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-   -   Cathode Follower (http://www.world-designs.co.uk/forum/showthread.php?t=7924)

emollusc 5th July 2020 01:04 PM

Cathode Follower
 
My existing pre-amp in basically a passive Pre2 with a DACT CT2 (50K) volume control and a DACT CT3 selector switch which works pretty well. I'm thinking of converting this to a Pre3 CF by inserting the relevant electronics.

Having no experience of a CF, I would be interested to understand what difference this change would make, if any?

Also, I'm assuming that I could keep the existing volume control and just plug in the electronics?


Brian

John Caswell 5th July 2020 03:03 PM

Re: Cathode Follower
 
Hi Brian,
Last question first - You would require all the bits for a Pre3 CF plus a PSU of some sort and the necessary interconnecting cables.
Advantages - A relatively low impedance output enabling you to use longer leads, simplicity itself. Can keep existing Vol control/input selector
Disadvantages - loss of gain -0.9dB, Large capacitor to isolate output DC, power supply and all attendant bits, cables etc.
As to how it would sound, I will pass on that, suffice to say I work on the Dr Lanchester principle "if it sounds right it is right" He quoted the maxim "If it looks right it is right" which applied to aeronautics
I know that this is going to create howls of protest here, but the only real criteria are your ears, equipment and listening room, and even music. I have had people say "I don't like the sound" when they really didn't like the music being played

John

Richard 5th July 2020 09:55 PM

Re: Cathode Follower
 
Hi Brian,

Completely agree with John and I/we have had the advantage of a direct comparison between a Passive pre as you have, a WD conversion CF pre, and a Transformer pre in one sitting in the same system a few years ago.

Short answer is the 3 of us all preferred our own, probably due to familiarity.

I had the passive on short i/cs near to the power amp. The power amp for all was 100K input and line sensitive. To my ears it simply offered attenuation and the sound was clear and open. (I should caution that I've tried the same passive pre with a 20K input ss power amp and it wasn't so good, so impedance matching, I think, is important with a passive.)

The CF was good but narrower sound stage and somewhat limited in open-ness and highs but the owner preferred the more focussed and tidier presentation.

The TX was super-sweet and creamy sounding I was amazed. It lacked dynamics and timing compared to the others but did sound special.

It was easy to hear the differences and we all agreed those but had our own preferences.

bob orbell 6th July 2020 06:35 AM

Re: Cathode Follower
 
Reading Richards post I found the TX pre harsh sounding in my system, the passive was OK but weak, the CF did it for me, no gain is not a problem at all, I lived with this set up for a long time but changed to a kit from Glassware, the Aikido CF, this is basically a CF with active load but with significant improvements, and finally a separate power supply for each, pre and phono, with regulated HT, this now all sounds way above any active pre. Bob

John Caswell 6th July 2020 09:59 AM

Re: Cathode Follower
 
Chacun à son goût as they say.


John

emollusc 6th July 2020 02:15 PM

Re: Cathode Follower
 
Quote:

Originally Posted by John Caswell (Post 91361)
Hi Brian,
Last question first - You would require all the bits for a Pre3 CF plus a PSU of some sort and the necessary interconnecting cables.
Advantages - A relatively low impedance output enabling you to use longer leads, simplicity itself. Can keep existing Vol control/input selector
Disadvantages - loss of gain -0.9dB, Large capacitor to isolate output DC, power supply and all attendant bits, cables etc.
As to how it would sound, I will pass on that, suffice to say I work on the Dr Lanchester principle "if it sounds right it is right" He quoted the maxim "If it looks right it is right" which applied to aeronautics
I know that this is going to create howls of protest here, but the only real criteria are your ears, equipment and listening room, and even music. I have had people say "I don't like the sound" when they really didn't like the music being played

John

Hi John,

completely agree with regards to the sound... Like a lot of people I'm always open to improving the sound, but understand that a lot of changes are a bit of a punt as you don't know if you like the change until you've spent the cash.

As I see it all I'll need is the electronics + power cable as I already have a PSU2, and a passive pre2 case with connections etc. Not sure, but I might even have a spare power cord kicking around.

Loss of gain should not be a problem as I'm currently at around about 1/4 turn from minimum volume.


Brian

emollusc 6th July 2020 03:13 PM

Re: Cathode Follower
 
Quote:

Originally Posted by Richard (Post 91363)
Hi Brian,

Completely agree with John and I/we have had the advantage of a direct comparison between a Passive pre as you have, a WD conversion CF pre, and a Transformer pre in one sitting in the same system a few years ago.

Short answer is the 3 of us all preferred our own, probably due to familiarity.

I had the passive on short i/cs near to the power amp. The power amp for all was 100K input and line sensitive. To my ears it simply offered attenuation and the sound was clear and open. (I should caution that I've tried the same passive pre with a 20K input ss power amp and it wasn't so good, so impedance matching, I think, is important with a passive.)

The CF was good but narrower sound stage and somewhat limited in open-ness and highs but the owner preferred the more focussed and tidier presentation.

The TX was super-sweet and creamy sounding I was amazed. It lacked dynamics and timing compared to the others but did sound special.

It was easy to hear the differences and we all agreed those but had our own preferences.

Thanks Richard,

what a fantastic opportunity to test all three types of amplifiers. Sounds, like I would need to 'suck it and see' or 'hear' in this case to see if I liked the change.

What do you class as short interconnects? I have 1m pre to power connections but I'm considering replacing them with low capacitance 0.5m ones. This is mainly due to DACT recommending a 10K attenuator and low capacitance interconnects as this increases high-end bandwidth and I have no intention or replacing my 50K attenuator due to cost. DACT have provided a attenuation curve calculator which may be of interested.


Brian

emollusc 6th July 2020 03:16 PM

Re: Cathode Follower
 
Quote:

Originally Posted by bob orbell (Post 91364)
Reading Richards post I found the TX pre harsh sounding in my system, the passive was OK but weak, the CF did it for me, no gain is not a problem at all, I lived with this set up for a long time but changed to a kit from Glassware, the Aikido CF, this is basically a CF with active load but with significant improvements, and finally a separate power supply for each, pre and phono, with regulated HT, this now all sounds way above any active pre. Bob

Thanks Bob,

are the power supply changes detailed on this forum anywhere?


Brian

John Caswell 6th July 2020 07:34 PM

Re: Cathode Follower
 
To be perfectly honest I would doubt if you will hear/notice any difference. Before you commit hari kiri on a new set of expensive cables see if you can borrow some.
1 Metre is not too long a length to worry about.

John

bob orbell 6th July 2020 08:16 PM

Re: Cathode Follower
 
Quote:

Originally Posted by emollusc (Post 91370)
Thanks Bob,

are the power supply changes detailed on this forum anywhere?


Brian

Not yet Brian, I have been trying for months to get one to work properly, now I have, all I will say at the moment is that it uses a LD1084 regulator chip and a IXCP 10M45S constant current source chip, I have one working at 200 volts DC and the other at 250 volts DC :thumbsup:. Bob


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