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Burns Orbit Three
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Old 3rd May 2014, 11:10 PM   #1
Aidan135711 is offline Aidan135711  United Kingdom
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Default Burns Orbit Three

Hi everyone,its been a while....

I have a Burns Orbit Three mid sixties transistor amp,60w,3x10inch 5ohm speakers.
One speaker is blown and the original wiring has been tampered with and is trashed.
Diagram shows load of 2 ohms.
I need advice on how best to wire in new speaker.
3 series gives 15ohm,20 per speaker.
3 para gives 1.666ohm 20w per speaker.
2ser/1 para gives 3.3ohm,10w 10w 40w per speaker.
2para/1ser gives 7.5ohm 10w 10w 40w per speaker.
Which configuration should I use?
Info about this amp is almost non existant-need help.

http://burns-amps.blogspot.co.uk/

Last edited by Aidan135711; 3rd May 2014 at 11:25 PM. Reason: adding info
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Old 4th May 2014, 12:19 AM   #2
famousmockingbird is offline famousmockingbird  United States
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I would think that all three speakers would have been wired in parallel. Seeing how one speaker is blown be careful wiring the remaining two in parallel if their power handling isn't adequate (30 watts each). You will get a loss of output power since the load impedance increased from 1.66 ohm to 2.5 ohm but shouldn't be too noticeable.

Or you could wire the remaining two in series but at a cost of a lot less power output.

Last edited by famousmockingbird; 4th May 2014 at 12:23 AM.
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Old 4th May 2014, 12:30 AM   #3
Aidan135711 is offline Aidan135711  United Kingdom
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I suspected 1.66 or 3.3 ohms was the right combination.Maybe the manufacturer just rounded the 1.66 ohms up to 2ohms for convience.
I tested the amp with 2 remaining speakers in paralell,unusually loud even at volume setting of 2.
i will wire all 3 in paralell methinks.
Now a new problem,vibrato has stopped working.I think squirt of contact cleaner on the pots is the first thing to try.
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Old 4th May 2014, 02:35 PM   #4
Nigel Goodwin is offline Nigel Goodwin  England
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Quote:
Originally Posted by famousmockingbird View Post
I would think that all three speakers would have been wired in parallel. Seeing how one speaker is blown be careful wiring the remaining two in parallel if their power handling isn't adequate (30 watts each). You will get a loss of output power since the load impedance increased from 1.66 ohm to 2.5 ohm but shouldn't be too noticeable.
Power handling doesn't alter as the speakers are in parallel - each speaker only gets 20W regardless of one, two or three speakers in parallel.

This is fairly normal with any transistor amp, but more so in this case (as according to the schematic on the link above it uses a 33V stabilised PSU).

However, I'd a little dubious about it's 60W power output, although I suppose it might just make it at high levels of distortion - but unlikely to at clean power levels.

Presumably the speakers were specially made?, as 5 ohms isn't a normal value?, and it was certainly unusual to have an amp made for 2 ohm speakers way back then.
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Old 4th May 2014, 06:26 PM   #5
famousmockingbird is offline famousmockingbird  United States
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"Power handling doesn't alter as the speakers are in parallel - each speaker only gets 20W regardless of one, two or three speakers in parallel."

How do you figure? Do you mean the speaker can only "handle" 20 watts instead of "gets" 20 watts?

The amp doesn't care how many speakers it has hooked up it just sees a load. With two 5 ohm speakers in parallel you get 2.5 ohms. The amp is rated at 60 watts into a 2 ohm load. I was assuming the manufacturer used 3 twenty watt speakers combining to handle the 60 watts. Take one speaker away and now you get a power handling of only 40 watts. Take another away and your left with one speaker than can only handle 20 watts. I agree if you are saying that with that one speaker left you have less of a load at 5 ohms so the amp will put out less power than the rated 60 watts but that doesn't mean that the amp will only put 20 watts through a 20 watt speaker.

Last edited by famousmockingbird; 4th May 2014 at 06:29 PM.
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Old 4th May 2014, 06:56 PM   #6
Bone is offline Bone  United Kingdom
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Found this circuit which may help. as you can see the transistors are germanium.
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File Type: jpg burns_orbit_3.jpg (124.5 KB, 103 views)
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Old 4th May 2014, 07:04 PM   #7
Bone is offline Bone  United Kingdom
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Just found the full circuit
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File Type: jpg Burns Orbit Three 3 schematic joined compressed.jpg (570.2 KB, 110 views)
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Old 4th May 2014, 07:23 PM   #8
sreten is offline sreten  United Kingdom
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Hi,

60W (rms) with a single 33V rail does require
a bit less than 2R load to get to that number.

rgds, sreten.
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Old 4th May 2014, 07:41 PM   #9
Kjeldsen is offline Kjeldsen  Denmark
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Quote:
Originally Posted by famousmockingbird View Post
"Power handling doesn't alter as the speakers are in parallel - each speaker only gets 20W regardless of one, two or three speakers in parallel."

How do you figure? Do you mean the speaker can only "handle" 20 watts instead of "gets" 20 watts?

The amp doesn't care how many speakers it has hooked up it just sees a load. With two 5 ohm speakers in parallel you get 2.5 ohms. The amp is rated at 60 watts into a 2 ohm load. I was assuming the manufacturer used 3 twenty watt speakers combining to handle the 60 watts. Take one speaker away and now you get a power handling of only 40 watts. Take another away and your left with one speaker than can only handle 20 watts. I agree if you are saying that with that one speaker left you have less of a load at 5 ohms so the amp will put out less power than the rated 60 watts but that doesn't mean that the amp will only put 20 watts through a 20 watt speaker.
The speaker can't handle more than 20 watt, when they are wired in parallel. In series it would be 20+20+20 = 60 watt for the whole system. But now it's 15 ohm and will require more power to play loud., but this i parallel and then 20+20+20=20. But now it's 1,66 ohm and will play louder than a 15 ohm system.
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Old 5th May 2014, 12:17 PM   #10
Nigel Goodwin is offline Nigel Goodwin  England
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Quote:
Originally Posted by famousmockingbird View Post
I agree if you are saying that with that one speaker left you have less of a load at 5 ohms so the amp will put out less power than the rated 60 watts but that doesn't mean that the amp will only put 20 watts through a 20 watt speaker.
Do the maths

It's hardly difficult - each speaker gets 20W, with three speakers the amp outputs 60W, with two speakers it outputs 40W, and with one speaker only 20W.

So yes, it DOES mean the amp will only output 20W through a single speaker (of the designated impedance).
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