RJM Audio Emerald Phono Stage Help Desk

[rjm]

Emerald Phono Stage

"A two stage op amp circuit, the Emerald has switchable voltage gain and loading options and features an active-passive hybrid RIAA with exceptionally accurate response. Single channel, dual-layer 10 cm x 8 cm board. The S-Reg voltage regulator circuit is built in to the boards, no additional regulation or filtering required."

Help desk and build thread. I've had a couple of people asking me to separate it from the (now 14 year old) VSPS and Phonoclone help desk. So here you go...

 

[WntrMute2]

Hello, I'm about to fire up my Emerald with switch-board input. I am planning on starting with a Hi-output Sumiko Blackbird. If I'm reading your instructions correctly, I should leave both jumpers out. Does that seem correct? All the switch-board switches are off for starters. I built it with the stock BOM parts.

Sumiko Blackbird
Output - 2.5mV
Internal Impedance - 135ohms
Load - 47K

 

[rjm]

If I'm reading your instructions correctly, I should leave both jumpers out. Does that seem correct? All the switch-board switches are off for starters. I built it with the stock BOM parts.

Sumiko Blackbird
Output - 2.5mV
Internal Impedance - 135ohms
Load - 47K

Yes, High Output MC carts are treated as MM carts for this purpose. You want to have the Emerald set to 47 kohms input impedance, and the MM level gain (about 40 db).

The switchboard would be left disabled (all switches open) for this cart, you don't need it.

/R

 

[Mark Tillotson]

I'm intrigued by the low gain of the first stage for MM of only x2, given the importance of keeping noise under control...

 

[WntrMute2]

Yes, High Output MC carts are treated as MM carts for this purpose. You want to have the Emerald set to 47 kohms input impedance, and the MM level gain (about 40 db).

The switchboard would be left disabled (all switches open) for this cart, you don't need it.

/R

Next cartridge will be the Sound Smith Paua. Should be here in a few weeks.
I'm assuming I'll need changes to the switchboard of the Emerald itself.

Output 0.4mv.
Load 470 ohms to 2,800(or so) ohms
Capacitance not specified

Suggestions as to changes to the Emerald or the switch board to accomplish the range of load resistance?

 

[rjm]

Set the Switchboard to Position 1 ON (100000) to give 980 ohm load. Optionally Position 6 ON (100001) to add 100 pF capacitance.

 

[WntrMute2]

Set the Switchboard to Position 1 ON (100000) to give 980 ohm load. Optionally Position 6 ON (100001) to add 100 pF capacitance.

I'm assuming I'd remove the load and gain jumper in the Emerald. If I wanted a range of load values, any way of accomplishing that? I socketed R1 thru R5 in the Emerald so I could easily swap resistors BTW.

 

[rjm]

Think of the Switchboard as an alternative to your on-board socketed resistor R1. Of course you can just swap out R1 or R2 for a different value, but when using switchboard you leave JP1_1 open to set the board input to 47kohms, then select the parallel resistance value on the switchboard to set the load. The gain setting is switched via JP1_2 as always, it is unaffected by the switchboard.

 

[WntrMute2]

Got that. I think I'll need to replace some or all of the resistors if I want a load variation from say 4k down to just below 1k. I'm assuming the sweet spot may be around 2,800k. Suggestions on what to populate the board with?

 

[WntrMute2]

I spun a variety af records today with excellent results. Adderly to Coltrane to Cowboy Junkies and finally a rocking' session with Humble Pie. Seemed perfect all around! This is with a HOMC Sumiko Blackbird. Pretty happy at this point.

 

[cal16v]

Reading on with interest as I wait for my boards to arrive...

 

[cal16v]

My Emerald boards have arrived and I'm very impressed. Overall my kit has all the required documentation, quality parts and fantastic looking pcb boards. Can't wait to get started now.

 

[WntrMute2]

My Emerald boards have arrived and I'm very impressed. Overall my kit has all the required documentation, quality parts and fantastic looking pcb boards. Can't wait to get started now.

Following with interest!

 

[DRONE7]

I have a few transformers in the spares box... conventional single-wound output, 24v centre tapped.(12v/side)

Presumably these will suffice using a single bridge. ?

Or is the double winding and twin bridges shown on the build page needed for some reason ? and if so why so ?

 

[rjm]

You can use a 24vct if you want. You'd use one bridge rectifier, in the conventional way, to get the positive and negative rails. The center tap connects to COM.

 

[DRONE7]

Thanks for the prompt reply !
What's the advantage of using twin outputs and bridges ?

Getting organised here in anticipation of a build....(boards ordered...Bob)

 

[rjm]

If you have dual secondaries, then using two bridges makes the connection more foolproof since the phase of the output winding isn't a concern.

 

[DRONE7]

Great thanks !
makes life easier... working through the BOM to see what I have on hand...and what I have to order....

Looking forward to this project...

 

[cal16v]

I have made a start assembling the boards. Still some parts left to solder...
I'm happy with the layout of the boards inside the aluminium case as well.

A question...
I am housing the transformer in a separate aluminium case connected by an umbilical. It was suggested in the VSPS thread to twist the power wires, so is this only for the mains wiring to transformer or does it also apply to the wiring from the plug shown to the phono boards?

Thanks

 

[rjm]

Both, or rather everything. I usually braid the power (V++,V--,COM) together, and twist the signal wiring (IN+,IN-) and (OUT+/OUT-) pairs. AC wiring (live, neutral) are twisted together, earth is separate. Individual secondary outputs twisted together.

See this post for examples. Comment about case size applies here too, but yours is just that little bit larger and more accessible, so you should be ok I think.