Pre-II Cath. Foll. wiring query.

[buddam]

Hi all

I'm making a PreII CF this week-end, but without the usual first stage of making a PreII. I'm not sure of the wiring arrangements, and the WAD site 'sample only' diagrams aren't absolutely clear. Heater wire seems clear enough, and earth too. But wanted to check high voltage wiring before I fire up, especially since voltage is double that in the old PreII. Am I right that wiring to PCB from transformers is replaced by new wring direct from Cliffcon socket to PCB?

Thanks

Adrian

[Greg.]

Hi Adrian,

You've not said if you are using the converted Pre II board or hard wiring as I have.

If you are using the Cliffcon socket at the rear of Pre II, then two wires from Cliffcon pin 2 carry the 200vdc HT to pins 1 and 6 of the 6922. Cliffcon pins 1 and 4 are the heater supply to valve pins 4 and 5. Configuration is not important here. Cliffcon pin 3 is earth.

I hope that helps. Email me your phone number and I'll talk through with you if you like.

Best wishes,

Greg

[buddam]

Hi Greg

thanks for that. I'm actually going to hard-wire on top of the pcb, which will be used for the valve base only.

Home phone is 0207 249 9653. Best if you let me have yours - I could phone when I get round to soldering later this evening

Adrian

[buddam]

Nearly done but have a small query. The FAQs say

"Solder to the input PCB pins one end of a .047uF (47nF) quality polypropylene capacitor, the signal input is to the other end of the capacitor... This capacitor is necessary to isolate the Volume control from any DC leakage, do not omit it!"

The query is, surely the end soldered to the pcb i/p pin (or if hard-wired the end closest to the volume pot) is the end that takes the signal i/p. To my eyes, the cct diag also suggests this, although I see the arrow from the cap to volume pot.

I'd appreciate it if someone (greg, are you there?) could clear up my confusion before I fire up.

Thanks

Adrian

[Greg.]

Hi Adrian,

As you are hard wiring, referring to Neal's notes on the use of the PCB can bring confusion. Those notes were written by Neal so that with little alteration, the original PCB and it's circuit could be used to make the conversion.

In your case it is simply, input from the 'phono in' goes direct to the pot and then signal goes direct to the end of .047uF cap. Earth from the pot returns direct to the earth post.

Best wishes,

Greg

[buddam]

everything measures ok on both psu & preII, but i'm mystified as to why the instructions refer to 6.3vdc to heaters when i'm getting 44v & 51V which according to the psu test point data is correct. Can anyone say how this figure becomes 6.3V and why the 2 halves of the valve seem to be fed different voltages?

Rather reluctant to put my Mullard valve in till I get an answer.

Thanks

Adrian

[Global]

Going by a memory of a circuit I don't have but........

51 - 44 = 7 which is nearly 6.3v.

The effective heater voltage is the difference between the two readings. The heater is raised above 0v so that the cathode - heater voltage does not exceed the insulation capacity. The upper (higher voltage) half needs the heater potential raised.

Sounds OK to me.

Mark

[Cyprus Martin]

Hi Adrian,
Have you got it fired up yet?
Interested in what you think as I'm delighted with the way mine turned out - no hum, good response and clarity. I got rid of the Alps and used a Goldpoint attenuator.

[buddam]

Firstly, thanks to those who gave advice on a job now well done. Particularly to Greg for BB and phone advice.

Secondly, was going to write up my findings last night but could not connect to the BB. No time now until tomorrow evening, when I'll post long reflections. By then it should have another 8 hours burn in under its belt, taking it to c.30. I'm hoping that something magical happens at 100hrs since at the moment I'm a little underwhelmed. I've long suspected that my Dave Berriman kit DBS7 floorstanders might not be revealing changes up-stream. But could be wrong

Adrian

[buddam]

Well, after 5 days running in the Cath Foll Pre II here are my impressions.

1. It's a nice integrated sound with no obvious accentuation of any part of the freq range. At first there was a definite lack of bass, but this has now filled in nicely.

2. I used all new components - including Kiwame resistors and Dynamicap caps - plus a NOS Mullard gold-pin E88CC (thanks to Steve Shiels). So perhaps the sound will improve further in the coming week.

3. Greg suggested on the phone that I might lose the last degree of detail that I was used to on the passive pre (with Panasonic pot & pseudo shunt mod using Vishays), but I have barely noticed this as run-in has progressed.

4. Nevertheless, I am a little disappointed that the system has not been transformed to the extent I'd hoped for/expected. I've long thought my system sounded rather 2-dimensional and 'wooden' (for want of a better word). I'd hoped for a more tarnsparent and walk-in sound that enveloped me in musicality and emotion. That hasn't happened, which leads me to wider issues.

5. What I've found over the last year or so is that boutique parts (some costing considerable money) provide an opportunity to tune & refine a system to a limited degree, but the basic configuration/design of its elements is of greater significance. So, I'm now considering whether the KEL84 and Dave Berriman DBS7 kit floorstanders (linked via twisted twin Cat5 cable) are the weak points. Other gear is Phono II, Pioneer DVD575 (tweaked a la Global/Mark), Garrard 401/Rega OL 250, Dynavector DV 20-Low. The power for all this passes through a Swampy filter.

6. All my kit is heavily modded - I've just a few mods left to do (a few Kiwames in KEL84, a change to the KEL84's choke to one from Phil @ Bluebell...). But I suspect that even after these mods I'll hanker after the WD 300B PP promised for the summer and a pair of either IPL TLs with ribbons or the WD floorstanders which I hope to hear at the phono meeting.

7. 2 final points. a) has anyone installed a switch between passive & active on the pre? Are there any issues stopping me taking the signal from the pot and switching between sending it to the preII circuitry and direct to output phonos? b) I think it was Clive who installed a switch on his PhonoII to protect valves when listening to another source. Am I right that it's best to switch the 200V off rather than the 6.3V for the heaters?

Thanks again to all who helped on this and looking forward to hearing others' results at Phono week-end

Adrian