Phono II advice Please!

[Lyndon Johnson]

I posted this yesterday in the wrong section so re-posting a more concise version here:-

Back in 2000/01 my last World Audio build was the Series II Phono amp with power supply, as an upgrade to a 'Hart Linsley Hood' kit I had built some years earlier. (I didn't buy the pre-amp II module as I already had a KLP I that had been converted to 'passive' by removing the cathode follower.)

The build went well, all test voltages checked out (within 15%) and when connected up it was lovely and quiet, no hum or hiss.
However, I was disappointed with the sound - it seemed a bit 'ragged' and generally uninspiring. Thinking that it just needed running in I ran it for a couple months but found no improvement. So I reinstated my Hart and satisfaction returned. Eventually my Phono II went up to the loft.

It's back down from the loft now, test voltages rechecked (still within 15%), still quiet and still sounds muddled and uninvolving with little dynamic range.

One thing worth mentioning is that I still use that passive pre-amp, so the Phono II is feeding directly into my WAD 300B PP via a potentiometer.

Any ideas where I should be looking to pinpoint what is wrong?
Many thanks,
Lyndon.

[bob orbell]

Well Lyndon, the CF would have been my choice and the passive would quite possibly be the reason for poor sound, the CF as you most probably know has no gain, but nor does the passive, what the CF does have is current gain and this may be the weakness in you currant set up. You have not mentioned your turntable arm and cartridge, it may be helpful to know. Bob

[Lyndon Johnson]

Thanks for your response Bob. I use a Linn LP12 turntable with an Origin Live DC motor. The cartridge is a DNM Reson MM.
My old Hart Phono unit sounds great in this set-up but maybe it's design better enables it to drive my power amp without any further amplification or current gain.

I disabled the CF section of my KLP1 soon after building it because I couldn't get the hum down to a acceptable level. In light of your comment though it sounds like I should reinstate it and see if that allows my Phono II to perform as it should.

An even better option would be to lay my hands on a Pre II but I fear they are rare now!

Lyndon.

[Phil Y]

Hello Lyndon,

What value pot is in the passive Pre?

Phil.

[bob orbell]

Lyndon, the Pre II was, in my opinion, because I had one, ****, the Pre III however is light years better, as would be the Pre III CF from Mathew, but for me I use a John Bronski Akido Cathode Follower based on CF with active load, or it can be built as a White CF, most power amp's do not need any gain and my WA 88 sounds very good being driven this way, this system will now hopefully take me to the end. Bob

[Lyndon Johnson]

Phil,
It will be 100k, a Panasonic one, fitted as an upgrade in 1997 to replace the Alps Blue that came with the KLP I kit.

[Lyndon Johnson]

Bob,
I was interested in your comment about the Pre III CF. Who's Mathew?

[bob orbell]

Matthew owns World Design and the forum, very nice chap, go to the bottom of the page, right hand side - CONTACT US or WORLD DESIGN for the products. Bob

[Greg.]

The right honourable Matthew Snell, proprietor of this forum and WD.

From what has been said, I think considerations around your passive pre is a red herring, particularly if it works ok with your PLH Phono. The Panasonic is an excellent well balanced pot and driving it with your Phono ll into the 300B PP should work very well albeit, changing to a cathode follower option would bring a bit of sparkle to the sound.

Which 300B do you have. Is it the original circa 1995 single chassis amp or the later mono-blocks?

I am inclined to think the issue is, as you suspect, in your Phono ll. The original Phono ll was a fine phonostage. Although I’ve moved on with my system and sold mine, I like and respect it so much that I’ve asked the buyer to give me first option on a buy back should he ever decide to sell it.

As your voltages are all correct you know it is operating as intended, so my suggestion would be your next step might be to get it checked out using a scope to see if you can identify where in the circuit the problem is coming from. You may know someone in your locality, or you could approach Nick Gorham who lives in Halifax as he is happy to do this sort of thing. He is contactable through his LDA company email (don’t let the company bit put you off. He is a historical user of WAD gear and is very happy to help out other hobbyists) info@longdogaudio.com Otherwise, if you are willing to post, John Caswell of this parish would, I know be very happy to help you out.

I hope that helps a bit.

[Greg.]

PS. I think before getting it scoped, I would try another set of valves first.