MA1 GERMANIUM mic pre support thread

[ppa]

- R16=10M or nothing on somebody´s BOM. My BOM just says 10M. Is it for different PCB versions or just different aplicattions ? (di bass, keyboards...)

you could avoid it to have the higher DI input impedance possible.

thanks
kind regards

 

[ppa]

Also I´d like to know about EA/Cinemag trafos in this pre. For what I read my guess is Cinemag would put things a little more upfront? More presence? Maybe a little bit more compressed sounding?. Maybe I´m totally wrong... Any thoughts would be great  Thx a lot

I have never tried the Cinemag transformers in this pre and I think taht nobody had tried them on it if I remenber well.
On the contrary quasi all have used EA transformers on MA1 eccept a Diyer who has used Haufe transformers with success.

thanks
kind regards

 

[pachi2007]

Thanks a lot Pier.
I´ve got continuity between the 2 holes next to C4 and C8 and the hole GND next to R21/R22. They all have continuity with GNDA and GNDP but not with CHASSIS. I´m sorry but I´n still not sure if a need to make this little mod.

 

[ppa]

ok, regarding chassis, is not necessary connecting it to gnda.

 

[ppa]

I´ve got continuity between the 2 holes next to C4 and C8 and the hole GND next to R21/R22.

the mod required should be done as in the following steps on the following posts.

On the photo attached there is the pcb zone of the mistake, you can see the ground plane is not connected to this hole.  : :

 

[ppa]

this is the hole that's the central point of the analog star ground (gnda):    8)

 

[ppa]

step1:

remove the solder on the top layer on the zone in the pic just scratching the solder.

We should have a little of copper of the ground plane to make the solder joint  , so.......

 

[ppa]

this is the zone scratched so the copper is now ready to be soldered over.  8)

 

[ppa]

step 2

here the solder joint made during the soldering process 

 

[ppa]

this is the only mistake of the PCB  ;D

 

[pachi2007]

Thank you Pier for your patience 

 

[mus1k_freak]

this is how i soldered in my ac126, to match the silk screen and the pin layout, is this correct? works fine with DI but not on mic input, trying different trannies now

 

[ppa]

ok, but there are two mistakes: C28 and C2 are 47pF not 470nF since you have used caps of 470nF for them, this is the reason of the dark sound i think. 

 

[ppa]

check R23 please, it should be 6.8k on the PCB to be right.

 

[mus1k_freak]

OK I'll  change those things and report back, I think this build is cursed ha very unlike me to make so many mistakes I think we almost got it

 

[mus1k_freak]

ok, but there are two mistakes: C28 and C2 are 47pF not 470nF since you have used caps of 470nF for them, this is the reason of the dark sound i think.

on your schematic c28 is 2.2uf and c2 is 47pf, so c28 should be 2.2?

ok c2 and c29 is 47pf, checking all my values now just to make sure, i see c28 you have on the bom as 1uf or higher so were good  8)

 

[ppa]

yes, 2.2 is good and better that 1uf but only theorically because the Ft is of 0.25 Hz with no phase rot. at 20Hz , with 2.2 uf ft is near to 0.1Hz

 

[mus1k_freak]

so after quite a bit of trouble shooting, shorted out transformers, a couple miss labeled silk screens and a few component errors i finally got this bad boy working! sounds great, definitely has a more warm and vintagey vibe to it then my other pres, looking forward to trying it out on electric guitar today!  8) ill post up some sound samples if anyone is interested

 

[ppa]

thanks for comments! much thanks.

regarding the sound sample they would be helpfull a lot!

Pier Paolo

 

[mus1k_freak]

here's a sample of the ma1 pre on electric guitars, just a short little ditty to test out how it sounds, ill try to get a sample of clean guitars up later.

https://soundcloud.com/mike-cantilina/ma1test