Hi Audiofun
I find it quite interesting that the telefunkens added more weight and body. Along with the Seimens tubes I find telefunkens to be leaner and more transparent, not necessarily the most preferable choice if weight and body is a consideration. I have tried many combinations of tubes with the teles being the least preferable in my system. I've have the zh270 for almost 10 years with Merlin VSMs and though I haven't heard the zh230 would expect the results with this tube to be similar. What I like most about the amp is that you can get color flavors from source and pre-amp choices. The Berning can be the foundation of presenting a signal to the speakers while minimizing colorations found in most tube amps. Not a choice for everyone of course but I find no loss of harmonics at all, just less exaggeration brought on by second order distortions and less evident in this design. Of course the ZOTLs work nothing like a typical OTL or transformer coupled one or any amplifier I am aware of, efficient operation, flexibility and superb performance.
The feedback setting, for a more resonant fuller sound would be low which also increases output impedance/damping. The tradeoff is less extended highs and low frequencies and a bit of loss of transparency relative to normal and medium settings, the beauty being you make the choice of what works best in your system and to your taste. There are many avenues to explore with this amp as I have discovered over the years which is why it still has this fascination, it is never the limiting factor.
I find it quite interesting that the telefunkens added more weight and body. Along with the Seimens tubes I find telefunkens to be leaner and more transparent, not necessarily the most preferable choice if weight and body is a consideration. I have tried many combinations of tubes with the teles being the least preferable in my system. I've have the zh270 for almost 10 years with Merlin VSMs and though I haven't heard the zh230 would expect the results with this tube to be similar. What I like most about the amp is that you can get color flavors from source and pre-amp choices. The Berning can be the foundation of presenting a signal to the speakers while minimizing colorations found in most tube amps. Not a choice for everyone of course but I find no loss of harmonics at all, just less exaggeration brought on by second order distortions and less evident in this design. Of course the ZOTLs work nothing like a typical OTL or transformer coupled one or any amplifier I am aware of, efficient operation, flexibility and superb performance.
The feedback setting, for a more resonant fuller sound would be low which also increases output impedance/damping. The tradeoff is less extended highs and low frequencies and a bit of loss of transparency relative to normal and medium settings, the beauty being you make the choice of what works best in your system and to your taste. There are many avenues to explore with this amp as I have discovered over the years which is why it still has this fascination, it is never the limiting factor.