[tubesforever]

First, I have purchased a full rack 16.75 x 3.75 x 14 inch Lansing black anodyzed box for this project.

I plan to run four incoming rca jacks and use a selector switch to run the signal into a second selector switch for the Picallo or the Cornet2. 

I plan to use separate power for the Picallo and the Cornet2

I have plenty of room in the case to put the Picallo into its own aluminum enclosure if it dislikes the big Hammond Xformer.

Question about the Picallo.... It has settings for zero gain and 47k output.  Is this essentially a bypass setting?  Or is the signal still going through active components?  I might be able to eliminate one switch if I can set the Picallo to process LOMC or bypass MM signals.

More importantly, I want to run two front switches a DP three way for Mute/Stereo/Mono and a power on off for the Cornet2.  Other than twisting the power wires is a drain shield or conduit a good idea for such a switch?

[Bill Epstein]

The first time I built the Cornet II I tried to have three inputs to use it as a switch from all my sources to integrated amp. Used a very high quality Greyhill rotary switch on the front. None of the several shieldings and topologies I tried  :lol:could defeat the hum.

When I recently re-built it with Cinemags inside http://www.audiocircle.com/index.php?topic=43660.0 I wanted to use a MM/MC input/switch and was talked out of it over hum issues.

I always have a few phono stages around so I have the luxury of a dedicated MC Cornet. Otherwise, I would have put the Cinemags in a separate box as I am doing with the Piccolo.

Despite these warnings, I'm hoping you can pull it off and share your results with us.

[tubesforever]

Bill,

Reading the various posts here it looks like ground loops are the main hum culpret.  But Jim H mentioned the C2 does hum because of the proximity of the inputs and outputs to the hammond xformer.

I am going to try either a braided shield or even conduit for the Picallo output to the C2 input. 

I might need to run the Picallo in its own shielded  piece to keep the transformer from bleeding back...

Hard to say. 

I might end up with a big ol box and only a C2 inside!  That would be a shame.  I might not cut out any aspect of the box until I test the circuitry and noise levels first.  It would be easier to just buy another small half rack box than put a c2 in a full rack box.

BTW where did you source your high quality switches?

[Bill Epstein]

The switch was from, shudder, Welborne. A Greyhill. Small and a little fussy but very good. Percy has Seidens and there's some very good gear with Alphas and Mountains you can get from Mouser.

My pal Steve says the TI Shield from Percy is very effective for RF isolation around power supplies. It's pretty flexible and cuts with scissors.   

[hagtech]

I'd suggest powering the PICCOLO from the heater supply on the CORNET2.  Eliminates the need for an extra power supply and possible grounding issues.

On the C2 inputs, it is only a hum issue when using 100 ohm loading on an MC cart.  If you use 47k loading, you don't get the induced hum.  With twisted pair wiring the problem isn't very bad, but it is still there, so not perfect.

jh

[tubesforever]

Understood on the heater supply voltage. 

I was going to modify the Piccolo for 25/50/75/100/150/47k ohms since I am using a Denon DL 103R. 

Sounds like I might get a hum.  Would putting this inside a separate aluminum housing help shield things.  I will star ground everything in the case.

My big question is if I can use zero gain and 47k as a bypass setting so I do not need to run a separate MC/C2 selector switch.  I hear I might get some hum from such a switch when reviewing Bill Epstein's notes.

I plan to run shafts from the front case and do all the selecting at the back of the case to eliminate as much wire length as humanly possible.

[hagtech]

You won't get hum in your wide chassis.  Just move the inputs a few more inches away from the power tranny.  It's a LF magnetic field issue, so no amount of aluminum is going to do anything worthwhile.  Distance is the answer.

The 0dB gain of a PICCOLO is not a bypass.  It's just a gain of 1 amplifier, which does nothing but add a little noise. 

jh

[tketcham]

Hi, Tubes,
just curious why you're including the 47K resistance setting for a moving coil preamp? If you didn't bother with the 47K setting you could add another intermediate setting between 25 and 50, say +/- 35, to give you a better range where the cartridge is likely to be more sensitive to loading. You'd end up with: 25/35/50/75/100/150. Just a thought.  Tom

[tubesforever]

Hi Tom!

I am going to use block like ecir88 built.  I am going to steal his idea.....but give him full credit.  That way I can replace these easily. 

I plan to mount the Piccolo in the extreme right back corner of the larger case and have very short leads out the back to  the resistors.  Then comes in input jacks and switches for MC/MM and these will all be driven with long shaft mounts to the front of the case. 

It should be very quiet (pray for me!) and elegant!

[tketcham]

I like the idea of external resistor clamps. Makes it easy to have course settings to quickly narrow down the range and then install more narrow range for fine-tuning the the sweet spot of the cartridge. Housing the components in a full-size chassis makes a lot of sense. I'm looking forward to your assessment of the finished (beta) product.

Tom