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Old 15th May 2003, 05:10 AM   #11
Brian is offline Brian  United States
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Thank You for all the replies fellas. It's great to have somewhere to turn for answers to audio questions.
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Old 15th May 2003, 07:52 AM   #12
dhaen is offline dhaen  Europe
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Default Series OP transformers

Hi,

I gave this idea some tought overnight (sag git), and realised that it would be completely load dependant. The load on each secondary would affect the primaries impedance and hence the proprtion of signal they got.
Certainly a no-goer.

Cheers,
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Old 15th May 2003, 07:01 PM   #13
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I started another thread Differential SE Amp which involved 2 OPTs -- not in the same manner thou -- in a single channel.

I also have seen a number of inexpensive stereo amps which introduced a 3rd transformer which was used to drive a bass speaker, (snippet of the circuit trace below). I am still not completely comfortable with my understanding of what is happening here althou i have my suspicions. What happens if you leave off the bass speaker or leave out the big OPT completely?

There was also a Crowhurst schematic published in a recent audioXpress that used dual OPTs -- it has me completely baffled.

dave
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Old 15th May 2003, 08:48 PM   #14
dhaen is offline dhaen  Europe
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Dave (P10),

That is pretty much what I was thinking of. The word "inexpensive" doesn't fill me with much confidence about it's prospects. [Though it'll have Joel salivating]
And yes, it all falls apart if you disconnect the big speaker.

Cheers,
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Old 15th May 2003, 09:12 PM   #15
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Hi,

Quote:
And yes, it all falls apart if you disconnect the big speaker.
Even to the point of destroying the OPT when signal is present...

Much easier to build another set of amps and use the passive filtering at the input, I reckon.

Cheers,
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Old 15th May 2003, 09:21 PM   #16
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Quote:
Even to the point of destroying the OPT when signal is present...
Thanx.

OK. I'll either leave it out if i ever rebuild it... make sure there is a bass speaker, or add another couple tubes and use it as a separate summed bass channel.

This one isn't high in the queue, but i was curious about it so had traced the circuit (i have learned much by doing this)

dave
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Old 16th May 2003, 01:57 AM   #17
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Designed and optimised for a specific application, by a <i>good</i> engineer (like Crowhurst), it could be made to work but it could be a real dogs breakfast otherwise.

Sakuma-san did a couple of designs with seperate secondaries on the same core iirc.
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Old 16th May 2003, 02:19 AM   #18
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ok guys u mention a transformer with separate windings for lf and hf, how about 2 transformers connected in serial or parallel. Output impedance should be higher in serial i think double and half when in parallel rite. This way we can use small output trans for higher output wattage. Small output trans should have better hf response compared to its 1 single opt of the same wattage of the 2 connected together. I think parrallel is the one where the wattage is double, i thinking of using it. Am i going in the right way? looking at the 12ese they have multiple connections for different impedance ratio 10000,5000,2000 i think but only 80ma dc current. When planning for a se with kt 88 or even 300b the current wouldn't be enough. Hence an idea of using 2 12ese connected in parrallel, their ratio would be 10000 to 8. Hence when connected parallel togehter it should be 5000 to 8 roughly rite? Please advise, i am not aiming for excellent sound just for getting my feet wet in se design but need the power hence kt88. The current should be double the capacity to 160ma. of course in real world the trans would be excatly the same resistance so real current sharing would not exist so maybe one trans might draw more current. Please advise me on this?
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Old 18th June 2003, 01:03 AM   #19
jlsem is offline jlsem  United States
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Sorry, late to this thread. Paul Klipsch actually designed a dual output transformer 2A3 PP amp ca. 1946. The really interesting part is that a passive crossover appears in the schematic between the 2A3's and the two output transformers. One transformer was wound to advantage for LF and the other for HF. Both transformers had an impedence of 5K.

John
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Old 18th June 2003, 09:34 AM   #20
Brian is offline Brian  United States
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Thank You John, that is what I had in mind.
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