New project, "Ultimate Studio Preamp"

[nandrewjackson]

Hello, I've been a member here for a few years but I don't vistit too often mainly because I haven't been building anything for a couple years.
This new project is due to the fact that I love tinkering with JCM/<MESA RECTO/ Soldano type high gain preamps, but I have really gotten sick of changing components out to get new sounds.  Hopefully **** I can pull this off without too much noise due to the amount of wiring/pots in the signal chain. 
All of the pots/switches are basically the most things I tinker with in my homemade preamp (originally the Hoffman Preamp with an extra stage).

here are my first two chicken scratches on paper, I have yet to start the actual build.
Let me know if you have any thoughts about this project.

Thanks. Noah.

[sluckey]

I would put a resistor in series with each cathode pot (maybe 500Ω) just to prevent dialing in zero ohms. Zero ohms will result in zero volts bias and the tube will go into heavy conduction.

[kagliostro]

Also a large resistor in parallel with the boost switch as to avoid pop

or you can use the arrangement you can see under V2a here



---

as you want to use all those pots may be it will be more safe to use this architecture using non conductive bars

or, at least a small piece of non conductive material in the middle, this will avoid electro shock and the use of long wires that can cause other problems



K

[SILVERGUN]

I would put a resistor in series with each cathode pot (maybe 500Ω) just to prevent dialing in zero ohms. Zero ohms will result in zero volts bias and the tube will go into heavy conduction.

Thanks for that sluckey,,,,obvious, but easily omitted

[PRR]

> Zero ohms will result in zero volts bias and the tube will go into heavy conduction.

The tubes with 150K plate resistors won't get hurt.

They may sound awful, and the 150K may smoke if not big enuff. But zero-bias on a tube with large plate resistor is not death-to-tubes.

(POWER stages with negligible dead resistance will, of course, melt quickly.)

[nandrewjackson]

yeah, sluckey, I thought about putting some sort of safety resistor under the cathode pot to prevent a zero situation, I just didn't think of it before I drew the circuit out.

I really didn't consider the "pop" with the cathode switch, kagliostro, but I will definitely keep that in mind.  And I also like the idea of extending the pot control like that.  I've been considering how close the board needs to be to the control panel, but your idea might make things a lot easier!

Thanks for all the input.
Noah

[kagliostro]

Nowadays you can see those long shaft pots used by some HiFi guy

in the past the use of long shaft was common in Radio Frequency equipment

K

[jazbo8]

Can 1/4" jacks be used for the output since it has pretty large voltage swing on it? What's the rating for them anyway?

Jaz

[nandrewjackson]

the output will be 1/4". With the cathode follower, then the EQ, then another cap to isolate DC and a 1M volume pot, it would be fine to run it right into anything 1/4"    (mixing console, power amp, etc.)

[Bluemeany]

Also a large resistor in parallel with the boost switch as to avoid pop

or you can use the arrangement you can see under V2a here



---

as you want to use all those pots may be it will be more safe to use this architecture using non conductive bars

or, at least a small piece of non conductive material in the middle, this will avoid electro shock and the use of long wires that can cause other problems



K

What amp is this schematic for? I like the look of it!

[kagliostro]

That was only one of the idea I had about the conversion of a modulator for Radio Frequency Transmitter in guitar amp

http://www.el34world.com/Forum/index.php?topic=10392.0

The one I posted is my preferred, the other two, as I see things now, requires a Source Follower (IRF820 Mosfet used as CF) between the ef86 tube and the Tone Control

K

[nandrewjackson]

here is the circuit board and the front panel.  It is 3U rackspace.
circuit board is done, the frontpanel is not even close to done.  17 knobs and 6 switches for a single channel preamp.  Wow, can anyone say "overdone". lol

I've decided I"m going to add a "fender" EQ inbetween the first and second stages, and have it switchable "in" or "out".

[kagliostro]

Why do you want to limit you to a Fender Style TS, you can plan to build a switchable small multi purpose board as to try very different circuits (FMV - Baxandall - James - BoneRay - Tilt Coltrol - Raw Control ...............)  

Using this pots

http://it.rs-online.com/web/p/potenziometri/0393841/

you can stack it in parallel as to have a "multi Layer" pot so in one shaft you can have 2 pots (or more) of different value to be used for different TS configuration without have a forest of knobs

It will be interesting also to be able to shift the TS from one gain stage to one other 

K

[nandrewjackson]

 
the "mad scientist" bug is alive in this project.
I only want the fender ts between stage one and two for the deep mid scoop capabilities, and fender ts and marshall ts at the output because they are most popular.

I'm thinking of making a bass pre for my bass player friend. maybe in pedal form.  I will probably usemore exotic eq's in that project.  and it will have way less stages lol.

[kagliostro]

Bass Preamp ?

Alembic F2B (if it is for me I'll add a mosfet source follower as CF for the correct output impedance)

Pedal
http://forum.gtlab.net/cgi-bin/yabb2/YaBB.pl?num=1227650675

Rack U1
http://moosapotamus.net/ideas/alembic-f-2b-preamp/

or

http://www.lorcan.me/wordpress/wp-content/uploads/2009/12/Alembic-F2b-LMD09.zip


Someone also realized a Blackface-style Preamp for bass

http://www.frontiernet.net/~jff/af2b/Dual_Channel_Blackface-style_Preamp_for_Bass_Guitar.html

K

[nandrewjackson]

thanks for the links, kagliostro, those look like good projects.

I've been studying bass specific schematics trying to see what the major differences are between them and guitar circuits.
I'm beginning to  think bass players are more picky than guitar players!