Great River MP-2 , info, schematics & discussions

[Rogy]

Hi Greg,

I'd certainly be interested in having a copy of the gain switch board gerber

my mail address: [email protected]

I will definately make some of these to have another option in my sound pallet.

Thanks!



Rogy

 

[AudioJunkie]

I'm confused. Is Gustav or Ptownkid going to be making the boards? I couldn't see anywhere on the thread where Ptownkid was going to do it. But looks like Gustav was going to let him make the boards instead.

If no one is going to make the boards, where would be a good place to send the gerbers to have a few made up for myself then?

Daniel

 

[Ptownkid]

Yes i will be getting them made.

 

[AudioJunkie]

AH. Very good. I just couldn't remember seeing you mention that you were going to do so, and had thought Gustav said he was going to.

Excellent. I'll keep my eyes open for when they are ready.

Daniel

 

[Bryson]

[quote author="bernbrue"]Hi,
initially I had no idea what the discussion was about. After reading a short description of the preamp, it seems that a very interesting DIY project is coming upon us. Thanks to all, who contributed to this project with their knowledge and enthusiasm. For better understanding (for newbies like me):

http://mercenaryaudio.com/greatrivelmp.html
[/quote]
That is the newer MP-2NV which is more Neve like than the original MP2, which was more of a neutral (but sweet) sounding amp. I think Dan may still offer the MP-2 on special order.
Way cool of him to wave us forward on this project.
I hope no one ruins it for us by adding it to their eBay offerings.

 

[Bluzzi]

This is it! This is the preamp project I was waiting for!

I'll compile the BOM into Excel and try and get prices/minimums etc.

Will someone be trying to get the FETs and inductor from Dan? I guess it should be Ptownkid? This way we can get the PC Board along with the Fets and inductors in 1 shipment.

I am very excited about this project. Lets not let it slide...please.

jim

 

[Ptownkid]

not to worry, i am already working on all the details and I will be offering parts kits as well as the pcbs

 

[madriaanse]

that *R*U*L*E*S*! Thanks Ptownkid!! Keep us updated!! :thumb:

Martin

 

[joe-electro]

Count me in for two kits whenever!

 

[Bluzzi]

[quote author="Ptownkid"]not to worry, i am already working on all the details and I will be offering parts kits as well as the pcbs[/quote]

Great! Looking froward to that.

I almost have the BOM finished.

Also how much juice is needed for a 2 channel unit? Is the 30VA transformer for a 2 channel or just 1?

For those wanting to solder the resistors directly to the 24 position switch it would be Elma 04-1100 or 04-1103 (same switch just a gold coating difference). There is also the 04-1130 and 04-1133.

jim

 

[Bluzzi]

Another few question.

24 position switch resistors. 1% 1/4watt Metal Film OK?

On the 24 position switch wiring R22 is two 17.4 ohms resistors. I am presuming we can sub with one 34.8 ohms?

Same for R23. Sub with one 28.7ohms instead of 17.4ohms plus 11ohms?

Lastly R24 sub with one 22ohms in lieu of two 11ohms?


Jim

 

[udo]

I understand that the original Toshiba 2SK389 comes 3 different IDSS classifications:

GR: 2.6 - 6.5mA
BL: 6 - 12 mA
V: 10 - 20 mA

Can anybody please tell me which of these types should be used in this circuit?
Thx, Udo

 

[okgb]

Note that the switch pcb [ was ptown able to forward it to you ? ]
is double sided with resisters on each side .

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


The xister question is a good one for Dan ,
I have some questions in to him and waiting for a response
will check it out , regards Greg

 

[Bluzzi]

Greg, thanks for the transformer info.

What about the values for the rotary switch? (see question from me a few messages back). (the switch pc board is for surface mount resistors which I presume not everyone wants to use.)

I'll complete the BOM soon and I will post it on my site (unless someone else wants to put it up).

jim

 

[okgb]

Some answers from Dan

Regarding peterubber's question of the switch capcitor bank ;

From the Dan

I was trying to reduce the worst of the parasitic effects, ESR as the
major one. The reason I didn't bias the center point is due to the
rather poor leakage specs
of electrolytics, any bias shows up at the output, as well as causes dc
shifts when the gain changes. If they were perfect it'd be a good idea,
on the other hand
I wouldn't need to bias 'em if they were perfect.

Re the xistors

>I understand that the original Toshiba 2SK389 comes 3 different IDSS classifications:
>
>GR: 2.6 - 6.5mA
>BL: 6 - 12 mA
>V: 10 - 20 mA
>
>Can anybody please tell me which of these types should be used in this circuit?
>Thx, Udo

Dan used the " V " s

Re; the switch resistors

>On the 24 position switch wiring R22 is two 17.4 ohms resistors. I am presuming we can sub with one 34.8 ohms?
>
>Same for R23. Sub with one 28.7ohms instead of 17.4ohms plus 11ohms?
>
>Lastly R24 sub with one 22ohms in lieu of two 11ohms?


Again Dan sez

They're in parallel actually, so it's 8.7 ohms, 6.7 ohms and 5.5 ohms,
good luck buying these...

o.k. hope that brings everyone up to speed , regards Greg

 

[clintrubber]

[quote author="okgb"]Some answers from Dan

Regarding peterubber's question of the switch capcitor bank ;

From the Dan

I was trying to reduce the worst of the parasitic effects, ESR as the
major one. The reason I didn't bias the center point is due to the
rather poor leakage specs
of electrolytics, any bias shows up at the output, as well as causes dc
shifts when the gain changes. If they were perfect it'd be a good idea,
on the other hand[/quote]
Thanks for passing on this info.

I wouldn't need to bias 'em if they were perfect.

Nah, that's a cool quote but is cheating a bit of course :thumb: :grin:

It's actually entangling two different things.

You CAN wish that a perfect electrolytic had zero leakage. Cool. But would it be reasonable to expect from a normal electrolytic polar cap that it suddenly lost its '+' & '-' upon entering a perfect world ? :shock:
Yep, in a sense one could say, as in that it became a bipolar (non-polar cap), but...

All cool, read more about that 'center-tap' in the cap-thread that's now going on.

Or just skip that, 'cos it'll take more than a few cups of coffee to digest the info over there. Quick conclusion from there is that the center-tap resistor isn't the holy grail, just use a recent bipolar. Dunno if these are easy to get in such values as needed here though.


Cheers,

Peter

 

[Bluzzi]

Thanks greg for clearing up the switch resistors.

Also thank Dan for his generosity.

I will also make a BOM for the power supply even though many will probably choose to make their own (or JLM maybe?).

Ptownkid, will you be making PCBs for the power supply too?

jim

 

[Purusha]

Great, more preamps on the horizon :green:

Guys, let me know if you need a specially designed racks for this projects. :thumb:

 

[okgb]

The man checks in very so often , but i'll thank
him for everyone

 

[Ptownkid]

Well, not those specific psu's, but I'll have some that'll do the job.