Can the step up transformers be mounted in the same chassis?

tomw · « **on:** 2 Jan 2006, 12:00 pm »

I'm in the midst of putting together a Cornet2 and am toying with the idea of mounting the Lundahl step up transformers in the small corner space close to the input jacks. Will hum be a problem?

Many thanks in advance

Regards

tomw

mgalusha · « **Reply #1 on:** 2 Jan 2006, 01:37 pm »

I have a pair of Jensen step up's mounted inside my Cornet (original version) and there is no problem. I suspect the Lundahl's will be OK as well. Just keep the leads short and tidy to reduce the possibility of picking up noise.

mike

hagtech · « **Reply #2 on:** 2 Jan 2006, 09:36 pm »

You can add the stepups in the original Cornet because the inputs were opposite the power transformer. Doesn't work with the Cornet2, unless you move the inputs to the front panel. You can't put stepups near the power tranny, nor can you run the cables past it.

jh

Eric H · « **Reply #3 on:** 4 Jan 2006, 06:33 am »

Hi Jim,

Getting some stepups for my Cornet2 and trying out some MC carts is something I'm seriously considering. What's the best way to set this up? How far away from the PT do the step-ups need to be? I guess we're talking about 2 sets of interconnects - one from tt->step-up and one from step-up->Cornet2? Should the stepups be closer to the tt or the Cornet2? Thanks...

Eric

hagtech · « **Reply #4 on:** 4 Jan 2006, 06:26 pm »

The stepups do not have to be that far away. Depends on shielding, etc. Inches make a difference. The main problem was the narrow chassis, forcing the routing too close to the power tranny. A wider chassis would be ok, or routing the inputs into the front side. Basically, don't run the low impedance signals right next to the power tranny. It's a magnetic induction problem, which is why it doesn't show up with 47k loading.

Think of it this way, 6" or closer to the tranny is bad. 12" is great.

jh

queg · « **Reply #5 on:** 4 Jan 2006, 08:17 pm »

I've got some Lundahls inside my classic right now, and they're humming a bit. Would it help to shield them with copper foil?

hagtech · « **Reply #6 on:** 5 Jan 2006, 01:07 am »

Copper does not shield low frequency magnetic fields. You need iron. Or high permeability mu-metal. Magnetic shielding works different from electric, you don't 'block' the field, you re-route it. Any 'core' material will work.

You'll notice that all of the tubes are in a line? That's the null field from the power tranny. It cancels itself along this line. Keep the Lundahl's close to this line and don't route the MC cables past the power tranny. It may not be the Lundahls at all, but the wiring.

jh

queg · « **Reply #7 on:** 6 Jan 2006, 10:33 pm »

I've decided to wire them outside the Cornet, and have a question which I already posted on audio asylum, but figure you'd know best:

Do you think it would be best to install the step-ups closer to the cartridge output: short phono cable to step-up, longer cable to preamp.

Or the opposite: long phono cable, short cable to preamp input?

Answer will also determine where I'll direct-solder and where I'll use connectors...

Thanks!

hagtech · « **Reply #8 on:** 7 Jan 2006, 03:59 am »

I prefer to put the longer wires between MC and tranny. Short wires from tranny to phono.

The reason is capacitance. Like resistance gets divided by 100 by a 10:1 tranny (47k down to 470), the capacitance gets multiplied by 100. So a 100pF cable on the output of the tranny reflects back to a 0.01uF load on the cartridge. It also starts to limit bandwidth on the high impedance side.

The MC has more than enough oomph to drive a long cable.

jh