connect to it using a conventional TRS plug balanced to a TS plug unbalanced cable as outlined in my Mackie mixer manual I get the weird 'feedback' problem mentioned above.

So I don't know what's going on with the output connections. Maybe it's not a balanced output at all. I'm carrying put the tests Hugh suggested with just sleeve and tip connected on the output.

Thanks.

Ris

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Electronica: http://soundcloud.com/army-of-mice

I hope it's not exactly like the one in the picture. That one is for 120V mains!

Does it have a solid metal earth pin? As far as I can see, it's not double insulated so it should.

Is the unit connected to anything else at all that has an earth? If so then an earth loop is by far the greatest likelihood.

Do you have a small battery operated headphone amp (I believe these are essential bits of kit - no matter how crappy). If so, connect that to the spring and absolutely nothing else and see if it still hums.

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It wasn't me!
(Well, actually, it probably was)

Quote Ris of Serig:

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Yes, the hum is still there when I use a DI box, There's no difference in the hum level if the input is connected or not.

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So not a ground loop then.

Quote:

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The input level control makes no difference to the level of the hum.

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So the hum is not being picked up from the external input...

Quote:

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Moving the reverb as far away I can get from any power supplies in the room possibly reduces the hum a little, but not significantly.

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So probably not induced hum.

Quote:

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The power supply is a brand new adaptor 24V 100ma. So shouldn't be faulty. It's this one:

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The question is 'is it a regulated DC supply' and how good is that regulation? I can't tell from looking at the image. It sounds to me like the power supply may be the culprit here, but going down that road needs some DIY electronics experience.

Quote:

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Can I try grounding the unit somehow, as you suggest?

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It normally will be grounded through the audio connections (I assume the power supply is double insulated) -- but by all means you could wire an earthed lead to the screen of an input or utput socket and see if that makes any difference.

I think this is going to need the close and personal attention of an electronics technician. There's nothing complicated in there, and fault-finding should be pretty easy, but it's not easy to do remotely via the forum!

Hugh

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Technical Editor, Sound On Sound

Hmm. I really must pay more attention. I'd missed the bit about the DI box

Power supply regulation (or lack of) was going to be my next suggestion too

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It wasn't me!
(Well, actually, it probably was)

I had a GBS (new) back in the day - it's basically a bunch of springs in a plastic guttering down pipe (literally) and as such is prone to pick up all manner of gunk and interference like a radio antenna! It's also susceptible to acoustic interference and in one mix, I couldn't figure out what that the queer speech noise was in the background. I'd stuck the drain pipe well out of the way of the rest of the gear (to avoid hum and buzzes, etc.) and the sound was people chatting at the back of the control room being picked up by the springs.

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