Rerurn to Romy the Cat's Site
In the Forum: Melquiades Amplifier
In the Thread: Valve Preamplifier for Macondo/DSET
Post Subject: The Placette has diedPosted by anthony on: 5/10/2019
Well, probably not up in smoke, but it is just not functional any more. I was away for a few days and came back to my room to find the Placette refusing to change volume or select a source input, so something is amiss. Perhaps something has been amiss for some time which may explain why I have not found it as transparent as Romy and others.
There is no time at the moment to look under the hood for the fault. I've been listening to my dac directly connected to the DSET and it is so nice...but not loud. The amps are getting the full 1.5V output but it is not loud enough, of course.
On another point, I have been reading a little about pre-amplification and current output and output impedance. Up to this point I had not realised that the ability of a preamp to drive capacitive loads has almost nothing to do with low output impedance, but is all to do about current output. A beast such as the DSET with 6 x triodes and a few inductors and capacitors at the input is likely to be a mighty capacitive load. This needs to be measured. If one stage cannot sink enough current into the next (i.e. the current clips) higher frequencies will roll off. The limiting factors are input capacitance of the DSET, desired frequency response, preamp voltage output and desired headroom.
DSET Input Capacitance: to be measured
Desired Frequency response: The RAAL ribbons are good to 50kHz or so I think, so I choose that
Preamp voltage output: 4VRMS to drive DSET to clipping
Desired Headroom: x10 (20dB)
So, I have to measure the input capacitance of my DSET and then do some math to figure out how much current my preamp needs to produce in order to satisfy the load.Rerurn to Romy the Cat's Site