Double Shot..my new project, tube preamp..layout & pcb

[dschwartz]

well.. i don´t know if anyone still cares.. but

this thing is noiseless now!!!!!!
i rewired the output section, bypassed a master volume pot and the passive fx loop, just to hear what happened with a properly grounded output..
and this thing is quiet as a dead mouse!!!!!!! really really good!!!
i think is due to the different angles i attacked the problem. (heaters regulation, filtering and ground reference, B+ filtering, star grounding, shielding wires, perpendicular wiring, jack isolation, chassis shielding, etc..)

one more thing..it had a strage ugly clipping..allways present...i reversed the mosfet and voilá!!! really great smooth clipping!!! that´s odd cause i originally put the mosfet according to the datasheet pinout...well.. i think, if it sounds better, then is correct...

Now i know that the hum was not coming from the main board or input signal cables, the layout is OK..i have to redo now the master volume and fx loop section, but with proper grounding and shielding..

The next step is tweaking the tone..change some caps here and there..

One question though: i used the scaled down tonestack version from gaussmarkov´s dr boogey (all resistors 10 times lower, all caps 10 times higher) in order to get better output impedance..but my bass tone control is not quite effective..i mean, it doesnt change anything at all.. remember i have a mosfet buffer, probably with a lower output impedance than a tube...is that OK? 

The sound has a nice low end whoomp, so it´s not a lack of bass content..i think the freqs affected by the control were shifted down.. any suggestions?

MAN I´VE LEARN A LOT!!!!!!!!!!!!! THANKS TO ALL YOU GUYS!!!! REALLY!!!

[Auke Haarsma]

well.. i don´t know if anyone still cares.. but

this thing is noiseless now!!!!!!

Awesome! I've been following this thread since it was posted. Keep it up man!

[Mandrake754]

i too have been following this thread. ordering the parts to build my own very soon.

Cant remember now if it's been said, but what power transformer are you using, and is your preamp voltage way lower than mesa's for any particular reason? (theirs are run around 400v)

Reason I ask, is that weber makes a 260Vsec/100ma, 6.3V/3a transformer for $15 that could possibly do the trick as long as 330-350v is ok (or better? closer to original?) for running the preamp...

[dschwartz]

i´m running it from a back to back pair of transformers.. ordinary ones...

220-12 to a 9-220.. that gives me around 320V of b+ ....is enough...

[slideman82]

yes peter, that´s the traditional way when you have 6.3V AC..

i´m using 12VDC regulated.. so it´s not necessary to twist the wires..

God's sake!!!! (is this correct?) Daniel, do not blasfem!

Ampere's law tell us about how magnetic flux and current are related, and that's the first principle U must use coaxial cables on videocable TV or AC or DC (yeeeeeeeeeeeeeah! AC/DC!) filaments! And experts always say "just twist the, doesn't matter..."

So why, in the name of God, I have to spend 4 months of my life studying Physics nº2 at the university (well, they were 8, I have to do the course twice...) learning about these???

Va en castellano:

Para què carajo estudio para poder ser (lo serè?) ingeniero electronico, cuando una de las materias me explica sobre los flujos magenticos y su relacion con las corrientes por el mismno conductor que genera ese flujo magenetico, para que alguien diga "enrollalos, nad mas"?? El cable mallado aka coaxil/coaxial se creo para eso! Asi no tenes señal saliendo o entrando al cable (bueno, si la malla fuera completamente sin huecos...)

A proposito, Daniel, tu laburo es del carajo!!!!! Muuuuuuy bueno, y me quedo corto! Pero fijate, que los PCB de las paginas mencionadas no son comercializables (invente una palabra?)

[dschwartz]

a qué PCB´s te refieres??
..

okay, i.m not an electronic´s engineer, so dont get so mad man!!! ..i twisted the wires anyway!!!

[12afael]

slideman, you need a variable magnetic field to have electromagnetic induction, if you use DC on the heathers they shouldn´t induce noise on the signal unless you have a mecanical vibration of the wires.

I did that class two times too  = tambien di ese maldito ramo 2 veces...
saludos

[d95err]

Seems like you made it work after all! I admire your persistence and patience. good work! Now you can get down to the fun part - fine tuning and tweaking. I hope we'll get to hear some clips of it... 

[dschwartz]

yeah thaks!!
i´ll be posting some clips this weekend.. as soon as i tweak the sound as i like..

[slideman82]

slideman, you need a variable magnetic field to have electromagnetic induction, if you use DC on the heathers they shouldn´t induce noise on the signal unless you have a mecanical vibration of the wires.

I did that class two times too  = tambien di ese maldito ramo 2 veces...
saludos

yes, you're right, a time dependent magnetic field (function of t...). Anyway, I always use shielded cable!

[dschwartz]

I have to add something...

i left out all the bypass caps ground lifting for less gain ideas..it was screaming GROUND LOOPS!!!!!!!!! and the sound was not very nice either because of the wider band of amplification and harsher clipping.. instead, for a hi/lo gain switch, i placed a switchable resistor to ground  parallel to the OD gain pot..it works much better and quieter.. and its so simple...

[Plinky]

yeah thaks!!
i´ll be posting some clips this weekend.. as soon as i tweak the sound as i like..

Can't wait to hear them. Awesome project. Kudos to your hard work.

[dschwartz]

OK.. is showtime!!!!!!!!
i finally recorded some demos...
the preamp is going directly to the sound card, through my korg ax1000 amp sim (not so good) no added effects..
now..the goods:

- clean channel..tweaking from clean clean to mean crunch:
http://diynoise.googlepages.com/clean2.mp3

- high gain channel..tweaking from lower gains to higher ..
http://diynoise.googlepages.com/gain.mp3
Notice the super low noise!!! thanks guys!!!
especially to richon and d95err...

some pics:
front:


back:


point to point tonestack (what a mess!!!):



main board an PS:


guts:

[petemoore]

  Wow! glad it is working great !
  Both sides too !
  the Soundclips brightened up my day !
  Thanks
 
 

[Auke Haarsma]

IN-CRED-IBLE!

Man that thing sounds good! Really really nice clips!

(and nice chops too!)

[bensoniski]

It sounds great - well done!

[andronico]

Fantastic man ! 

[dschwartz]

Thanks for your replies!!..
anyway, did you noticed a bit of excess of bass content on the high gain clipping?..at max gain sounds a little fuzzy i think....

[alfafalfa]

This thing rocks !!

What tubes did you use ? 
Oh yes, Is your schematic up to date now ?

Alf

[dschwartz]

no.. i have not updated the schem.. as soon as i have the time i will