RFC BB3 build

OK folks

after a lull during which I was sorting out a few issues and schoolboy errors such as not scraping the lacquer off the foot base of my copper shield plate (to ensure it grounded properly with star washers), we're back in business after trying various valves. I didn't see the point of posting anything more until I'd tried a few things.

Firstly to shielding. You will need a minimum 250mm wide case if using E&I trannys or preferably full width if you have room (440mm). The advantages of an E&I over toroids are that unlike toroids, the parasitic hash from the mains and core won't be coupled to the secondaries so theoretically distortion will be lower as will S/N (caveat coming) providing you shield and ground it properly. The other advantages are that you don't get large inrush current's (although in this application the draw is minimal anyway) and that E&I's rarely have any issues with insulation breaking down. I've suffered this with two toroids in the past causing the transformers to short due to overheating.  For shielding, none of my kit that uses E&I's have nor need Mu metal shields. Place one of these anywhere close to phono signals, especially low MC signals and you'll find out that Mu metal has it's own issues being a magnetic alloy.

For line level or MM signals, copper, steel or aluminium shielding is perfectly fine but the E&I needs (in the case of the BB3) to be close on 3 inches distant from the PCB or more preferably. Mine is 2 inches away and on MM I have ZERO hum even with the volume ramped all the way up.  On MC I have a little but only once volume would destroy your ears and speakers...

The other thing that people almost always forget is that when fitting any E&I, there is a trick in finding the null point (or lower point in the EM field). Simply rotate the orientation a little at a time and try for hum. You don't need the traffo bolted in but best to have the frame grounded using a ground wire to eyelet as normal, then without a shield start parallel to the PCB away as far as possible, switch on and listen for hum. Switch everything off then move it a little more and try again. You'll find a sweet spot where hum is either non existent (a nil in the field). Bolt in to that position and add your shield.

Back to the build. I don't know about others, but I cannot stress importantly enough how important valve choice is for this stage. Anything seven slightly microphonic in V1 will magnify that to V2, affect RIAA and also magnifying microphany in V3. It'll ring like a bell. Initially I thought that my NOS Phillips would be fine and sounded ok until I sorted the shield and now the hum is gone I found it rang badly and failed the Subbuteo flick test!

I have found very inexpensive and decent sounding PCC88's that cure this completely: Pinnacle PCC88's. Mine were non microphonic and passed the flick test with flying colours.

I believe that Oli tried Tele PCC88's and found the same. I ordered some before I saw that the Pinnacle I discovered in my pile of valves did the trick so needn't have spent out! If you're on a budget, I definitely recommend the Pinnacles.

Onto The middle valve. I tried a JJ initially as it was described as low microphonic (JJ 12ax7/ECC83s). It wasn't. Mine may have been faulty as shaking it I could hear part of the structure vibrating inside the glass envelope as well as feel it. Not recommended.

I tried the Phillips 1971 production ECC83 short plate (possibly re-badged from Mullard production as Phillips owned Mullard). Not good.

Finally I put in a new Tungsol ruggedised ECC803s short plate with spiral heater filament (low noise) and gold pin connections. Perfect. Very silent and non microphonic. These have got a little spendy in recent years at £24 plus postage but they're worth it and having some superb NOS Mullards here reserved for the TRON, it performed equally as well as they did.


I noticed with the Phillips and the JJ that the sound-stage was quite flat and 2-D and my RFC Canterbury's had lost their remarkable trademark depth of sound-stage (peculiar to DC drivers, related to phase and time alignment). Once the Tungsols went in, out popped that more 3D depth I was used to and value. I thought this might be phsyco acoustics at play so swapped back and forth but nope, definitely a big improvement. This shouldn't theoretically happen, at least I can't think of any reason why a V2 (or V3) valve would make the slightest difference to this, but it simply does so I don't question it; I value it.

It may come as a surprise to note that V3 can be left in even if microphonic. Leaving my Phillips in V3 made little to no difference, partly as the signal's not as sensitive as at the input end. Although this doesn't matter as much I'll be adding another Pinnacle or the Teles's on order.

I noted that one JFET per channel was used and have been in discussion with Oli and Oli I know has been chatting with Alan and coincidentally were also considering this. By doubling the JFETs so you have 2 in parallel you can gain an increase in S/N of 3dB (ie a halving of noise). You can go to 3 or 4 but usually doubling is enough apparently.

The other issue I've found is at switch-off there's sparking across the switch contacts and a loud bang from the speakers and also the jump in current to the power amp trips the circuit. I tried a contact suppressor (0.1uF, 100 Ohm x2 rated) across the switch outputs (probably better to put it across the transformer inputs) but no difference. That only leaves the circuit rails. On switch-off there's a sudden drop to zero V and this causes a large voltage spike across switch contacts hence the issue on switch off. I'll be muting output at the preamp before turning the 'stage off but I understand that Alan has recognised this and may be working on a soft stop pcb that can be added?


Sound quality: Having fiddled and fettled and had time for a listen I'm quite impressed. It does pip the Hagerman Cornet. Lower noise, slightly better separation and definition with better bass. I tried it in MC against the TRON but imho the TRON still has it for me (lower noise and something more 3 dimensional and detailed on sound with a controlled deep low end similar to the BB3 but somehow better defined). I used 330 Ohm load resistors for MC.

It's a premature comparison though as the BB3 neeeds time to bed in a bit more so I know I'll need to revisit this across a wide spectrum of recordings to return more meaningful observations.

The stage shows real promise and is a diamond in the rough but I see this as a good thing. It means you can make of it what you want. It will no doubt yield more performance with some revisions and fettling or you can use it just as it is confident that you'd have to spend a lot more to better it in valve land where currently prices are going crazy.

I hope that this is an encouraging and fair initial assessment but the fact I want to keep listening singles it out as a winner for the outlay to my mind.

Thanks for a comprehensive review Paul, not that I would expect anything less from yourself.

The comments about transformer choice are very pertinent for ultimate performance, I have even found at least partial nulls when rotating toroidal transformers, so a very good tip.

The turn on/turn off wobbles on the output are unfortunately to be expected when the supply rises or collapses with valve gear, I have a couple of delay pcbs that came yesterday, once fitted with a two pole relay they would be perfect to mute the outputs on switch on/off.
I will post details once done.

Glad you are liking it so far.

For valve choice I have been surprised how microphonic the Tesla valve are. I have a Telefunken in V1, a Russian 6N2P-EV in V2 and a Matsushita (Japan) in V3. No microphonics, yay.

Was this one known during testing Alan?

I never have experienced this with my builds.

A few are reporting this but again, I've built a fair few of these and never had any noise.

Quite simply, switch your power amp off first, as you should be anyway when switching things on or off.

I wouldnt read too much into the TRON comparison, in all honesty.

The TRON is a different listen altogether. It is holographic, yes, but it also paints a picture with a largly warm hue.

The HF of the Tron also sounded quite rolled off to me in listening tests I've done with one, and i used an ART7 and AT33PTGII with it. Anyone who's heard these carts know they do not curtail the HF!

Also, the mids and Bass were rich and supplied less detailed information in the lower registers.

Dont get me wrong, the Tron Convergence is a good phonostage, Ultra quiet due to using in built SUTs (which is a huge negative for me) and has great liquidity, but it fatigued me after a while as everything sounded the same.

The Bigbottle is more revealing, more detailed and doesn't sound rosey....its a far more neutral and transparent sound and, I think that's where the decision on "what's preferable" will ultimately be made.

No issue with Paul feeling the Tron has the edge, he's paid his money, built a BB3 and had a listen. Massive respect.

Personally, I wouldn't be judging the phonostage critically until I had irradicated ANY hum at ANY volume, and put the best valves in that I can afford. Hum is a parasitic result, so if you have it, it will be having some effect, even if you cant hear it until you turn the wick up.

I removed my traffo altogether and I can honestly say it made a huge difference...even with very minor hum when it was in the case with the PCB.

There are Telefunkens on the way to Paul, and if my feeling is right, I suspect I know what the outcome will be once Paul's had a listen with them in. The Telefunkens will only raise the transparency of the BB3, taking its presentation further away from that of the Tron.

Cheers for that. I think I've said I'm putting my transformer in a separate box so hopefully I won't have any hum issue anyway.

I've yet to buy the valves and was looking at these:

Differing opinions over bits of kit....on a forum! I cant believe it

Yes, totally constructive and totally acceptable. No problem.

I know you'll keep trying to get the best out of it, as will we.

Haha! That's ingenious

Well done Alan.

That's what forums are for Oli, sharing of opinion, and sources of valuable information and advice.  If we all liked the same thing it would be a boring old world! 

That's all fine and I am truly not being funny but I did assume I was buying a fully sorted stage. I didn't realise it was still being developed in this manner. I get changes happen but these developments are being offered before I've even mounted a component on the one I have here....

I guess there's different takes on these things Scotty.  Must admit, I approached this very much as a DIY build where sharing of ideas was still very much in play.  You could still make it up with no issues as it stands and it would work fine, but I think the things that Oli, Alan and myself batted about were more development of an already completed design could yield yet more improvements.  You could take any piece of audio kit off the shelf I guess and point towards where audio improvements could be had.  I do this frequently with speakers for example.  Mine had a few issues with noise but that could have been a one off due to one of the JFETs being at fault, and Oli was on it straight away and has posted some more out to me...can't say fairer than that.  It was whilst discussing the JFETs that I threw in a suggestion that paralleling them could lose another 3dB off the noise floor hence a suggested improvement.  If it already had this, you could further argue improvements by adding more etc.

Oh I can be quick if I want to, lol. I had the boards on order a few days ago actually.

The board connects to the signal outputs of the board, not the transformer connections.
It acts to short circuit the signal outputs, so preventing any pops or DC. Once the 30 second delay is over all that is connected across the outputs is an open relay contact, so no affect to the sound.

Alan and I fettle absolutely everything that we either buy or build. Look at his brand new Paradise, it's already stripped down and being rebuilt!!!!

He only had it 1 day!

We've explored improvements to absolutely everything, including a Tron Convergence.

The philosophy is that we never rule anything out unless we've tried it and if there is a gain to be had by pairing up Jfets, then we will explore it, implement it and release the mod!

Even the mod will be free if you build it yourself.

Spot on Andy.

I do feel I must reiterate that I have absolutely no Hum at all. There is only an very minor audible pink noise when the volume is up way past any level that would be safe for my speakers.

This investigation into Fets and the doubling of, is just that, investigation.