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Melquiades Amplifier
Topic: Super Melquiades, Macondo and Class A2

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Posted by Romy the Cat on 12-05-2007

I do not know why people go into low-sensitive loudspeaker and they go crazy in order push the last drop out of the class A2 operation. From a different perspective the Macondo’s woofer towers with 97.5dB sensitivity are low low-sensitive loudspeakers – so how Super Milq’s low frequency channel behaves when it drives 6C33C into A2? Armed with Dima’s lecture about details of A2 operation I desired to measure it in my own setup. At Super Melquiades full power, max preamp output (unity gain) and playing regular symphonic repertoire I was able to develop at the very stressful orchestral moment no more than 30V AC on the 6C33C’s grid. Considering the minus 92V of 6C33C bias the Milq is far from A2.  Well, I need higher stress I figured and I employed the contemporary loud, compressed, electronic music. I took Leonard Cohen’s album “Ten New Songs”, the beginning of the cut “In my Secret Life”. When I maxed out my preamp, I was forced to stay dos one channels as it was imposable to stay in the room – it was VERY loud. I was playing right channel and measuring the proximity of   6C33C’s grid AC voltage to bias voltage. At a few peaks the stage did entered into A2 and the peaks were clipped quite aggressively and 6E5P has preassembly no current to drive it. However, I was not able to do it for a long time as it is cool in Boston, the window are closed and I was afraid that bass could break the windows in my home – it was intolerably and earsplittingly loud.

I set the preamp at a few dB down and set the volume to very loud, I would say 10-12dB louder then I would normally listed this music. Then I monitored the 6C33C’s grid AC voltage – it did not enter the class A2. Below is a photograph made with exposure of 8 seconds. It is 10V/div, with one channel (top line) set the bias voltage (-92V) and “0” volts at 9 division down – one division above. I think the commentaries are not necessary. With Classical music I was getting even less AC voltage swing….

Rgs, Romy the caT

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