Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Paramount => Topic started by: Rick58 on April 01, 2010, 01:26:17 PM
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I saw a comment about using the 8 ohm tap on a tube amp to drive 4 ohm speakers (Klipsch of some sort); they were very pleased with the result: more 'life', more (but maybe 'looser') bass, etc. but at reduced volume potential (not an issue with really sensitive speakers).
I have some Triangle Tituses which I listen to in the nearfield, and currently roll off the amps at their inputs at 60Hz (use sub <60Hz). I get more than enough volume, and my amps are currently wired for 4 ohms. The Tituses (2002 vintage) have a flat 4 ohm impedance with a gradual-slope peak of 12 ohms at a few kHz and other peaks in bass port-tuning region).
I know the system would have less damping factor ... has anyone tried this? I would likely just add another RCA jack to each amp ...
TIA, - Rick.
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What would the other RCA jack be for? :^)
To change the impedance of the output on a Paramount, you have to re-wire the output transformer secondary. I'll attach a diagram for using a 2-pole, 3-throw switch to achieve 4-8-16 ohm switching; if you only need two choices you can use a DPDT switch.
The effect of using a 4 ohms speaker when the output transformer is wired for 8 ohms would as you say decrease the damping factor - looser bass and a shift in the spectral balance to favor frequencies where the impedance is higher. The Paramount is fairly conservative in transformer design, so you would probably see more output power, but at increased distortion, mostly second harmonic. The increased second harmonic can sound warmer and more immediate on small-group music, or just muddier on spectrally dense music such as big symphonies. If you are running on the edge of clipping, the increased headroom might give a more relaxed and dynamic presentation.
Not much help I suppose; it's a tradeoff that depends a lot on what music you listen to, how loud, and your specific speakers' performance.
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Thanks Paul! I realized after I posted this that I would likely have to put a switch in there as well.
Since I am 'lazy' and don't really want to drill holes, I will probably just rewire it for 8 ohms sometime and try it for a while. I usually only listen at low to moderate volumes, even on large orchestral/choral works, but maybe some peaks get the amp close to full power? but I am rolling it off (6dB/octave at 60Hz) at the output of the preamp ...
Interesting experiment, anyway. Hey, I will likely wait until I get the soft-start circuit. Like I said, I am lazy and would rather do two things at once rather than tear it all apart (and find room on my workbench!) several times. I may add the switch anyway, so it is great to have the information.
Thanks again, - Rick.