Its quite possible that John Chapman's modules can not be implememted manually.
Lightspeed Attenuator - Best Preamp Ever?
The question is a bit rhetorical. No preamp is the best ever, and much depends on system context. I am starting this thread beacuase there is a lot of info on this preamp in a Music First Audio Passive...thread, an Slagle AVC Modules...thread and wanted to be sure that information on this amazing product did not get lost in those threads.
I suspect that many folks may give this preamp a try at $450, direct from Australia, so I thought it would be good for current owners and future owners to have a place to describe their experience with this preamp.
It is a passive preamp that uses light LEDs, rather than mechanical contacts, to alter resistance and thereby attenuation of the source signal. It has been extremely hot in the DIY community, since the maker of this preamp provided gernerously provided information on how to make one. The trick is that while there are few parts, getting it done right, the matching of the parts is time consuming and tricky, and to boot, most of use would solder our fingers together if we tried. At $450, don't bother. It is cased in a small chassis that is fully shielded alloy, it gets it's RF sink earth via the interconnects. Vibration doesn't come into it as there is nothing to get vibrated as it's passive, even the active led's are immune as they are gas element, no filaments. The feet I attach are soft silicon/sorbethane compound anyway just in case.
This is not audio jewelry with bling, but solidly made and there is little room (if any) for audionervosa or tweaking.
So is this the best preamp ever? It might be if you have a single source (though you could use a switch box), your source is 2v or higher, your IC from pre-amp to amp is less than 2m to keep capaitance low, your amp is 5kohm input or higher (most any tube amp), and your amp is relatively sensitive (1v input sensitivity or lower v would be just right). In other words, within a passive friendly system (you do have to give this some thought), this is the finest passive preamp I have ever heard, and I have has many ranging form resistor-based to TVCs and AVCs.
In my system, with my equipment, I think it is the best I have heard passive or active, but I lean towards prefering preamp neutrality and transparency, without loosing musicality, dynamics, or the handling of low bass and highs.
If you own one, what are your impressions versus anything you have heard?
Is it the best ever? I suspect for some it may be, and to say that for a $450 product makes it stupidgood.
I suspect that many folks may give this preamp a try at $450, direct from Australia, so I thought it would be good for current owners and future owners to have a place to describe their experience with this preamp.
It is a passive preamp that uses light LEDs, rather than mechanical contacts, to alter resistance and thereby attenuation of the source signal. It has been extremely hot in the DIY community, since the maker of this preamp provided gernerously provided information on how to make one. The trick is that while there are few parts, getting it done right, the matching of the parts is time consuming and tricky, and to boot, most of use would solder our fingers together if we tried. At $450, don't bother. It is cased in a small chassis that is fully shielded alloy, it gets it's RF sink earth via the interconnects. Vibration doesn't come into it as there is nothing to get vibrated as it's passive, even the active led's are immune as they are gas element, no filaments. The feet I attach are soft silicon/sorbethane compound anyway just in case.
This is not audio jewelry with bling, but solidly made and there is little room (if any) for audionervosa or tweaking.
So is this the best preamp ever? It might be if you have a single source (though you could use a switch box), your source is 2v or higher, your IC from pre-amp to amp is less than 2m to keep capaitance low, your amp is 5kohm input or higher (most any tube amp), and your amp is relatively sensitive (1v input sensitivity or lower v would be just right). In other words, within a passive friendly system (you do have to give this some thought), this is the finest passive preamp I have ever heard, and I have has many ranging form resistor-based to TVCs and AVCs.
In my system, with my equipment, I think it is the best I have heard passive or active, but I lean towards prefering preamp neutrality and transparency, without loosing musicality, dynamics, or the handling of low bass and highs.
If you own one, what are your impressions versus anything you have heard?
Is it the best ever? I suspect for some it may be, and to say that for a $450 product makes it stupidgood.
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- 1866 posts total
I see that George recommended lowering my gain of the amp or source. My amp input impedance is 47k ohms and output impedance of my DAC has been confirmed at 600 ohms by Rega. What numbers do I need to look for in an amp or source to match with my 98 DB sensitive speakers so that I achieve lower volume in the "0" volume setting? |
I don't think it has much to do with impedance. It is the input sensitivity of your amp, it gets to full power output too easily. For example, my amp I use with a passive only needs .8v to reach max. power output. My other amp that I use with an active line stage requires something like 2.8 v to reach max. output, and in most cases requires the gain provided by an active line stage. The other side of the chain would be to reduce the output voltage of your source so the overall gain structure is lowered. I have no idea how you do any of that. No matter why you do, the LSA in any system that it is appropriate for will still produce some volume a zero setting, and just should not be that intrusive, except with high sensitivity amps and speakers combined. |
04-12-12: GooddominoSensitivity (the input voltage that will result in the amp putting out its maximum output power) is not directly relevant. What is relevant is the gain of the amp (the relation between output voltage and input voltage). Comparing sensitivity numbers is only meaningful if put in the context of the power capability of the amp. For example if two amps both have an input sensitivity of 1 volt, but one of them is rated at 50 watts and the other at 500 watts, the 500 watt amp will produce much more volume in response to a given input signal than the 50 watt amp will produce. The suggestion George made earlier about trying a pair of Rothwell attenuators seems to me to be well worth trying. They would be connected directly to the input jacks of the amp, with no intervening cable. In conjunction with the 47K input impedance of your amp, the 10 db version would result in the LSA seeing a load impedance of about 30K, which is on the low side but I suspect would still be ok, given that it won't vary significantly with frequency and given the 620 ohm output impedance of your source. I am not familiar with the characteristics of the 20 db version, but I would guess that it would present a load impedance that is significantly higher (and therefore even better). Regards, -- Al |
- 1866 posts total