lash up lenco

cressy · Post by **cressy** » Wed May 21, 2008 11:05 pm

this is the earth arrangement as it stands, the tf earth in the phono stage is just the tf casing. i cant see a loop in there myself, maybe im too close to the problem. the earth in the amp is the bus bar for all the earths

david C · Post by **david C** » Wed May 21, 2008 11:13 pm

I may be talking rubbish but I always thought there should only be one path to earth through the main amp and all earth lines should go through that, having a second path can cause a loop,

cressy · Post by **cressy** » Wed May 21, 2008 11:45 pm

im not too sure tbh, the earth always ends up in the same place i.e the mains, the one place i can think of is in the step up as the sowter website for the 9575f replacement recommends grounding the transformer earth to the signal earth in the amp. as is, i earthed it straight to earth via the binding post on the phono stage instead. on the step up itsself there is a binding post for this earth instead of it being linked to the signal earth on the output side. id have thought that this should be attatched to either the busbar in the amp as that where the signal grounds to, or to the outer part of one of the output sockets on the step up casing. i think it might be a clip lead job this one. i did try grounding it down on of the -ve speaker binding post but that didnt work either.

Paul Barker · Post by **Paul Barker** » Thu May 22, 2008 8:58 am

cressy wrote:im not too sure tbh, the earth always ends up in the same place i.e the mains, the one place i can think of is in the step up as the sowter website for the 9575f replacement recommends grounding the transformer earth to the signal earth in the amp. as is, i earthed it straight to earth via the binding post on the phono stage instead. on the step up itsself there is a binding post for this earth instead of it being linked to the signal earth on the output side. id have thought that this should be attatched to either the busbar in the amp as that where the signal grounds to, or to the outer part of one of the output sockets on the step up casing. i think it might be a clip lead job this one. i did try grounding it down on of the -ve speaker binding post but that didnt work either.

The transformer shell is meant to shield the susceptible low signal levels within the transformer from interference. For a faraday shield to work it has to have an electric current passed through it, earthing it is normally sufficient.

As to how to earth, ideally one singal connection to the household earth. Which could be from any one of the stages, as long as all other stages are earthed (for safety) via it. A stage being a power amp, a preamp etc.

I would have thought the best way to go would be to work on the star earth principle. Pick a stage which is central, take your single connection to household earth (green and yellow protective conductor) from that stage. Inside that unit use a star ground i.e. every grounded part has a unique ground leed to the star point (which can be made from a loop of bare wire 1cm diameter for ease of soldering). The same principle for every other component, where possible pick a position inside the unit which is central to all the components requiring a ground. To maintain the centrality the stage best selected for ground would be in the midlle also.

There shouldn't then be any earth loops.

Post by **Nick** » Thu May 22, 2008 9:42 am

Does the black earths meet the red earths at any point, or are they isolated?

I would start at the amp and connect towards the turntable and see at what point the hum starts.

cressy · Post by **cressy** » Thu May 22, 2008 10:41 am

the back and red earths are separate all the way through, thats whas puzzling me. i tried this and the hum was there as soon as the phono stage was connected. i took it to bits and i cant see any loops inside it at all. i took it all out of the case (its only plastic so nothing to earth on that) and tried moving the transformer as far away as poss. no change again and this was with nothing on the other end of it. im wondering if theres some sort of interference in the area that its picking up. the only thing i can think of is the bootlace aerial for the radio. if you look at the pic of the amp and tt the aerial is running down th right hand corner of the alcove but switching the radio on and off doesnt make any difference. there isnt anything else that is close enough to produce any rfi, but when i initially set it up i could actually hear some sort of radio transmission, voices and everything, if the volume was up full. at the time though there want much discermable hum. something seems to have happened in the meantime to cause the hum. the only happenings recently have been an el34 packing up and being replaced and the amp being moved out and back into its space and reconnected

andrew Ivimey · Post by **andrew Ivimey** » Thu May 22, 2008 11:28 am

Rather like what Nick hinted, I'd start by taking out all the earth wires,

then

add one component at a time with its signal wires

and find where the hum begins.

It looks to me like all that red connections is the Big Earth Loop.

The rest just confuses the issue.

Post by **Nick** » Thu May 22, 2008 11:48 am

It looks to me like all that red connections is the Big Earth Loop.

Yes, agreed, thats why I asked if the two earts meet at any point in any kit.

So with nothing pulgged into the phono stage, plugging the phono stage into the amp creats a hum. Yes?

Does the hum start with one cable, or only when both are connected.

Does the hum change if you connect shorting plugs to the input of the phono?

Andrew · Post by **Andrew** » Thu May 22, 2008 12:56 pm

Does it humm when the motor unit is switched off but everything else is on?

cressy · Post by **cressy** » Fri May 23, 2008 7:40 pm

ive just bought an old phono stage off ebay for 35.00, hopefully this one might eliminate the problem as if im reading the specs right is has low and high level outputs. the ll one apparently gives a gain of 11db and the high gives +34.5db i dont know if i can stick the coral mc on the end of the hl output without the step ups but im hoping so. its a shure m64 2e. the attatchment is the spec sheet, have a look at the roll off graph! btw phil i recieved the peter and the wolf cd thanks alot, it brought back some fond memories and shut the kids up for a while!

pre65 · Post by **pre65** » Sat May 24, 2008 12:07 am

[quote="cressy" btw phil i recieved the peter and the wolf cd thanks alot, it brought back some fond memories and shut the kids up for a while![/quote]

Glad you liked it again !

It took longer than expected cos i had forgotten how to use EAC and could not find my "instruction sheet".

cressy · Post by **cressy** » Tue May 27, 2008 8:50 pm

i think im coming a little closer to the solution to the earth problem. i completely disconnected and reconnected the entire system, added a clip lead to the bus bar in the amp to use as an earth point and rewired the step up so the transformer earth went to the signal ground. this has made quite a difference. it sounds like ive eliminated 2 or 3 loops as iheard a the frequency change quite markedly as i added the earths. theres still one though, a low level hum that wont go away. the end seems in sight though as i heard is shut up an then start again as the arm traversed the record. this leads me to believe that its the arm cable, probably the connection between the arm cable itsself and and the output leads. ive got a new set of internal wire coming shortly so i think i'll add a set of sockets instead of captive leads. why does it always come down to the last thing you look at! they do say assumption is the mother of all cockups though and i assumed id done that bit right!

Dave the bass · Post by **Dave the bass** » Wed May 28, 2008 10:03 am

Hmmmm.... hum as the arm moved across the TT came up on the LL forum a while back. I seem to remember certain Grado Cartridges were particularly susceptible to the flux of the motor unit (or summat like that).

DTB

cressy · Post by **cressy** » Thu May 29, 2008 12:52 pm

i recieved a new set of internal arm cabling today from the usa, the seller was dualparts on ebay. these guys were brilliant to deal with and they even terminated them whith cart connectors for me for free! very well recommended. we shall see if adding this cable and adding on a set of sockets instead of the crappy block connector helps out with the hum! im tipping the sound will be alot better with this cable as the other stuff came off an old video game control pad! i shall report back..............

cressy · Post by **cressy** » Sun Jun 01, 2008 1:31 pm

the hum is almost cured. i rewired the arm completely with a new loom and soldered the arm cable directly to the output cables. i clip leaded the earths directly to the busbar in the amp just after the signal earths and its now all but shut up. the only thing thats humming now is the actual phono stage (bloody thing) so hopefully the shure one that ive got coming should cure it completely! its about time. i might be able to enjoy it properly then. the new loom is a hell of a lot better than the previous wiring, alot more spacious and delicate sounding. strangely ive got abit more volume or so it sounds, might be less resistance in the wiring or something. the amp was left alone from taking it out to reconnecting so the volume wasnt changed at all. wierd that. not that im complaining! all i need to do now is to add a grounding post to the back of the amp instead of the clip lead. when i can be bothered to anyway!

audio-talk

lash up lenco

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