Tekton Double Impacts

I believe I had the volume up to between noon and 2 using a streaming device as the input before Tom’s amp started soft clipping, which was on 90 db speakers, on the 8 ohm taps. It also depends on the level of the recording. Les Zeppelin needed to be raised much higher than say Pearl Jam, for instance. The entire system sensitivity and desired level of listening comes into play heavily for sure.

I should have some pics up maybe as early as the weekend, depending on what the lady has in store for us when she comes up. And Tom, you also have a tube regulated power supply using those OD3 regs on either side of the transformer cover :-)

First, kudos to Dave (Dlcockrum) for what IMO is an astute, perceptive, thorough, and exceptionally well written review he provided yesterday of his experience with David_Ten’s excellent system. And likewise with respect to the similarly well written comments provided by Laaudionut.

Regarding inline attenuators, for many and probably most applications I would suggest going with the Rothwells rather than the Harrison Labs devices. Based on measurements I recall that one of our members provided here some time ago the resistor values used in the Harrison devices are low enough to be a problem in many systems. Especially if the attenuator is driven from a tube-based component which has coupling capacitors at its outputs.

FYI, resistance measurements I’ve taken of 10 db unbalanced Rothwell attenuators that I have show that they consist of a 22K resistor in series between their input and output, and a 10K resistor in shunt between their output and ground. Therefore, depending on the input impedance of the component whose input they are connected to, the component providing the signal to them would see a load impedance in the rough vicinity of 30K or so. The corresponding numbers for the Harrison Labs attenuator are far lower.

Re the gain questions that have been discussed, first, it’s probably fair to say that among the countless amplifier models that are available gain and maximum power capability tend to have a **loose** correlation. But many examples can certainly be found of lower powered amps having higher gains than higher powered amps.

Charles, it can be calculated from the specified 0.7 volt sensitivity and 8 watt power rating of your Franks that their gain is approximately 21 db when their 8 ohm tap is used to drive an 8 ohm load. IIRC your speakers are nominally 14 ohms, and given the Frank’s output impedance of 1.8 ohms (as stated in a TAS review I’ve seen), their gain from the 8 ohm tap into 14 ohms would be close to a db more than that, or around 22 db.

Re the Pass XA60.5, like most Pass amps it has a specified gain of 26 db, which corresponds very closely to what John Atkinson measured in Stereophile’s review of that amp. Correspondingly, it has a specified sensitivity of 1.1 volts for its rated output of 60 watts into 8 ohms. However its maximum power capability into 8 ohms (after transitioning from class A to class AB) is 130 watts per JA’s measurements, which can be calculated to require an input of about 1.6 volts to be reached.

Best regards,
-- Al

P.S: I realized after the editing window closed on my post just above that Laaudionut’s amplifier is the XA60.8, while the last paragraph of my post referred to the XA60.5. However the gain, sensitivity, and maximum power specs of the two amplifiers are identical.

Best regards,
-- Al

Thank you Al for the kind words. Much appreciated.

Dave