Great River MP-2 , info, schematics & discussions

[Bluzzi]

I was just checking resistors on one of my kits and I seem to have an extra 20 OHM resistor and a missing 10 OHM one (R47).

Anyone else?

jim

 

[Neeno]

Thank you for your help Jim !
I have a extra 20R 1W and a missing 10R also.

 

[Bluzzi]

Does anyone know if we need some "contact paste" for the heatsinks or just mount without is OK.

jim

 

[Bluzzi]

[quote author="Neeno"]Thank you for your help Jim !
I have a extra 20R 1W and a missing 10R also.[/quote]

Neeno, no peoblem. Glad to help in any way I can. Let me know if you still need picts of my ugly switch work.

I haven't checked the capacitor values yet so if anyone gets to that please post results. Thanks.

jim

 

[okgb]

A question for the Man

i got it in to him , will let you know & post the answer

regards Greg

 

[Ptownkid]

The bom lists r47 as 20R, while the parts layout ans the schem say 10R...I have no idea which one is correct.

 

[Bluzzi]

More missing parts!

D1 and D2 are both 1N5258 but there is only one diode other than the 1N4148 and its not marked.

I presume its D16 which is 1N4748 since there is only 1.

Again the BOM is not showing those parts but the schematic is!

However D1 and D2 are missing nonetheless!

Please check your parts as it may be only me (both my kits have same diodes).

How do I know the single diode is a 1N4748 as in schematic?

Ptownkid, its probably a 1N4750 as in BOM right?

So another question for THE MAN !

I'm going to go ahead and start soldering the 1N4004 and 1N4148 for now.

jim

 

[Ptownkid]

I have not looked at the schem at all, i used the bom exclusively.

 

[Ptownkid]

the single is a 4750

 

[okgb]

the earlier Question answered fron Dan

Either will work, it's a tone issue. The 10 ohm is a little cleaner and tighter, the 20 just a bit tubbier. The output transformer is sensitive to driving impedance, which is determined by the value of this resistor.

i will clarify if this is only an issue when using the output xfmr

regards Greg

 

[Bluzzi]

thanks Greg.

I'm not using an output transformer for now so I'll just use the 20 for now.

(got my Lundhals today! Tiny things. Do you have the wiring for the terminals since you used these?) Thanks.

jim

 

[okgb]

I printed the info from the lundahl site , there is two windings on the primary ,
but i just went with the 1:5 version of it .
If you can't find it , i'll look for mine , just a matter of tying pins together ,
if you pick up a strip of copper clad perf board that will secure the xfmr
when you solder it , careful as the pads may be close to each other
and that you don't accidentialy ground the the perfboard to the case
[ if at all , it should go back to the i/o ground bar ]

regards Greg

 

[Bluzzi]

Thanks Greg.

I can always put some insulating material between the case and the board.

Here is the link to the DWG for the Lundhall if anyone needs it.

http://www.lundahl.se/pdfs/datash/1538_8xl.pdf

jim

 

[Dan Kennedy]

Sorry for the confusion.

This stuff is all pulled from obsolete drawings, so they don't all necessarily reconcile.

The 20 ohm/10 ohm issue is minor, very slight change in the sound, since the transformer is sensitive to driving impedance. I prefer the 10 ohm, or I did 10 years ago...

The zener around the 48 volt regulator should be a 1N4750A.

 

[Bluzzi]

Thanks for taking the time to answer Dan!

I'll use the 20 for now as I'm not using an output transformer. I'll make notes in case I add one later on.

Likewise, I guess the two 1N5251 in the BOM replace the two 1N5248 in the schematic?

and thanks again for making this available to us. Its my first mike preamp as well as my first solid state project.

jim

 

[Ptownkid]

WOW, really? You have 500 posts and no mic preamp...damn man.

 

[Dan Kennedy]

Yeah, I moved the value of the zeners up at some point, a little better headroom on extremely high level inputs.

This preamp basically went out of production about five years ago, and it was always a moving target, so if something doesn't make sense, be sure to ask, I'll try to remember...

 

[Bluzzi]

[quote author="Ptownkid"]WOW, really? You have 500 posts and no mic preamp...damn man.[/quote]

OK, I guess I asked for that one! No this is my first DIY pre. I have 27 others that I didn't make.

500 posts! You noticed? Do I get a prize? maybe the missing parts from the kit?


jim :grin:

 

[okgb]

there ought to be a rating , a ratio of started projects Vs Completed
projects , but who would admit it ? [ whenever i get stuck , i move on
to another one , because there is ALWAYS something else to work on !]

When i get some time , i'll mp3 ya some classical stuff Bluzzi

Who will finish their PM-2 first ?

 

[Ptownkid]

[quote author="Bluzzi"][quote author="Ptownkid"]WOW, really? You have 500 posts and no mic preamp...damn man.[/quote]

OK, I guess I asked for that one! No this is my first DIY pre. I have 27 others that I didn't make.

500 posts! You noticed? Do I get a prize? maybe the missing parts from the kit?


jim :grin:[/quote]

I meant DIY pres, and technically, you arn't missing any parts. Speaking of which, if you are...e-mail me. Posting it here is just making the thread longer.