xdoomx wrote:
Get rid of the step down and just get the transformer changed to 240V. Ive done this to my Mesa Triaxis preamp and Mesa SimulClass poweramp. It cost me around R700 to do each one. And that's nothing compared to what you've spent on this amp. Look up transformer rewinders in the yellowpage, you should find quite a few in Gauteng.
The most important part of your sound is power, if you're getting bad power your tube amp is going to SUFFER.
I'd rather get one from Mesa. Transformer specification and design is a critical part of the way in which a valve amp works. There are so many variables. So, I would say that If you want true to form reproduction, get Mesa to send you an export transformer that was designed right instead of taking your transformer to someone to tinker with to get it to 'work'. I would also advise against using a step down unless you're sure that you're getting almost exactly 120V out of it (or whatever the amp calls for). It would be interesting to measure the actual voltage coming out of your stepdown. Due to the nature of rectification, small variation in Vin translates to large variation in Vout, so by being a couple of volts up or down at your input, B+ ranges dramatically and this changes everything in the setup of the gain stages of the amp, resulting in more/less headroom etc.
Nicholas L wrote:
True what you say karoo the PSU section should be able to compensate for the difference in Hz ripple, but unfortunately that is usually not the case. Even those amps that have the 120/240V selection tend to sound a little bit different because of the 20Hz difference in ripple rectification. Ex for those who would like to know what I'm referring to. Input voltage of 120V/60Hz once rectified the freq doubles to 120Hz before the smoothing caps and thus 240V/50Hz gets has a 100Hz freq once rectified. Now the smoothing caps are generally designed around the freq of the country and even though the voltage gets rectified it's still not pure DC (hence the ripple), but for all intense and purposes it's a DC signal. So with the freq being 100Hz there is a slight bigger voltage decline in the ripple for the caps to work with. However not too sure if it should be unable to produce the chug chug chug mesa tone though, infact it should feel slightly more spongy.
selbydoodl wrote:
Could the 60Hz v/s 50 Hz be contributing to the problem?
karoo wrote:
I don't think that its because of the 60/50Hz issue. The first basic step is that the sine wave is rectified anyway. And I would think Mesa will be smart enough to design filters in the power supply that can handle the 50Hz ripple. SO from then on its basically DC.
you guys..
The main area where a relevant 50Hz vs 60Hz tone difference will be observed is in the power transformer, and this will be a result of the magnetic characteristics of the transformer. Do some research, and meanwhile try not to misinform people.
MoTheO, it is almost certain that the Mesa transformer is conservatively designed, so it's likely that it won't be a problem, at least in the short run. If I were you I would monitor the temperature of the iron, as running it at a lower frequency that it was designed for will influence the saturation characteristics of the core, which causes more current to be drawn to oppose the EMF causing it to heat up. If its operating like that, there will be a big impact on the response of the transformer, as in its capability to supply current when big changes in the current that the amplifier is trying to draw occur, for example strumming a big chord.
Other than that, your filter networks are trying to filter 100Hz ripple instead of 120Hz ripple. This will actually result in an amp with slightly more ripple in the B+ rail, but it won't have an impact on tone and you probably won't even notice the increase in noise.
