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From Albert Von Schweikert:3. The "secret" to achieve "killer" sound quality is to ensure that the amplifiers have exactly the same input sensitivity. The amplifier with the lowest numerical rating, i.e. 100mV is much more sensitive than an amplifier with a rating of 500mV - the higher the number, the lower the sensitivity. You'll need to reduce the higher sensitivity by using a series input resistor. This can be installed inside your amplifier, directly at the RCA female jack leading to the input stage. If this sounds a little scary, then build an adaptor to house the resistor outside the amp. If you contact Michael Percy at www.percyaudio.com, he will advise you on what you'll need to get from him. Usually, a female RCA jack, a male RCA plug, a high quality metal film resistor, some plastic sleeving, and a short piece of high quality hookup wire is all that is required. Basically, you're inserting the resistor between the "hot" connection from the female RCA jack to the male RCA plug, and then using hookup wire to connect the ground leads. The entire assembly can be only a few inches long and installed into a plastic or Teflon sleeve to prevent short circuits. This adaptor is inserted into the signal path between your preamp and the most sensitive amplifier. As you can infer from this description, the adaptor is used in between your interconnect and the input jack of the amplifier.Michael Percy sells these parts for less than $100 for everything you'll need, and he'll also help you select the proper value of resistor to match the sensitivities. Although this simple technique may sound like a "Micky Mouse" setup to "sophisticated" engineers that design chip OP AMPS and sell electronic crossovers to the PA industry, it is a very "pure" form of passive matching that will stomp the crap out of any electronic crossover I have ever tried.
Wow, the sound of crickets in here is deafening... regardless, I'll try one more time...I posted this earlier in the bi-amping sticky:If I know the input sensitivity and gain of each amp - how do I calculate the resistor value?Specifically, I am looking to use my DIY ICEpower 1000asp based monoblocks (2.96V input sensitivity) on the LF cabinet with a pair of VTA m-125 monoblocks (1V input sensitivity) on the HF cabinet. From Albert's statement above the m-125 is more sensitive than the 1000asp so I need to add a series resistor to its input. Since I am building the m-125 from a kit I want to add the resistor inside the amplifier. What value will I need?Thanks,Martin
Martin - I am not sure you will get there w/ math.I say that b/c I run a very similar set up w/ the jr's.You can make a resistor ladder and play around w/ different values. I played around w/ some different attenuator values and ended up w/ a 7 dB attenuator after lots of listening.CI Audio makes a device that is passive and will allow you to adjust your gain to match the level for both amplifiers. It is not cheap.I sent my jr's in to VSA for the Gen IV upgrade and when they came back as 8 ohm across the speaker and I'll be damned if the problem just kind of fixed itself, so no more attenuators.If you are able to calculate mathematically, please share as I never was never able to do so.Good luck - I know I did not answer your ? specifically, but when it works, it sounds really good.BTW - my bottom cabinet uses a pair of Wyred 4 Sound mAmps and my top cabinet uses a set of Primaluna Dialogue 7 mono blocks.Eric
That sounds fantastic but a bit of a tangle with the powercords and the the ICs, no? Any chance for a photo?Or better yet, why don’t you pack it up and haul it all over to my house so that I can give a listen? Fall colors are starting to change but perhaps bring snow tires. I’ll make lunch.All best,Lester
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