Notes on the Leak Stereo 60

1. SNR is quoted at -80dB, no weighting quoted, nor which input. Source for this is Audio! Audio!, not any Leak documentation I can find.
2. I was unable to get better than -48dB unfiltered, or -66dB filtered (300Hz HP 3rd order).
3. On investigation it turns out that L1 is a design disaster.
It is specified as 0.3H, when all sanity and experience and RDH equations and simulations show that it should be > 6H.
In other words it is a factor of at least 20 too small.
4. This causes it, in conjunction with C12/13 and C14/15 considered as in series,
to have a resonance at 50Hz, exactly where you don't want it, and only -3dB at 100Hz, where you are already looking for far more.
5. The unit presented for service had 75R in series with the choke leading to C12/13,
as did another unit available for purchase by the owner.
Was this a factory modification?
Modelling this, and taking into account L1's DCR of 17R and the GZ32's source impedance of 160R per plate
shows that the resonant peak is flattened and the response at 100Hz somewhat improved,
but nowhere near what is required.
6. Increasing C14/15 to 32uF each and increasing C10/11 to 100uF each, in conjuction with 100R in series
(all that was available) improved the unfiltered SNR to -48dB, which is considerably better but nowhere
near the quoted figure.

You should not have to do all this.
Was there another fault?
The AC ripple at C10 was still over 100mV.
Removing V1 moderated but did not eliminate the hum.
Removing V2 had more effect, which is surprising as the hum should cancel within this phase splitter.

THD+N was within limits provided the 300HZ HP filter was engaged.

7. I changed the choke to a Hammond 193K 2.6H (the biggest one that would fit) and C14/15 to 100uF each, and retained the series 100R.
8. SNR unfiltered is now -51dB L and -57dB R.
9. At Steve Spicer's site: http://www.44bx.com/leak/Stereo60.html, see picture of the choke, which is much larger than the unit I removed. Below the picture he says 'It has been reported (but not confirmed) that some Stereo 60 units had a large choke (like that shown), but most were much smaller that this.'
I find this rather conclusive.


Esmond Pitt
10 April-9 May 2019