microTower Revisited - Page 9

cogitech · 14th January 2021, 06:24 PM

It is a big paradigm shift for me to be thinking about reversing decisions I made and components I chose based on the EL70 roll-off. Everything from DAC chips, to opamps, to tubes in my amps, I have always chosen the "brightest" most "analytical" in order to squeeze what I could out of those drivers.

I probably should have done what you did and thrown some super-tweeters into the mix rather than brightening up the entire system. Whatever, hindsight is 20/20. It won't be difficult to bring the balance back. In fact, it will be enjoyable.

cogitech · 14th January 2021, 09:47 PM

I forgot to mention that I wired up the 16 ohm taps on my Tubelab SSE last night. With approximately 12 ohms of speaker impedance connected, the result is 3.75k ohms of primary load on the tubes (vs. 5k ohms ideal SSE design spec). With 12 ohms on the 8 ohm taps, the resulting primary load is 7.5k ohm.

Reducing primary impedance increases power and distortion, and increasing primary impedance reduces power and distortion. However, it is not linear and the computer modelling is not perfect. In the end, it is a matter of looking at output tube specs and using ones ears.

In this case, I have chosen the 16 ohm taps because a) EL34, 6L6, KT-88, etc. can easily handle loads as light as 3.6k ohms, b) SE Amp CAD shows a negligible increase in distortion, c) I get a bit more power, and d) it sounds excellent to me.

Not really important to anyone but me, however someone may find this useful if they are running a tube amp and considering microTowers with dual P7.2HD.

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14th January 2021, 06:24 PM	#81
cogitech diyAudio Member Join Date: Jan 2011 Location: Kamloops, BC	It is a big paradigm shift for me to be thinking about reversing decisions I made and components I chose based on the EL70 roll-off. Everything from DAC chips, to opamps, to tubes in my amps, I have always chosen the "brightest" most "analytical" in order to squeeze what I could out of those drivers. I probably should have done what you did and thrown some super-tweeters into the mix rather than brightening up the entire system. Whatever, hindsight is 20/20. It won't be difficult to bring the balance back. In fact, it will be enjoyable.

14th January 2021, 09:47 PM	#82
cogitech diyAudio Member Join Date: Jan 2011 Location: Kamloops, BC	I forgot to mention that I wired up the 16 ohm taps on my Tubelab SSE last night. With approximately 12 ohms of speaker impedance connected, the result is 3.75k ohms of primary load on the tubes (vs. 5k ohms ideal SSE design spec). With 12 ohms on the 8 ohm taps, the resulting primary load is 7.5k ohm. Reducing primary impedance increases power and distortion, and increasing primary impedance reduces power and distortion. However, it is not linear and the computer modelling is not perfect. In the end, it is a matter of looking at output tube specs and using ones ears. In this case, I have chosen the 16 ohm taps because a) EL34, 6L6, KT-88, etc. can easily handle loads as light as 3.6k ohms, b) SE Amp CAD shows a negligible increase in distortion, c) I get a bit more power, and d) it sounds excellent to me. Not really important to anyone but me, however someone may find this useful if they are running a tube amp and considering microTowers with dual P7.2HD.