SRA of London Decca Reference cartridge

[ShawnZH]

With a digital microscope, with a few friends, we started to look closely into the SRA of different carts. We ended up finding different cartridges apply different stylus and mounting, which lead to very diversified ways to get the SRA close to 92 degrees.

A very dramatic case is Decca London Reference, a unique MI cartridge without a cantilever. The stylus is directly mounted to the end of the coil. This is a unique design while the sound is also uniquely good if mounted well.

Normally we align the cart with the shell perpendicular to the record surface. However when the London Decca was mounted this way, from the Microscope, the SRA is only 70ish degrees. You can see from the photos attached.

If you’d like to get the SRA close to 92 degrees, you have to mount the cart at a ridiculous angle with the tip of the cart much lower than the back of the cart. You can see from the photos how weird it looks.

When perpendicular to record:


70ish degree SRA


Mounted in a strange way:



Close to 92 degrees SRA

 

[ShawnZH]

I’d like to seek for experiences of anyone who had for this cartridge and ever studied the SRA of it.

 

[Solypsa]

Did it sound better that way?

 

[ShawnZH]

Did it sound better that way?

It sounded different, not necessarily better. I assume the “good” SRA digs out more details from the groove while the steep raise alters the way coils generates signals.

 

[leyenda]

Interested to know which setting you prefer ShawnZH. Is it intentional by Decca to use 70ish degree? I like the Decca sound but I do not know what degree SRA I have in my setting. It is difficult to see needle tip, leave alone to use microscope to find the tip and to capture it - kudos to you and your friends!

 

[ShawnZH]

Interested to know which setting you prefer ShawnZH. Is it intentional by Decca to use 70ish degree? I like the Decca sound but I do not know what degree SRA I have in my setting. It is difficult to see needle tip, leave alone to use microscope to find the tip and to capture it - kudos to you and your friends!

It was an experiment to mount the Decca like that, just trying to see how it sounds when the SRA is close to 92 degrees. Eventually, I restore back to the “normal” position, headshell perpendicular to the record. As said above, the 92 degrees setting sounded quite different, hard to say it’s an improvement and finally I just didn’t like that sound, feel like something was twisted but difficult to describe. Normal position makes Decca more relaxed and natural.

I read from some other forum about this and there are actually quite a few who noticed this issue. They wrote to Decca designer John Wright and was told that the mounting has to be like that due to the design and the type of stylus used.

I assume we have to live with 70ish SRA when listening to Decca. Anyhow, SRA is only one piece of how to make a cart sing.

 

[brtsai]

I do have two London Reference cartridges. I have experimented with raising its SRA near 92 degrees but found no advantage in sound or measurements such as IMD. The whole purpose of setting the SRA is to minimize the IMD according to the original paper, so if IMD does not improve then there's no point. Using the AnalogMagik software, in fact I found the lowest IMD for this cartridge occurs when the arm is roughly two degrees lower than horizontal.

BTW, by observing IMD, I found some cartridges are more sensitive to VTA being accurate than SRA.

 

[brtsai]

I have also asked J. Wright about the awkward SRA of this cartridge. He simply replied that his design is different from all others.