|
|
Surfing the web I discovered that Ortofon had
designed a new Moving Coil stepup transformer Verto and that the stepup
transformers was delivered by Lundahl, which we have had very good
experience with from our 6C33 amplifier (check Links page for a link to
Lundahl). It was getting exciting and it got
even better when I looked at Lundahls web and discovered that they had made
a new Moving Coil stepup transformer: the LL1931. This is from the data sheet
description:
"LL1931 is a high performance moving coil step-up transformer. The
transformer combines our unique uncut amorphous cobalt core and our dual
coil structure with Cardas high purity copper wire in an over sized design.
The objective is to provide the best possible MC transformer,
cost-no-object. The dual-coil structure greatly improves immunity to
external magnetic fields from power supplies, motors etc.. The transformer
is housed in a mu-metal can."
So I ordered two LL1931, and build a Moving Coil stepup transformer, and I
must say I am very pleased with the finished result. The sound is better
compared to my Nelson Pass (x)ono Moving Coil preamplifier, the LL1931 has less hum
and I have got rid of very low frequency subsonic sounds. Below you can see
some pictures of the finished design (click on the picture to enlarge it).
A little warning! I have modified my Lenco L75
from a 5 DIN connection to two RCA connections and made a separate ground
wire from the Lenco chassisground to the MC stepup transformer / direct to
the RIAA amplifier, but I still have some hum (too much) in 18dB mode, so be
aware about this potential problem if you intend to build my MC stepup
transformer and use it in 18dB mode!
The empty pcb.
You can select
between 8 or 16 times amplification (18 or 24dB) by placing one or two
jumper(s).
The third jumper selects between unbalanced or balanced Moving Magnet amplifier.
|
 |
Pcb file updated
2009.04.13 |
You may have to place
a resistor on the secondary side of the transformer to ensure that you
use the right impedance load on the pickup side, my brother has made a
calculator you can use to calculate this resistor.
The calculator is partly based on a spreadsheet made by
www.kandaudio.com and can be used with all Lundahls MC stepup
transformers: LL1678, LL1681, LL1931, LL1933, LL1941, LL1943, LL9206 and LL9226.
Updated! We have added the new LL1941 and
LL1943 MC stepup
transformer to the calculator program.
|
 |
MC StepUp
Calculator v2.4 2011.01.02 |
In this example we
want a pickup impedance load of approx. 20ohm @ 24dB with the LL1931.
Updated! We have added the new LL1941 and
LL1943 MC stepup
transformer to the calculator program.
|
 |
|
In this example we want to
know what the pickup impedance load is without a resistor @ 24dB with
the LL1931 (place a tick in no resistor in parallel). This is the way I
use the LL1931!
Updated! We have added the new
LL1941, LL1943 MC stepup
transformer to the calculator program.
|
 |
|
| The finished result, I use it
in 24dB and unbalanced configuration. |
 |
|
I was not satisfied with my old
enclosure so we have ordered a new aluminum front, open the pdf to check
out this very nice design.
|
 |
|
It is of course the same story regarding
the back, open the pdf to check out this very nice design.
|
|
|
The aluminum has arrived and I have
assembled the new enclosure. I must say I am very pleased with the
result, just look at this picture on the new frontplate.
|
 |
|
With the new enclosure it was
possible to add a switch between the two amplification factors: 18dB and
24dB. I will have to modify my Lenco L75 to support 18dB mode, as the
Lenco case ground is connected to left signal ground according to the 5
DIN standard and this is incompatible with the LL1931 input grounding
scheme. I think this is okay, and maybe I will get rid of the very small
amount of hum I experience when I crank the volume to 100%?
I choose not to add a unbalanced/balanced switch as my RIAA amplifier
doesn't support this.
I have changed the chassis ground connection so it is
connected direct to the chassis and not the transformer input, this has
removed most of the hum in 18dB configuration.
|
 |
|
Take a look
into the finished Moving Coil stepup transformer. I have soldered a wire
to the switch washer to ensure a good ground connection. The 18dB/24dB
switch connection is easy to implement with a four pole switch, the
connections are shown on the bottom side of the pcb.
|
 |
|
|
Here are the CAD design files if
you want to order out front, back, bottom and top aluminum plates. |
 |
CAD files
updated 2009.07.30 |
This page was last updated
2011-01-02.
|
