Building bass tube preamp. (Stupid) questions?

[gerryc]

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

As Brett suggested look at that SVT preamp schematic. Since that's a bass amp, the turnover frequencies should already be appropriate for a bass guitar application as opposed to guitar. Just use the values that are there and build it that way. You can always tweak the values a bit later if you want to, using your ear as well as the tone stack calculator if you like. Give it a shot. You most likely won't be far off and you just might find it acceptable. Ignore the values from the Alembic preamp.

 

[t_blizzard]

Madisqbu,
It sounds like you want to do a custom design.
Why are you using the Alembic circuit?

 

[madisqbu]

yes, i thought i want custom design, until i found out that actually i don't know anything about designing one. Hehee. So i desided to use cirquit that would work, and then start to modify it, when i want to. That's how i can "turn back time" and learn in the progress what does what.

About the preamp building. I've finished constructing the PSU section, everything seems to work normally. I'm waiting for some caps i don't have jet, then i'm able to put it all together. Though i have problem regarding schematics.

In these schematics http://moosapotamus.net/IDEAS/F2B/alembic.htm there is cap C8 (22uf/350v) in main cirquit and R4 470k/3W in the PSU section

but in this schematics http://www.geofex.com/FX_images/alembpre.gif there isn't.

what's the thing????

I tried the first one in practice, adding the R4 to PSU drops the voltages.

 

[t_blizzard]

Any specific reason for wanting to use 6SN7's?

 

[t_blizzard]

R4 will cause a little more draw on the supply.
C8 is a filter cap for the supply as well.
Neither are very critical in values.

You might be suprised at how difficult it is to get schematics working that are off the net.

You may end up going custom from the begining......

 

[Brett]

Any specific reason for wanting to use 6SN7's?

It helps to quote at least part of the original post so people have some idea of what you're talking about.

 

[Brett]

You might be suprised at how difficult it is to get schematics working that are off the net.

I've never had any difficulty at all.

 

[t_blizzard]

ok, i think im going to use the original alembic diagram. My concern is the power section.

I found this schematics from internet

http://moosapotamus.net/IDEAS/F2B/AlembicF2B_PSU.gif

what do you think about it? Decided not to buy the Hammond transformer. How should i modify this schematic to use 220v to 12 vDC power adaptors? What to add, to get around 300v from the high voltage section?

thanks,

ps. I'm a real newbie, this is my first DIY project.

Read this PDF on gain stage design and you can use the same procedures for your 6SN7 gain stages.

Gain Stage Design:
http://www.trentonblizzard.com/My_Homepage_Files/12AX7 Gain Stage.pdf