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RE: Foil Project for IIIa's

For starters, just use your current active electronic XO to tune your XO points. You need to find out how sensitive the new midrange comes out, and how resolving it is vs. the ribbon - which will play into where you want to XO. You will also want to measure the FR, at least with a Rat shack SPL meter.

As for ribbon amps, you want either a class A SS amp or a high biased SS class A/AB with stability into 2 ohms and MOSFET or JFET output. as the ribbon is ruthless in revealing the grain and thinness of bipolar transistors. These amps don't need to be more than 25 watts (8 ohm - they will have higher output into the 3ohm tweeter). You can also use a tube amp and a 2ohm resistor to raise the load impedance In which case you need at least 50W.

The better choices are the Pass Aleph series amps, XA 30 and its successor. Classe have high wattage amps rated for 2 ohms that have a highish bias into class A. The older Classe DR series amps designed by David Reich are my favorites for bang for the buck. The older DR 3 and DR3VHC will likely need a refurbishing since they run hot and tend to cook their caps in relatively short order - but would be the best for the role. I use a DR-9, and the model 10 is similar. These give you 8-10 watts of class A and really good class AB for the rest.
A cheaper Pass design is the Forte 4.

If you are willing to put fans in your amps, quite a few can be biased up to provide unbelievable improvements in their sound, but they are not designed to dissipate so much heat, so must have fans installed. These would include the older PS

Of the Class D amps, Wyred 4 Sound would be a good choice for you since it was reported to have less of the top octave TIM that plagues so many of these amps. Besides which, your high frequency hearing loss makes it more likely to work for you. The PS Audio GCA series class D amps may do well too, but may require a mod (see at cullen circuits for options) if the high freq TIM is audible to you,

Go look at the lists I put together for other options at lower price points. Just search for them.

Once you have chosen an amp and checked out the options for XO freqs we can help you build a PLLXO.

If you want the flexibility of a digital device, get a behringer DCX 2496 and have it modded at Endler audio (the most cost effective).


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