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Old 7th February 2013, 06:58 AM   #21
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Can you supply the schematics ?
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Old 7th February 2013, 06:12 PM   #22
midmoe is offline midmoe  United States
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yes, schematics will be uploaded soon. Still doing final adjustments. I am shifting all entries to my "medium power OTL circlotron amplifier" thread. Please submit replies to that. See you there. midmoe.
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Old 9th February 2013, 10:40 AM   #23
Elvee is offline Elvee  Belgium
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This project could be of interest: it is an impedance meter, well suited to amplifier measurements and it can be made to float easily.

Although it is a DIY-grade instrument, the measurement accuracy will be much better than any indirect method based on variable loading.

In order to make proper measurements, it is essential to work on a completely silent amplifier (and it should also have a low noise of its own, but that is not difficult to achieve in a PA)

Impedance-meter add-on for the simplistic THD meter
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Old 9th February 2013, 01:29 PM   #24
midmoe is offline midmoe  United States
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elvee...thank you for your intresting reply, however my circlotron impedance falls somewhat out of the range of the intended target of your device's scope, being in the 200 ohm area. However a quick cobbling together of parts outlined in your discription has led to an intresting new form of distortion meter formatting, of which I will soon begin a rudimentary study and report back results here when assembled and calibrated. midmoe
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Old 9th February 2013, 04:54 PM   #25
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by midmoe View Post
elvee...thank you for your intresting reply, however my circlotron impedance falls somewhat out of the range of the intended target of your device's scope, being in the 200 ohm area.
You can easily add other ranges as required: for a 1K full scale range, R13 would become 1.5K, the calibration trim 1K, and R15 should preferably become 31K (or be paralleled with a 560K)
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Old 9th February 2013, 05:50 PM   #26
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How about these methods.

I think one post mentioned the second one.
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Old 9th February 2013, 08:44 PM   #27
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Quote:
Originally Posted by DUG View Post
How about these methods.

I think one post mentioned the second one.
The first is in substance the one I propose (with some added bells and whistles, like phase indication) and the second is the one mainly advocated in this thread (disappointing with non-perfect amplifiers)
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Old 10th February 2013, 12:06 AM   #28
DUG is offline DUG  Canada
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The 1K in the first example is just a suggestion.

If you use a resistor that gives you a ratio of >10:1 for V1:V2 then the phase will not be a significant factor in the magnitude calculation. ( <1% error)
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Old 10th February 2013, 08:10 AM   #29
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by DUG View Post
The 1K in the first example is just a suggestion.

If you use a resistor that gives you a ratio of >10:1 for V1:V2 then the phase will not be a significant factor in the magnitude calculation. ( <1% error)
No, but knowing the phase of the impedance is in itself a valuable information
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Old 18th June 2014, 04:46 AM   #30
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Hello All,

I have been reading this thread and chapter 8 in the Loudspeaker Design Cookbook 7th edition by Vance Dickeason.

In post #7 Dr DF96 is right on with the theory and in post #3 CounterCulture is right on with the maths.

Reading the Loudspeaker Design Cookbook it is apparent that not only is the Amplifier output impedance important so is the internal impedance of the crossover network. Throw in the amplifier output impedance, 10 meters of zip cord and the series resistance of the chokes in the crossover and all our assumptions about system Q are completely wrong.

DT
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