Phono II advice Please!

[Lyndon Johnson]

Greg,
Lovely to hear from you. I remember you helped me a lot when I was having grief from some KLS 3's that I bought on eBay - (they're sounding great now-thanks).

My 300B P-P is the original 1993 design with the special transformers at the phase-splitter stage. I didn't build this one, I bought it from a forum member 3 years ago and love it.

I will reactivate the CF inside my KLP I anyway, just to put that idea to rest. Then I will try a valve swap as you suggest and take it from there.

Thanks for the contacts and I do hope I haven't offended Mathew. This is a hobby I put down in the early 00's and since then have just dipped in occasionally - so I am out of touch with the 'World'

[Lyndon Johnson]

A small correction - I have just taken the lid off my KLP I and the Panasonic pot is 40k. (motorised).

[Phil Y]

That should be fine. It was just a thought that if it was very low in value it might have been loading the o/p of the Phono too much and effecting performance.

Phil.

[Lyndon Johnson]

***Update***
I have now restored my KLP I to 'CF' operation and tried again.

My verdict now is that things are a bit better and I am no longer convinced that my KLPP II is faulty. Playing it back-to- back with my Hart I would say that it is still less dynamic and with a leaner sound but other than that, probably comparable.

I need to further correct my statement about the Panasonic Pot it's 20k not 40k! (I wouldn't make a very good witness!).

Do you think that this could be still playing a part? The original Alps blue was 50k.

[Greg.]

You are being trapped (owing to other posts here) into exploring things that are not really that relevant. Your issue is the performance of your Phono ll, and not your cathode follower pre. I understand, you’re looking for an easy way out.

Let’s get back to thinking on the Phono and the specific problems. Have you tried a new set of valves? If so, and that hasn’t fixed it, time to get it properly scoped and analysed, don’t you think?

[Richard]

20K is a bit low if Phono has 4K output. WAD used a 100K pot (which mostly sets the input impedance) on original Pres and there may be some loss of frequency response. Certainly worth checking,

http://www.world-designs.co.uk/forum...ead.php?t=7138

[Lyndon Johnson]

Thanks both of you - much appreciated.
I have been wanting to do the easy and zero-cost things first...

On the valves - there seem to be a few different makes and grades of ECC83 available - any recommendations?

On the pot - the 20k Panasonic was a relatively expensive (and highly effective) upgrade - any recommendations how I can match or improve on that quality in the process of trying 100K?

[bob orbell]

Lyndon, if your Phono has had very little use, then the supplied valves will be fine, try some different ones by all means, but you may find it is money wasted, I know I did , I still think your problem is with that KLPP. Bob

[Richard]

Re pots the 100K Panasonic for Audio was about the best I found, sweet, detailed and neutral. Alps 27 is a fraction of the price but always had a signature fog to my ears. Perhaps your Pan 20K version is also very good used with the low OP impedance Hart phono amp but not so with the higher OP impedance Phono for the electrical reason.

Impedance "matching" may be a confusing term. For best power transfer we match the output and input impedances. We don't want that here though (there is almost no power being transferred) we want the full range of frequencies to be transferred. I've always used a rule of thumb of at least 10x for the load compared with source. I think I got it from Bruce Rozenblit many moons ago but a quick Google has this excellent article these days,

https://www.soundonsound.com/techniq...ding-impedance

scroll to Voltage Matching to see if you'll find it interesting or just go back to the 10x rule of thumb.

On valves I tried several and favourites were near eqivs, GE 5751, which Matthew has in the shop,

http://www.world-designs.co.uk/valves.htm

not cheap but I never wore a set out In comparison to regular ECC83 they are less strident and more soul-full but it may well just come down to preference.

[Lyndon Johnson]

Again, thank you both.
While I wait to get my hands on some spare valves I have been trying to think of a way to easily and cheaply test the theory that my 20k pot is putting a strain on the output stage of my Phono II......
I still have the 50K ALPS blue that came with the original KLP 1 kit and thought it could easily be patched in to the earth return from my Panasonic as per the diagram I have attached. Now with the wiper of the ALPS at one extreme it is out of the circuit and at the other extreme there will be a full 70k across the output of my Phono II. Hopefully somewhere between these extremes is a suitable listening volume where I can hear my Phono II driving significantly more than 20k.

Does this sound sensible?

Thanks!