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Old 21st June 2004, 02:25 AM   #21
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Quote:
He just use ordinary 120V+120V of 300VA primaries
the only difference between power transformer and audio transformer as far as i can see is that the former operates on a single line frequency, 60 or 50hz depending on the location, wheras the latter operates on a band of frequencies, 20hz to 20khz typical...

so for the zen v7, assuming no losses, the transformer will see about 35volts rms...so that with the 120 volts rating, & 60hz rating, the traffo should have a decent response down to about 20hz...

in manila, we have this "booster" amps, composed of input transformer, with split secondary driving a few pairs of bipolar power transistors, mj2955 in a push-pull configuration, now these ouput trannies operate in an emitter-follower mode, the output transformer is connected to the emiters and the supply of 12 votls is connected to the output traffos' center tap..
the output itself provides for a unity voltage gain,
speakers are then connected to the emitters of the output trannies...

input source is typically a car stereo feeding the input tranformer...

this our local low cost solution to providing lots of power as this setup can really drive 12inch speakers .... although admittedly, sound quality is not so good...
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Old 21st June 2004, 02:15 PM   #22
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"the only difference between power transformer and audio transformer as far as i can see is that the former operates on a single line frequency, 60 or 50hz depending on the location, wheras the latter operates on a band of frequencies, 20hz to 20khz typical..."

Do the words 'air gap' have any meaning to you?

"in manila, we have this "booster" amps, composed of input transformer, with split secondary driving a few pairs of bipolar power transistors, mj2955 in a push-pull configuration, now these ouput trannies operate in an emitter-follower mode, the output transformer is connected to the emiters and the supply of 12 votls is connected to the output traffos' center tap..
the output itself provides for a unity voltage gain,
speakers are then connected to the emitters of the output trannies...

input source is typically a car stereo feeding the input tranformer...

this our local low cost solution to providing lots of power as this setup can really drive 12inch speakers .... although admittedly, sound quality is not so good..."

Why not eliminate the output transformer?

http://patft.uspto.gov/netacgi/nph-P...y=PN%2F4130725
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Old 22nd June 2004, 12:05 AM   #23
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Default can't imagine how

Quote:
Why not eliminate the output transformer?
output transistors are in push-pull configuration, single supply of 12volts...

these amps seems to sound best with pnp germanium power transistors...too bad they are not around anymore..


however, a dual voice coil can be used to eliminate the transformer, but it hasn't been tried before....and dual voice coil woofers are not common here....

thanks djk for the info...
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Old 22nd June 2004, 01:59 AM   #24
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"however, a dual voice coil can be used to eliminate the transformer, but it hasn't been tried before....and dual voice coil woofers are not common here...."

Hundreds of thousands of 6 X 9 car stereo speakers were sold using that patent. The bias allows the elimination of the crossover distortion that would otherwise result from the darlingtons.

You will also note that Carver used it on the original Amazing Subwoofer.

http://patft.uspto.gov/netacgi/nph-P...S=PN/5,748,753

"a pair of separate voice coils wound about the former ...Positive and negative signal amplifiers having inputs and outputs are provided with their outputs coupled to respective different ones of the voice coils. An audio signal processor including a power supply is coupled to the inputs of the amplifiers for alternately energizing the voice coils during positive and negative voltage swings of the audio signal. "
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Old 22nd June 2004, 05:55 AM   #25
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"but it hasn't been tried before" .....by me

thanks djk...
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Old 2nd April 2007, 08:06 AM   #26
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I disagree with adding an air gap to a transformer...they are designed to transfer energy, not store it. Air gaps are used in inductors for increasing saturation current...to store the field in a less permeable medium.

Also, MOSFETS used in a push-pull configuration will naturally self-correct an imbalanced core...one transistor will take more of the current and increase resistance, decreasing current in that winding.

Having DC in that transformer is not bad, as long the flux is canceled out by an equal amount on a reversed winding like in most push-pull tube amps.

Do you know if this amp worked well at one time but does not now? Is it a mass-produced one? Do you have pictures?
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Old 2nd April 2007, 08:15 AM   #27
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Quote:
Also, MOSFETS used in a push-pull configuration will naturally self-correct an imbalanced core...one transistor will take more of the current and increase resistance, decreasing current in that winding.
Now that I think about it, this may not occur fast enough in audio situations...hmmm
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Old 3rd April 2007, 04:34 AM   #28
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Audio can also be highly asymetrical, causing the core to walk to one side and saturate.
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Old 3rd April 2007, 09:38 AM   #29
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Default Re: Transformer output solid state

Quote:
Originally posted by lumanauw
In the gates, the sinusiodal are good. but in the Drain of the final mosfets (which drive the final output transformer), the sinusoidal becomes distorted. Looking at the output with scope, (speaker attached), the sinusoidal in the speaker is somehow not a good sinusioidal.
Can you give a sketch of the signal? It may be at a bad bias point of the MOSFET. This would tell.
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Old 3rd April 2007, 12:21 PM   #30
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Hi, Boris,

The (partial) help for the amp at that time (2004) is to raise bias. It helps a little, but the problem (distorted piano sound) is not cured totally. And the amp becomes very hot only to reduce the problem a little degree.

Maybe there's something wrong with the initial design, tried 2 of them, all behaves the same.

I've got no sketches now, the amp is already taken by the owner in 2004
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