Noisy Phono3s

[pre65]

I'm trying to optimise my vinyl replay.

The 401 now has a slate plinth, and the 811a SET amp is just wonderful, but the background "noise" from my Phono3s has now become intrusive.

Some time ago I replaced the CF valve with (I think) a 5751 from our Bob so perhaps the first step is two more low noise Ecc83 type valves.

Anyone got two to dispose of ?

Also, I seem to remember Dave Cawley saying that there were "earthing mods" on the Phono3 units he had re engineered for Matthew to sell. Any ideas what these earthing mods were ?

[bob orbell]

Philip, I asume you have the earth wire from the arm to the phono earth post, dose it make any diffrence if you remove the pickup arm plugs from phono, are you using SUT's, my phono 3 is very quiet, but if the arm earth wire is removed it becomes noisy. I have 2 mullard ECC83 valves that you can borrow or buy but don't think it will be the valves. BOB

[pre65]

Hi Bob, removing the arm earth wires from the phono, or even removing the arm interconnect does not stop the noise, or even alter it.

The noise is not hum, just hash and increases as the pre3 volume pot is wound up.At normal listening levels this hash can only be heard on very quiet passages when playing.

I'm using MM at the moment as I don't currently have a MC cartridge.

On the CD input Pre3 is as quiet as you want.

[John Caswell]

Hi Philip,
Earthing is most unlikely to affect this problem. ,I am guessing that this is a "standard" phono III built with the supplied components which are ordinary commercial types good but not that good.
So first thing to do is swap the ECC83/5751 valves around to see if this reduces the noise which is a combination of "shot" and "johnson" noise from valves and resistors and is inherent in high gain stages
Once you have the quietest valves in the first positions, if the noise is still obtrusive it can often be reduced by changing the anode, grid and cathode resistors on the first and second stages for something quieter usually a carbon film/metal oxide type resistor. Anode resistors have the greatest effect then the grid then the cathode resistors.
If you don't have these type of resistors pm with an address and I will send you some.
I have a Phono III and the noise is unobtrusive with signal and only really is a problem with no signal and the gain way up ie 3o/c on the vol control

To give you an idea my system is GyroSEOrbe platter/SME 309/Ortofon Jubilee/Sowter 8055SUT/PhonoIII/PreIII/WAD 300Bpp/ProAc response D28s and at normal listening levels is silent.

John

[pre65]

Thanks John

I guess having quite sensitive speakers is not helping. They are open baffle with a 4 inch Fostex FE127 and an 18 inch Fane bass unit.

I will get a couple of low noise ECC83 variants and see what happens. My other valve pre also uses ECC83 for the phono stage so It won't hurt to have a couple of spares.

[Really Aardvark]

Hi Philip

I've got 3no 5751 by Electro Harmonix as here in my PhonoII

http://www.hotroxuk.com/catalogsearch/result/?q=5751

Slightly less gain but as quiet as anything

[David Roberts]

Hi John,

I was interested to read your comments about the resistors that WAD ordinarily supplied. For some reason, I was under the impression that they were metal film types chosen for low noise. From what you say, this appears to be incorrect... Whilst metal film types are generally considered quiet, does that notion also extend to carbon film types?
Regards,
David

[John Caswell]

Hi David et al,
Well no not incorrect, every WAD/WD phono II/III kit I have built/repaired has had carbon film types supplied which I would expect to be normal given the basic cost of the kit and their noise level would generally suffice, but as Philip says "I guess having quite sensitive speakers is not helping."
Carbon film types are quieter in comparison to "ordinary" carbon types which have generally fallen out of favour, and metal film/metal oxide types are quieter than carbon film. Quite what 'boutique" tantalum resistors are like I am at present not able to say.
The main problem is that given the high gain of Phono stages every little bit of noise becomes apparent and additive and compounds the felony.
You could always go for wirewound at about £10.00 ea or if feeling really flush Vishay bulk foil at about £22.00 max ea. As always the question is, is it worth it?
Of course if you run everything at absolute zero the amp noise problem goes away but the refrigeration plant noise then becomes obtrusive

John

[pre65]

I've been "rolling" a few different valves, and using my single 5751 in left or right channel cuts the noise in that channel. Putting a noisy ECC83 in the CF position did not seem to make any difference.

So looks like a pair of EH gold 5751 are in order, unless Dr John would like to sell a pair of his B339 for less than an arm and leg.

[pre65]

What is the part number of the LDO regulator fitted to current PSU3 builds ?