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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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20th Jun 2017, 10:42 pm | #1 |
Hexode
Join Date: Apr 2016
Location: Yeadon, West Yorkshire, UK.
Posts: 251
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Impedance converter for prewar loudspeakers
Hi all. I have recently bought a Marconi loudspeaker from the late 20s / early 30s and I understand these old speakers have a very high impedance of around 1500 ohms compared to the single digits of today. I remember seeing about an impedance converter that converted an 8 ohm signal into a 2000 ohm signal but I can't seem to find one anywhere.
Does anybody know where to find one of if anybody has any circuit diagrams so I could make my own? Thanks Peter |
20th Jun 2017, 11:08 pm | #2 |
Heptode
Join Date: Apr 2011
Location: Edinburgh, UK.
Posts: 805
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Re: Impedance converter for prewar loudspeakers
What are you driving it with (what sort of amplifier)?
For low power, audio signal transformers with 8 ohm secondaries are here (you'd run it backwards). http://www.mouser.co.uk/Passive-Comp...mer+2K&FS=True |
20th Jun 2017, 11:39 pm | #3 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,082
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Re: Impedance converter for prewar loudspeakers
Horn loudspeakers are pretty efficient, so (depending what sort of amplifier you are using) you may get fairly decent results just connecting as-is!
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21st Jun 2017, 9:02 am | #4 |
Dekatron
Join Date: Mar 2008
Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.)
Posts: 3,183
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Re: Impedance converter for prewar loudspeakers
Hi,
I'd be inclined to just use the output transformer from a scrap valve radio and connect it 'in reverse'. In the far off days of my misspent youth I ran a modern low impedance speaker from a 1920s wireless using the frame transformer from an Ekco TV. Cheers, Pete.
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21st Jun 2017, 12:37 pm | #5 | |
Hexode
Join Date: Apr 2016
Location: Yeadon, West Yorkshire, UK.
Posts: 251
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Re: Impedance converter for prewar loudspeakers
Quote:
The speaker has an output transformer built in and has instructions to connect the input sockets to different terminals on the transformer depending on if the input is above or below 1500 ohms |
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21st Jun 2017, 2:44 pm | #6 |
Guest
Posts: n/a
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Re: Impedance converter for prewar loudspeakers
Bypass the transformer, i.e. simply connect the 'speaker proper to the source. It won't matter much if the original transformer is still in circuit.
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21st Jun 2017, 2:47 pm | #7 |
Nonode
Join Date: Aug 2015
Location: Cambridge, Cambs. UK.
Posts: 2,198
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Re: Impedance converter for prewar loudspeakers
If it's a moving coil speaker unit, the voice coil itself is unlikely to be of high impedance, but is probably 3 or 4 ohms. Can you access the connections to it and connect it direct to your amplifier to save doubling up on transformers? The internal transformer will sit quite happily in parallel - just leave its high impedance primary floating.
Martin
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21st Jun 2017, 5:14 pm | #8 |
Hexode
Join Date: Apr 2016
Location: Yeadon, West Yorkshire, UK.
Posts: 251
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Re: Impedance converter for prewar loudspeakers
Yes, it's possible thanks
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21st Jun 2017, 11:42 pm | #9 |
Dekatron
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,339
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Re: Impedance converter for prewar loudspeakers
I was once given a high impedance 1920's BTH horn loudspeaker. I think they were intended to be connected directly in series with the output valve. I found that I could get it to work by using a transformer from my odds and ends box that had 600Ω and 3Ω tappings, 600Ω to speaker, 3Ω to the loudspeaker output of my EL3302 cassette recorder. I still have the transformer, but not the speaker. If it is a high impedance speaker, I wonder if a transformer for a 100V line might work?
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