ACA with 16 ohm Altec?

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I have bi-amp setup with 300b tubes powering large MantaRays and solid state powering 16 ohm 460Z Altec 15" in K-15 Karlson cabinets (AR crossover). Crossover point is 500 hz. I don't find any threads about the Amp Camp Amp with 16 ohm speakers. Has anyone had any experience with ACA and 16 ohm 'horns'?
I use my ACA monoblocks with Zu Audio Druids, which have a 16 Ohm impedance. I use a 25 Ohm resistor across the speaker terminals. The resistor cleans up the bass and makes a noticeable improvement in the sound.

My speakers are full range and not horns, though. YMMV.
I read somewhere that NP had recommended “snubbers” (resistors) to be placed across the speaker terminals of some Zu speakers that have high impedance, when running First Watt amps.

I chose the resistor value based on how they lowered my speakers impedance. Zu says my Druid speakers change from 16 Ohm to 11 Ohm with the 25 ohm resistors. If I used a 10 Ohm resistor they would be about 7 Ohms. I wasn’t factoring in the amp other than the lower impedance might be a better match for my amps.

Zu audio sells the resistors on their site, about $20 a pair, and there are a few different values.

I bought the 25 Ohm pair and figuring it might help and it was cheap enough not to hurt. I tried my speakers with and without and the with was a much improved sound, noticeably in the bass. I have not tried a lower value to see if there is even more improvement to be had.

The resistors might help with your speakers. They just slide over the speaker terminals, so it’s an easy add or removal. And they’re inexpensive as audio fixes go.

Buy them from Zu or Mouser/ Digikey and the like.
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The recommendation for resistors across the Zu speakers applies to the
SIT-3, which best appreciates a load in the 4 to 8 ohm region. The current
source amplifiers F1 and F2 also benefit.

The others, not so much....


Well, that solves the mystery, Shaggy. It was Professor Pass with the SIT-3, F1 and F2 amps the whole time. Not the ACA’s as I suspected. It’s the back of the Mystery Machine for me.

Thanks for the update, Papa. I’m going to hold on to my resistors for those F2 boards I’ve got sitting in the garage.

See you at BAF.
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