Change speaker impedance??

[allante666]

Hi, prob a dumb question which i shoudl know the answer to but I have an amp that should have a 30 ohm speaker in it, I dont have one, is there any way I can put a 4 ohm one in temporarily without damaging the output? (its only a little cheap Orange 10 watt amp) i.e. if i put a resistor in series (or parallel?) so that the output sees 30 ohms or wont that alter the impedance?

[g1]

A 10 watt resistor of around 26 ohms in series should work.
30 ohm speaker? I've heard of 32 ohm in some SVT's but have never seen anything over 16 ohms myself.

[Enzo]

Me either, that would be a darned odd speaker.


I have a 32 ohm SVT speaker on my shelf, and I use dto get the 1 ohm speakers for the Bose 802s. Those are the extremes I am aware of.

[olddawg]

Me either, that would be a darned odd speaker.
I have a 32 ohm SVT speaker on my shelf, and I use dto get the 1 ohm speakers for the Bose 802s. Those are the extremes I am aware of.

I remember those .47 ohm Bose speakers. A shop I worked for in the late 70s covered the pilot market for Bose. The neanderthal installers tried to use them for car stereo speakers since they were free and fried their finals.

[allante666]

Ive never seen one either, I cant measure a resistance across it to get a rough idea either as its o/c but it definitely states '30 ohm, 15 watt' on it. Its in a little 10 watt 'Orange Crush 10'

[J M Fahey]

Hi allante.
Definitely it can't be a 30 ohm speaker there.
Maybe there is a "30" number printed somewhere, but it must mean something else.
If it is some kind of rubber stamp, (something very common on cheap chinese speakers), ink may have smeared *or* that was written by some chinese guy copying what for him are "drawings" that he does not understand.
I have a chinese symbols printed T-Shirt that draws smiles or even repressed laughter whenever I visit a Chinese Supermarket.
I ask them what it means, they tell me it means nothing, those symbols have missing traces and added extra meaningless ones, they might have been poorly copied from a rice bag inscriptions.
I also once saw the picture of a Khyber Pass counterfeit gun, (gun copies made by tribe ironsmiths in northern Pakistan) clearly labelled "Wade im Russia" (sic)
Just out of curiosity, post some picture; also state what the power chip is (most certainly a TDA20something) and the power rails voltage.
That will answer your question for sure.

[allante666]

Hi, yes you are probably right, it may have been copied by some ten year old working an 18 hour shift for a bowl of rice! however as you can see from the pic, it is very clearly marked as 30 ohm. Ive put the amp back together now (minus the speaker of course) but you are right, the output was just the common bog standard 5 pin IC. probably a TDA 2030 or 2050. I cant find a diagram on this so without checking on Monday i dont know for sure. Im hoping its wrongly marked as I happen to have a good spare speaker which is 15 watt and 4 ohm. (sods law of course will say that the correct one will be 8 or 16 ohm just so i cant use my 4 ohm one!!)
Ill now attempt to attach the pic so this may go horribly wrong!
did it work??

[J M Fahey]

If you have a 5 pin TDA and around +/-15V Power Rails (which you did not measure), your 15W 4 ohms speaker will do fine.
30 ohms?: no way !!
The only application where you can find a cheap chinese 30 or 45 ohm speaker is, maybe, a Color TV where they already have a, say, 45 to 60V power supply, made for something else , some kind of sweep circuit, whatever, and they don't want to add another tap, diode, and filter capacitor to get, say, 12V, and prefer to use some special funky power IC and a special funky voice coil.
I have already seen some stuff like that.
Hey!! , 20 cents less in a million TV sets mean 200000 $ !!! or 400 TONS of rice.
And that bowl of rice is a grown up salary, the kid will only get a few spoonfuls of rice for his 18 hours shift.

[jrfrond]

Lots of misprinted stuff out of Asia. With a TDA2050, you have no issues. Ihave personally never seen a 30 ohm speaker, and my recone supplier stocks only one 32 ohm coil, and THAT is for SVT 10's.

[allante666]

Just out of curiosity ill check what the chip is tomorrow and measure the supply rails. watch this space...

[allante666]

Ok, it has a TDA 2030 output chip and +/- 20 volt rails. On the back of this info I fitted my 4 ohm 15 watt speaker and it works fine, I gave it a good blasting for about twenty minutes with no problems so I guess it will be ok?

[Gibsonman63]

You can measure the DC resistance of your "30 ohm" speaker to get an idea of the impedance. If memory serves correctly, the DC resistance is about 3/4 of the impedance.

[allante666]

I cant...its open circuit! but worth knowing for future thanks

[Gtr_tech]

Foiled again Batman......

[allante666]

Yeah well, if it wasnt for those pesky kids....