Great River MP-2 , info, schematics & discussions

[okgb]

See earlier post for input Xfmrs , best deal i think is on Cinemag
which is on the Dan recomended list [ needs a 1:5 ]

I'm about to try them but vouch for the 1538xl that i used

From a kit provider standpoint the elma & surface mount could be trouble
for end users , the switch may be best handled by the individual

regards Greg

 

[Ptownkid]

I'll happily order the switches and trannies, but those will definitely be money up front purchases.

The psus will be a pcb and parts

 

[Bluzzi]

Yes I got a quote for the transformers (CMMI-5C) from Dan and a group buy would bring down price.

Good news about the power supply in kit form. Are you using a proven design or a new one of your own?

As far as the switch the standard would have to be the solder lug one not the PC mount one for me.

jim

 

[udo]

Hey Greg (+ Dan)!
Thanks for the info regarding the IDSS classification for the 2SK389! Even better - of course - that I can get these FETs and the inductors from you! Especially the 2SK389 seems to be hard to find anywhere. I can't say enough how excited I am about this project! :grin: :grin: :grin:
I plan to build a total of 4 of these preamps using the Elma switches and SMT GR switch PCBs.
Did you say you might have the GR switch SMD resistors available as well? :thumb:
Please pm me regarding payment and shipping.
Can't wait to hear these micpres in action!
Cheers, Udo

 

[okgb]

Yeah another Cinemag groupbuy would be great , could use a
1:10 as well
to avoid large taxes i think best handled from someone in the U.S.

Anything in Canada that somebody wants ?

regards Greg

 

[okgb]

the only tricky bit i believe , regarding R46 on the schematic

From the desk of Dan

R46 is determined by putting a FET in the circuit, then adjusting
for minimum output offset. This value drifts some with temperature, so
I try to adjust for <.5mv when the circuit is warmed up.

I just power the board up, it already has the feedback resistor, and put
a 2K or so pot in for R46, adjust for minimum, let things warm up some
more and readjust. After 15 minutes or so I'll take the pot out of the
circuit, measure and replace with a fixed resistor of the closest 1%
value and then retest for warmed up minimum offset.

It takes a little while, but it's something you can walk away from in
between tweaks.

End quote

shouldn't scare anyone off !

regards Greg

 

[udo]

Just an FYI regarding the Elma switches:
I contacted Elma and received this info on the part numbers:

04-1103-20
"The price is $31.48 each.
These switches turn continuously around and around without a stop. A stop cannot be added later, so the switch will always turn around and around. This switch is a one-wafer switch with PCB pins.

The same switch that has a stop from the factory between position 24 and
1 is 04-1130-20.
These are $28.88 each. You can add a stop anywhere in the 24 positions
on this switch.
The stop screws are part number 4124-21 for a 10 pack of screws. The
price is $2.99 per pack."

So I ordered the 04-1130-20 ... I don't think just under $30 for for a GR switch or pot is too much for a Micpre like this.

Cheers, Udo

 

[Ptownkid]

word

 

[okgb]

i had ordered some recently for a friend @ 27.40 each
Did you speak with mark ?

and careful for a number 04-1130-20 the -20 specifies
pc mount which may be a slight increase in cost , but you get a gold flashed switch , the heavier gold version in 37.00 ish
i think the one you got is fine .

happy camp'in

 

[madriaanse]

Any word on the progress of this project?

M.

 

[Ptownkid]

It's moving along, just waiting for some parts that Dan is supplying and waiting on a few quotes for pcbs.

Soon

 

[Bluzzi]

Just a bump and curious as to progress on the parts kit from Ptownkid.

Hope I'm not too much of a PITA.

thanks

jim

 

[Ptownkid]

There's some parts on their way from Greg to myself, when those arrive I'll order up the pcbs and parts.

I'm thinking we're about 4 weeks out.

 

[Bluzzi]

OK, thanks. See you in 4 weeks.

jim

 

[synthi]

its comming... :thumb:

Synthi

 

[okgb]

100 fets & inductors are indeed on their way to Ptown , if you're doing your own boards , email me and i can send an inductor & fet
but my numbers are limited so only ask IF you have already made a pcb
[ and not just to stockpile ]

regards Greg

 

[kazper]

Bump... Don't want to forget about this one

 

[Ptownkid]

There'll be an update in the very near future

 

[Ptownkid]

We could go with Edcor too

any idea which one would be appropiate out ofthese three styles, I can't figure out the difference.


http://www.edcorusa.com/products/transformers/mx/index.html

 

[Dan Kennedy]

Use the XSM600/600 for outputs

Use MX5cs for input, if you must, for cheap, you'll need to determine a zobel network to damp any input ringing empirically.

You're better off with the Cinemag, Jensen or Lundahls.

These things don't have any significant magnetic shielding, gonna be sensitive to transformer hum from the power supply.