RE wiring 8-15 Ohm speakers.....HELP!

surfguy13 · October 2013

Hi Guys

Just acquired a couple of old Vox 2x12 cabs from 1971'ish loaded with Fane POP 50 speakers...one pair is '71 and the other '73.

http://i956.photobucket.com/albums/ae45/guymerchant/Fane POP 50s and Vox 2x12 Cabs/FanePOP50sandVox2x12Cabs014_zpsf94fb6fc.jpg

http://i956.photobucket.com/albums/ae45/guymerchant/Fane POP 50s and Vox 2x12 Cabs/FanePOP50sandVox2x12Cabs016_zps1699161f.jpg

The speakers sound amazing and so will re-wire the cabs and reinstall the speakers. However......never come across speakers that have a 8 -15 ohm range. Hmmmmm? So not too sure how to wire them.

http://i956.photobucket.com/albums/ae45/guymerchant/Fane POP 50s and Vox 2x12 Cabs/FanePOP50sandVox2x12Cabs018_zpsfa89c7d7.jpg

Checked the cone codes and although I'm sure they have nothing to do with anything here they are:

http://i956.photobucket.com/albums/ae45/guymerchant/Fane POP 50s and Vox 2x12 Cabs/FanePOP50sandVox2x12Cabs019_zpsc0131c35.jpg

I'm happy to use them at 8 or 16 ohms as they'll be used with different heads but on the basis of the 8-15 ohm range any ideas on how I would wire them?

Cheers

Guy

ICBM · October 2013

I think from memory that these are more like 15 ohms than 8, but the best way to be sure is to measure them with a multimeter. The reading you get will be about 3/4 of the correct impedance, ie if they read 12 ohms they're 16-ohm speakers. Don't worry too much about it, the impedance is not actually that critical and if you *assume* they're 15s and they turn out to be 8s or vice versa, its unlikely to do any harm.

Be careful with them though - although they sound wonderful, these speakers are very fragile and the 50W rating is ludicrously optimistic. The old-timers used to say they were called "Pop 50s" because if you showed them anything like 50W, they popped

. I would rate them possibly as low as 10W each in terms of what 'cranked amp power' they will take, 15-20W max. A cranked 50 watt amp into all four of them combined is as high as I'd go really.

What impedance settings do your amps have? Do you (or can you, if the power is low enough) want to have the option to run one cab, or always both? That might dictate the cab wiring.

surfguy13 · October 2013

Thanks ICBM.....really helpful!!

I hear what you're saying about 'actual' watts.....I'm always careful with older speakers and yes, I've heard the old quip about them 'popping' if you wound them up!!

They'll probably be used with a 1972 Marshall PA20 so that should be OK but I will be doubly aware based on your advice.

I wasn't too sure how to measure the speakers.....do I just set the multimeter to the lowest ohm setting (on this one 20 ohms) and them put the red probe on the positive terminal and the black on the negative? If so it's reading 0.00!!!! I'm sure I'm doing something wrong!

Could you tell me how to go about this?

The PA20s can do 4, 8 or 16 but need to be changed internally....just solder from one connection to another on the transformer. The other head I might use them with is an old '65 Treble and Bass and that has 7.5 ohm and 15 ohm outs. So, makes sense to wire them to 8 ohms?

I would probably just run one cab, or that's what I'd intended, but it might be interesting to run both cabs? I assume I'd need a Y-lead but then there's the issue of series/parallel I believe?

ICBM · October 2013

Are you sure that's 20 ohms and not 20K ohms? The lowest range on most modern multimeters is 200 ohms. If it's a 20K range, any speaker will appear to be a short circuit (0 ohms).

With those amps, I would avoid wiring the speakers in parallel since that will make "4-8 ohm" cabs which will then present a "2-4 ohm" total load to the Selmer, which is the amp you may need to use both cabs together with due to the power (you'll need a split cable to do that, yes) and it doesn't have a 4-ohm tap.

If you wire each cab with the speakers in series, it will be "16-32 ohms" which is how old PA columns were usually done. It's then safe to run either one or two cabs from the Marshall with it wired to 16 ohms, which is how they came stock, and will avoid needing to keep switching it. It won't mind a possible 32-ohm load if you only connect one cab.

ecc83 · October 2013

Isn't it amazing the things they got away with desciptionwise years ago????

Those speakers are neither "Heavy Duty" nor "Hi Fidelity"!!

I would wire 4 as 15 Ohms. Then should they happen to fall onto the jack of an ID 60 they might survive!

Dave.

surfguy13 · October 2013

Oh dear, having a moment! You're right, I was on the 20K setting.....duh?!

I have set it to 200 and voila! It works....these are the readings for the 4 speakers:

8.8 ohms
9.5
9.7
10.0

Does that make any difference to your suggestion to wire in series? Given those readings they are nearer 8 ohms than 16 ohms.

Assuming you advise to go ahead and wire in series, should I use a standard Y-lead to run both cabs? I have one which, I assume, is wired in parallel? Is there any way to check?

ICBM said:

Are you sure that's 20 ohms and not 20K ohms? The lowest range on most modern multimeters is 200 ohms. If it's a 20K range, any speaker will appear to be a short circuit (0 ohms).

With those amps, I would avoid wiring the speakers in parallel since that will make "4-8 ohm" cabs which will then present a "2-4 ohm" total load to the Selmer, which is the amp you may need to use both cabs together with due to the power (you'll need a split cable to do that, yes) and it doesn't have a 4-ohm tap.

If you wire each cab with the speakers in series, it will be "16-32 ohms" which is how old PA columns were usually done. It's then safe to run either one or two cabs from the Marshall with it wired to 16 ohms, which is how they came stock, and will avoid needing to keep switching it. It won't mind a possible 32-ohm load if you only connect one cab.

ICBM · October 2013

Yes, definitely connect them in series in each cab. They look like they're meant to be about a 12-ohm nominal impedance (with serious tolerance problems!) which will make each cab 24 ohms. That's then definitely safe to run either one cab or two from the Marshall set to 16 ohms, and safe with the Selmer with both cabs from either output. You do need a Y-lead, you can't really connect one cab to each jack - that will 'work', but it will produce a mismatch between the two cabs.

Impedance matching is not actually very critical contrary to popular myth, and barely at all unless the amp is cranked. At low volume it doesn't matter in the slightest, except that it will marginally change the tone.

Easy to test if the Y lead is parallel - with the multimeter see if all three tips are connected to each other. If they are it's parallel, if only two are it's series.

surfguy13 · October 2013

Brilliant, thanks a million for that.

Series it is! One of the PA20s is wired to 16 ohm as per factory setting so will use that.

So I can use either the 8 or 15 ohm out on the Selmer if the cabs are wired in series?

Finally, not sure if I'm being a bit thick but didn't quite understand the bit about testing the tips of the Y-lead? Could I ask you to explain again? Also, what setting on the multimeter do I use to check the lead? As you can see, I'm not an expert with a multimeter!!!!!

ICBM said:

Yes, definitely connect them in series in each cab. They look like they're meant to be about a 12-ohm nominal impedance (with serious tolerance problems!) which will make each cab 24 ohms. That's then definitely safe to run either one cab or two from the Marshall set to 16 ohms, and safe with the Selmer with both cabs from either output. You do need a Y-lead, you can't really connect one cab to each jack - that will 'work', but it will produce a mismatch between the two cabs.

Impedance matching is not actually very critical contrary to popular myth, and barely at all unless the amp is cranked. At low volume it doesn't matter in the slightest, except that it will marginally change the tone.

Easy to test if the Y lead is parallel - with the multimeter see if all three tips are connected to each other. If they are it's parallel, if only two are it's series.

ICBM · October 2013

Set the multimeter to the 'beep' continuity test setting, or any resistance range if it doesn't have one. Meter from one of the three plug tips to the others in turn, you should get a beep or a 0 ohm reading from any of the combinations if it's a parallel cable.

Alternatively, just connect it between an amp and only one cab leaving the other plug loose. If it works, it's parallel!

JayGee · October 2013

ecc83 said:

Isn't it amazing the things they got away with desciptionwise years ago????

Those speakers are neither "Heavy Duty" nor "Hi Fidelity"!!
I would wire 4 as 15 Ohms. Then should they happen to fall onto the jack of an ID 60 they might survive!

Dave.

I remember these as being very much the "Cheap & Cheerful" end of Fane's "general purpose" range, often sold through the RSC chain, and definitely not to be confused with the mighty Fane Crescendo...

I used (somewhere around '75-'76) to have a pair of them in home built 1x12 cabs cabs which I used with an RSC Bass Regent amp, fortunately I don't think the amp got anywhere near its rated 50 watt output either :-)

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RE wiring 8-15 Ohm speakers.....HELP!

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