Building bass tube preamp. (Stupid) questions?

[madisqbu]

Yes Brett, I am a talkbasser.

I modified the schematic a bit - erased some parts from it (when being correct). What do you think - can I do such modifications - will it work?

[Brett]

Originally posted by madisqbu
Yes Brett, I am a talkbasser.

I modified the schematic a bit - erased some parts from it (when being correct). What do you think - can I do such modifications - will it work?

Too much gain. Each stage has 36dB or so and removing the Fender stack whic has an insertion loss of 20dB flat or 14dB in the centre detents is too much. Way too much.

Redesign around a higher transconductance tube like the 6N1P.

[madisqbu]

..so when replacing yhe 12xx-type tube with 6n1p-type one, it could work?

[Brett]

You'll need to recalc the anode and cathode resistors as well as the series resistors in the PSU (but I'd also redo this to get better filtering a la MJ's suggestions in VA). 6N1P likes substantially more current than a 12AX7.

[madisqbu]

oh, this is getting too complicated for me, i think i'll stay to the original design. But, yes, my original purpose was to make something like a tube di (with gain and vol controls) what could also power a power amp. So its something like A-designs REDDI or (as mentioned above) Lowend truevoice. Does anyone know how to make something like this? Schematics? should i instead look for mic preamp schematics, when i want to make something like it? My goal is to make something as simple as possible and sounding as neutral/flat as possible?

greetings,


Madis

[gerryc]

Originally posted by madisqbu
oh, this is getting too complicated for me, i think i'll stay to the original design. But, yes, my original purpose was to make something like a tube di (with gain and vol controls) what could also power a power amp. So its something like A-designs REDDI or (as mentioned above) Lowend truevoice. Does anyone know how to make something like this? Schematics? should i instead look for mic preamp schematics, when i want to make something like it? My goal is to make something as simple as possible and sounding as neutral/flat as possible?

greetings,


Madis

If you want to stay to the original design, the only thing I would suggest is to replace the Fender-style tone stack with a Baxandall arrangement (look at the preamp section of almost any Ampeg bass amp, e.g. http://www.drtube.com/guitamp.htm#Ampeg ) and you can pretty much just lift the bass/treble arrangement and substitute it into the F-2b circuit. The reason that I say this is that you stated that you wanted something that is as neutral / flat as possible. You can get that with the Baxandall arrangement, but not with the Fender style tone controls. Check out Duncan Amps tone stack calculator and play around yourself.

[madisqbu]

to gerryc. Good idea. I did a little search and found this - http://amps.zugster.net/articles/tone-stacks#Baxandall

As I understand, this version is made for using with guitar amps. What should i modify? (for example: replace the 500k pots with 250k pots?, or just loo ampeg preamp schematics and take values (resistors/caps) from there or from original (alembics) design.

So as you already noticed, i'm a bit (not to say very) confused.

regards,


Madis

[Brett]

Go to duncanamps.com and download the tone stack generator program. Change values till you get what you want.
In the first instance, copy values from a bass head such as the SVT. And I'd probably tweak the values of the caps first.

[Brett]

http://members.aol.com/portaflex/schems/svtpream.gif

[Geek]

Originally posted by Brett
http://members.aol.com/portaflex/schems/svtpream.gif

That's a pretty bright setpoint for a bass Baxandall treble control...