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Old 11th May 2010, 10:02 PM   #1
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Default Strange little circuit

Hi guys. I'm simming this little circuit, which seems to work in the virtual world, but haven't seen it the the real world.

Resistor 25 is the only way I can get this thing to make an amplified signal. Seems that the load on the mosfets is just about perfect, according to the sim's power/voltage graph.

Normally, I took the output from the mosfet drains (which were connected to + with a pair of 330 ohm resistors) to the transformer and just left the primary center tap alone.

This is kind of a backwards way of doing the same thing, or is it? Changing the value of R25 has a dramatic affect on gain.

Any comments?
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Old 12th May 2010, 02:42 AM   #2
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It looks workable to me, but there might be an issue with
your transformer model.

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Old 12th May 2010, 05:47 AM   #3
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Quote:
Originally Posted by Nelson Pass View Post
It looks workable to me, but there might be an issue with
your transformer model.

With Simetrix, I simmed an "ideal" transformer (which doesn't really exist). The primaries are 10H each. The step up is 4 to 1. I noticed that for the same overall gain, the step up takes a lot of load off the mosfets; their power curves are more uniform. Still, I can't help but wonder if the transformer creates more distortion than it cures--guess I'll have to locate an interstage transformer and find out.
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Old 12th May 2010, 09:48 AM   #4
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I just finished this weekend one drek CD player , worth 1k7E ;
Beyerdynamic microphone xformers instead zillion OP's in I/V conversion and lowpass ;
that's pure music now .

even if that's distortion , I like it ; my friend ( who is owner ) is happy camper now .
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Old 12th May 2010, 05:01 PM   #5
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Quote:
Originally Posted by Zen Mod View Post
I just finished this weekend one drek CD player , worth 1k7E ;
Beyerdynamic microphone xformers instead zillion OP's in I/V conversion and lowpass ;
that's pure music now .

even if that's distortion , I like it ; my friend ( who is owner ) is happy camper now .
Sounds interesting, Choky. I'm trying to locate some decent interstage transformers for this project. Perhaps you could guide me? I've noticed that the bandwidth is a bit limited on many models in the catalog (the internet ) I put a bug in Tom's ear down at Hammond... maybe they can stir me up a custom gadget.

According to the sim, the current is very low, less than 100uA, so that should help with size, because it needs lots of inductance--on the order of 10H to 30H in the primaries, and lord only know what that does to the secondaries, because I want to try a step-up device.

Lots of fun...
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Old 12th May 2010, 05:44 PM   #6
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Quote:
Originally Posted by Zen Mod View Post
I just finished this weekend one drek CD player , worth 1k7E ;
Beyerdynamic microphone xformers instead zillion OP's in I/V conversion and lowpass ;
that's pure music now .

even if that's distortion , I like it ; my friend ( who is owner ) is happy camper now .
We wan't to see pics ...

Manu
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Old 12th May 2010, 06:02 PM   #7
Zen Mod is offline Zen Mod  Serbia
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even if offtopic

Primare CD31 Zen Transformation - DIYAudio.rs

Dokoni Prestoni?ani u poseti srcu Drevne Ba?ke - DIYAudio.rs

you'll see usual suspects , including Albi ,Papa ,p18 , Juma , Spavleski , Mighty ZM

Woodie - regarding IT - I'm really not familiar right now with your side of market;
anyway - you know what to chase - L of primary , ratio ,, lowest Rdc of both primary and secondary

don't be afraid of current through primary - as long LTP is DC balanced .
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Old 12th May 2010, 07:30 PM   #8
Manu is offline Manu  Europe
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Thanks for splendid pics, ZM ... Tasty work ...

Sorry woody for OT ...

Manu
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