Hey there everyone and cheers Amir for the work.
I am heavily thinking about using this Topping Pre90 to feed the Purifi 1ET400A directly (e.g. I would get VTV's "EVAL build", which mimicks Bruno's EVAL build, which Amir tested to be outstanding and more particularly so without the pre-gain stage of the OPamp).
On the voltage side it seems this is fine: Amir sees excellent results on the Topping Pre90 all the way up to 8Vrms (I would be using balanced XLR in/out everywhere too) and even though this has not been tested, I would assume that you can go up to 15Vrms on the Topping's output without loosing much of what makes that preamp a transparency champ. Nominally, with balanced in/out, this preamp is advertised to go all the way up to 50Vrms if my memory is not failing me.
Question is the impedances. I have basic electronics understanding but little experience plugging audio devices together in such non standard ways. Is there anyone around here which could give an informed opinion on whether it would really make sense to wire the Topping Pre90's balanced output to a Purifi 1ET400A directly (bypassing the pre-gain stage of the EVAL build) ?
(Before people ask: yes, I need that preamp because of switching sources and also because the DAC I use does not have volume control nor any form of added preamplification)
Reaaally appreciate you guys providing input on this. I have a feeling I'm not the only one willing to try this, on the basis that working with high voltages as early as possible is always the best thing to do. This preamp + bypassed-amp setup seems to me like it would be a nice poor man's version of a Pre90 + Benchmark AHB2 combination (which again Amir notes could be special interest since in low-gain mode the Benchmark would be fully driven with ~8Vrms, which the Topping Pre90 has no problem delivering).
EDIT: I have actually asked VTV about this and all they say is that - yes, you can bypass the OPamp's pre-gain stage on their Eigentakt-EVAL build but - they advise you not to do this bypassing. When asked why, they answer that the low input impedance of the 1ET400A alone could be problematic. Now of course, it's not that I absolutely want to be the rogue kid who doesn't listen here, but there's also the fact that from VTV's manufacturing standpoint *of course* they discourage you to do that (firstly, if one does not need a pre-gain, things start to look more and more straightforward on the DIY side when thinking about combining a powerful preamp with the Purifi modules and, secondly, it's a manufacturer's recommendation ... of course that consists in saying "don't do weird stuff with our products / you should use it as such because it is designed as such to not generate any problems", etc.). This all tells me that maybe it is nonetheless a very sensible thing to do (and maybe even a good thing) to wire the Pre90 to the Purifi modules directly
. Again, comments welcome.