Great River MP-2 , info, schematics & discussions

[guavatone]

[quote author="clintrubber"]Something else: the bank of 680 uF caps.
Since they're anti-series already, how about polarizing them with a high-valued resistor to the neg. supply rail ? (connecting the bank in the centre where the '-'connections meet)
Don't want to tamper with the original design but it seems a nice opportunity.
[/quote]

that network of caps (that add up to what # I am not sure) looks like one hell of a DIY bipolar cap. They must be like that for a reason, which I'd be curious to know.


I can't find any info on the jumper connections from PS to preamp.

Thanks Dan! Very, very BIG of you to hand this out.

 

[JimiB]

This is incredible. Is there a list I need to get on?

 

[okgb]

the five pin header on the bottom right of the audio card is power in
for the card

previous info re gain switch & input xfmr
Elma 0806

04-1103-20

i bought a couple of these and they seem exactly
the same except for slightly longer shaft and they fit the mini pcb

Eventually i will have a couple gain switch pcb
with sm resisters to give to someone

Also quote from Dan " You can get Cinemags from Tom at cinemag.biz, the CMMI-5C for inputs is virtually identical to the JE-13K7 " less dough

I have used two of the Lundahl 1538 XL which i like and gotten a couple
of the Cinemags for my quad
,

 

[Ptownkid]

what is the mini pcb?

what do you mean by a gain switch pcb to give someone? So it can be laid out and made along with the channel pcbs?

Do we want to go that route, or should we select another 1x24, shorting with solder lugs?

 

[rlaury]

That bank of caps caught my eye also. Are they to couple the output to the transformer primary or somehow for the power supply?.
I don't think it's for the power supply. Just curious.

RonL

 

[SALSA]

The capacitor bank is in fact one big non-polar capacitor in the gain control : double value polar capacitors in series-parallel.

This reduces the height required in the enclosure , smaller values are probably easier to find and maybe there are some other advantages like lower resistance etc.

Cheers,
Mike

 

[guavatone]

Greg, it is unclear how the 2 schematics connect. PS has 8 connections while the Preamp has just 5. So I was trying to figure which pin would go where. Maybe thery are for 2 preamps and the ground is split to both of them....

Great work getting this together man.

 

[clintrubber]

[quote author="SALSA"]The capacitor bank is in fact one big non-polar capacitor in the gain control : double value polar capacitors in series-parallel.

This reduces the height required in the enclosure , smaller values are probably easier to find and maybe there are some other advantages like lower resistance etc.

Cheers,
Mike[/quote]
My first bet was on the height as well. In my Green-micpre-channels I use a single axial 4700uF/channel and had to put it flat to fit 1RU.


W.r.t. electrical differences between many smaller caps or one big cap:

DC-leakage seems to scale a little bit less than linear, so that is no plus for the many caps use.
For ESR the many caps seem to have a benefit.

Both just based on some figures from some Philips caps; other caps may give different conclusions.


Hmm, that center-node of the composite cap is still begging to get a resistive pulldown to the neg. supply :wink:

Regards,

Peter

 

[okgb]

Hey Rubber , Dan sez experiement all you like , that'd be a gas if you
could come up with an improvement !

Ptk , the switch is a pc mount type as the originals had a small pcb with surface mount resisters , maybe that part gets dropped ? Too hard for
me to see , but then again , will of the grp , not sure if there is a gerber for the gain switch board , but it would be a mother with all those wee resisters , but then again maybe i'm a wimp !

The psu pcb is designed for the quad pre so there are four headers that also include the comparitor input , I didn't realize that the regulators seem
only for the comparitors with the raw D.C. going to the local regulation of
of each preamp pcb , headers on the lower left hand side of schematc .

Without worrying about a psu pcb one can simply copy the first part of the circuit and not worry about the comparitors to make it easier if you like .

Best wishes everyone

 

[clintrubber]

[quote author="okgb"]Hey Rubber , Dan sez experiement all you like , that'd be a gas if you
could come up with an improvement ![/quote]
'Experiment' perhaps too big a word for a 100k...1M resistor from that center-node to neg. supply. :wink:

But most likely this will have already been tried and either did not much or did make things worse in case of a not clean enough supply.

if you could come up with an improvement

I'm just following this thread out of interest; I shouldn't build these pre-amps, however tasty they are (there are a few other things waiting to be finished)...


Have a good weekend,

Peter

 

[okgb]

I guess we'll put that in the question to Dan list

thanks for contributing

 

[mik]

another question :

what's the right turn ratio for input trasformer ?

P.S.
I love this place !
thank you folks !

 

[okgb]

power xfmr requirements = An off the shelf 30va 22 + 22 transformer will power this up just fine
you don't need to build the supply in the schematic , although it is nice

Suggested input Xfmrs
Cinemag CMMI-5C 150:3750
Lundahl 1538 XL 1+1:5
Jensen JT-13K7 1:5

Gain switch , anything 24 position shorting
[ the elma # Elma 04-1103-20 is p.c. mount ]

these , psu , gain switch & input xfmr are what you will need in addition to
the preamp board and hardware to complete the pre

 

[Flatpicker]

[quote author="okgb"]...virtually identical to the JE-13K7 "...[/quote]
You mean JT-13K7?

 

[okgb]

other than the main pcb for the Preamp , there is allot of flexability for going cheap [ er ] or convenience by making your own psu , choosing
the input xfmr you prefer and using a regular solder lug switch for gain
or even a reverse log 2k2 pot to get you started .

power xfmr requirements = An off the shelf 30va 22 + 22 transformer will power this up just fine
you don't need to build the supply in the schematic , although it is nice
with o/l l.e.d. drivers

Suggested input Xfmrs
Cinemag CMMI-5C 150:3750
Lundahl 1538 XL 1+1:5
Jensen JT-13K7 1:5

Gain switch , anything 24 position shorting
[ the elma # Elma 04-1103-20 is p.c. mount ]

For those of you brave enough , Dan has dug up [ Dig it ? .......Dug ! ]
the Gain switch pcb gerber , which is made for the smt sized resisters
I'll get it to Gustav & PtownKid , works with above elma number

these , psu , gain switch & input xfmr are what you will need in addition to
the preamp board and hardware to complete the pre

Regards Greg

 

[originalmusician]

Dan's generosity continues through the years. Quite some time ago he sent me some 2SK170BL FET's (free of charge), so I could mod some of my mics via the Scott Dorsey mods. I was sick and poor at the the time, so it meant a lot to me. Also, the FET's were nearly impossible to get in small quantities.

My health is good these days, and I'm looking forward to plowing into some more gear projects. BTW, this site rocks! I thought I was addicted to gear, but most of you guys are total gear pigs (I'm envious). Hopefully you will allow me to stick around and learn some things.

Raul Black

 

[Gustav]

[quote author="okgb"] Dan has dug up [ Dig it ? .......Dug ! ]
the Gain switch pcb gerber , which is made for the smt sized resisters
I'll get it to Gustav & PtownKid ,

[/quote]

It looks like Ptownkid is more updated on this project than I am, so I think it would be best to leave it solely to him if hes gonna have some boards made.

Gustav

 

[Ptownkid]

This is gonna be a sweet project, I'm getting excited!!!

I don't think I've said this yet, but you rule Dan, thank you very much for your generosity.

 

[udo]

I had a small run of 6 PCBs made for this project ... wanted to get familiar with gerber files and PCB fab order process, aside from making 2 of these for myself of course (thank you Dan! :grin.

So now I have 4 PCBs left over if anyone is interested. This is only the main PCB. I paid $78 for 6 ($13 each) and I would sell them at cost ($13 + $2 for U.S. shipping: $15 total each).

Please be advised that these are prototype PCBs (incl. soldermask and sikscreen) but were not electrically tested.
Anyone interested?
Thx, Udo

Edit: SOLD!

 

[okgb]

its a proven design so if the boards are exact , should have a great
preamp.
i have a gerber for the gain switch if you can deal with smt resisters
regards Greg