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Over the last few days I've finaly gotten around to building Allen Wright's FVP5A design, well the line stage at least. I have had it running for about 40 hrs now. The sound is just fantastic. Actually, it doesn't really have a "sound". I should say the results of using it in my system have been fantastic. Very wide and deep soundstage. Great instrument placement, not overly warm or analytical, just right! I'm currently using Amprex 6922's on the lower tube and more generic NOS stuff on the top. If anyone has been thinking about building one of these, I'd really recommend it. Yes, a bit more complex than some designs, but worth the effort for sure. Right now I'm using it with a phono stage based on an audible illusions design. For the power supply I used a tube rectified and choke input filter, then after a 220uf cap, it goes to a CCS on top of two VR tubes for 250v out (an 0A2 and 0B2). Very quiet design, too. No hum at all. The transformer I used for this is a current mfg Dynaco replacement for the St-35. It is (IIRC) 330-0-330 at 180ma (over kill I suppose), but it also has two 6.3v windings, which support the two heater levels needed for this amp. I actually float the heater for the higher tubes, and use it for the rectifier at the same time. So far seems okay. So Kudos to Allen for making his design public for DIYer's like me. Thanks!
Follow Ups:
PSU: may I ask for more details? Transformers Vrms, choke size, rectifier, CCS and residual hum?I have such a PSU in my line stage and I still can hear some hum in my (115dB) horns.
115dB/watt is an EXTREME task for an amp!
This is the power transformer I used: http://www.triodeelectronics.com/pa7dynst35sc.htmlThe choke (IIRC) is 15h at 100ma, Hammond.
The CCS is a Gary Pimm CCS, but I suspect other CCS's might work just as well. I'd really like to save my penneys and try out the actual "Super Reg" from Allen. At any rate, when I had this on a scope, the hum was low enough that I could not distinguish it from just noise (I'd say less than 2-3 mv). On the heaters for the amp, I used AC on the top, again, just ran it from the rectifier tube's supply (used a 6CA4), and on the bottom tubes I used DC, well filtered (3x 6800uf + 0.1uf).
The only hum I get at the speakers are from the power amp, and that's pretty low, too.
Ut's highly recommended for ALL single ended preamps - in fact I say vital!Happy you like the sound of this design - in it's latest version, it's available a s a full kit - the SVP-1. See my site...
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