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Old 28th August 2012, 07:36 PM   #421
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Does post 414 also work with the collectors connected to the input ?
Dirk, i build circuits like that when absolutely the lowest noise is necessary and they work well. The transformers are kind of expensive though.
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Old 28th August 2012, 07:42 PM   #422
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Quote:
Originally Posted by Joachim Gerhard View Post
Does post 414 also work with the collectors connected to the input ?
Dirk, i build circuits like that when absolutely the lowest noise is necessary and they work well. The transformers are kind of expensive though.
I think one of the advantages is that you can use a cheap transformer and still get good results. I haven't tried it myself.
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Old 28th August 2012, 07:44 PM   #423
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I think that KSC3503-KSA1381 is promising too.
Yes, the 2SA1407 is much worse in early voltage then the 2SC3601 so this is not such a good match.
I have also measure some ring power transistors from sanken and toshiba, and the curves where even better than the bd140, but it seems a little bit overkill use a TO3P in a MC pré.

the ksa1381 seems fine. but is something wrong with the curve tracer in the datasheet from fairchild
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Old 28th August 2012, 07:46 PM   #424
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Yabba Dabba Do!

very low distortion. Like zip. too many zeros to count.
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Old 28th August 2012, 07:47 PM   #425
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Does post 414 also work with the collectors connected to the input ?
I don´t see any problem. it should work
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Old 28th August 2012, 07:53 PM   #426
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Yabba Dabba Do!

very low distortion. Like zip. too many zeros to count.
maybe you are using an ideal transformer. no distortion
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Old 28th August 2012, 08:23 PM   #427
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maybe you are using an ideal transformer. no distortion
Nope, it is modeled after the Lundahl LL1517. There all kinds of capacitances and winding resistances and core types in the non-linear transformer model I'm using. I've switched to the LME49990 and performance is even better. I'm not going to hijack this thread so I'm not going to talk about this any more. As an amateur, I want certain results, so I will probably build something like this. I don't have a model for the LME49600 buffer, but that's the one I'm going to use (instead of the BUF whatever that's in there). The buffer is required because the feedback network has very low impedance.

So, anyway, back to our regularly scheduled TV programming.... as they say.
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Old 28th August 2012, 08:24 PM   #428
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What he does is canceling the secondary DC impedance of the transformer. That helps in the bass but not in the treble. That is more complex.
I will now modify my circuit for balanced input.
I got rid of the hum though with other measures using the single ended circuit.
I found though that balanced can sound better.
Common mode distortion should not be much of an issue but common mode noise can be. There is a difference between quiet and dead quiet.
At the moment there is a tiny bit of hum left when i crank it full to un sane levels.
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Old 28th August 2012, 08:30 PM   #429
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What he does is canceling the secondary DC impedance of the transformer. That helps in the bass but not in the treble. That is more complex.
I will now modify my circuit for balanced input.
I got rid of the hum though with other measures using the single ended circuit.
I found though that balanced can sound better.
Common mode distortion should not be much of an issue but common mode noise can be. There is a difference between quiet and dead quiet.
At the moment there is a tiny bit of hum left when i crank it full to un sane levels.
Well, just to give a little background, one of the reasons balanced lines were invented was to make very low signals immune from the huge local hum field. They were doing skin resistance measurements for EKG's or something so they needed to isolate the signal from the noise. It was also used in the telephone industry to allow signals to travel for miles and miles. Anyway, I think the first example is the one I'm thinking of in regards to phono cartridges. The rest of the signal chain doesn't have to be balanced since the signal is then a lot stronger and the connections are short.
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Old 28th August 2012, 09:04 PM   #430
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I agree. I made a balanced phono amp, the FPS, for Linear Audio 0.
It is a discrete INA. I worked in the High Tech industry in the 80th and knew circuits like that from brain scanners.
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