Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: theundeadelvis on October 29, 2011, 09:58:53 pm
-
I'm getting ready to start a new build (mentioned in this thread: http://www.el34world.com/Forum/index.php?topic=12513.0 (http://www.el34world.com/Forum/index.php?topic=12513.0)), and I was curious if using a master volume and a VVR was useful or overkill? I'm curious if having both will give me more options, or will I only use one or the other? Experiences? Thanks in advance!
-
Inserting a VVR you can chose some different solutions:
. PowerScale only the output stage - this way you must insert a PPIMV to have a better control about the distortion level via a compensation of the signal coming from the PI
. PowerScale the output stage + the PI - this way you have a better control of the distortion level but may be is required to scale the power also of one more gain stage ahead the PI to eliminate the PPIMV
. PowerScale the complete amp will give you a Variac effect (without the problems related to lowered Heater Voltage)
the way I've seen used mostly is to reduce output stage + PI voltage & at the same time have a PPIMV
Kagliostro
-
Yay. The more volume control throughout the circuit the better (IMO).
-
Finished a JTM45 Build a couple of weeks ago. Powerscaled the output, but also need to install PPIMV. If you scale the power tubes to like 10% of max, the preamp will overdrive excessively and the distortion was not very good in the 12ax7 hard hitting el34's (I prefer el34's to KT66 in a JTM 45). Changed over to scale the whole amp and it became a weak sounding amp overall. It was either thin or boomy. Changed *increased to 330pf) the cap on treble volume and it helped some. I simply did not like it. I took it back out. It doesn't seem to work well with fixed bias. I ended up using a dual 500 pot, a very nice one where both pots measured exactly the same. My initial thought was Power Scaling instead of MV, the problem with a JTM 45 is THE sound is jumped with one volume at lease 8 ant the other at least at 6. I kept the PPIMV simply because wide open it makes no difference. Once again I have learned that the best method is the proper amp for the size room you are playing. In my experience, nothing makes an amp sound good except the power tubes running hard. I put a switchable Hall Amplification VVR cathode bias in a 5f4 and it worked very good, much better than a MV. Still doesn't sound like the 5f4 cranked, but worked better than the fixed bias JTM45 Build.
-
Some good info to consider. I though I might Just order a Hall vvr kit and give it a try (not sure if it scales the entire amp or not), and the mv is simple enough to implement, so I'll probably give them both a whirl and see what it sounds like. Thanks!
-
I though I might Just order a Hall vvr kit and give it a try (not sure if it scales the entire amp or not
It depends on how/where you wire it in to the circuit. It will/can do the whole amp or just the power amp or the power amp and PI.
Brad :icon_biggrin: