My New Aikido Cathode Follower Preamp

simon · Post by **simon** » Thu Aug 22, 2013 10:43 pm

I've built a few of JRB's kits as the pcbs are lovely to use, really immense. But I've point to pointed a number too - the circuits are simple enough if you have a little experience.

There's acres and acres of his doodlings on his blog but finding stuff isn't easy. I always end up googling "tubecad" + whatever I'm looking for. And the ACF manual doesn't open, and hasn't for a long time either. But this blog might help
http://www.tubecad.com/2010/06/blog0188.htm

The Aikido consists of two sections - the first is the gain stage (the gain is roughly half of the mu of the valve used) followed by the ACF. One of the strengths of the Aikido is the inherently good PSRR.

The Broskie Cathode Follower is different, I use it to take a balanced signal and convert it to SE in my DAC buffer. With a shunt reg PS it works really well.
http://www.tubecad.com/2012/05/blog0229.htm

He reckons to get 100s of emails (a day?) and is notoriously difficult to get a reply from. That said when I had a problem he has responded, but don't expect endless support cos you won't get it. But the circuits are simple and resilient so problems should be minimal. Definitely worth trying his stuff.

simon · Post by **simon** » Thu Aug 22, 2013 10:48 pm

What do you have in the way of novals Greg? Within reason it's quite easy to simple change valves without changing any components - you probably won't be running the valves at the same OP but you can chop and change. 6N6P would probably be good, but you need the good ones, and JRB often talks about 6DJ8 which is analogous to 6922/ECC88 etc.

Me, I'd use a 5687 cos I like them, but the pin out is different so if you're going to use a PCB you can't use them (without butchering the PCB).

IslandPink · Post by **IslandPink** » Fri Aug 23, 2013 12:12 am

Good NOS 5687 will be a safe bet . 6N6P's can also be excellent , but DO NOT get the nice-looking early-90's ones with gold-grids that are common on EBay now. They sound very hard and glassy and not nice at all, compared to the very good ordinary 1980's ones in plain brown packaging .

Paul Barker · Post by **Paul Barker** » Fri Aug 23, 2013 4:50 am

simon wrote: The Broskie Cathode Follower is different, I use it to take a balanced signal and convert it to SE in my DAC buffer. With a shunt reg PS it works really well.
http://www.tubecad.com/2012/05/blog0229.htm

Excellent informative link.

All those in path capacitors scare me to death though.

We need a balanced dac DC to first valve circuit.

Broskies Aikido implementation he first came up with from the 1990's he shows in that blog further down where the transformer is involved is exactly what a bunch of us were taking about in vintage tubestalk at that time and quite a few of us did it. We found it did sound good with it's power supply noise rejection, and it had a good effect on filament noise. I think we hadn't rationalised it in the way Broskie has since done turning something which was folklaw practice into a well documented scheme.

People mutated these capacitor connections into other things and gave them different names which drew the attention of the masses in other directions, but I recall quite clearly a few of us doing exactly what broskie pictures in that blog, and knowing we were employing power noise to cancel noise at the filament and vice versa. the capacitor ratio you played with empirically until it sounded best to you.

it simply went out of fashion at the time that all the "new ideas" of Monkeys, Free lunches and DRD's became vogue.

Post by **Nick** » Fri Aug 23, 2013 8:20 am

The one thing that I wonder about this circuit is the effect of the two DAC outputs seeing what I think are different loads.

ed · Post by ed » Fri Aug 23, 2013 8:22 am

one more vote for aikido as a dht driver...I've never felt the need to change mine.

As a pre, the only experience I have is with Steve Cresswell's when he kindly let me use his with the F4 when I first brought it out. The best I've ever heard the F4, but then it really likes a lot of gain in the front end.

Greg I have a sort of index of Broskie blogs if you're interested. They are challenging to wade through if you're looking for something specific.

David · Post by **David** » Fri Aug 23, 2013 9:03 am

Hi Greg,
I have started by building the standard AFC 9ba kit on the supplied pcb. I also ordered the cap set in addition to the standard resistors, but if you plan to upgrade the caps I would skip that part.

The kit comes with:

4 x Wima 0.68uf

These are the input caps and the voltage ref caps. So if you use eg Mundorfs or others as input caps you only need two of these (or equivalent)

The output caps are 3.7uf polyprops. These are the ones I intend to upgrade to Mundorf Alu /oils at some point.

The remainder of the caps you do not need. There four small electrolytics: two for heater smoothing which you don't need if using PSU3. Two are for cathode bypass which you would only need if you wanted more gain (and distortion).

You can use a lot of different valves as listed, and the kit includes resistors for all the types listed. You need to change the 4 cathode resistors to suit each valve. So you can try with different valves, then upgrade with your favourite resistors and Eh voila! I mentioned it would be interesting to try with the 12AU7s. These need 250v ht, which is fine with PSU3, so they could be good to try. I'm sticking with the Mullards as I have two lovely Gold Pin ones to hand, otherwise I would have used the TJ 12AU7s.

I will try and upload the circuit diagram later or if that fails I will e mail it to you Greg.

As mentioned, I think I will implement Broskie's own psu decoupling between channels that he uses on the Cathode Follower all in one kit he supplies (circuit on the Broskie Website under manuals) as I think this would provide worthwhile benefits.
David

David · Post by **David** » Fri Aug 23, 2013 9:54 am

The Aikido circuit file is too big to upload but I will happily e mail it to anyone interested. Greg, you have it unless you've changed e mail.

I swapped in my Mundorf silver /oils this morning and they reaped their usual magic!
David

Greg · Post by **Greg** » Fri Aug 23, 2013 12:50 pm

Thanks for all the help, guys, and David for emailing the circuit and parts list. I was going to buy just the PCB at £15.42, but shipping is nearly £20. If you facter in the likely import duty and handling charge, the overall cost seems disproportionate.

I am going to have a go at this but I'll do it point to point. I need to finish fettling my 2A3PSE first

simon · Post by **simon** » Fri Aug 23, 2013 5:24 pm

None of the few parcels I've had from JRB have been stopped, but I'd agree anyway, point to point it to find out what works

Greg · Post by **Greg** » Fri Aug 23, 2013 5:30 pm

Thanks Simon. Unfortunately since the RM has tightened it's procedures, every purchase I've made from the states has attracted the charges.

simon · Post by **simon** » Fri Aug 23, 2013 6:31 pm

Interesting point Greg, I didn't realise they had. It's a while since I ordered anything from John, and the last couple of parcels from the US have both been stopped.

Post by **Nick** » Fri Aug 23, 2013 7:41 pm

one more vote for aikido as a dht driver...I've never felt the need to change mine.

Yep, I would agree entirely with that.

Ali Tait · Post by **Ali Tait** » Sun Aug 25, 2013 12:46 pm

Greg wrote:The website suggests several valve choice options. These are 6AQ8, 6CG7, 6DJ8/6922A, 6H30, 12AU7, 12AT7, 12BH7, 5963, 5965 and ECC99.

Please can you knowledgable valve aficionado's give me some guidance on which valves worth prioritising here?

Thank you.

Greg

John Broskie seems to favour the ECC99 -

http://www.tubecad.com/2011/01/blog0198.htm

I've ordered one to have a go with.

colin.hepburn · Post by **colin.hepburn** » Sun Aug 25, 2013 8:00 pm

David
You Have PM

audio-talk

My New Aikido Cathode Follower Preamp

#16

#17

#18

#19

#20

#21

#22

#23

#24

#25

#26

#27

#28

#29

#30