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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

bob orbell 6th July 2020 08:23 PM

Re: Cathode Follower
 
Quote:

Originally Posted by John Caswell (Post 91373)
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

But before you try and borrow some, try this, simply remove the interconnect you are thinking of changing, clean the terminal ends, replace and listen, you may be surprised, ;) fancy cables are a rip off. Bob

Greg. 6th July 2020 10:14 PM

Re: Cathode Follower
 
Lots of things to think about here from Richard’s take on various pre performances to how long should your interconnect cable be.

On cables, I strongly suggest you make your own interconnects by buying the cable and connectors and solder it up yourself. Much cheaper and you will get best connectivity/performance at a fraction of the price of a commercial product. All my Interconnect cables are home constructed for the best part of the last 30 years. Making your own means you can be specific about length and I have always applied a rule that as short as possible is best, at least with analogue cables. Digital is a bit different. Shout out if you want guidance on good cable to make your own interconnects.

I was not involved in Richard’s pre amp performance comparison so can’t comment on that. All I can say is that I originally had a Pre2 which, because of close proximity to the power amp hummed. I converted Pre2 to passive. Hum went away but the sound was a bit flat. I introduced the cathode follower mod and the sparkle to sound came back.

Moving on, like Bob, I fitted a CF circuit as per the FAQ which, realise is nothing to do with WAD. Certainly the circuit was used in earlier Hi-Fi World (WAD) DIY products, but the circuit has been around for years, and for best interpretation, read ‘Valve Amplifiers’ by Morgan Jones. I found that the CF circuit brought life and detail back to the sound. I was not aware of any frequency limitation or poor channel separation. I was well chuffed with the result and hung onto it. Like Bob, that sent me to discover the ‘Glassware Audio Design’ website and in particular their CF Aikido circuit. I incorporated that and it was a sound revolution. So quiet in the background and so alive in presentation of all frequencies. It really was a revelation in sound.

I have moved on and no longer use this kit, but for nostalgic reasons, I have retained my WAD 2A3 PSE and have bought back my pre amp units which includes the Glassware CF. A great combination of kit to listen to for a bit of fun every now and then.

emollusc 7th July 2020 09:34 AM

Re: Cathode Follower
 
Thanks guys for the replyies they are most useful.

Don't worry John I have no intention of cutting up my existing interconnects as you never know when you might need the extra length.

Greg, great minds think alike, I was intending to make up my own cables, using some silver plated phono plugs I have found from China that look like they are worth a punt, but I've yet to decide on the cable.

My original thought was to pumb in the WD CF circuit, but I will do a bit of research first to see what my options are.


Brian

John Caswell 7th July 2020 10:43 AM

Re: Cathode Follower
 
Brian,
You are now entering a world of snake oil and the like. Some home made cables are rubbish and some are very good, to whit Greg used a TNT cable consisting of stands of cat 5 network cable, which he swore was the cats whiskers but someone else tried this same cable on a Naim amp and it was goodbye output transistors. As I keep telling customers "nirvana doesn't exist"
There are lots of good basic cables out there without paying a fortune and you certainly don't need to get dragged into the "Well it cost £6000 so it must be better" disease. My usual answer to that comment is "define better" Often met with a blank stare:confused:
You will need to "cut the coat etc" There are lots of cables I would like to try but as my cable run is 11 Metres and I biwire that is goodbye to 44 Metres! Even the so called affordable L/S cables at £200/metre would equal £8800. I think not!

John

pre65 7th July 2020 11:33 AM

Re: Cathode Follower
 
I needed to make up some long interconnects from preamp to monoblocks sited by the speakers, about 4Mtrs.

I searched online for info on good, but inexpensive, and ended up ordering some Sommer 300-0024 Tricone MkII Unbalanced Cable (Green). It should be delivered today/tomorrow, so I won't know what it sounds like for a while, but at £0.98 Mtr it's worth a go, and it looks good ! Other colours are available.


https://www.studiospares.com/Cables-...een_546830.htm

What type of plugs to fit is another conundrum.;)


*

Richard 7th July 2020 12:56 PM

Re: Cathode Follower
 
Quote:

Originally Posted by emollusc (Post 91369)
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


Hi Brian,

I used 0.5M of low cap cable (100pf/M). I agree with John that 1M should be no problem but be aware some real cheapies can be several hundred pF/M.

The comparison day was very enjoyable, quite a while ago now 2006, and included a lot of what we are still discussing in your recent threads. Nice to re-visit those days.

I've dug out 2 threads, the first about the 300B stereo amps and clone versions made by Greg and friends, and the second about the meet up we had to listen to them, pre-amps, SB, dacs etc. Wordy but you might find parts of interest :thumbsup:

Old 300bpp Ringing

300B PP NottFest Meetup

bikerhifinut 7th July 2020 02:25 PM

Re: Cathode Follower
 
My sixpence worth...…….

Using a CF or transformer output preamplifier circuit, (Or for that matter a simple op amp buffer or emitter follower in silicon) will give you a nice low output resistance which more or less means cable capacitance hasn't got the effect, if any, that it would if connecting things up off the wiper of a pot or switch in a passive volume control ( you can't really call it a preamplifier to my mind).
So That's one concern out of the way.
I'm 100% with Bob on the relative merits of expensive connecting wires. And Bob and I don't see eye to eye on everything but here we do.
For a while in the old listening room I was using a 10m length of cable from preamp to power amps due to the layout I was using. I first had some fairly basic single core screened cable (it claimed to be OFC copper but who knows). That seemed perfectly satisfactory to me and I couldn't detect much if any difference to my usual 1.5m of the silver plated soniqs branded stuff from Matthew. Incidentally if making your own wires up that's a good value product and looks quite sexy...…….
Then I tried some bandridge "professional" microphone cable. It was cheap from maplins at the time in one of their regular stock clearances, wish I'd bought the drum of it when they closed down for a tenner! Again it was excellent, I wired it up "semi balanced" i.e the screen only earthed at one end and the inner wires completing the circuit. I had a Hum loop issue at the time, I never really got to the bottom of it and since then I have moved to a new listening space and also rebuilt the power amp, reverting to a stereo rather than the 2 monoblocs. And also the WD KT88 amp now is set up as an integrated with the relay board and a home fitted Hi Fi Collective remote volume control.
Anyway I found the "Cooking" pro grade mic cable to be every bit as good as any fancy stuff I have odd examples of.
As Greg says...…… your mileage may vary.

I also have the Aikido CF board in a pre3 case. It's about as good as any CF gets, again I think you'll find very little to choose between that, the current WD CF kit which will be excellent value as a kit of parts, and a standard "Bootstrapped" CF circuit.
Confession time now...….. my preferred preamp these days is a solid state Rega Cursa3 which I really like, its very neutral and has the advantage for me of having an easily adjusted gain setting in 3 steps from unity to enough to drive a pair of quad11s that need 1.4 Volts on them.

here's a good explanation and practical example of a Bootstrapped CF
http://www.valvewizard.co.uk/accf.html

Andy

Greg. 7th July 2020 03:26 PM

Re: Cathode Follower
 
Quote:

Originally Posted by John Caswell (Post 91384)
Some home made cables are rubbish and some are very good, to whit Greg used a TNT cable consisting of stands of cat 5 network cable, which he swore was the cats whiskers but someone else tried this same cable on a Naim amp and it was goodbye output transistors.

John

Hang on John, this discussion is about interconnects. I have never used cat 5 cable for interconnects and for years have always used the WD Soniqs cable or the slightly heavier duty version sold by IPL Acoustics as IC2.

I followed the TNT recipe for ‘Twisted Twins’ speaker cable and for sure, like many others, found it to perform excellently. It is also well documented that this is a high capacitance design which is fine for use with valve amplifiers with O/P transformers. The likes of Naim and NVA have always warned their customers that high capacitance speaker cables are not suitable and will damage their amplifiers. The example you gave does not indicate a bad DIY cable, but rather user error. I no longer use cat 5 and have settled for single runs of Bluejeans (Belden 5T00UP) cable as I found no benefit to bi-wiring. It just doubles the capacitance and doubles the cost, IMHO.

John Caswell 7th July 2020 05:35 PM

Re: Cathode Follower
 
I don't believe I said or even implied that you used cat 5 as "interconnects". If L/S cables aren't interconnects then I don't know what they are.

John

pre65 7th July 2020 06:03 PM

Re: Cathode Follower
 
Must admit I've always understood "interconnect" to refer to a cable connecting two pieces of equipment other than loudspeakers. But that's just me.

John Caswell 8th July 2020 09:08 AM

Re: Cathode Follower
 
Just thinking, about it I cannot see any reason why you could not use Screened Cat/6 as an "interconnect" after all they have all the necessary attributes, insulated cores, a screen, insulated covering. It would probably sound OK as well in short lengths. It would probably work well as a balanced cable as all the cores are effectively twisted pairs. Must try some experiments.

John

emollusc 8th July 2020 01:42 PM

Re: Cathode Follower
 
Quote:

Originally Posted by pre65 (Post 91388)
I needed to make up some long interconnects from preamp to monoblocks sited by the speakers, about 4Mtrs.

I searched online for info on good, but inexpensive, and ended up ordering some Sommer 300-0024 Tricone MkII Unbalanced Cable (Green). It should be delivered today/tomorrow, so I won't know what it sounds like for a while, but at £0.98 Mtr it's worth a go, and it looks good ! Other colours are available.


https://www.studiospares.com/Cables-...een_546830.htm

What type of plugs to fit is another conundrum.;)


*

Really low capacitance as well!

I have ordered 10m of the Sommer 300-0272 Tricone XXL Advanced Instrument Cable (Blue) for less than £20 delivered. It's basically the same as the Tricone MkII but with a 0.5mm² core.

My plugs are coming from China and so will be a while, but if I like the combination I can slowly replace some of my more annoying interconnects.

A Stuart 8th July 2020 09:54 PM

Re: Cathode Follower
 
Quote:

Originally Posted by emollusc (Post 91410)

As a matter of interest - can anyone explain how the Insulation resistance is 1Gohm per km length, but only ~0.3Gohm per 1000 feet (~one third of a km)?

Not like me to be nit-picking or anything :confused:. Just a typo or am I misunderstanding some fundamental?


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