input impedance for morgan jones amp?
Mar 18, 2007 at 1:10 PM Thread Starter Post #1 of 10

headphonejunkie

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I am trying to figure out what the input impedance for the morgan jones amp would be so I can create (through Duncan amp PSUD) a 6x4 rectifier supply. Can anyone help?
 
Mar 18, 2007 at 2:31 PM Post #3 of 10

headphonejunkie

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Using the PSUD it asks for the load the supply will be seeing (.i.e. its impedance?).
 
Mar 18, 2007 at 2:36 PM Post #4 of 10

ericj

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Quote:

Originally Posted by headphonejunkie /img/forum/go_quote.gif
Using the PSUD it asks for the load the supply will be seeing (.i.e. its impedance?).


The input impedance isn't the load that the power supply will be seeing, it's the load that the audio source will be seeing.

You don't need to specify a resistive load in PSUD, you can specify an arbitrary amount of current.

If you read the article, it says "Alex Cavalli recommends a minimum power supply current rating of 220V @ 50mA for the optimized and feedback amplifiers, figuring 20mA peak per output section and 8mA for the input stages for about 48mA total."

So, plug 48mA into PSUD.
 
Mar 18, 2007 at 2:52 PM Post #5 of 10

headphonejunkie

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Thanks. But now how do I figure what my output voltage is going to be? I can't measure across the constant current source. I am getting confused.
 
Mar 18, 2007 at 3:54 PM Post #6 of 10

headphonejunkie

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Here is a thought. Using the spec of 220volts with 48 ma I could use ohms law to derive a resistance of 4583 ohms. I can use this for my resistive load. That seems to at least give me a load to measure my output voltage against. I am not sure if I understand how to use duncans PSUD.
 
Mar 18, 2007 at 4:13 PM Post #7 of 10

ericj

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Quote:

Originally Posted by headphonejunkie /img/forum/go_quote.gif
Thanks. But now how do I figure what my output voltage is going to be? I can't measure across the constant current source. I am getting confused.



Run the simulation. The default simulation is really just the spike when it first turns on, so set a reporting delay of 5 seconds or so.

Then look at the RMS voltage of V(I1). This is the output voltage of the power supply.

Don't use a resistive load. Your amp is not a resistive load. It's not really a constant current load either, but why add another layer of confusion by pretending that it's a resistor?
 
Mar 18, 2007 at 6:13 PM Post #8 of 10

headphonejunkie

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Thanks eric. I will figure this out sooner or later.
 
Mar 19, 2007 at 1:08 AM Post #9 of 10

ericj

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fwiw i think 48ma is the worst-case-scenario load out of a cavalli-jones running standard 6dj8 types.

I mean, the bender-cavalli-jones (the 6n1p version - many more volts) has a nominal running current of 28ma.

What you get out of PSUD isn't gospel - be prepared to tweak resistor values after you get it built to get the voltage you need. PSUD will just get you really close.

If your transformer isn't one of the models in the PSUD library, check the actual regulation of your trafo by measuring the VAC on the output with no load. You may need to adjust the regulation factor in PSUD to get realistic results.
 
Mar 19, 2007 at 1:26 AM Post #10 of 10

headphonejunkie

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Thanks again. I will not be building a complete supply anyway. I am using the didi01 p/s bd but was hoping to do some tweaking possibly. Plus I wanted to learn how to use the psud. I basically started playing around with it today. Using the 6x4 tube should be interesting. I found a schematic of an old c22 Mcintosh preamp that uses that tube as a rectifier too.So, the morgan jones will be playing with the big boys.

Thanks
 

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