Great River MP-2 , info, schematics & discussions

[Bluzzi]

[quote author="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 ?[/quote]

I'll admit to one unfnished LA2A (turret board done and heaters wired), 2 GSSL not even started!

The MP-2 is my latest and I'm farther ahead than the previous!

Glad to see I'm not the only sick one here!

There is a 1073 project starting to happen and I'm looking forward to that one too!

I'm taking my time on this one as its my first PCB project. The parts discrepancy does not have me worried. Dan's message gives the impression that there is some flexibility to some of the parts and the design was in constant change.

I'm also waiting on a printer to give me some sample back of a trial panel marking design. This is my biggest problem. PANELS!
If it works out I'll report back here.

I'm stuffing from smallest to biggest components (for you veterans out there that is probably boring but someone else starting it can save a lot of pain).

If anyone wants I can post pictures of the progress.

jim

 

[Bluzzi]

[quote author="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.[/quote]

I sent you a PM. Don't worry about making this thread longer. Having notes on parts is useful for future DIYers.

jim

 

[Dan Kennedy]

Don't feel bad guys, I've got a mic project here that I've been sitting on for three years. Got the capsule, the supply, the cable, the screens, the tubes, the brass rail, just no time.

I just pulled a StaLevel out of the backroom, first time I thought of it in five years. Now that they're getting hot, I think it's time to see if it works and get some cash out, it's been another backburner project.

I've got an Ampex AG-440 to rebuild back there too, and one down in Missouri I have to go pick up.

Oh, yeah, forgot the 224XL that needs some TLC.

Happens to everybody...

 

[Ptownkid]

Glad you found those diodes Jim, I told you so...lol

 

[okgb]

Yep , the " from scratch " projects always slow down for me in the hardware and panel , we all know when it looks nice EVERYONE feels better about it !
Then i keep delaying parts orders cause i want to get everything in one
drop , but then subs & backorders and new projects ................

Haven't seen Drpats finished thread in a while ,

 

[Bluzzi]

[quote author="Dan Kennedy"]Don't feel bad guys, I've got a mic project here that I've been sitting on for three years. Got the capsule, the supply, the cable, the screens, the tubes, the brass rail, just no time.

I just pulled a StaLevel out of the backroom, first time I thought of it in five years. Now that they're getting hot, I think it's time to see if it works and get some cash out, it's been another backburner project.

I've got an Ampex AG-440 to rebuild back there too, and one down in Missouri I have to go pick up.

Oh, yeah, forgot the 224XL that needs some TLC.

Happens to everybody...[/quote]

Dan, I have access to an MM1000 that is no longer being used! 16 channels of AG440 (I'm not sure which version as I'm not in front of it).
Would you need anything from it that would help?

jim

 

[josh]

I'm going to attempt to build the power supply right from the schematic. What do you guys use for that sort of thing?

I like to mock up cases and panels out of cardboard until the real thing gets designed/completed. I dont think that would work in this case

my 1176 is pretty unique at this point though. :green:

 

[ulysses]

Since the 2SK389 is so hard to find now, I thought I'd offer my suggestion on what to do about it. The Linear Systems stuff has been fine for me, and easy to buy directly from them, but the different package configuration on the LSK389 makes it a deal breaker as far as I'm concerned.
The 2SK389 is just a matched pair of 2SK170 FETs, so the best sub option right now is a pair of hand-matched 2SK170s (or you can use LSK170 from Linear Systems). I've had good luck matching 170s into pairs for discrete op amps (a dumb idea for production, but fine for one-offs). The 2SK389 has 7 pins, but you can ignore the middle pin. I believe the two 2SK170s will have to face opposite directions, but check the pin-outs to be sure. It would be nice to thermally couple them, which is harder to do in this arrangement but I doubt it'll be the end of the world. I suppose you could stick them to a common heatsink.
To match the 170s, I measure a bunch of them by applying a voltage to the drain (I've generally used 18V), grounding the gate, and putting perhaps 200 ohms from the source to ground. Measure the voltage on the source and you've got a reasonable metric for the FET. It's tricky because this measurement is temperature sensitive, and the amount of time the part spends in your hand while putting it into the test jig will affect its temp. The amount of time you leave it in the test jig will also affect its temp. If you can manage to treat several pieces the same, you should be able to get a pair matched to within say 2% or so. This is much easier to do if you have a pile of them to measure, so it may be worth a group effort (if it comes to that - there are still 389s out there someplace). I've never built Dan's amp, so I can't say for sure this level of matching will be acceptable, but it seems to be about the same as the degree of matching between the devices on the LSK389 so I think you're better off than trying to twist the leads around on the wrong package.
2SK170s are still available from Newark / MCM. They aren't in the catalog, but they show up if you search correctly on their web site. Beware: I bought 1000 pieces from Newark, and they showed up individually packaged in their own antistatic bags - in four giant boxes. I still haven't unwrapped them all. They could all easily fit in just one of these bags. In hindsight, I should have refused delivery.

 

[okgb]

Everyone with boards has the fets , if a second run is done i think
ptown was thinking about modding the board for the new part , but

thanks for the simple but good idea [ & shipping heads up ]
how's bussiness going ?

regards Greg

 

[dissonantstring]

hi guys,
i'm not even close to getting this started, but i've been loading my head with info for when i do. i have a question about the PSU...

there's onboard regulation for the +/-24VDC on the amp board and i do not see the 48V regulation so rectification and 48V regulation needs to be on a seperate PSU correct?

greg, do you have any idea of how much current each amp board is pulling?
thanks for your help!
-grant

 

[nrgrecording]

[quote author="dissonantstring"]
there's onboard regulation for the +/-24VDC on the amp board and i do not see the 48V regulation so rectification and 48V regulation needs to be on a seperate PSU correct?[/quote]

There is a small LM317 nearby the relais with a zener... i think this is for the phantompower. At least its routed to the 6K81 resistors. :wink: When shorting pin 1 and pin 2 on J6... 48V is on.
Wiring is something like this: (untested)
http://www.nrgrecording.de/temporary/MP2 Wiring1.pdf

switchpcb: (untested)
http://www.nrgrecording.de/temporary/MP2 Wiring1.pdf

Frank.

 

[dissonantstring]

wow frank! :shock:
you've got very good eyes...or mine are really bad! :wink:
now i see the 317 v-reg. in the TO-92 package with the zener. i did see the 6K81 resistors, but just thought they were mounted for current limit without the regulator on-board, but now i see (with the help of your always awesome wiring diagrams)!
that clears things up. :thumb:
thanks so much!
regards,
grant

 

[Bluzzi]

The first link is not working for me. The second is OK.

Thanks Frank.

jim

 

[nrgrecording]

[quote author="Bluzzi"]The first link is not working for me. The second is OK.[/quote]
My fault. Now it works.

 

[Bluzzi]

It works now Frank but they seem exact same to me? Are they?

jim

 

[okgb]

As answered yes , the 48v regulation is onboard each preamp
feeding it a raw dc of a bit more than 50v should be fine ,
there is an input for it on the power connector at the rear of the board.
current wise i'm not sure , but i'd say at least as much as the most
power hungry microphone
[ what could that be 25 ma ? ]

 

[ulysses]

[quote author="okgb"]at least as much as the most power hungry microphone [what could that be 25 ma?][/quote]

14mA. But that would be into a dead short, which would leave you with no volts. I doubt there's a microphone out there that functions while pulling more than 10mA from a proper phantom supply.

 

[Bluzzi]

When installing MJE-171, MJE-172 etc and mounting to heatsink is it necessary to use heat conductive paste? between heatsink and component?

Thanks

jim

 

[okgb]

Don't think it would hurt , so why not ?
attention to detail , make it as good as possible
perhaps you know someone to borrow ?

 

[Bluzzi]

Thanks Greg, I wasn't sure. Since its not mandatory, I'll find some locally later then unscrew the part and apply.

Most of the transistors are not marked by P/N in the parts layout. I'll be modifying it to include the correct P/N so if anyone wants it let me know.

jim