modwright 36.5 dm clicking noise when using rca but not xlr

hifinutt · « **on:** 29 Jan 2017, 11:25 pm »

hi guys

I am using an ss power amp and getting some slight imbalance when I use xlr cables . this happens regardless of pre amp so not the 36.5 causing

anyway so I have recently started using rca connections to power amp . only trouble is I get a regular clicking from right channel when using the 36.5 this way . does not matter if ground switch is up or down . the pre is relatively new with not a huge amount of hours .

now if it was a tube , why should it only do it with RCA connections ?
and if it is a tube which ones do you replace given that there are 6 valves . it is under warrenty but not valves

Phil A · « **Reply #1 on:** 30 Jan 2017, 01:44 am »

So apparently you have an extra preamp to try in the loop but not an extra amp? If so, can you borrow an amp or bring the unit to a store that has one?

hifinutt · « **Reply #2 on:** 20 Feb 2017, 10:05 pm »

yes I have found the imbalance in the power amp was caused by the xlr cables so that is sorted

now no other pre amp does this clicking with my sources . I have tried a few .

now I tried the dm via rca into a beautiful audio research d70 [balanced circuits]and it hummed in the speakers badly . it did this with ground switch up or down . I tried another valve pre into the arc and there was no humming !!

most odd . and yet the dm performs beautifully xlr to xlr . any more suggestions

Phil A · « **Reply #3 on:** 20 Feb 2017, 10:51 pm »

Up until 6 months (or so) ago, I was using balanced cables from the 36.5DM to the KWA150 SE but I made new (RCA) cables I liked better. Have your tried another set of XLRs? Have you tried to measure the SPL with a meter separately from each channel on a mono source? If so, how much of an imbalance do you have?

hifinutt · « **Reply #4 on:** 25 Feb 2017, 02:44 pm »

yes I have had the new xlr cables tested and they were perfect . there is perfect balance now xlr to xlr . but I still get ticking from rca . and what the heck is causing that humming when I connect the d70 .

testing spl is a bit above my capabilities sadly !!! I am not an engineer

Phil A · « **Reply #5 on:** 25 Feb 2017, 03:41 pm »

Quote from: hifinutt on 25 Feb 2017, 02:44 pm

yes I have had the new xlr cables tested and they were perfect . there is perfect balance now xlr to xlr . but I still get ticking from rca . and what the heck is causing that humming when I connect the d70 .

testing spl is a bit above my capabilities sadly !!! I am not an engineer

I had humming and low output from my right channel for a bit (hooking the LS36.5DM to the KWA 150SE) and it turned out that when I was trying a couple of things the locking connector on the Mundorf RCA from the cables I made was not seated in the amp properly. Drove me nuts (and I am not the most flexible person in the world crawling back there to make connections).

If you or someone you know has a smart phone, you can get an spl meter app - e.g. http://www.studiosixdigital.com/audiotools-modules-2/spl-modules/spl_meter.html

Really not that difficult.

hifinutt · « **Reply #6 on:** 25 Feb 2017, 06:05 pm »

thanks for that phil , appreciated . yes so many things can affect . I used to use those virtual dynamics cables a lot , [still have one ] and they have great big magnets in the cables and it affected my radio reception once !! now I keep aerial cables away from them

hifinutt · « **Reply #7 on:** 3 Mar 2017, 06:15 pm »

well awaiting engineer to fix this problem but it does seem very difficult to get these amps repaired . very annoying really

hifinutt · « **Reply #8 on:** 5 Mar 2017, 02:33 pm »

well I have checked the braid on one interconnect [Kimber select] which was coming loose . I have removed a power cable containing big heavy magnets [virtual dynamics on the power amp]

I have checked and rechecked all other cables in system that no metal touching

I have plugged the dm psu into the high power section of a mains conditioner earthed to a big copper rod under the lounge

so `ticking noise is much reduced but still there very slightly . good to see some progress in this situation from such a fabulous pre amp .

it has such an airy top end and so natural with piano it is worth persevering to get the best sound

mikeeastman · « **Reply #9 on:** 5 Mar 2017, 03:30 pm »

hifinutt do you have a separate ground rod for audio gear and one for rest of house? If so, are two rod tied directly together, if not you have a potentially bad situation especially if you live in an area that gets thunder storms.

hifinutt · « **Reply #10 on:** 5 Mar 2017, 05:46 pm »

ah thanks mike

yes very good point ....I can just imagine being lifted out of my comfortable chair in the lounge

yes the ground rod is totally separate . we have a chap in England called russ Andrews [much maligned by hi fi forums sadly due to high prices ]

he has a book called optimising grounding

http://www.russandrews.com/system-grounding/

so my copper rod is deep in ground under lounge in moist ground connected to the isotek conditioner which has a dedicated earth point

mikeeastman · « **Reply #11 on:** 5 Mar 2017, 11:36 pm »

So there's no connection at all between any audio gear and the rest of your power, even at the main panel. Because if there is and your house ground isn't tied directly to audio ground and you have a lighting strike hit the ground it will be closer to one of the ground rods and that surge will want to travel to the other ground rod and the eases path is through all your wiring and anything plugged into. I installed solar system for over 20 years and they always have at least 2 ground rod per system and standard practice and code required a ground wire from one rod to the next.

G Georgopoulos · « **Reply #12 on:** 6 Mar 2017, 12:06 am »

Quote from: hifinutt on 25 Feb 2017, 02:44 pm

yes I have had the new xlr cables tested and they were perfect . there is perfect balance now xlr to xlr . but I still get ticking from rca . and what the heck is causing that humming when I connect the d70 .

testing spl is a bit above my capabilities sadly !!! I am not an engineer

check RCA joint/connection

hifinutt · « **Reply #13 on:** 6 Mar 2017, 09:40 am »

thanks both . I notice that it doesn`t tick when in theatre bypass mode . that bypasses volume control . could it therefore be related to the volume control in some way ?

hifinutt · « **Reply #14 on:** 8 Mar 2017, 10:11 am »

well the ticking has all but stopped , still doing it a bit . still waiting for an engineer to look at it . its very very drawn out business getting stuff repaired in UK !!

hifinutt · « **Reply #15 on:** 11 Mar 2017, 07:00 pm »

managed to get engineers appointment now so that is great . the dm is sounding awesome in xlr format . no issues at all . vol pot is totally silent with no crackling at all at 0 , its only in RCA format the vol knob is crackly at zero .

Phil A · « **Reply #16 on:** 11 Mar 2017, 08:35 pm »

Quote from: hifinutt on 11 Mar 2017, 07:00 pm

managed to get engineers appointment now so that is great . the dm is sounding awesome in xlr format . no issues at all . vol pot is totally silent with no crackling at all at 0 , its only in RCA format the vol knob is crackly at zero .

Sounds great - glad you got it worked out. Love my preamp.

hifinutt · « **Reply #17 on:** 12 Mar 2017, 05:30 pm »

thanks phil , well not fixed yet ! just managed to get an engineer . if any unemployed valve engineers want a job in old blighty then i am sure they would find lots of work !!

hifinutt · « **Reply #18 on:** 23 Apr 2017, 07:01 pm »

23rd of april and unit still with engineer , nothing found as yet though !! been enjoying the modwright anniversary while its away

hifinutt · « **Reply #19 on:** 30 Apr 2017, 05:47 pm »

hoping to get my dm back tomorrow . engineer has checked it thoroughly and not really found any problems so I will see what happens . been a real blessing in disguise as had a chance to try a solid state Italian pre that is truly epic . looking forward to comparing the 2 pre amps