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Old 18th April 2006, 01:48 PM   #1
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Default OPT for transistors

Hello,

I'm a tube guy, but with limits. I have built gainclones and discrete amps that sound really nice, but tubes offer me a warmt that I like. The reason is the opt transformer, the output transformer is a funky device becouse it puts a colour on the sound that I have yet to make with bandpass, low pass and all other kind of filters that I have tried. Nor do this happend with a input transformer. So her is the question, does any one know were to get op transformers for transistor circuits? And that must be hifi, not the very small dirt used in portable radios and a little powerfull(1-15w). I guess I need a load of 200-500ohm.

Best regards,

Magnus Kofoed
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Old 18th April 2006, 02:04 PM   #2
edl is offline edl  Hungary
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Hi,

the tube circuts nice sound isn't caused by the OPT.
Of course you can bulid a solide state circut with OPT (some design can handle the transformer on the output), but why?
The OPT will degrade the whole sound quality.

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Old 18th April 2006, 03:08 PM   #3
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Hi,

well, my experience says that it is the opt that has most with the warmt of the sound to do. I don't say that will sound like a tube amp with transistors and opt. But for me I think a transistor amp with opt will sound better, I guess it's a taste thing. Tube pre amp sound better than transistors, yes, I think so, but they lack some of the warmt, a tube pre will improve the sound quality of transistor power stage, but still, no warm sound. I respect they who don't agree. This is not ment to be a tube vs transistor thread.
A opt may degrade the whole sound quality, but for me it sounds most right. Again, a taste thing.

But, I might be completly wrong, thats why I want to get some transformer to test.

Ill guess I'm crazy...

Best regards,

Magnus
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Old 19th April 2006, 06:26 AM   #4
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Old 19th April 2006, 06:35 AM   #5
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Maybe this thread by Susan-Parker may interest you:

Zero Feedback Impedance Amplifier

Cheers Michael
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Old 19th April 2006, 12:55 PM   #6
lndm is offline lndm  Australia
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I have heard some people mention this before. I do think though, that it would be much easier to get a warm sound by replacing your speaker crossover resistors, and amp resistors with carbon films. I think this makes up part of the rich tapestry that is the tube sound.
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Old 19th April 2006, 01:42 PM   #7
EJ is offline EJ
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First of all, all transformers are natural low-pass filters. This could be one of the many reasons that characterize OPT amps.

Second, an output transformer is a current-driven-current-source, which behaves very differently from normal voltage-driven-voltage-source solid state amplifiers. According to physics, force applied to coils is linear to the current through the coil, not the voltage applied across the coil. Controlling the voltage accross the coil to be linear does not make the motion of cone linear if the impedance varies with time or frequency.

This could explain why fullrange driver speakers usually doesn't sound as good when driven by an OTL.
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Old 19th April 2006, 02:19 PM   #8
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Hi,

Thanks!
It was big help with those links.
I have a lot of reading to do now.

Best regards,

Magnus
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Old 19th April 2006, 10:47 PM   #9
rozak is offline rozak  Israel
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Hi, Magnus.

You are not crazy. Transformer coupled amplifiers sounds better
than regular SS amplifier.
But this is because of topology similar to tube amplifiers.
If you just connect transformer to the output of SS amplifier you degrade the sound.

Hi, EJ.

Susan Parker and my amplifiers are normal voltage source amplifiers with output impedance of push-pull souce follower/n^2.
(n=Turns Ratio Np/Ns).
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Old 20th April 2006, 07:51 AM   #10
EJ is offline EJ
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Hi Rozak,

All transformers are current controlled current source. The windings are coupled by magnetic fields (flux, to be precise), and magnatic fields are generated by current, NOT VOLTAGE. The only relation between input winding and output winding is I1*N1=I2*N2 (except when saturated). Voltage is just a result of current flowing through the resistor (or whatsoever) and doesn't matter. Only Current matters. This is the physical nature and has nothing to do with circuit topology.

The circuit before the tranformer is a voltage amplifier. The voltage output generates current through the primary windings of the OPT, and the OPT controls the current through the secondary winding by magnetic field coupling. It controls ONLY the current. It doesn't control the voltage. That's why I said it's a CCCS.
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