Gear interaction problem drip v72+175b

[Govinda Doyle]

Hey there,
So I have these two great sounding pieces of gear, the drip v72 and 175b!
They don't love each other, by themselves they have not much noise and a great sound, when used for recording they sound amazing together tonally, but the 60hz hum is really annoying, I have tried moving transformers, both units are using R-cores, I tried a Hammond for the v72 but it went faulty after a few weeks of use!!
So I have checked the obvious grounding plane issues, pin 1 and chassis to pin one combinations etc!
Now here's the fun part, if I pull them out of the rack and sit them a foot away from each other the hum is almost acceptable, but when I put them back together (ontop of each other in any combination out of the rack) the big old hum returns! Now the 175b compressor is ok with other preamps, and the 175b is ok if I record with the v72 and add the 175b love post/after the recording, with the v72 switched off!!!
The only other clue I have is that the 175b's R-core has an audible hum to your ears at the same frequency, could the r-core be faulty?
What about if I shielded the tranny?, like with that transformer shielding tape stuff?
Another thing I thought of was the v72's output impedance etc?
This ones ever so annoying!!
Sorry to ask but after a week of fooling around on this one issue I'm kinda stumped!!
Any ideas?
Thank you very much in advance!
Govinda

 

[peters]

I have built these units but have no issue with 60 Hz hum.
They do deviate from the Drip recommended components (especially transformers) and I did my own chassis layout. I like to keep power supply on left, signals on right, see:

http://home.comcast.net/~ps8899/175/
http://home.comcast.net/~ps8899/v72/

The EF86 tubes in my V72 are fairly microphonic, especially at higher gains, so it might be that you are picking up physical hum.

--Peter

 

[Govinda Doyle]

Hi Peter!!
Thanks for chiming in, I built my v72 off your recommendations and added a tweak or two, there is an electrolytic in the signal path of one of the valves, the 10uf 400v, I changed it to a polypropolyne cap, a jantzen, also tried a black solen, the black solen smooths out the high mids if they are shrill and the jantzen pretty much has no sound, I did the mundorf on the output and jenson tranny on the input, massive difference! Really love this preamp!
I had no idea the ef86 was so microphonic, this could make sense of why when stack together in either order I get the hum!! Side by side it's acceptable! Is there anything I can do to shield this noise?
Both my power supplies are at the rear right of the units of you are
Looking from the front panel!
I have been meaning the change the 175b input tranny as I feel the transformers are way to neutral sounding to my ear!
Again thanks for your input, I'm doing some further investigating as we speak!
G

 

[Govinda Doyle]

Ok so I tinkered and tinkered, to no avail!
I played with the position of the two units and the best I could do is separate them with a 3 space unit, still got hum but it's a few DB less now!
Not sure what else I can try, tried the 0.1 and 1 meg resistor terminated to ground made zero difference!
Dang I'm out of ideas!
Thanks for the suggestions Peter!

 

[alexc]

Replace one R-core and see if there is a difference.

Maybe some pics -perhaps something might stand out as an issue. Also, what freqs are the noises at? Fundamental of mains or 2nd harmonic? Have you ruled out grounding issues?

But, if the units are noising when in proximity to each other and mechanical vibration can be ruled out by damping the mechanical coupling, then all that remains is EM coupling either thru free space or thru magneto-resistive conduction.

Personally, I've not seen a case of magneto-resistive conduction - that is, propagation of the magnetic field thru the chassis such that the transconduced  magnetic field couples into audio circuits.

Sounds to me like plain old cantankerous psu transformer syndrome.

Howabout trying a different, non inductor  mic preamp in proximity to each of these noisers? Do you get still get noise ?

If not then  you have a case of double R-core coupling into many-turns iron or a case of supernatural EM heebyjeebys.
EM poltergiests. Don't laugh. It can happen!

The 175 has quite a bit or signal iron and with quite high impedances. And the v72 has that many turns inductor and that high step up ratio mic traffo.

Could add up to trouble in the presence of a pair of R-cores, which I believe are not the most contained EM field units around. I have one in a high gain amp and I would not do  it again.

Even quite large Edcors I have used with no real radiated noise issues - without any artisan level wiring techniques and amongst many unshielded signal irons.

What you describe sounds to me very much like unshielded inductances near noisy psu traffos to me.

Either way you're forked.

So, the worst case suggestion would be - replace one R-core and see if it helps. And recheck with a nearby non inductor  mic pre.

I'm just starting my driop 175 and next Orange 86 build.
I'm using for 175, Edcor psu traffo and choke with sowter signal  iron and for Orange 86 toroid psu and edcor signal iron.

Good luck and don;t give up - there is almost always a way forward!

 

[Govinda Doyle]

Hey Alex!
Thanks for the tips, I think the 175b r-core is poopied, I can send up a pic for sure, I went solid state rectifier, because I honestly couldn't hear the difference when it was valve rectified!! And I know the difference in guitar amps!!
The r core actually has noise which you can hear through the unit, with just mains on and not patched in! The v72 r core is dead quiet which makes me suspicious!! I might get another and try my luck again!!
It's the only way forward I think at this stage, when plugged in and both units on full volume you can move them ontop etc and hear the hum come and go from position so it's def transformer radiation or whatever getting into the audio circuit!! Like I said the v72 has worked flawlessly in my system until mr 175 came along! 1st he had his own hum issues then he got fixed now he doesn't like mr v72!
Funny thing is if I put my 4 1290s ontop of the 175b it causes a slight hum but a heap lower than the v72 ontop of the 175b!
Oh la la I'm forking hating the hummmm!
The noises seem to be at the fundamental power supply frequency in Australia which is 60hertz I think, I said 50hz but I'm pretty sure it's 60hz!
Dang!

 

[alexc]

Well it does sound like 175 r-core could be the one to try replacing. It's a bother but what else can you do?

And here is Oz it is 50Hz and harmonics.

Good luck with it!

 

[Govinda Doyle]

Thanks Alex!
R core into the bin! Lol

 

[gemini86]

Might consider a decent toroid, check antekinc.com for good deals there.

 

[Govinda Doyle]

Thanks Rodney!

 

[radardoug]

Did you use US transformers? Often US transformers don't have enough metal for use on 50 Hz mains, and so have higher circulating currents in them. Get some good 50Hz toroids.

 

[gemini86]

Unless the transformer is being used right at it's limits, or is cheap and not designed well, it shouldn't make much different 50Hz vs 60Hz. In fact most transformer makers specify either mains frequency for almost all their transformers.

 

[radardoug]

Yes, you are right, cheap! Most of the classic Eventides have trouble on 50 Hz, and in addition their transformers are not potted, so they rattle. I have seen this problem many times.

 

[Govinda Doyle]

Ok so you guys recomend a really good toroidal?
I have tried a Hammond or two but have had a few failures, as in faulty units!
Ok I will check this out, will the toroidal give me any grounding noise interference problems?
Thanks so much for your responses guys!
Govinda