WAD Phono 2 noise.

[jemm]

Hi all,
I built my MM-only.Phono 2 about 6 years ago. A teething problem was sorted out with the help of Forum members and has not recurred. I've been really happy with it and currently using Denon DL110. It's always had a small amount of background hiss, but I have the impression this has been more apparent recently. Right and Left channels are equal, and the music otherwise still sounds good. No other relevant system changes.
Any advice would be appreciated. I wondered if valves needed changed.
Maybe I've just got the volume turned up a bit more!(but I don't think so).

[Greg.]

Were your Pre II valves supplied as new or did you use something used? Has the increase in hiss appeared with the introduction of the Denon DL110?

My inclination would be to swop your valves around first and if that makes no difference, try a new set of valves before doing anything else. It's always good to have a spare set anyway.

[bob orbell]

Hi jemm, hiss is normal at high volume with all phono stages, more so with M/C, can you hear it when playing music? or just with the volume turned up, what is your amp.? int. or pre power, what make? Do try as Greg. says, and let us know. BOB

[John Caswell]

Hi Jemm,
One of the problems with all phono stages is the high amount of gain. The nett result of this is such things as "shot" noise in the valves as well as "Johnson noise" is amplified as well. If after swapping valve around you still have the problem then you need to try some of the following ideas - New/NOS valves, I have found some of the modern ECC83/12AX7 although measuring to spec are useless in the noise area, my own phono III now has Mullard/Brimar ECC83 selected for lowest noise. - Change the anode/cathode/grid resistors in the first and second stages for metal oxide or similar types - if you can afford it, bulk foil types in the first stages work very well but are very expensive at about £15-20 ea.
With these ideas it is quite possible to get the residual noise levels to down to a point where they cannot be heard at your normal listening levels.

John

[Richard]

Yes agreed with the others plus a suggestion,

I also use the DL160 which is a high output moving coil with about half the output of many moving magnets. This will result in you having the volume control up a little higher and hearing more noise.

Two things I did,

1) as John suggests change the 100K anode resistors R19/20 of the first stage to metal films, the small blue 0.6W from Maplin are fine

2) add bypass caps to the first stage cathode resistors which increases the gain nicely

Here's the bits,

[jemm]

HI all,
Many thanks for your replies.
The main amp is a Marantz PM11S1 integrated. It has an internal MM/MC phono stage. Using the internal phono on MM with DL110, there is no hiss even at quite high volumes. But the music sounds way better through phono 2! The hiss is not intrusive when music is playing, but is audible in the silences(if you see what I mean). I listen to quite a lot of classical, so that's a bit of an issue.

Valves are the original supplied.

With hindsight, the hiss may have got worse after changing to DL110 from Goldring 1042. I may not have noticed because DL110 was so much better in every way that I was really delighted with it.

To be honest, I'm a bit scared at messing around with the internals. I confess to being completely ham-fisted and lacking in practical skills and electronic knowledge. I was amazed(but very chuffed) that it worked in the first place.

My soldering skills did improve greatly during the build. As a bit of an aside, I was so inspired that I would have built the remote version of Pre 2 if it had ever appeared(I phoned to enquire a couple of times), and probably kt88 power amp. Anyway, I'm a bit less gung-ho now.

Here's my game-plan:-
1) Swap valves around - that's within my abilities.
2)Buy new valves - any advice on supplier/manufacturer would be welcome.
3)If the above fails, I will take a deep breath, summon up my courage, and seek your guidance about caps etc.,which I hope you will provide in the simplest possible terms.

Thanks again, and I will report back.

Jim

[Phil Y]

Hello Jim,
The output of the Goldring is 6.5mV where as the Denon is only 1.6mV so any noise will be much more apparent.

Regards, Phil.

[jemm]

Hi Phil,

Thanks for the figures. The more I think about it, the more it seems logical that the change from the Goldring to the DL110 may be the main explanation.

I've swapped the valves around, and my first impression is that the hiss is less apparent. I'm suspicious of first impressions and wishful thinking, so I think I'll listen a bit more out over the next few days before I do anything else.

I'll report back

Jim