help! moving coil hum with tube amps

at the moment i don't have a the cartridge, but i had hooked up the exp head amp to give it some time to settle. there is however, quite noticeable hum.

i have replaced my un shielded interconnects between the 2se and the pre and between the exp and the 2se. the tonearm cable is also shielded. between the pre and the power amp the interconnects are still unshielded as is the one between the cd and the pre.

all the units except the turntable motor, are run through wm's power master, could that be an issue, tony?

graham slee recommended putting ferrites on the speaker cables, near the amp end. does anyone have any thoughts, or better ideas? i don't think the speaker cables are shileded, would this be an option, or benefitial?

any ideas? do i have to scratch the slee stuff and try something else?

 

Hum is an earthing issue so ferrites aren't going to do anything. Earthing problems can be a bitch as it's often the last thing you expect it to be - finding it is a process of elimination, and is t-e-d-i-o-u-s.

 

I get a tiny bit of hum that I've never managed to get rid of, it comes I think from the transformers on my amp interfering with the phono stage. I can't move them any further away, and it only seems to me that is paranoid enough to hear, I just live with it now. Every so often I move all the wires round but to no avail.... It's one of the problems of amplifying a very quiet source your MC cart

 

graham said that it was to do with tranformers and the tiny signals involved. he even said it was not the best idea to mix mc and tubes... still there has to be a solution. the cart is going to have a much lower noise floor than what i'm getting from the phono amplification!

 

Hi,

Well, first, if you do not get the same hum with line level sources AT THE SAME VOLUME STETTING, you can absolve the tube amplifiers from blame.

Secondly, it is possible that the headamp/phonostage pick up noise, this is best tested by making a pair of shorting plugs, insert them first into the input of the MM Phono stage and test for noise, then connect the MC Stage with the inputs shorted test for noise. If you get hum try to move the boxes around also turn them to see if this reduced the hum.

If all is still quiet with MC Pre-Pre and MM Pre connected and the MC input shortcircuited, then the Tonarm grounding or tonearm cable screening is at fault.

In other words, work your way slowly forward from the Poweramp/Preamp combo towards the cartridge to eliminate one by one the possible sources of hum.

BTW, as for noise and Tubes, my system is "all tube" and my MC input Tube Phonostage is VERY, VERY quiet, that despite the fact that it is unscreened in a wooden frame/case. As usual, it is not what you do that matters so much as the how.

Ciao T

 

tube amps absolved...

will try shorting the inputs tomorrow.

i have tried grounding the the table to the head amp and to the mm amp, in turn. would it be a good idea to try both at the same time?

what mc stage are you using?

 

Well, I use a (cheapo) tube PS with a (cheapo) MC cart and have no background or hum noise issues. The only "problem" (if you can call it that), is that obviously there is a lower amount of gain, which means that I have to turn the volume up a little bit higher when listening to the TT.

Of course, this raises the "noise floor" higher and possibly near the levels that your ears are more sensitive too.

Certainly doesn't spoil my enjoyment.

DT

Anyway, if you're going to do the whole vinyl "thang", you might as well go the whole hog and have MC carts, tube phono stages and tube amplifiers. Its all about euphonics, man :MILD:

 

BTW, nice system Blake. I can see myself getting a VPI scout front end and EE pre and some point.

DT

 

Hi,

My own Design.

Input is a Stevens & Billington TX-103 MC Stepup, to get from MC levels to MM.

The actual valve circuit is derived from the old German Telefunken/TAB Microphone Preamplifiers (which in turn go back to an interesting if sinister german research program from the mid 1930's) using high performance german valves (Siemens E810F input and Siemens D3a output) with a Stevens & Billington 600 Ohm LCR RIAA EQ Module between the two stages.

Pretty overbuild powersupply to go with that, loads of Chokes and 6pcs of 120uF Ansar Film Capacitors, no electrolytic capacitors anywhere except heater supply (which is also choke filtered), basically "all out" on all counts.

Overall I get 66db Gain, very low noise and the ability to drive the Stevens & Billington Volume Control Transformers without problem.

So the whole preamp part of the system from MC Pickup to Poweramplifier is 2 Valve Stages, no feedback 2 Coupling Capacitors, one LCR Module (2 Inductors for EQ, 5 Resistors and 2 Capaictors for impedance compensation) and two transformers with overall up to 72db Gain (same as CAT SL2 with overall six stages, but no transformers!!!) and very little noise at all and no hum.

Here a picture:



The button between the two front valves selects the 3 available inputs (for my three tonearms), as I often change stuff the connections are on top (which looks untidy but is very convenient), the big metal cans are the RIAA Modules and Input Transformers.

The matching linestage was this:



This was build into an Opera Reference Line Stage Case (you could say it was the prototype for the Opera Reference 1.3 Passive preamp).

All the information needed by experienced to build this Phonostage is in the Public domain, a few copies have been build and and well received, next to CAT's, Aesthetix and other serious High$$$$ gear. Cost in parts etc around £ 1,000 plus a lot of time.

Ciao T

 

Hi,

I can only comment on the way I'm handling that for the Music First Audio MC Stepup and the forthcomming Phonostage (which is a variation on my "all out" DIY design).

There the recommendation is as follows:

1) Connect tonearm (and turntable where applicable, eg. the Oracle Delphi I used to have) ground to the MC Stepup's ground post.

2) Connect a second piece of wire (decent crossection, silverplated PTFE insulated is worthwhile IMHO) between the MC Stepup Ground Post and the Phonostage Groundpost.

3) Use screened interconnects between MC Stepup and MM Phonostage.

4) Experimentally, if neccesary try running a seperate ground wire from your turntables metal parts to the MC stage, similar to how this was done on the Oracle, that was in the specific case a cable from the floating subchassis to the Motor unit and from there to the MC Stepup.

5) If neccesary consider increasing the distance between the powersupply transformers in mains powered gear and the MC Stepup/MM Phono signal sections.

With the above I invariably got the the humiest combinations quiet, unless there was a severe design fault somewhere (at least one I was responsible for myself, learned from that too).

Ciao T

 

i will give it a go.

i'd be curious to try a different mc stage in it's place to see if that resolved the problem too.

i have to say for a diy effort that's a huge amount in parts!!! they must be premo premium parts!

you based in london?

 

I am bit out of my depth on technical matters but when we moved into this house five or six years back my system picked up a lot of hum through the amps( I bi-amp using Talk Tornado monoblocks) and cured my problems by undoing my 13amp wall sockets and tightening all connections.
It worked well for me so I thought I would pass It on.

 

Cant wait to listen!

 

I've found the VPI does pick up hum far more than my Rega ever did,the only cure was to keep the phono stage well away from everything else,turn off digital sources,and make sure the cart loading is absolutely correct,if not it will really hum,the Rega didn't at all.

 

Hi,

Well, it all adds up. The S&B Transformers are very good but priced accordingly, a 6-Pack of custom made Ansar 120uF/500V Film capacitors , 9 Chokes, a powertransformer more suited to powering a small power amplifier and a load of rare Old Stock valves with spares all add up.

I was quite shocked at the total once I added things up as well...

Yes, Edmonton.

Ciao T

 

i have to admit, that's a bit of london that i hadn't even heard of before. i had to check it on streetmap.co.uk.

 

Of probably no consequence, but I'm running the same preamp and (with a Dynavector P75 phono stage) there's no hum when using a MC, which would suggest that the preamp is probably fine as you concluded. Hum can also come from RFI - depending on how close your cartridge is to the nearest big transformer. Looking at the avatar you have, the turntable is only inches away from your Wadia, and it could then be something to do with the way it's arranged. Have you tried moving the turntable or cd player apart, so that there's a bigger gap?

 

i will have to have a look at the placement of the components. i am planning a wall shelf at some point.

actually the thing that jsut occured to me is the whole lot is still hooked up to a (broken, ie. no needle) dynavector 20xh. high output model, could this have anything to do with the hum?!?! i think i might have to waite until the new low output mc is in place to know for sure.