Thou shalt not bypass a Black Gate

[tpatton]

My Transcendent Sound SE OTL has two Black Gate F's, 680 uF, as its output caps, the last thing the signal sees on its way to Oris 150 horns.  I had a pair of Russian Teflon FT-3's, 0.1 uF, that I couldn't find room for in any of my Bottlehead amps or phono preamps.  So yesterday I broke that subject line Commandment.  I did it first in one channel, and listened to a couple of good mono LP's one channel at a time, and liked the channel with the bypass well enough to do the other channel too.  I'm usually uncertain whether a change I've made has done any real good, but not this time.  The highs were sweeter, the detail sharper and clearer--unless I'm simply deluding myself (always a possibility).  The FT-3's had been broken in a la Grainger with 96 hours of continuous loud music.  I'd love to hear any of your comments, on whether the improvements I think I heard are even possible, or not only possible but predictable, or whatever.

[Jim R.]

I think it really depends on what type of BG and where/how it is being used.  I always bypass NNH and NXs s they alway seem a bit etched on the top end to me.  I've had mixed results with FKs and Stds depending on whether they are used for signal coupling or filtering -- generally I feel they are best left alone as coupling and cathode bypass caps, but can often benefit when used as supply filter caps.

Hope this helps.,

Jim

[tpatton]

Thanks, Jim.  Here's what I'm using: http://www.partsconnexion.com/capacitor_ele_blackgate_f.html.  It's marked "F", as I recall.  I should know which of your categories the "output cap" in an OTL belongs to, but I don't, so maybe you could enlighten me.  As I said, the output signal goes to one end of it, through it, and on to the speakers.  What kind of cap does that description make it?

[Jim R.]

Tom,

In that position this would be a coupling cap, but a power amp output coupling cap as opposed to an interstage coupling cap.  I think the *rule* of not bypassing black gaes came from some purists who believe them to be the best caps, more or less for everything, however, to my mind, some black gates do in fact sound better when bypassed.  I'm not aware of any technical reason why you shouldn't bypass a BG, and my rule is that if it sounds better bypassed, then so be it.  Sometimes they sound better bypassed, and sometimes not, and I'm sure some of this has also to do with the quality and proportion of the bypass cap.

-- Jim

[tpatton]

Thanks again, Jim.  I never had any doubt about whether I'd keep the Russian Teflon FT-3's in as bypasses, I trusted my ears on that.  I mostly just wanted people to know that it sometimes works, and the details you added will be very useful to others too.  Praise for the Russian Teflon FT-3's is of course implicit in all this.