Impedance and Sensitivity
Hi All,
I have made a move from inefficient speakers and large amps with high current supply to smaller amps and more efficient speakers. Think like 300 to 500 WPC at 8 ohms changing to 25 or 50 WPC at 8 ohms and speaker efficiency increasing to 98 or 100 Dbl from 87 Dbl.
I have always kept an eye on the output impedance of the preamp compared to the input impedance of the amp. I understood that if the input impedance of the amp was not at least 10X of the output impedance of the preamp, I could experience a negative impact on the bass response of my system.
As I try different preamps and amps with more efficient speakers, I have run into a new problem. This problem is that the gain of one of my preamps is 26dbl and, pairing it with a tube amp with an input sensitivity of 0.5 volts, results in not being able to adjust the preamp volume control so that my system plays more quietly. I run out of clicks for it to play more quietly.
I realize that either a preamp or a amp change can fix this. Not sure if in line attenuators is an answer as I suspect it adds a distortion or tonal coloration.
In the meantime...does this "gain" imbalance impact sound quality or is it just a loudness problem?
Thanks for listening,
Dsper
Mostly loudness. My preamp has a switch to add in +10 of gain for driving say a 20dB gain amp. It is always nice when the low level volume is around 9 o’clock and we never hit full volume when we want to crank it.
More importantly though, do the new speakers sound any better than the old ones? |
I ran into this problem with my pre and power amp, my temporary solution has been in line attenuators 10db on my power amp input. it works and I can not hear any degradation of sound quality, but I still don’t have a lot of volume adjustment before it gets too loud. First my plan is to get a new dac as it also has a high output 4v. Have my eye on a dac with a tube output at 1.5v which should maybe help my situation. Also have a dream power amp in future that has variable input gain but that is for when times get better economy wise. |
@dsper You have put your finger on why lower powered amps also have less gain, since its an expectation they will be used with a more efficient loudspeaker. A higher powered amp usually needs more gain since its more likely to be used with a low efficiency speaker. When you start mixing the two you run into problems like this. What you might notice here is that the amps and speakers have differences in gain and sensitivity while the gain of the preamp can usually remain a constant, although in the last 25 years the gain of the preamp hasn't been as important. 26dB is a lot of gain in a preamp line stage these days. |
My CJ 17LS2 is probably twenty years old and has 26 dB gain with no switching to a lower gain. My CJ LP66S tube amp (50wpc) is also about twenty years old with 0.5 V input sensitivity. Interestingly, my newer First Watt F7 is 0.53 V input sensitivity and 25 wpc. I was thinking that, for example, a pair of Quicksilver mid monos at 1.5 V input sensitivity might do the trick. My problem is that I do not know how to relate amp input sensitivity to preamp gain. One Volt less of amp input sensitivity equals how many preamp dB? Whoopee, this is fun! Thanks for listening. |
@dsper Wrote:
I would go with Quicksilver Horn Mono's Mike
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In preamps, 6dB one way or another is a doubling or halving of the voltage. From 1 to 2 volts is a 6dB increase and so on. You have so much gain (especially with speakers like that) that you might consider a passive volume control. I'm not a big fan of them; an attenuator would work but means that you would be amplifying and then knocking the signal back down. If you keep the passive volume control as close to the amp as possible that seems to work better. |
Benjamin at Mojo Audio, who made my DAC (1.5 V), also suggested that a passive might be the way to go. I do have a Luminous Axiom passive that I can try.
Can you share your thoughts on why the horn mono's would be a better choice than the mid monos? Everyone, I appreciate the feedback. Thank you! |
@dsper Wrote:
The horn mono’s have lower gain I find work better with high efficient speakers. i.e. lower noise. My speakers have an efficiency >2.6% and a sensitivity of 96 dB SPL @ 1 watt 2 meters @ 8Ohm. For my system controlling gain is important for good sound quality. From Quicksilvers site: The Horn Mono Amplifier is designed specifically for use with very efficient loudspeakers. It has extremely low noise and distortion as well as having 18db less gain than Quicksilver’s standard amplifiers. This avoids the noise and gain problems that normally appear when using horn speakers. The amplifier is designed to sound good at the extremely low levels (milliwatts) that horn loudspeakers require. Many amplifiers actually have higher distortions at these low levels.
Mike |
@dsper Wrote:
My speakers are hybrid with two 15'' woofers and a horn, system 4435. See below:
I agree with calling Quicksilver and asking for their advice. Mike https://www.lansingheritage.org/html/jbl/specs/pro-speakers/1984-4430-35.htm
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