Tube Preamp

rasco22862 · July 03, 2007, 06:23:37 PM

Hi, im looking for a preamp for the out of a pod, may be with a tube. What do you recommend?
Thanks

soulsonic · July 03, 2007, 06:52:53 PM

Are you looking to buy or build? For something to build, I've been mulling over some simple ideas with low-voltage tubes that could be used for that sort of thing. Another idea could be the tube preamp pedal project you can find at http://www.el34world.com It looks like an interesting project and lots of people seem to like it and Hoffman sells all the parts. For something to buy, the Presonus Blue Tube is a nice inexpensive preamp that works really well with guitars. It has a tube in a "starved plate" circuit that can get some crunchy sounds when overdriven or just add some warm fuzzies to the sound.

Are you looking for a tube preamp to add overdrive to the POD's output, or just something clean to maybe "warm it up" a bit?

rasco22862 · July 03, 2007, 06:58:49 PM

Thanks for your reply.

Im looking for building a tube preamp just to warm it up, like you say.

soulsonic · July 03, 2007, 07:24:19 PM

The "Tube Preamp Pedal in a Box" project at EL34World is the first one I can think of off-hand. It's meant to be clean for recording and it has tone controls. There's a full description of how to do it there - look under the "Library of Information" section of the site to find the project.

The PAiA "Tube Head" kit is a starved-plate tube thing - kinda like what you find in a Presonus Blue Tube or a Tube Driver pedal. It's meant for "warming" things more than actually being a true tube preamp. Find it here: http://www.paia.com/proddetail.asp?prod=9305HSR

I don't have any ready-to-go tube preamp projects myself, but I have worked on a couple and I've been planning on doing something to post up here, so if you don't mind waiting, I might have a project ready in a couple weeks.

jonathan perez · July 03, 2007, 07:29:53 PM

DOD intergrated tube is the closest ive gotten to tube simulation under 50 bucks. and it beats out alot of the top players, i admit. it gets that David Gilmour hiwatt tone EASILY...anyways, i use it when im playing a solid state amp to give it the tone of the hot blowing tube preamp....

rasco22862 · July 03, 2007, 07:30:15 PM

thanks , i think im going for the tube pedal. Thanks

rasco22862 · July 03, 2007, 07:31:12 PM

Quote from: thebattleofmidway on July 03, 2007, 07:29:53 PM
DOD intergrated tube is the closest ive gotten to tube simulation under 50 bucks. and it beats out alot of the top players, i admit. it gets that David Gilmour hiwatt tone EASILY...anyways, i use it when im playing a solid state amp to give it the tone of the hot blowing tube preamp....

any schematic or layout for that?

rasco22862 · July 05, 2007, 07:22:30 PM

i´m trying to build the tube preamp from this site:
http://www.el34world.com/projects/tube_box_3.htm

I dont know too much about power supply, can anybody do a simple sketch with a simpler power supply for that project, for me

.?(without the toroidal and so)

+Thanks

QSQCaito · July 05, 2007, 09:13:48 PM

Rasco, you've got the power supple schematic in the same page posted above.

He says it's quiet. Anyway, for other schematics seen I would certainly apply more filtering after the 2nd diode bridge.

Bye bye

hope it helps

DAC

puretube · July 06, 2007, 05:22:20 PM

nice rack, there...

rasco22862 · July 06, 2007, 11:08:31 PM

I worked in a basic layout, here it is:

Remember that i live in Argentina, and i have 220vac.
Big Capacitors are mounted in the other side of the pcb.
NOT REVISED.

soulsonic · July 07, 2007, 04:51:11 AM

Two, things I would consider doing differently:
-Have the power supply section on a separate board, so that it's noises are more separate from the sensitive circuit.
-Use an LM317 for the voltage regulator and run the filaments at 6v instead of 12. The ripple reduction would be of better quality and the filament circuit will be quieter.

Also, note that the input voltage for the power supply is only 12VAC. You can simply use a 12VAC wall transformer intended for your voltage and the rest of the circuit can remain the same. I think the grounding needs to be more strict in your layout, and I see several mistakes in the circuit. I will draw up a revised layout and post it up sometime this weekend. It would be easier for me to draw it than describe it.

Yeah, I wonder where Mr. Hoffman gets those boxes. They certainly look familiar.....

QSQCaito · July 07, 2007, 05:49:07 PM

Quote from: soulsonic on July 07, 2007, 04:51:11 AM
Use an LM317 for the voltage regulator and run the filaments at 6v instead of 12. The ripple reduction would be of better quality and the filament circuit will be quieter.

I was planning on building the preamp of the JCM800. Would you recommend doind this too, (from 12v to 6v on filaments) if so.. would it hcange the sound?

soulsonic · July 07, 2007, 09:39:19 PM

In most cases it really doesn't make much difference in the sound as far as I could tell, but in the case of the Hoffman project, the 12v transformer barely gives enough voltage when rectified to be enough for the regulator to work efficiently, so the idea is to use a different regulator and have it set to a much lower voltage, so it will be doing the maximum work and getting rid of the maximum amount of noise. And the LM317 is a better regulator anyway - less noise and more versatile.

So, my suggestion is more about clean power than anything that would do much to change the tone.

brett · July 08, 2007, 07:59:35 AM

Quotethe 12v transformer barely gives enough voltage when rectified to be enough for the regulator to work efficiently

This is surprising to me, because many small amps and pre-amps use this approach. They seem to work ok.
Calculations indicate that 12 V recified typically gives about 15 (and a bit) V and 12.6 V gives about 16 V. So there's sufficient regulation loss and output voltage to be had.

In my experience the safety factor is usually large enough to use a forward-biased diode on the common leg, which increases the regulated voltage to 12.7V . This is good, because that's more like the desired voltage for heating a 12AX7.

Good luck with your project.
cheers

QSQCaito · July 08, 2007, 12:03:03 PM

Quote from: soulsonic on July 07, 2007, 09:39:19 PM
In most cases it really doesn't make much difference in the sound as far as I could tell, but in the case of the Hoffman project, the 12v transformer barely gives enough voltage when rectified to be enough for the regulator to work efficiently, so the idea is to use a different regulator and have it set to a much lower voltage, so it will be doing the maximum work and getting rid of the maximum amount of noise. And the LM317 is a better regulator anyway - less noise and more versatile.

So, my suggestion is more about clean power than anything that would do much to change the tone.

Let me se if i got this one.. A transformer giving up 12v, when rectified will give less. And it's not a good idea to give less voltage to a 12v voltage regulator.

What if i used a 220v-15v and another 15v-220 15v. 15v rectified and a 12v voltage regulator would be fine, right?? And I'd still be getting 220 for B+.

soulsonic · July 09, 2007, 12:40:41 AM

Quote from: QSQCaito on July 08, 2007, 12:03:03 PM

Let me se if i got this one.. A transformer giving up 12v, when rectified will give less. And it's not a good idea to give less voltage to a 12v voltage regulator.

What if i used a 220v-15v and another 15v-220 15v. 15v rectified and a 12v voltage regulator would be fine, right?? And I'd still be getting 220 for B+.

No, that's not what I mean. I'm only saying that it would work BETTER at lower voltages with a different regulator. It'll still work with the "standard" setup. I'm just trying to suggest improvements.

QSQCaito · July 09, 2007, 10:20:23 AM

Roger that

I believe I'll better start my own thread when I've got the PCB done of the JCM800 with im´provements.

Bye bye

puretube · July 11, 2007, 04:35:44 PM

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Tube Preamp