Hi Fi News Test Record

[samz]

There are two bands of deadwax on each side, on side 1 after track 5 and a smaller area of deadwax on side 2 before the last track.

With the stylus in the middle of the deadwax as mentioned above, should the stylus remain stationary i.e. not move towards inner or outer groove. I don't see anything on the information that came with the records but was wondering if this can be used to set adjust the bias of the tonearm.

Thanks

Samz

 

[sonddek]

There are two bands of deadwax on each side, on side 1 after track 5 and a smaller area of deadwax on side 2 before the last track.

With the stylus in the middle of the deadwax as mentioned above, should the stylus remain stationary i.e. not move towards inner or outer groove. I don't see anything on the information that came with the records but was wondering if this can be used to set adjust the bias of the tonearm.

Thanks

Samz

I always set bias using this phenomenon, as follows.

Record speed is about twice as high at the lead-in (before track 1) as at the lead-out (exit from the last track). Consequently, any affect which surface speed has on frictional force will produce a different skating force in these two places. If you can find a record with a flat lead-in (i.e. no lip), watch the arm swing when the stylus is lowered onto the lead-in flats. Adjust bias so that the skate acceleration inwards when stylus is lowered onto the lead-in is about equal and opposite to the skate acceleration at the lead-out. That way, correct anti-skating should occur around the middle of the programme, which is the best you can hope for, assuming your arm has constant anti-skating force. This also assumes that the diamond profile doesn't produce an eccentric force. Using a conical stylus for setting bias guarantees that the stylus profile isn't skewing the result. Also, you may want to do this for each of the record speeds you listen to, as 45's will obviously produce a higher skating force, and require more anti-skate. Also, it goes without saying that you do this after setting downforce.

People worry that tracking angle is only right at two moments during a record. Anti-skate is only right once, unless the arm has some fancy mechanism which applies anti-skate as some function of arm angle. Roy Gandy's view that bias isn't something to get too worked up about would seem to make sense with most cartridges on most decks playing most records, when you consider that you can see that required anti-skate isn't the same at any two different radiuses.

 

[samz]

thanks for the reply sonddek. I will go through my collection of LP's and look for a suitable record with a flat lead-in as you mentioned. By the way, I am installing a Nagaoka MP-50 onto a AO modified Rega RB251 tonearm which is on my LP12.
Thanks again
Samz

 

[sergeauckland]

Setting bias on a blank LP will result in considerable underbias. Bias is a function of friction on the stylus, so the friction caused by the two sides of the stylus rubbing against the groove walls is a lot more than the end of the stylus resting against smooth vinyl.

Arms don't all have constant bias, as those with a hanging weight will have a different angle between weight and arm depending on arm position. As the pull on the arm depends on the angle, this will change as the arm goes across the record.

Also, as the linear velocity of the LP passing under the stylus is faster at the outside, the amount of bias at the outside needs to be greater than at the inside, so arranging the angle of the thread accordingly is sensible.

Having said all this, I rather agree with Roy Gandy that bias isn't that critical, but getting it right ensures that mistracking, when it occurs, happens equally to right and left channels, so has a benefit there. It also maintains the generator better centred on the cartridge centre line, which may help reduce distortion or at least equalise it between left and right channels.

S.