JENSAMP-51X (Germanium Mic-Pre by Darius Kubarth)

[mylesgm]

I really like my pair and would consider building another pair but I would like to see an on board pad. Any chance of adding this?

 

[[silent:arts]]

I would like to see an on board pad. Any chance of adding this?

I talked to Darius about the PAD, and he is negative about it.
He suggests different pads for 600R / 2k4 which makes it too complicated to implement.

I do not want to change anything the designer doesn't suggest or isn't fine with it.

 

[[silent:arts]]

Ok, started ordering parts for 50 more kits.

 

[dmp]

Why don't you fix the DI problem before ordering more kits?
Or remove it. A fixed value pad would be much more useful on these than an unusable DI.

Edit: missed your post saying you made a mod.
Has anyone confirmed this fixes the DI problem? I'd like to try on my pair, but haven't had the time.

 

[[silent:arts]]

Why don't you fix the DI problem before ordering more kits?
Or remove it. A fixed value pad would be much more useful on these than an unusable DI.

Edit: missed your post saying you made a mod.
Has anyone confirmed this fixes the DI problem? I'd like to try on my pair, but haven't had the time.

Well, different people with different application needs. Most Jensamp users do not use a PAD.
Most people use the DI without any mod, and like it.
Why change anything if 80% or more of the users like it "as is"?
Now the designer tells us (me) it would change totally the sound and application he designed it for.
I will change or "fix" nothing he is not happy with!
This isn't meant to be a universal PreAmp for all sources.

Btw, no pad (in front of the mic input transformer) would change anything with the DI.

 

[Dr Gris]

This is so cool!!
Thanks for doing this. Although I'm not in the market for pres at the moment,
this and your PMV and OV pres are so tempting.
Come to think of it, it's fantastic that these not so known well engineered pres exist in kit form.
I hope they'll be around the day I can't resist anymore.

Best
Magnus

 

[dmp]

OK, I changed the DI to the 68nf/100k on one of my Jensamps. It didn't make a noticeable difference to the observed problem.
I confirmed it works fine when using a separate DI in front of the mic input on the Jensamp (either a Jensen DB, or Bo-Hanson Active).
I was using a Fender P-Bass with a passive pickup. Would get pops when using the Jensamp DI - it sounds to me like a DC problem also, although I don't know why it would happen looking at the schematic.
Maybe this is a case where the design doesn't work very well for passive pickups - putting the DI signal unbuffered to the first transistor? It probably would work fine with a keyboard or something, if that is what "80% or more of the users" are using.  Or maybe some transistors work better than others?
Or a HighZ plugin to fix it?

 

[[silent:arts]]

Maybe this is a case where the design doesn't work very well for passive pickups - putting the DI signal unbuffered to the first transistor? It probably would work fine with a keyboard or something, if that is what "80% or more of the users" are using.  Or maybe some transistors work better than others?
Or a HighZ plugin to fix it?

Well, now we are down to too much level for the Jensamp in your application, sorry for this.
No transistor problem, nothing to fix. Use the external DI with this is the best, I guess.

 

[[silent:arts]]

added rev04 documents:

Jensamp-51X rev04 schematic
Jensamp-51X rev04 gain switch
Jensamp-51X rev04 PCB overlay
Jensamp-51X rev04 Parts-List

changed since rev03:
- C7 polarity
- C14 changed to 68nF
- R18 changed to 100k
- output transformer changed to Haufe RK494/3
!!! NOTE: the Haufe RK240/2M won't work any more, different footprints !!!

 

[Moreorless]

Jensamp-51X rev 03 with VU meter

 

[ssp3]

Legit question. I'm waiting for two major unknown prices: Haufe RK240/2M and ASY26.
Requested both today, but don't have an answer yet.

I'm a bit late to the party, therefore, please excuse my silly question. According to datasheet RK240 is an INPUT transformer (Eingangsubertrager). Why are you using it on output?

 

[[silent:arts]]

we used the Haufe RK240 since it worked very well on that output, and we had a major quantity in stock.
however, the new rev04 uses Haufe RK494/3.

 

[jarekvip]

Hi guys, I wonder if this ASY26 really adds something to the pre sound ?
Is there an audible difference when You compare it to full silicon Jensamp ?
As I see there is a writing "Germanium preamp", but there is only one germanium transistor, or am I wrong ?

BTW Very nice project!

 

[[silent:arts]]

Finally there are 50 full kits available again

 

[gouge]

hi silent arts,

I;m keen to grab a jensamp kit from you. hope you're selling them. sent you a pm.

cheers.

 

[egs]

Built one today. A tip for other inexperienced builders: do not solder the LEDs flush to the PCB. Look at this picture how they are to be mounted into the faceplate: http://www.benlindell.com/wp-content/uploads/2011/11/Jensamp-51X13.jpg

Besides that little stupid error everything went OK and the preamp worked when I tested it. 

 

[Upacesky]

Building the Jensamp (51x, rev04) was easy for a beginner like me. I never felt lost.
But now comes the troubleshooting.

From position 1 to 4 everything's fine.
after position 5, I get loud noise when switching and then a pulsating sound (who plays with a synth here?!?) as Benlindell describes in his post 108.

LEDs are working.
The problem seems to be independant from load, phase switch, 48V etc. It's always here.

Any thought?

 

[Winetree]

Check out my post #112. Never solved the problem. Just gave up on them.
If you find an answer, I'd be glad to hear it.

 

[culteousness1]

From position 1 to 4 everything's fine.
after position 5, I get loud noise when switching and then a pulsating sound (who plays with a synth here?!?) as Benlindell describes in his post 108.

I posted some sound samples over at Frank's forum a while ago.
Maybe you could compare your noise with the one in my sound file.
Watch your speaker's volume before listening. Kubi may have a solution...

Best,
Carsten

 

[Dr Gris]

Built my pair a week ago. Same pulsating thing in both of mine.
Haven't had the time to check them yet.
Transistors and transformers are spaced from the PCB and the stop pin in the Grayhill
is at 12 o'clock, component side horizontal facing up. I think that's correct?

I probably did something stupid....

Extremely nice kits. Thanks Volker!!

Best regards
//Magnus