Phono II advice Please!

[Richard]

You could give it a go depending on the volume pot position you normally listen at.

Due to the way a log track is scaled most of the resistance is on the series end of the divider (above the wiper in the drawing).

At 1/2 way mechanically a 20K pot has approx 17K on the top and 3K on the bottom. A 50K pot has about 40K on top and 7K on the bottom (similar divider ratio) which makes that setting about -16dB ref max.

So, assuming a usual playing volume of 1/2 way position mechanically;

To use the max amount of pot track (highest input resistance) for that -16dB vol setting using the 2 pots you'd wind down the 20K pot to min and set the 50K pot at 3K5 from ground. Phono would then see 23.5K instead of 20K.

You're limited by the 20K max for the series leg and all you can do is vary the 50K shunt. At lower volumes there'd be 20K to 23.5K total resistance. At higher volume there'd be more resistance but even at 3/4 volume level, about -9dB, you'd still only total 31K and for 70K you'd be just -3dB down from max vol.

[bob orbell]

Would it not be more sensible to change one pot for the other, I use a 50k Alps motorised pot and my sound is very good. Bob

[Lyndon Johnson]

I knew it couldn't be that easy!
It's 22 years ago now, but I still haven't forgotten what a massive improvement in detail and clarity that Panasonic pot gave, so I had been loathe to go back to the ALPS. However, in light of your responses I will give it a go and report back.
If the Phono II suddenly starts to shine relative to the Hart then I know where I am going.
Cheers,Lyndon.

[Phil Y]

Lyndon,

If i understand your drawing, you wont be able to reduce the volume to zero.
What about shunt connecting the Alps pot, in my and many other peoples experience this improves the sound. Any old resistor will do and if it works a Charcroft bulk foil resistor can be fitted for further improvement.

http://www.world-designs.co.uk/forum...ead.php?t=5795

Phil.

[Richard]

Hi Phil, I'm reading it that both pots are adjustable so the 20K will function as normal if the 50K has its wiper wound down to ground. (Zero vol would be with both wipers fully down on the drawing.)

[Richard]

A better way to increase impedance whilst keeping the 20K Pan pot would be to add a couple of small 20K fixed metal film resistors to the pot input terminals. It would then look like a 40K pot to Phono. Only downside would be the loss of 6dB through the pot range up to it's max travel but if 300BPP is being used without feedback there should still be enough gain at least for a decent listen. For example, the original level at 1/2 way position would then be found at 3/4 setting. Pic attached.

[bob orbell]

Now I know this may be stupid, but, have you connected the phono to the correct outlet on the Power supply ? it is quite possible that you plugged into the Pre outlet and this is only 100 volts as opposed to 250 volts required. Bob

[Lyndon Johnson]

Thanks Bob, yes, it's connected to the Phono output of the power supply.

Provoked by your earlier message, I set up my old ALPS 50k, wired normally and passive (no CF). This was a bit of a revelation in that the Phono II immediately sounded happier. The sound was noticeably smoother and with a more fulsome bass and I guess, in part, this is down to the sonics of the ALPS pot. My conclusion was that the 20k Panasonic and the Phono II were not a happy marriage.
Switching back to the Hart briefly I felt that the Phono II was now at least as good.

By this point I had my hands on a spare set of (Sovtek) valves, so following Greg's suggestion I swapped over. No real change and I think I preferred the original JJs so I will put those back in.

I could do with a further session of listening but right now I would say it's 'problem solved'. Today I will order some 22k and 47k resistors in order to follow up Richard and Phil's potentiometer suggestions.
Thanks everyone.

[bob orbell]

I would now try the CF with the Alps, you could be surprised. I too use and like the JJ tubes, had mine for over 20 years. On the subject of the shunt pot mod as has been mentioned, try this by all means, but I think that will find the sound too much in your face after some time, I did. On the subject of resistors, I would advise you replace R1 and R6, in PSU, no need to do R4 as you are not using that outlet, to Mills 5w jobs, pricy, but a good upgrade. Bob

[Lyndon Johnson]

I have tried some, but not all, the resistor/potentiometer permutations now.

When I turned over my Panasonic pot to put some series resistors in I found there were some WEL 33k ones already there! I'm guessing that these were supplied by Audio-Links when I bought the pot back in '97. Presumably to make up for the fact they didn't have any 50k pots in stock. So my Phono II has been driving into 53k all along, not 20k.

I tried some Takman carbon film resistors both in series with the Pana and in shunt configuration with the ALPS. Neither inspired me and my favourite permutation so far is using 47k Audio Note Tantalum non-magnetics in series with my Panasonic. This seems to be less strident than with the original resistors but with a more open sound than the ALPS.

Bob - I was interested in your upgrade suggestion of the resistors in the HT supply. I've not heard of this one. I'll be in upgrade-mode soon and will be interested to know what difference I would expect to hear with this particular upgrade.
Cheers