My Cathode follower with active load.

[bob orbell]

Time to report on the Akidio, after removing the passive and putting the Akidio into the system, I put on a few of my best liked music, all sounds very nice, there is no hum, no buzz, in fact almost total silence in between tracks, bass has more punch and the top end is less harsh than with the passive, all in all I am very impressed. If any one has any questions, I will try to answer them. BOB

[davebms]

hello all,,, bob what valves did you use, do you think its an improvement
on the pre 11 cathode follower ?

thanks dave

[bob orbell]

Hi Dave, the valves I am using are Mullard E88CC gold pin, I started off converting a Pre II to CF, and used it for many years, then decided to make a CF with active load, if you have read all this thread, you will be aware of the problems I had, so I purchased John Bronski's Akidio PCB and all components, Bikerhifinut also has one, and speaks highly of it, to be honest, there is little diffrence between the Pre II CF and the Akidio, other than the Akidio is totally silent with less distortion, it can also be configured to use many different valves and White CF also, I am now very happy with my system. BOB

[bikerhifinut]

Hi Bob, and everyone else.
As Bob says I use a unity gain buffer/pre based on the Broskie (Note correct spelling cos i am a pedant, also if you are looking it up on the net it will help.) ACF 9 pin PCB. ACF stands for Aikido cathode follower, if you look it up on Glassware Audios site JB explains its workings very well. basically its a tweaked up active load CF. The USP of this design as far as I can tell is that it is designed to use the individual Characteristics and non linearities of a particular double triode against itself so to speak, in order to make it more linear in response. The circuit can be adapted to use just about any double triode and resistor values are given for the more common varieties.
I use it with a fully regulated HT PSU, again one of JB's PCB's as it's as cheap to buy his bits as it is to homebrew your own. The PCB is very elegant and gives you a few options to fiddle about with, and the PSU board allows for various rectifier options, up to and including a voltage doubler for both HT and heater supplies which could get you out of a dilemma but I always prefer a good old full wave rectifier.
I think the ACF is about as neutral as it is possible to get with an active valve buffer. Also my findings seem to suggest it is fairly "agnostic" about different makes of the same valve type. As long as you use the correct resistor values on the cathodes and the equalisation network that allows the load half of the triode pair to work against the top half that takes the signal I found that I cannot tell the difference between a fairly cheap and cheerful ECC82 or an expensive box plate mullard and all things in between. This to me suggests the design is good and takes out variations in valve parameters for a given type. I actually use a pair of 5814 which are some sort of US made near equivalent of an ECC82 but I think its just as good with a pair of "Edicron" ECC82 of unknown nationality. This suggests to me that it is a good design that has designed out manufacturing variations in valves.
So if your thing is "valve rolling" its possibly not for you.
A point to note........... if you need to use 6.3V heaters (and I did) on pins 4+5 shorted together as per 12A*7 types (ECC82/81/83 types etc) then you need to do a bit of lateral thinking and a bit of twisted wire to connect the heaters up and leave out the capacitors from pin 9 to ground that JB has designed in. They aren't necessary anyway. He designs the boards to use 12.6V heaters with links for series or parallel connection which means Bob with an ECC88 is fine as they have a 6.3V only heater connection across pins 4 and 5.

It's also available as an Octal PCB for those who like big butch 6SN7 types!

Andy

[bob orbell]

Very well put Andy, yes I concur with Andy's comments, one thing Andy has not said is that my board can also be configured to Eric White;s, White Cathode Follower. And thank's for the correct spelling Andy. BOB

[davebms]

hello all,, thanks for the reply's, bob, andy.. Mullard E88CC gold pin !!
I found a pair on ebay only £350 a pair
thanks for the technical info andy I have found the web site; need a
bit of time to read up;; looks promising most people seem to like broskies
products so I will give it ago

I have a kit build OTL headphone amp with ecc99/6922 I changed the 6922
for 6n1p eb, I preferred 6n1p, I also like 6h23p as a 6922 type

its all personal opinion I suppose, but can ££££ NOS valve be worth the
money ?

dave

[bob orbell]

Hi Dave, do people actually pay these crazy prices ?, the two I am using are new and came to me from one of our members, for a small donation to his requested charity, . Don't forget that you may or may not get a bill from customs, I did, and they will not deliver until it's been payed . BOB

[pre65]

Bob, did you get asked to pay a handling charge by Parcelthief as well ?

[bob orbell]

Hi Philip, yes, because the goods came from the USA there could be a customs charge, and I got it . BOB

[bikerhifinut]

Originally Posted by bob orbell

Hi Dave, do people actually pay these crazy prices ?, the two I am using are new and came to me from one of our members, for a small donation to his requested charity, . Don't forget that you may or may not get a bill from customs, I did, and they will not deliver until it's been payed . BOB

If you would rather build the circuit from scratch, and it's simple enough, you can always use the published circuit which is in the public domain. That would save you a few bob and the parts are not esoteric apart from the resistors used in the correction network, but again I wonder just how critical they are?

A.