Klp1

[colin.hepburn]

AH. just realised this KIp1 is the original of the CF pre we have but with an older PSU
Isn’t it what’s the plan Bob

[Greg.]

Yes, I'm also intrigued about what the plan is. Surely if it is just a no gain buffer stage you want, going the CF conversion route as in the FAQ would be the preferred option as you already have the much better PSU in Pre 3. If memory serves me correctly, Neal Gibbons copied the KLP1 circuit anyway, with some reference to Morgan Jones for the FAQ option. Incidentally, I am currently putting together the Glass Ware Audio Design ACF Aikido Cathode Follower to go in Pre2 chassis powered by modified PSU2. Board is stuffed. Just the wiring to do now.

[bob orbell]

Hi Colin, Greg, and all, I have had this board for a long time, it came from the skip at the closure of WD Great Gidding, I also have a transformer, somewhere, that if my memory serves me correctly is, 100 volt with 3.15-0-3.15, secondary, I would like to put it all together and try it, I already use a CF on a Pre II board in a Pre III case and like it, so, it's just a project to keep me amused on rainy days I also followed Bikerhi-finut's Aikido pre, he liked it, so I hope you do too Greg, keep us posted and I will do the same. BOB

[bikerhifinut]

Originally Posted by bob orbell

Hi Colin, Greg, and all, I have had this board for a long time, it came from the skip at the closure of WD Great Gidding, I also have a transformer, somewhere, that if my memory serves me correctly is, 100 volt with 3.15-0-3.15, secondary, I would like to put it all together and try it, I already use a CF on a Pre II board in a Pre III case and like it, so, it's just a project to keep me amused on rainy days I also followed Bikerhi-finut's Aikido pre, he liked it, so I hope you do too Greg, keep us posted and I will do the same. BOB

Just picked up this thread.

Good luck Greg, I think you'll like what you hear on the ACF. What I liked about it was how "Agnostic" the circuit is about valve brands. I think because the circuit uses one half of a double triodes nonlinearity against its other half it irons out those little differences that we attribute to a valves "sound". it's certainly the only design that I actually prefer a cheapo ECC82 in. I found I couldn't really determine any differences between a pair of cheap and cheerful Edicron branded ECC82/12AU7 and a pair of much more expensive NOS Mullards. I did take pains to make sure I used the correct resistor values, to the extent of making a small parallel network on the bottom cathode resistor to get the values "bang on". I plumped for the metal film 1% resistor set with the PCB kit from JB on the basis that he specifies resistor values to 2 decimal places of a kOhm. A bit OCD perhaps but as they are provided in the kit it seemed churlish not to use them. I also modded the heater wiring on the board so i could use 6.3V heaters with 12A*7 series valves (ECC81/82/83). Not so difficult with a bit of lateral thinking and some twisted wire.
Damn good unity gain circuit and as good as it gets in my opinion. I also used his regulated PSU board but that's another story and for my next project I intend to build a brand new PSU3 board up with nice new capacitors before going down any complicated routes. That will be the pre3 circuit for my "one box" preamp.
Bob, here's a curved ball for you, John Broskie has versions of the circuit where he has worked out values for valves that will work nicely with 100V HT. I figure you should get around 130V DC at least from a 100V transformer and that opens out a lot of options for valves without fiddling around with voltage doublers which are the work of the "horned one" I think and only for desperate men as they put a huge stress on electrolytics. Massive ripple currents as I remember from Jones' books. I think an ECC88 type is very happy at 100V HT? And as a friend of mine has discovered, you can even get an ECC82 to work at 24V Ht. I don't think you'd get much voltage swing though............................
Good luck and do let us know how it ends up Greg, I'm very interested in what you think of it.

Andy.

[bob orbell]

Hi all, got this little pre up and running as I type, it does sound very good, there is more bass weight to the music than with my CF pre, and channel separation seams better, out of curiosity, dose anyone know why Neal Gibbons changed the value of two components on his conversion of the Pre II CF, the original uses 33nF input capacitor, NG changed this to 0.47uF, and the cathode resistor was 470 ohms, NG changed this to 820 ohms. BOB

[bikerhifinut]

Originally Posted by bob orbell

Hi all, got this little pre up and running as I type, it does sound very good, there is more bass weight to the music than with my CF pre, and channel separation seams better, out of curiosity, dose anyone know why Neal Gibbons changed the value of two components on his conversion of the Pre II CF, the original uses 33nF input capacitor, NG changed this to 0.47uF, and the cathode resistor was 470 ohms, NG changed this to 820 ohms. BOB

without knowing the anode voltage of the units all I can think is to move the operating point of the valve.
The input capacitor value is fairly arbitrary bob, with the input resistance of a Bootstrapped cathode follower running at about 10meg or more, you can actually get away with 10nF so the bigger cap may just be because he could?
I'd need to see the circuits to make any observations. If it was a fixed bias CF then the input resistance is defined by the grid leak resistor. Bootstrapped ones have a higher input resistance hence the smaller input capacitor.
What's the circuit of the KLP1?
A.

[bikerhifinut]

Another thing comes to mind, What valves are you using?
A CF is one of those few areas where (in my useless opinion) the ECC82 is a good choice of valve because its usually not very good distortion characteristics aren't an issue due to the almost 100% Negative feedback reducing distortion to very low levels. Other valves in the same sort of family could include *SN7 types and 6CG7 which may even sound better, maybe, perhaps.
Another point to ponder, The ECC82 will work very nicely at an HT of 250V so no mucking about with dropper resistors from PSU3. Not that its that much of a problem, and can offer another stage of smoothing/decoupling.
Not bad for what was really a telly valve not originally destined for audio use.
I hope I am making a bit of sense here.

Andy.

[bikerhifinut]

Just did a bit of digging.
As far as I can see, the KLP1 uses 2x ECC88/6922 and is a line only preamp.
Thus I would deduce/assume it probably consists of a standard common cathode triode amplifier feeding a cathode follower output stage.
If that's the case Bob we are comparing apples with oranges I think when pitting this against a straight Cathode follower as differences in presentation/sound quality will be influenced by the characteristics of the ECC88 gain stage, and could explain the differences you are hearing?

Unless they did a unity gain CF only option.

Andy.

[bob orbell]

Thanks Andy,

[bob orbell]

Andy, I tried to put the diagram on post 19, but it is too large, so I will try and explain, ,the KLP1 is a two valve cathode follower, one for left channel and one for right, only half of each valve is used, it is cathode biased, the FAQ, pre II conversion to cathode follower is the same circuit, as the KLP1, but with the two different component value's, as mentioned, the power supply is from a transformer with 100 volts sec. and 3.15-0-3.15 sec. the HT use's full wave doubler, the heater's use 6.3 AC, the C/T is connected via. a resistor and capacitor to the HT rail, I amuse to elevate the heater voltage, the valves are ECC88 / 6922, as I have said, it dose sound more weighty, it is not completely silent, this may be because of the AC heaters, but I can hear nothing from my normal sitting position, next step is to build it in a case and then I may consider the Akido, are you still using yours, if so do you still rate it. BOB