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OTL Asylum OTL, Output Transformerless Amplifier User Group. |
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OTL Asylum OTL, Output Transformerless Amplifier User Group. |
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In Reply to: Modified Futterman OTL amplifier posted by cellai@space.it on June 2, 2008 at 04:44:44:
This is the measured output spectrum with a low level 1 KHz tone applied at the OTL input. The OTL output level is the maximum possible without saturating the A/D converter of my PC audio card.
For measurements I have used the free SW (Visual Analyzer) available at: http://www.sillanumsoft.org/
Visual Analyser is a complete professional real time (FREE) software that transform your PC in a complete set of instruments (no new hardware necessary, you can use the Sound Card of your PC).
The corresponding harmonic distortion of the OTL amplifier is lower than 0.1%.
In order to reduce the even harmonics (due to SEPP gain imbalance) a 5.4 Ohm fixed compensating resistor has been added to the schematic (see my previous mail on the subject).
The measured signal has been picked up in parallel to my speakers and I can assure that carrying out the measurement with a strong 1 KHz signal in your ears is not pleasant at all. I suppose this is the reason why dummy load resistors are used instead of real speakers.
In my opinion this measurement demonstrates that it is possible to obtain a reasonably good performance (with the proposed schematic) without resorting to the more complex 'true modified Futterman' that requires additional tubes and a 450 V additional voltage rail.
For sake of completeness I have also measured the output spectrum with no signal applied (see my next post).
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- Measured Harmonic Distortion Modified Futterman OTL amplifier - cellai@space.it 08:27:21 07/18/08 (1)
- Measured Noise Spectrum of the Modified Futterman OTL amplifier - cellai@space.it 08:41:11 07/18/08 (0)
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