Nightmare on EL34 Street

[S-Man]

All was going well until HexFREDdy Krueger invaded my power amp leaving a bunch of 4 slow and dirty 1N4007s out in the cold. Thankfully I have managed to scare off the HexFREDdys with the tip of my soldering iron and the 1N4007 are once again basking in the glow of 4 EL34s.

Seriously though, replacing 4 1N4007s with 4 HFA06TB120s in my EL34 based PP power amp made it sound like a mediocre SS amp. This was exactly the opposite result to what I was expecting. So what's going on here? Maybe low tRR and QRR don't matter that much when the things are not used at SMPS switching speeds and with inductive loads (my amp uses a simple diode bridge + big caps for the HT rail). Maybe in this situation the high slope resistance of the FRD versus the 1N4007 matters more?

Anyway, it's not the 1st time I have had opposite results to many opinions posted on the web

[andrew ivimey]

Was there really THAT much difference?

I don't know your partic. Hexfreds and have never bothered with hexers with PP. PP seems so forgiving thatalmost anything will do as a rectifier ..... BUT .... with class, quality and that really right sound, only valve rects and choke loading will do; more expensive but worth the effort, dammit.

So, are you sure your bridge of hexfreddies were wired up properly? And were you trying to get away with a big cap, only?

[S-Man]

Yes the difference was very noticeable - to the point where I would not want to listen to the Freddy'ed version for very long. I had expected no difference or a minor cleaning up of the top end. The IR HEXFREDs are amongst the ones to have according to this:
http://www.wduk.worldomain.net/forum...read.php?t=210

This confirms the excellent and soft swtiching characteristics:
http://www.avtechpulse.com/appnote/techbrief9/
which is why I wonder if soft+fast is not the most important parameter.

Yes the FREDs were installed correctly, I have built 10s of SS power amps and preamps over the last 20 years as well as designing and building a couple of phono stages. I'm not hugely experinced with valves, having only built a "Daniel Vacuum Tube Preamp" (which was ****) and a Grounded Grid preamp from scratch.

[pre65]

Originally Posted by andrew ivimey

.. BUT .... with class, quality and that really right sound, only valve rects and choke loading will do; more expensive but worth the effort, dammit.

Hi-i am a little confused by Andrews post.

I built an 832a P-P amp with a basic bridge & big cap for the power supply,and i thought Andrew preferred that to the one he built with a valve rectumfrier !

Or have i misunderstood ?

[S-Man]

I try not to make sweeping statements because there is often an exception to the rule. e.g.
P-P versus PCB (WD84 is generally considered to be better than an ST20)
SET is better than PP (depends on the design(er) and speakers)
etc etc

Therefore I would not assume valve rectification is better than solid state in all situations. The PP EL34 I am now using has all of the strengths of the ST20 I used to own (which had a Mullard valve rectifier, hard-wired etc) but is hugely better in terms of bass perfomance, treble quality and transparency/realism. Yet it partially uses pcbs, has 1N4007s in the PS and has no boutique parts in it at all.

Some years back I compared my SS AKSA 100N to KAT6550 and 34 at WADs demo room. The AKSA sounded better there than in my own system and was better than either of the 2 WADs. Nick was stunned that a SS amp could sound that good with no fancy parts and running class A/B. Then he urged me to listen to the 300B SE. The 300B trounced all of them, even to my surprise, in the bass. The lessons I learned from this are never to assume anything and that system matching is paramount.

In the same vein as my FREDdy experiment I can remember putting a few Black Gates in my AKSA (at the suggestion of the designer). Initially I thought it was great but after a while realised it was just sonic MSG and reverted back to the original build.

Anyway, after all that rambling, I would never assume that FREDs willl make the sound worse in every application but I would certaiinly be cautious of just putting them in a new build because they have good specs.

[andrew ivimey]

No Philip, gritted teeth ................ I said then and again that PP is so foirgiving compared to PP amps. Your 832, our 832 is easy and try as I might, using valve rect. it just didn't do it, but with Ss it did. that's PP for you.fullstop.

there is more but I'm busy.