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In Reply to: RE: Quicksilver tubes on the midrange panels/ribbons - MGIIIa's posted by ejhoove on April 26, 2015 at 10:14:23
I don't think your issue is power related. Those two amplifiers (Quicksilver/Acurus) appear to have a large difference in voltage gain. That's why you're not getting the necessary volume with the Quicksilver amps.
As Andy noted, 25w amps should be sufficient for ribbon-only usage.
Just to confirm, I would connect onto the 8 ohm taps of your Quicksilver amplifiers.
Voltage gain issues have fooled folks into thinking they have power issues for many years. Your experience is not unusual.
Cheers,
Dave.
Follow Ups:
Considering the XOs he has the relative output and absolute voltage available should allow for compensation for a low gain tweeter amp.
That is unless he bought the mono horn amp which has deliberately reduced gain by 18 db. But that one does not spec a 2ohm tap
Mini Specifications
Power Output 25 watts into 2, 4 or 8 ohms
Power Bandwidth 13 Hz to 50 KHz
Peak Power 50 watts
Input Sensitivity 1 volt
Input Impedance 100 Kohms
88 mono Specifications
Power Output 80 watts into 4 or 8 ohms from 20Hz to 20 KHz
Power Bandwidth 13 Hz to 80 KHz
Input Sensitivity 1 volt
Input impedance 100 K ohms
Damping Factor 15
IM Distortion 1% or less at 80 watts
Mono Horn amp Specifications
Power Output 25 watts into 4 or 8 ohms
Power Bandwidth 15 Hz to 100 KHz
Peak Power 50 watts
Damping Factor 20
Input Sensitivity 6 volts
Input Impedance 100 Kohms
Thanks for your thoughts. Are you talking input voltage? I can increase the db gain from my crossover, but have no idea how much. is there a formula for impeadance difference? The input impedances are different - 100k for the Quicksilvers, and 20K for the Acurus. The QuickSilver's seem fine on the Midrange panels, but seem very week on the Ribbons. Is it safe to run a 2 ohm load into a 8 ohm output on a tube amp? I always thought this was a huge no-no.
Regards,
Jim
Computing the voltage gain gets a little tricky sometimes because of confused manufacturers specifications, but in this case 1.1VRMS yielding 200wpc/8ohm (Acurus) results in voltage gain of 31db, and 1.0VRMS yielding 25wpc/8ohm (Quicksilver) results in a voltage gain of 23db. So, theoretically, you'd need to up your voltage drive to the Quicksilver amplifier by 8db to provide the same ribbon output level as when using the Acurus. Make sense?
The difference in input resistance of these amplifiers is irrelevant in this case since you're driving with an active crossover.
Attaching to the 8 ohm tap simply couples across more of the output transformer secondary and provides an effective increase in voltage gain. You don't have a preferable impedance match, but this is just a test and you're not going to damage anything.
Cheers,
Dave.
It is the mini mono with 2 ohm taps. The output impedance of the Behringer analog outputs are 160 Ohms.
Thanks,
Jim
The output impedance of the Behringer and the input impedance of the amps are irrelevant.
These kind of relative voltage gain differences are one of the many issues active crossovers have the ability to solve. If using the Quicksilver amp, simply raise the output level on the tweeter outputs of your Behringer to compensate. If you can't get it high enough, lower the level of the other outputs.
Dave.
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